Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 6128 insertions, 0 deletions

diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
new file mode 100644
index 0000000000..0c9f541977
--- /dev/null
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -0,0 +1,6128 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+   drbd_receiver.c
+
+   This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
+
+   Copyright (C) 2001-2008, LINBIT Information Technologies GmbH.
+   Copyright (C) 1999-2008, Philipp Reisner <philipp.reisner@linbit.com>.
+   Copyright (C) 2002-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
+
+ */
+
+
+#include <linux/module.h>
+
+#include <linux/uaccess.h>
+#include <net/sock.h>
+
+#include <linux/drbd.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/in.h>
+#include <linux/mm.h>
+#include <linux/memcontrol.h>
+#include <linux/mm_inline.h>
+#include <linux/slab.h>
+#include <uapi/linux/sched/types.h>
+#include <linux/sched/signal.h>
+#include <linux/pkt_sched.h>
+#include <linux/unistd.h>
+#include <linux/vmalloc.h>
+#include <linux/random.h>
+#include <linux/string.h>
+#include <linux/scatterlist.h>
+#include <linux/part_stat.h>
+#include "drbd_int.h"
+#include "drbd_protocol.h"
+#include "drbd_req.h"
+#include "drbd_vli.h"
+
+#define PRO_FEATURES (DRBD_FF_TRIM|DRBD_FF_THIN_RESYNC|DRBD_FF_WSAME|DRBD_FF_WZEROES)
+
+struct packet_info {
+	enum drbd_packet cmd;
+	unsigned int size;
+	unsigned int vnr;
+	void *data;
+};
+
+enum finish_epoch {
+	FE_STILL_LIVE,
+	FE_DESTROYED,
+	FE_RECYCLED,
+};
+
+static int drbd_do_features(struct drbd_connection *connection);
+static int drbd_do_auth(struct drbd_connection *connection);
+static int drbd_disconnected(struct drbd_peer_device *);
+static void conn_wait_active_ee_empty(struct drbd_connection *connection);
+static enum finish_epoch drbd_may_finish_epoch(struct drbd_connection *, struct drbd_epoch *, enum epoch_event);
+static int e_end_block(struct drbd_work *, int);
+
+
+#define GFP_TRY	(__GFP_HIGHMEM | __GFP_NOWARN)
+
+/*
+ * some helper functions to deal with single linked page lists,
+ * page->private being our "next" pointer.
+ */
+
+/* If at least n pages are linked at head, get n pages off.
+ * Otherwise, don't modify head, and return NULL.
+ * Locking is the responsibility of the caller.
+ */
+static struct page *page_chain_del(struct page **head, int n)
+{
+	struct page *page;
+	struct page *tmp;
+
+	BUG_ON(!n);
+	BUG_ON(!head);
+
+	page = *head;
+
+	if (!page)
+		return NULL;
+
+	while (page) {
+		tmp = page_chain_next(page);
+		if (--n == 0)
+			break; /* found sufficient pages */
+		if (tmp == NULL)
+			/* insufficient pages, don't use any of them. */
+			return NULL;
+		page = tmp;
+	}
+
+	/* add end of list marker for the returned list */
+	set_page_private(page, 0);
+	/* actual return value, and adjustment of head */
+	page = *head;
+	*head = tmp;
+	return page;
+}
+
+/* may be used outside of locks to find the tail of a (usually short)
+ * "private" page chain, before adding it back to a global chain head
+ * with page_chain_add() under a spinlock. */
+static struct page *page_chain_tail(struct page *page, int *len)
+{
+	struct page *tmp;
+	int i = 1;
+	while ((tmp = page_chain_next(page))) {
+		++i;
+		page = tmp;
+	}
+	if (len)
+		*len = i;
+	return page;
+}
+
+static int page_chain_free(struct page *page)
+{
+	struct page *tmp;
+	int i = 0;
+	page_chain_for_each_safe(page, tmp) {
+		put_page(page);
+		++i;
+	}
+	return i;
+}
+
+static void page_chain_add(struct page **head,
+		struct page *chain_first, struct page *chain_last)
+{
+#if 1
+	struct page *tmp;
+	tmp = page_chain_tail(chain_first, NULL);
+	BUG_ON(tmp != chain_last);
+#endif
+
+	/* add chain to head */
+	set_page_private(chain_last, (unsigned long)*head);
+	*head = chain_first;
+}
+
+static struct page *__drbd_alloc_pages(struct drbd_device *device,
+				       unsigned int number)
+{
+	struct page *page = NULL;
+	struct page *tmp = NULL;
+	unsigned int i = 0;
+
+	/* Yes, testing drbd_pp_vacant outside the lock is racy.
+	 * So what. It saves a spin_lock. */
+	if (drbd_pp_vacant >= number) {
+		spin_lock(&drbd_pp_lock);
+		page = page_chain_del(&drbd_pp_pool, number);
+		if (page)
+			drbd_pp_vacant -= number;
+		spin_unlock(&drbd_pp_lock);
+		if (page)
+			return page;
+	}
+
+	/* GFP_TRY, because we must not cause arbitrary write-out: in a DRBD
+	 * "criss-cross" setup, that might cause write-out on some other DRBD,
+	 * which in turn might block on the other node at this very place.  */
+	for (i = 0; i < number; i++) {
+		tmp = alloc_page(GFP_TRY);
+		if (!tmp)
+			break;
+		set_page_private(tmp, (unsigned long)page);
+		page = tmp;
+	}
+
+	if (i == number)
+		return page;
+
+	/* Not enough pages immediately available this time.
+	 * No need to jump around here, drbd_alloc_pages will retry this
+	 * function "soon". */
+	if (page) {
+		tmp = page_chain_tail(page, NULL);
+		spin_lock(&drbd_pp_lock);
+		page_chain_add(&drbd_pp_pool, page, tmp);
+		drbd_pp_vacant += i;
+		spin_unlock(&drbd_pp_lock);
+	}
+	return NULL;
+}
+
+static void reclaim_finished_net_peer_reqs(struct drbd_device *device,
+					   struct list_head *to_be_freed)
+{
+	struct drbd_peer_request *peer_req, *tmp;
+
+	/* The EEs are always appended to the end of the list. Since
+	   they are sent in order over the wire, they have to finish
+	   in order. As soon as we see the first not finished we can
+	   stop to examine the list... */
+
+	list_for_each_entry_safe(peer_req, tmp, &device->net_ee, w.list) {
+		if (drbd_peer_req_has_active_page(peer_req))
+			break;
+		list_move(&peer_req->w.list, to_be_freed);
+	}
+}
+
+static void drbd_reclaim_net_peer_reqs(struct drbd_device *device)
+{
+	LIST_HEAD(reclaimed);
+	struct drbd_peer_request *peer_req, *t;
+
+	spin_lock_irq(&device->resource->req_lock);
+	reclaim_finished_net_peer_reqs(device, &reclaimed);
+	spin_unlock_irq(&device->resource->req_lock);
+	list_for_each_entry_safe(peer_req, t, &reclaimed, w.list)
+		drbd_free_net_peer_req(device, peer_req);
+}
+
+static void conn_reclaim_net_peer_reqs(struct drbd_connection *connection)
+{
+	struct drbd_peer_device *peer_device;
+	int vnr;
+
+	rcu_read_lock();
+	idr_for_each_entry(&connection->peer_devices, peer_device, vnr) {
+		struct drbd_device *device = peer_device->device;
+		if (!atomic_read(&device->pp_in_use_by_net))
+			continue;
+
+		kref_get(&device->kref);
+		rcu_read_unlock();
+		drbd_reclaim_net_peer_reqs(device);
+		kref_put(&device->kref, drbd_destroy_device);
+		rcu_read_lock();
+	}
+	rcu_read_unlock();
+}
+
+/**
+ * drbd_alloc_pages() - Returns @number pages, retries forever (or until signalled)
+ * @peer_device:	DRBD device.
+ * @number:		number of pages requested
+ * @retry:		whether to retry, if not enough pages are available right now
+ *
+ * Tries to allocate number pages, first from our own page pool, then from
+ * the kernel.
+ * Possibly retry until DRBD frees sufficient pages somewhere else.
+ *
+ * If this allocation would exceed the max_buffers setting, we throttle
+ * allocation (schedule_timeout) to give the system some room to breathe.
+ *
+ * We do not use max-buffers as hard limit, because it could lead to
+ * congestion and further to a distributed deadlock during online-verify or
+ * (checksum based) resync, if the max-buffers, socket buffer sizes and
+ * resync-rate settings are mis-configured.
+ *
+ * Returns a page chain linked via page->private.
+ */
+struct page *drbd_alloc_pages(struct drbd_peer_device *peer_device, unsigned int number,
+			      bool retry)
+{
+	struct drbd_device *device = peer_device->device;
+	struct page *page = NULL;
+	struct net_conf *nc;
+	DEFINE_WAIT(wait);
+	unsigned int mxb;
+
+	rcu_read_lock();
+	nc = rcu_dereference(peer_device->connection->net_conf);
+	mxb = nc ? nc->max_buffers : 1000000;
+	rcu_read_unlock();
+
+	if (atomic_read(&device->pp_in_use) < mxb)
+		page = __drbd_alloc_pages(device, number);
+
+	/* Try to keep the fast path fast, but occasionally we need
+	 * to reclaim the pages we lended to the network stack. */
+	if (page && atomic_read(&device->pp_in_use_by_net) > 512)
+		drbd_reclaim_net_peer_reqs(device);
+
+	while (page == NULL) {
+		prepare_to_wait(&drbd_pp_wait, &wait, TASK_INTERRUPTIBLE);
+
+		drbd_reclaim_net_peer_reqs(device);
+
+		if (atomic_read(&device->pp_in_use) < mxb) {
+			page = __drbd_alloc_pages(device, number);
+			if (page)
+				break;
+		}
+
+		if (!retry)
+			break;
+
+		if (signal_pending(current)) {
+			drbd_warn(device, "drbd_alloc_pages interrupted!\n");
+			break;
+		}
+
+		if (schedule_timeout(HZ/10) == 0)
+			mxb = UINT_MAX;
+	}
+	finish_wait(&drbd_pp_wait, &wait);
+
+	if (page)
+		atomic_add(number, &device->pp_in_use);
+	return page;
+}
+
+/* Must not be used from irq, as that may deadlock: see drbd_alloc_pages.
+ * Is also used from inside an other spin_lock_irq(&resource->req_lock);
+ * Either links the page chain back to the global pool,
+ * or returns all pages to the system. */
+static void drbd_free_pages(struct drbd_device *device, struct page *page, int is_net)
+{
+	atomic_t *a = is_net ? &device->pp_in_use_by_net : &device->pp_in_use;
+	int i;
+
+	if (page == NULL)
+		return;
+
+	if (drbd_pp_vacant > (DRBD_MAX_BIO_SIZE/PAGE_SIZE) * drbd_minor_count)
+		i = page_chain_free(page);
+	else {
+		struct page *tmp;
+		tmp = page_chain_tail(page, &i);
+		spin_lock(&drbd_pp_lock);
+		page_chain_add(&drbd_pp_pool, page, tmp);
+		drbd_pp_vacant += i;
+		spin_unlock(&drbd_pp_lock);
+	}
+	i = atomic_sub_return(i, a);
+	if (i < 0)
+		drbd_warn(device, "ASSERTION FAILED: %s: %d < 0\n",
+			is_net ? "pp_in_use_by_net" : "pp_in_use", i);
+	wake_up(&drbd_pp_wait);
+}
+
+/*
+You need to hold the req_lock:
+ _drbd_wait_ee_list_empty()
+
+You must not have the req_lock:
+ drbd_free_peer_req()
+ drbd_alloc_peer_req()
+ drbd_free_peer_reqs()
+ drbd_ee_fix_bhs()
+ drbd_finish_peer_reqs()
+ drbd_clear_done_ee()
+ drbd_wait_ee_list_empty()
+*/
+
+/* normal: payload_size == request size (bi_size)
+ * w_same: payload_size == logical_block_size
+ * trim: payload_size == 0 */
+struct drbd_peer_request *
+drbd_alloc_peer_req(struct drbd_peer_device *peer_device, u64 id, sector_t sector,
+		    unsigned int request_size, unsigned int payload_size, gfp_t gfp_mask) __must_hold(local)
+{
+	struct drbd_device *device = peer_device->device;
+	struct drbd_peer_request *peer_req;
+	struct page *page = NULL;
+	unsigned int nr_pages = PFN_UP(payload_size);
+
+	if (drbd_insert_fault(device, DRBD_FAULT_AL_EE))
+		return NULL;
+
+	peer_req = mempool_alloc(&drbd_ee_mempool, gfp_mask & ~__GFP_HIGHMEM);
+	if (!peer_req) {
+		if (!(gfp_mask & __GFP_NOWARN))
+			drbd_err(device, "%s: allocation failed\n", __func__);
+		return NULL;
+	}
+
+	if (nr_pages) {
+		page = drbd_alloc_pages(peer_device, nr_pages,
+					gfpflags_allow_blocking(gfp_mask));
+		if (!page)
+			goto fail;
+	}
+
+	memset(peer_req, 0, sizeof(*peer_req));
+	INIT_LIST_HEAD(&peer_req->w.list);
+	drbd_clear_interval(&peer_req->i);
+	peer_req->i.size = request_size;
+	peer_req->i.sector = sector;
+	peer_req->submit_jif = jiffies;
+	peer_req->peer_device = peer_device;
+	peer_req->pages = page;
+	/*
+	 * The block_id is opaque to the receiver.  It is not endianness
+	 * converted, and sent back to the sender unchanged.
+	 */
+	peer_req->block_id = id;
+
+	return peer_req;
+
+ fail:
+	mempool_free(peer_req, &drbd_ee_mempool);
+	return NULL;
+}
+
+void __drbd_free_peer_req(struct drbd_device *device, struct drbd_peer_request *peer_req,
+		       int is_net)
+{
+	might_sleep();
+	if (peer_req->flags & EE_HAS_DIGEST)
+		kfree(peer_req->digest);
+	drbd_free_pages(device, peer_req->pages, is_net);
+	D_ASSERT(device, atomic_read(&peer_req->pending_bios) == 0);
+	D_ASSERT(device, drbd_interval_empty(&peer_req->i));
+	if (!expect(device, !(peer_req->flags & EE_CALL_AL_COMPLETE_IO))) {
+		peer_req->flags &= ~EE_CALL_AL_COMPLETE_IO;
+		drbd_al_complete_io(device, &peer_req->i);
+	}
+	mempool_free(peer_req, &drbd_ee_mempool);
+}
+
+int drbd_free_peer_reqs(struct drbd_device *device, struct list_head *list)
+{
+	LIST_HEAD(work_list);
+	struct drbd_peer_request *peer_req, *t;
+	int count = 0;
+	int is_net = list == &device->net_ee;
+
+	spin_lock_irq(&device->resource->req_lock);
+	list_splice_init(list, &work_list);
+	spin_unlock_irq(&device->resource->req_lock);
+
+	list_for_each_entry_safe(peer_req, t, &work_list, w.list) {
+		__drbd_free_peer_req(device, peer_req, is_net);
+		count++;
+	}
+	return count;
+}
+
+/*
+ * See also comments in _req_mod(,BARRIER_ACKED) and receive_Barrier.
+ */
+static int drbd_finish_peer_reqs(struct drbd_device *device)
+{
+	LIST_HEAD(work_list);
+	LIST_HEAD(reclaimed);
+	struct drbd_peer_request *peer_req, *t;
+	int err = 0;
+
+	spin_lock_irq(&device->resource->req_lock);
+	reclaim_finished_net_peer_reqs(device, &reclaimed);
+	list_splice_init(&device->done_ee, &work_list);
+	spin_unlock_irq(&device->resource->req_lock);
+
+	list_for_each_entry_safe(peer_req, t, &reclaimed, w.list)
+		drbd_free_net_peer_req(device, peer_req);
+
+	/* possible callbacks here:
+	 * e_end_block, and e_end_resync_block, e_send_superseded.
+	 * all ignore the last argument.
+	 */
+	list_for_each_entry_safe(peer_req, t, &work_list, w.list) {
+		int err2;
+
+		/* list_del not necessary, next/prev members not touched */
+		err2 = peer_req->w.cb(&peer_req->w, !!err);
+		if (!err)
+			err = err2;
+		drbd_free_peer_req(device, peer_req);
+	}
+	wake_up(&device->ee_wait);
+
+	return err;
+}
+
+static void _drbd_wait_ee_list_empty(struct drbd_device *device,
+				     struct list_head *head)
+{
+	DEFINE_WAIT(wait);
+
+	/* avoids spin_lock/unlock
+	 * and calling prepare_to_wait in the fast path */
+	while (!list_empty(head)) {
+		prepare_to_wait(&device->ee_wait, &wait, TASK_UNINTERRUPTIBLE);
+		spin_unlock_irq(&device->resource->req_lock);
+		io_schedule();
+		finish_wait(&device->ee_wait, &wait);
+		spin_lock_irq(&device->resource->req_lock);
+	}
+}
+
+static void drbd_wait_ee_list_empty(struct drbd_device *device,
+				    struct list_head *head)
+{
+	spin_lock_irq(&device->resource->req_lock);
+	_drbd_wait_ee_list_empty(device, head);
+	spin_unlock_irq(&device->resource->req_lock);
+}
+
+static int drbd_recv_short(struct socket *sock, void *buf, size_t size, int flags)
+{
+	struct kvec iov = {
+		.iov_base = buf,
+		.iov_len = size,
+	};
+	struct msghdr msg = {
+		.msg_flags = (flags ? flags : MSG_WAITALL | MSG_NOSIGNAL)
+	};
+	iov_iter_kvec(&msg.msg_iter, ITER_DEST, &iov, 1, size);
+	return sock_recvmsg(sock, &msg, msg.msg_flags);
+}
+
+static int drbd_recv(struct drbd_connection *connection, void *buf, size_t size)
+{
+	int rv;
+
+	rv = drbd_recv_short(connection->data.socket, buf, size, 0);
+
+	if (rv < 0) {
+		if (rv == -ECONNRESET)
+			drbd_info(connection, "sock was reset by peer\n");
+		else if (rv != -ERESTARTSYS)
+			drbd_err(connection, "sock_recvmsg returned %d\n", rv);
+	} else if (rv == 0) {
+		if (test_bit(DISCONNECT_SENT, &connection->flags)) {
+			long t;
+			rcu_read_lock();
+			t = rcu_dereference(connection->net_conf)->ping_timeo * HZ/10;
+			rcu_read_unlock();
+
+			t = wait_event_timeout(connection->ping_wait, connection->cstate < C_WF_REPORT_PARAMS, t);
+
+			if (t)
+				goto out;
+		}
+		drbd_info(connection, "sock was shut down by peer\n");
+	}
+
+	if (rv != size)
+		conn_request_state(connection, NS(conn, C_BROKEN_PIPE), CS_HARD);
+
+out:
+	return rv;
+}
+
+static int drbd_recv_all(struct drbd_connection *connection, void *buf, size_t size)
+{
+	int err;
+
+	err = drbd_recv(connection, buf, size);
+	if (err != size) {
+		if (err >= 0)
+			err = -EIO;
+	} else
+		err = 0;
+	return err;
+}
+
+static int drbd_recv_all_warn(struct drbd_connection *connection, void *buf, size_t size)
+{
+	int err;
+
+	err = drbd_recv_all(connection, buf, size);
+	if (err && !signal_pending(current))
+		drbd_warn(connection, "short read (expected size %d)\n", (int)size);
+	return err;
+}
+
+/* quoting tcp(7):
+ *   On individual connections, the socket buffer size must be set prior to the
+ *   listen(2) or connect(2) calls in order to have it take effect.
+ * This is our wrapper to do so.
+ */
+static void drbd_setbufsize(struct socket *sock, unsigned int snd,
+		unsigned int rcv)
+{
+	/* open coded SO_SNDBUF, SO_RCVBUF */
+	if (snd) {
+		sock->sk->sk_sndbuf = snd;
+		sock->sk->sk_userlocks |= SOCK_SNDBUF_LOCK;
+	}
+	if (rcv) {
+		sock->sk->sk_rcvbuf = rcv;
+		sock->sk->sk_userlocks |= SOCK_RCVBUF_LOCK;
+	}
+}
+
+static struct socket *drbd_try_connect(struct drbd_connection *connection)
+{
+	const char *what;
+	struct socket *sock;
+	struct sockaddr_in6 src_in6;
+	struct sockaddr_in6 peer_in6;
+	struct net_conf *nc;
+	int err, peer_addr_len, my_addr_len;
+	int sndbuf_size, rcvbuf_size, connect_int;
+	int disconnect_on_error = 1;
+
+	rcu_read_lock();
+	nc = rcu_dereference(connection->net_conf);
+	if (!nc) {
+		rcu_read_unlock();
+		return NULL;
+	}
+	sndbuf_size = nc->sndbuf_size;
+	rcvbuf_size = nc->rcvbuf_size;
+	connect_int = nc->connect_int;
+	rcu_read_unlock();
+
+	my_addr_len = min_t(int, connection->my_addr_len, sizeof(src_in6));
+	memcpy(&src_in6, &connection->my_addr, my_addr_len);
+
+	if (((struct sockaddr *)&connection->my_addr)->sa_family == AF_INET6)
+		src_in6.sin6_port = 0;
+	else
+		((struct sockaddr_in *)&src_in6)->sin_port = 0; /* AF_INET & AF_SCI */
+
+	peer_addr_len = min_t(int, connection->peer_addr_len, sizeof(src_in6));
+	memcpy(&peer_in6, &connection->peer_addr, peer_addr_len);
+
+	what = "sock_create_kern";
+	err = sock_create_kern(&init_net, ((struct sockaddr *)&src_in6)->sa_family,
+			       SOCK_STREAM, IPPROTO_TCP, &sock);
+	if (err < 0) {
+		sock = NULL;
+		goto out;
+	}
+
+	sock->sk->sk_rcvtimeo =
+	sock->sk->sk_sndtimeo = connect_int * HZ;
+	drbd_setbufsize(sock, sndbuf_size, rcvbuf_size);
+
+       /* explicitly bind to the configured IP as source IP
+	*  for the outgoing connections.
+	*  This is needed for multihomed hosts and to be
+	*  able to use lo: interfaces for drbd.
+	* Make sure to use 0 as port number, so linux selects
+	*  a free one dynamically.
+	*/
+	what = "bind before connect";
+	err = sock->ops->bind(sock, (struct sockaddr *) &src_in6, my_addr_len);
+	if (err < 0)
+		goto out;
+
+	/* connect may fail, peer not yet available.
+	 * stay C_WF_CONNECTION, don't go Disconnecting! */
+	disconnect_on_error = 0;
+	what = "connect";
+	err = sock->ops->connect(sock, (struct sockaddr *) &peer_in6, peer_addr_len, 0);
+
+out:
+	if (err < 0) {
+		if (sock) {
+			sock_release(sock);
+			sock = NULL;
+		}
+		switch (-err) {
+			/* timeout, busy, signal pending */
+		case ETIMEDOUT: case EAGAIN: case EINPROGRESS:
+		case EINTR: case ERESTARTSYS:
+			/* peer not (yet) available, network problem */
+		case ECONNREFUSED: case ENETUNREACH:
+		case EHOSTDOWN:    case EHOSTUNREACH:
+			disconnect_on_error = 0;
+			break;
+		default:
+			drbd_err(connection, "%s failed, err = %d\n", what, err);
+		}
+		if (disconnect_on_error)
+			conn_request_state(connection, NS(conn, C_DISCONNECTING), CS_HARD);
+	}
+
+	return sock;
+}
+
+struct accept_wait_data {
+	struct drbd_connection *connection;
+	struct socket *s_listen;
+	struct completion door_bell;
+	void (*original_sk_state_change)(struct sock *sk);
+
+};
+
+static void drbd_incoming_connection(struct sock *sk)
+{
+	struct accept_wait_data *ad = sk->sk_user_data;
+	void (*state_change)(struct sock *sk);
+
+	state_change = ad->original_sk_state_change;
+	if (sk->sk_state == TCP_ESTABLISHED)
+		complete(&ad->door_bell);
+	state_change(sk);
+}
+
+static int prepare_listen_socket(struct drbd_connection *connection, struct accept_wait_data *ad)
+{
+	int err, sndbuf_size, rcvbuf_size, my_addr_len;
+	struct sockaddr_in6 my_addr;
+	struct socket *s_listen;
+	struct net_conf *nc;
+	const char *what;
+
+	rcu_read_lock();
+	nc = rcu_dereference(connection->net_conf);
+	if (!nc) {
+		rcu_read_unlock();
+		return -EIO;
+	}
+	sndbuf_size = nc->sndbuf_size;
+	rcvbuf_size = nc->rcvbuf_size;
+	rcu_read_unlock();
+
+	my_addr_len = min_t(int, connection->my_addr_len, sizeof(struct sockaddr_in6));
+	memcpy(&my_addr, &connection->my_addr, my_addr_len);
+
+	what = "sock_create_kern";
+	err = sock_create_kern(&init_net, ((struct sockaddr *)&my_addr)->sa_family,
+			       SOCK_STREAM, IPPROTO_TCP, &s_listen);
+	if (err) {
+		s_listen = NULL;
+		goto out;
+	}
+
+	s_listen->sk->sk_reuse = SK_CAN_REUSE; /* SO_REUSEADDR */
+	drbd_setbufsize(s_listen, sndbuf_size, rcvbuf_size);
+
+	what = "bind before listen";
+	err = s_listen->ops->bind(s_listen, (struct sockaddr *)&my_addr, my_addr_len);
+	if (err < 0)
+		goto out;
+
+	ad->s_listen = s_listen;
+	write_lock_bh(&s_listen->sk->sk_callback_lock);
+	ad->original_sk_state_change = s_listen->sk->sk_state_change;
+	s_listen->sk->sk_state_change = drbd_incoming_connection;
+	s_listen->sk->sk_user_data = ad;
+	write_unlock_bh(&s_listen->sk->sk_callback_lock);
+
+	what = "listen";
+	err = s_listen->ops->listen(s_listen, 5);
+	if (err < 0)
+		goto out;
+
+	return 0;
+out:
+	if (s_listen)
+		sock_release(s_listen);
+	if (err < 0) {
+		if (err != -EAGAIN && err != -EINTR && err != -ERESTARTSYS) {
+			drbd_err(connection, "%s failed, err = %d\n", what, err);
+			conn_request_state(connection, NS(conn, C_DISCONNECTING), CS_HARD);
+		}
+	}
+
+	return -EIO;
+}
+
+static void unregister_state_change(struct sock *sk, struct accept_wait_data *ad)
+{
+	write_lock_bh(&sk->sk_callback_lock);
+	sk->sk_state_change = ad->original_sk_state_change;
+	sk->sk_user_data = NULL;
+	write_unlock_bh(&sk->sk_callback_lock);
+}
+
+static struct socket *drbd_wait_for_connect(struct drbd_connection *connection, struct accept_wait_data *ad)
+{
+	int timeo, connect_int, err = 0;
+	struct socket *s_estab = NULL;
+	struct net_conf *nc;
+
+	rcu_read_lock();
+	nc = rcu_dereference(connection->net_conf);
+	if (!nc) {
+		rcu_read_unlock();
+		return NULL;
+	}
+	connect_int = nc->connect_int;
+	rcu_read_unlock();
+
+	timeo = connect_int * HZ;
+	/* 28.5% random jitter */
+	timeo += get_random_u32_below(2) ? timeo / 7 : -timeo / 7;
+
+	err = wait_for_completion_interruptible_timeout(&ad->door_bell, timeo);
+	if (err <= 0)
+		return NULL;
+
+	err = kernel_accept(ad->s_listen, &s_estab, 0);
+	if (err < 0) {
+		if (err != -EAGAIN && err != -EINTR && err != -ERESTARTSYS) {
+			drbd_err(connection, "accept failed, err = %d\n", err);
+			conn_request_state(connection, NS(conn, C_DISCONNECTING), CS_HARD);
+		}
+	}
+
+	if (s_estab)
+		unregister_state_change(s_estab->sk, ad);
+
+	return s_estab;
+}
+
+static int decode_header(struct drbd_connection *, void *, struct packet_info *);
+
+static int send_first_packet(struct drbd_connection *connection, struct drbd_socket *sock,
+			     enum drbd_packet cmd)
+{
+	if (!conn_prepare_command(connection, sock))
+		return -EIO;
+	return conn_send_command(connection, sock, cmd, 0, NULL, 0);
+}
+
+static int receive_first_packet(struct drbd_connection *connection, struct socket *sock)
+{
+	unsigned int header_size = drbd_header_size(connection);
+	struct packet_info pi;
+	struct net_conf *nc;
+	int err;
+
+	rcu_read_lock();
+	nc = rcu_dereference(connection->net_conf);
+	if (!nc) {
+		rcu_read_unlock();
+		return -EIO;
+	}
+	sock->sk->sk_rcvtimeo = nc->ping_timeo * 4 * HZ / 10;
+	rcu_read_unlock();
+
+	err = drbd_recv_short(sock, connection->data.rbuf, header_size, 0);
+	if (err != header_size) {
+		if (err >= 0)
+			err = -EIO;
+		return err;
+	}
+	err = decode_header(connection, connection->data.rbuf, &pi);
+	if (err)
+		return err;
+	return pi.cmd;
+}
+
+/**
+ * drbd_socket_okay() - Free the socket if its connection is not okay
+ * @sock:	pointer to the pointer to the socket.
+ */
+static bool drbd_socket_okay(struct socket **sock)
+{
+	int rr;
+	char tb[4];
+
+	if (!*sock)
+		return false;
+
+	rr = drbd_recv_short(*sock, tb, 4, MSG_DONTWAIT | MSG_PEEK);
+
+	if (rr > 0 || rr == -EAGAIN) {
+		return true;
+	} else {
+		sock_release(*sock);
+		*sock = NULL;
+		return false;
+	}
+}
+
+static bool connection_established(struct drbd_connection *connection,
+				   struct socket **sock1,
+				   struct socket **sock2)
+{
+	struct net_conf *nc;
+	int timeout;
+	bool ok;
+
+	if (!*sock1 || !*sock2)
+		return false;
+
+	rcu_read_lock();
+	nc = rcu_dereference(connection->net_conf);
+	timeout = (nc->sock_check_timeo ?: nc->ping_timeo) * HZ / 10;
+	rcu_read_unlock();
+	schedule_timeout_interruptible(timeout);
+
+	ok = drbd_socket_okay(sock1);
+	ok = drbd_socket_okay(sock2) && ok;
+
+	return ok;
+}
+
+/* Gets called if a connection is established, or if a new minor gets created
+   in a connection */
+int drbd_connected(struct drbd_peer_device *peer_device)
+{
+	struct drbd_device *device = peer_device->device;
+	int err;
+
+	atomic_set(&device->packet_seq, 0);
+	device->peer_seq = 0;
+
+	device->state_mutex = peer_device->connection->agreed_pro_version < 100 ?
+		&peer_device->connection->cstate_mutex :
+		&device->own_state_mutex;
+
+	err = drbd_send_sync_param(peer_device);
+	if (!err)
+		err = drbd_send_sizes(peer_device, 0, 0);
+	if (!err)
+		err = drbd_send_uuids(peer_device);
+	if (!err)
+		err = drbd_send_current_state(peer_device);
+	clear_bit(USE_DEGR_WFC_T, &device->flags);
+	clear_bit(RESIZE_PENDING, &device->flags);
+	atomic_set(&device->ap_in_flight, 0);
+	mod_timer(&device->request_timer, jiffies + HZ); /* just start it here. */
+	return err;
+}
+
+/*
+ * return values:
+ *   1 yes, we have a valid connection
+ *   0 oops, did not work out, please try again
+ *  -1 peer talks different language,
+ *     no point in trying again, please go standalone.
+ *  -2 We do not have a network config...
+ */
+static int conn_connect(struct drbd_connection *connection)
+{
+	struct drbd_socket sock, msock;
+	struct drbd_peer_device *peer_device;
+	struct net_conf *nc;
+	int vnr, timeout, h;
+	bool discard_my_data, ok;
+	enum drbd_state_rv rv;
+	struct accept_wait_data ad = {
+		.connection = connection,
+		.door_bell = COMPLETION_INITIALIZER_ONSTACK(ad.door_bell),
+	};
+
+	clear_bit(DISCONNECT_SENT, &connection->flags);
+	if (conn_request_state(connection, NS(conn, C_WF_CONNECTION), CS_VERBOSE) < SS_SUCCESS)
+		return -2;
+
+	mutex_init(&sock.mutex);
+	sock.sbuf = connection->data.sbuf;
+	sock.rbuf = connection->data.rbuf;
+	sock.socket = NULL;
+	mutex_init(&msock.mutex);
+	msock.sbuf = connection->meta.sbuf;
+	msock.rbuf = connection->meta.rbuf;
+	msock.socket = NULL;
+
+	/* Assume that the peer only understands protocol 80 until we know better.  */
+	connection->agreed_pro_version = 80;
+
+	if (prepare_listen_socket(connection, &ad))
+		return 0;
+
+	do {
+		struct socket *s;
+
+		s = drbd_try_connect(connection);
+		if (s) {
+			if (!sock.socket) {
+				sock.socket = s;
+				send_first_packet(connection, &sock, P_INITIAL_DATA);
+			} else if (!msock.socket) {
+				clear_bit(RESOLVE_CONFLICTS, &connection->flags);
+				msock.socket = s;
+				send_first_packet(connection, &msock, P_INITIAL_META);
+			} else {
+				drbd_err(connection, "Logic error in conn_connect()\n");
+				goto out_release_sockets;
+			}
+		}
+
+		if (connection_established(connection, &sock.socket, &msock.socket))
+			break;
+
+retry:
+		s = drbd_wait_for_connect(connection, &ad);
+		if (s) {
+			int fp = receive_first_packet(connection, s);
+			drbd_socket_okay(&sock.socket);
+			drbd_socket_okay(&msock.socket);
+			switch (fp) {
+			case P_INITIAL_DATA:
+				if (sock.socket) {
+					drbd_warn(connection, "initial packet S crossed\n");
+					sock_release(sock.socket);
+					sock.socket = s;
+					goto randomize;
+				}
+				sock.socket = s;
+				break;
+			case P_INITIAL_META:
+				set_bit(RESOLVE_CONFLICTS, &connection->flags);
+				if (msock.socket) {
+					drbd_warn(connection, "initial packet M crossed\n");
+					sock_release(msock.socket);
+					msock.socket = s;
+					goto randomize;
+				}
+				msock.socket = s;
+				break;
+			default:
+				drbd_warn(connection, "Error receiving initial packet\n");
+				sock_release(s);
+randomize:
+				if (get_random_u32_below(2))
+					goto retry;
+			}
+		}
+
+		if (connection->cstate <= C_DISCONNECTING)
+			goto out_release_sockets;
+		if (signal_pending(current)) {
+			flush_signals(current);
+			smp_rmb();
+			if (get_t_state(&connection->receiver) == EXITING)
+				goto out_release_sockets;
+		}
+
+		ok = connection_established(connection, &sock.socket, &msock.socket);
+	} while (!ok);
+
+	if (ad.s_listen)
+		sock_release(ad.s_listen);
+
+	sock.socket->sk->sk_reuse = SK_CAN_REUSE; /* SO_REUSEADDR */
+	msock.socket->sk->sk_reuse = SK_CAN_REUSE; /* SO_REUSEADDR */
+
+	sock.socket->sk->sk_allocation = GFP_NOIO;
+	msock.socket->sk->sk_allocation = GFP_NOIO;
+
+	sock.socket->sk->sk_use_task_frag = false;
+	msock.socket->sk->sk_use_task_frag = false;
+
+	sock.socket->sk->sk_priority = TC_PRIO_INTERACTIVE_BULK;
+	msock.socket->sk->sk_priority = TC_PRIO_INTERACTIVE;
+
+	/* NOT YET ...
+	 * sock.socket->sk->sk_sndtimeo = connection->net_conf->timeout*HZ/10;
+	 * sock.socket->sk->sk_rcvtimeo = MAX_SCHEDULE_TIMEOUT;
+	 * first set it to the P_CONNECTION_FEATURES timeout,
+	 * which we set to 4x the configured ping_timeout. */
+	rcu_read_lock();
+	nc = rcu_dereference(connection->net_conf);
+
+	sock.socket->sk->sk_sndtimeo =
+	sock.socket->sk->sk_rcvtimeo = nc->ping_timeo*4*HZ/10;
+
+	msock.socket->sk->sk_rcvtimeo = nc->ping_int*HZ;
+	timeout = nc->timeout * HZ / 10;
+	discard_my_data = nc->discard_my_data;
+	rcu_read_unlock();
+
+	msock.socket->sk->sk_sndtimeo = timeout;
+
+	/* we don't want delays.
+	 * we use TCP_CORK where appropriate, though */
+	tcp_sock_set_nodelay(sock.socket->sk);
+	tcp_sock_set_nodelay(msock.socket->sk);
+
+	connection->data.socket = sock.socket;
+	connection->meta.socket = msock.socket;
+	connection->last_received = jiffies;
+
+	h = drbd_do_features(connection);
+	if (h <= 0)
+		return h;
+
+	if (connection->cram_hmac_tfm) {
+		/* drbd_request_state(device, NS(conn, WFAuth)); */
+		switch (drbd_do_auth(connection)) {
+		case -1:
+			drbd_err(connection, "Authentication of peer failed\n");
+			return -1;
+		case 0:
+			drbd_err(connection, "Authentication of peer failed, trying again.\n");
+			return 0;
+		}
+	}
+
+	connection->data.socket->sk->sk_sndtimeo = timeout;
+	connection->data.socket->sk->sk_rcvtimeo = MAX_SCHEDULE_TIMEOUT;
+
+	if (drbd_send_protocol(connection) == -EOPNOTSUPP)
+		return -1;
+
+	/* Prevent a race between resync-handshake and
+	 * being promoted to Primary.
+	 *
+	 * Grab and release the state mutex, so we know that any current
+	 * drbd_set_role() is finished, and any incoming drbd_set_role
+	 * will see the STATE_SENT flag, and wait for it to be cleared.
+	 */
+	idr_for_each_entry(&connection->peer_devices, peer_device, vnr)
+		mutex_lock(peer_device->device->state_mutex);
+
+	/* avoid a race with conn_request_state( C_DISCONNECTING ) */
+	spin_lock_irq(&connection->resource->req_lock);
+	set_bit(STATE_SENT, &connection->flags);
+	spin_unlock_irq(&connection->resource->req_lock);
+
+	idr_for_each_entry(&connection->peer_devices, peer_device, vnr)
+		mutex_unlock(peer_device->device->state_mutex);
+
+	rcu_read_lock();
+	idr_for_each_entry(&connection->peer_devices, peer_device, vnr) {
+		struct drbd_device *device = peer_device->device;
+		kref_get(&device->kref);
+		rcu_read_unlock();
+
+		if (discard_my_data)
+			set_bit(DISCARD_MY_DATA, &device->flags);
+		else
+			clear_bit(DISCARD_MY_DATA, &device->flags);
+
+		drbd_connected(peer_device);
+		kref_put(&device->kref, drbd_destroy_device);
+		rcu_read_lock();
+	}
+	rcu_read_unlock();
+
+	rv = conn_request_state(connection, NS(conn, C_WF_REPORT_PARAMS), CS_VERBOSE);
+	if (rv < SS_SUCCESS || connection->cstate != C_WF_REPORT_PARAMS) {
+		clear_bit(STATE_SENT, &connection->flags);
+		return 0;
+	}
+
+	drbd_thread_start(&connection->ack_receiver);
+	/* opencoded create_singlethread_workqueue(),
+	 * to be able to use format string arguments */
+	connection->ack_sender =
+		alloc_ordered_workqueue("drbd_as_%s", WQ_MEM_RECLAIM, connection->resource->name);
+	if (!connection->ack_sender) {
+		drbd_err(connection, "Failed to create workqueue ack_sender\n");
+		return 0;
+	}
+
+	mutex_lock(&connection->resource->conf_update);
+	/* The discard_my_data flag is a single-shot modifier to the next
+	 * connection attempt, the handshake of which is now well underway.
+	 * No need for rcu style copying of the whole struct
+	 * just to clear a single value. */
+	connection->net_conf->discard_my_data = 0;
+	mutex_unlock(&connection->resource->conf_update);
+
+	return h;
+
+out_release_sockets:
+	if (ad.s_listen)
+		sock_release(ad.s_listen);
+	if (sock.socket)
+		sock_release(sock.socket);
+	if (msock.socket)
+		sock_release(msock.socket);
+	return -1;
+}
+
+static int decode_header(struct drbd_connection *connection, void *header, struct packet_info *pi)
+{
+	unsigned int header_size = drbd_header_size(connection);
+
+	if (header_size == sizeof(struct p_header100) &&
+	    *(__be32 *)header == cpu_to_be32(DRBD_MAGIC_100)) {
+		struct p_header100 *h = header;
+		if (h->pad != 0) {
+			drbd_err(connection, "Header padding is not zero\n");
+			return -EINVAL;
+		}
+		pi->vnr = be16_to_cpu(h->volume);
+		pi->cmd = be16_to_cpu(h->command);
+		pi->size = be32_to_cpu(h->length);
+	} else if (header_size == sizeof(struct p_header95) &&
+		   *(__be16 *)header == cpu_to_be16(DRBD_MAGIC_BIG)) {
+		struct p_header95 *h = header;
+		pi->cmd = be16_to_cpu(h->command);
+		pi->size = be32_to_cpu(h->length);
+		pi->vnr = 0;
+	} else if (header_size == sizeof(struct p_header80) &&
+		   *(__be32 *)header == cpu_to_be32(DRBD_MAGIC)) {
+		struct p_header80 *h = header;
+		pi->cmd = be16_to_cpu(h->command);
+		pi->size = be16_to_cpu(h->length);
+		pi->vnr = 0;
+	} else {
+		drbd_err(connection, "Wrong magic value 0x%08x in protocol version %d\n",
+			 be32_to_cpu(*(__be32 *)header),
+			 connection->agreed_pro_version);
+		return -EINVAL;
+	}
+	pi->data = header + header_size;
+	return 0;
+}
+
+static void drbd_unplug_all_devices(struct drbd_connection *connection)
+{
+	if (current->plug == &connection->receiver_plug) {
+		blk_finish_plug(&connection->receiver_plug);
+		blk_start_plug(&connection->receiver_plug);
+	} /* else: maybe just schedule() ?? */
+}
+
+static int drbd_recv_header(struct drbd_connection *connection, struct packet_info *pi)
+{
+	void *buffer = connection->data.rbuf;
+	int err;
+
+	err = drbd_recv_all_warn(connection, buffer, drbd_header_size(connection));
+	if (err)
+		return err;
+
+	err = decode_header(connection, buffer, pi);
+	connection->last_received = jiffies;
+
+	return err;
+}
+
+static int drbd_recv_header_maybe_unplug(struct drbd_connection *connection, struct packet_info *pi)
+{
+	void *buffer = connection->data.rbuf;
+	unsigned int size = drbd_header_size(connection);
+	int err;
+
+	err = drbd_recv_short(connection->data.socket, buffer, size, MSG_NOSIGNAL|MSG_DONTWAIT);
+	if (err != size) {
+		/* If we have nothing in the receive buffer now, to reduce
+		 * application latency, try to drain the backend queues as
+		 * quickly as possible, and let remote TCP know what we have
+		 * received so far. */
+		if (err == -EAGAIN) {
+			tcp_sock_set_quickack(connection->data.socket->sk, 2);
+			drbd_unplug_all_devices(connection);
+		}
+		if (err > 0) {
+			buffer += err;
+			size -= err;
+		}
+		err = drbd_recv_all_warn(connection, buffer, size);
+		if (err)
+			return err;
+	}
+
+	err = decode_header(connection, connection->data.rbuf, pi);
+	connection->last_received = jiffies;
+
+	return err;
+}
+/* This is blkdev_issue_flush, but asynchronous.
+ * We want to submit to all component volumes in parallel,
+ * then wait for all completions.
+ */
+struct issue_flush_context {
+	atomic_t pending;
+	int error;
+	struct completion done;
+};
+struct one_flush_context {
+	struct drbd_device *device;
+	struct issue_flush_context *ctx;
+};
+
+static void one_flush_endio(struct bio *bio)
+{
+	struct one_flush_context *octx = bio->bi_private;
+	struct drbd_device *device = octx->device;
+	struct issue_flush_context *ctx = octx->ctx;
+
+	if (bio->bi_status) {
+		ctx->error = blk_status_to_errno(bio->bi_status);
+		drbd_info(device, "local disk FLUSH FAILED with status %d\n", bio->bi_status);
+	}
+	kfree(octx);
+	bio_put(bio);
+
+	clear_bit(FLUSH_PENDING, &device->flags);
+	put_ldev(device);
+	kref_put(&device->kref, drbd_destroy_device);
+
+	if (atomic_dec_and_test(&ctx->pending))
+		complete(&ctx->done);
+}
+
+static void submit_one_flush(struct drbd_device *device, struct issue_flush_context *ctx)
+{
+	struct bio *bio = bio_alloc(device->ldev->backing_bdev, 0,
+				    REQ_OP_WRITE | REQ_PREFLUSH, GFP_NOIO);
+	struct one_flush_context *octx = kmalloc(sizeof(*octx), GFP_NOIO);
+
+	if (!octx) {
+		drbd_warn(device, "Could not allocate a octx, CANNOT ISSUE FLUSH\n");
+		/* FIXME: what else can I do now?  disconnecting or detaching
+		 * really does not help to improve the state of the world, either.
+		 */
+		bio_put(bio);
+
+		ctx->error = -ENOMEM;
+		put_ldev(device);
+		kref_put(&device->kref, drbd_destroy_device);
+		return;
+	}
+
+	octx->device = device;
+	octx->ctx = ctx;
+	bio->bi_private = octx;
+	bio->bi_end_io = one_flush_endio;
+
+	device->flush_jif = jiffies;
+	set_bit(FLUSH_PENDING, &device->flags);
+	atomic_inc(&ctx->pending);
+	submit_bio(bio);
+}
+
+static void drbd_flush(struct drbd_connection *connection)
+{
+	if (connection->resource->write_ordering >= WO_BDEV_FLUSH) {
+		struct drbd_peer_device *peer_device;
+		struct issue_flush_context ctx;
+		int vnr;
+
+		atomic_set(&ctx.pending, 1);
+		ctx.error = 0;
+		init_completion(&ctx.done);
+
+		rcu_read_lock();
+		idr_for_each_entry(&connection->peer_devices, peer_device, vnr) {
+			struct drbd_device *device = peer_device->device;
+
+			if (!get_ldev(device))
+				continue;
+			kref_get(&device->kref);
+			rcu_read_unlock();
+
+			submit_one_flush(device, &ctx);
+
+			rcu_read_lock();
+		}
+		rcu_read_unlock();
+
+		/* Do we want to add a timeout,
+		 * if disk-timeout is set? */
+		if (!atomic_dec_and_test(&ctx.pending))
+			wait_for_completion(&ctx.done);
+
+		if (ctx.error) {
+			/* would rather check on EOPNOTSUPP, but that is not reliable.
+			 * don't try again for ANY return value != 0
+			 * if (rv == -EOPNOTSUPP) */
+			/* Any error is already reported by bio_endio callback. */
+			drbd_bump_write_ordering(connection->resource, NULL, WO_DRAIN_IO);
+		}
+	}
+}
+
+/**
+ * drbd_may_finish_epoch() - Applies an epoch_event to the epoch's state, eventually finishes it.
+ * @connection:	DRBD connection.
+ * @epoch:	Epoch object.
+ * @ev:		Epoch event.
+ */
+static enum finish_epoch drbd_may_finish_epoch(struct drbd_connection *connection,
+					       struct drbd_epoch *epoch,
+					       enum epoch_event ev)
+{
+	int epoch_size;
+	struct drbd_epoch *next_epoch;
+	enum finish_epoch rv = FE_STILL_LIVE;
+
+	spin_lock(&connection->epoch_lock);
+	do {
+		next_epoch = NULL;
+
+		epoch_size = atomic_read(&epoch->epoch_size);
+
+		switch (ev & ~EV_CLEANUP) {
+		case EV_PUT:
+			atomic_dec(&epoch->active);
+			break;
+		case EV_GOT_BARRIER_NR:
+			set_bit(DE_HAVE_BARRIER_NUMBER, &epoch->flags);
+			break;
+		case EV_BECAME_LAST:
+			/* nothing to do*/
+			break;
+		}
+
+		if (epoch_size != 0 &&
+		    atomic_read(&epoch->active) == 0 &&
+		    (test_bit(DE_HAVE_BARRIER_NUMBER, &epoch->flags) || ev & EV_CLEANUP)) {
+			if (!(ev & EV_CLEANUP)) {
+				spin_unlock(&connection->epoch_lock);
+				drbd_send_b_ack(epoch->connection, epoch->barrier_nr, epoch_size);
+				spin_lock(&connection->epoch_lock);
+			}
+#if 0
+			/* FIXME: dec unacked on connection, once we have
+			 * something to count pending connection packets in. */
+			if (test_bit(DE_HAVE_BARRIER_NUMBER, &epoch->flags))
+				dec_unacked(epoch->connection);
+#endif
+
+			if (connection->current_epoch != epoch) {
+				next_epoch = list_entry(epoch->list.next, struct drbd_epoch, list);
+				list_del(&epoch->list);
+				ev = EV_BECAME_LAST | (ev & EV_CLEANUP);
+				connection->epochs--;
+				kfree(epoch);
+
+				if (rv == FE_STILL_LIVE)
+					rv = FE_DESTROYED;
+			} else {
+				epoch->flags = 0;
+				atomic_set(&epoch->epoch_size, 0);
+				/* atomic_set(&epoch->active, 0); is already zero */
+				if (rv == FE_STILL_LIVE)
+					rv = FE_RECYCLED;
+			}
+		}
+
+		if (!next_epoch)
+			break;
+
+		epoch = next_epoch;
+	} while (1);
+
+	spin_unlock(&connection->epoch_lock);
+
+	return rv;
+}
+
+static enum write_ordering_e
+max_allowed_wo(struct drbd_backing_dev *bdev, enum write_ordering_e wo)
+{
+	struct disk_conf *dc;
+
+	dc = rcu_dereference(bdev->disk_conf);
+
+	if (wo == WO_BDEV_FLUSH && !dc->disk_flushes)
+		wo = WO_DRAIN_IO;
+	if (wo == WO_DRAIN_IO && !dc->disk_drain)
+		wo = WO_NONE;
+
+	return wo;
+}
+
+/*
+ * drbd_bump_write_ordering() - Fall back to an other write ordering method
+ * @wo:		Write ordering method to try.
+ */
+void drbd_bump_write_ordering(struct drbd_resource *resource, struct drbd_backing_dev *bdev,
+			      enum write_ordering_e wo)
+{
+	struct drbd_device *device;
+	enum write_ordering_e pwo;
+	int vnr;
+	static char *write_ordering_str[] = {
+		[WO_NONE] = "none",
+		[WO_DRAIN_IO] = "drain",
+		[WO_BDEV_FLUSH] = "flush",
+	};
+
+	pwo = resource->write_ordering;
+	if (wo != WO_BDEV_FLUSH)
+		wo = min(pwo, wo);
+	rcu_read_lock();
+	idr_for_each_entry(&resource->devices, device, vnr) {
+		if (get_ldev(device)) {
+			wo = max_allowed_wo(device->ldev, wo);
+			if (device->ldev == bdev)
+				bdev = NULL;
+			put_ldev(device);
+		}
+	}
+
+	if (bdev)
+		wo = max_allowed_wo(bdev, wo);
+
+	rcu_read_unlock();
+
+	resource->write_ordering = wo;
+	if (pwo != resource->write_ordering || wo == WO_BDEV_FLUSH)
+		drbd_info(resource, "Method to ensure write ordering: %s\n", write_ordering_str[resource->write_ordering]);
+}
+
+/*
+ * Mapping "discard" to ZEROOUT with UNMAP does not work for us:
+ * Drivers have to "announce" q->limits.max_write_zeroes_sectors, or it
+ * will directly go to fallback mode, submitting normal writes, and
+ * never even try to UNMAP.
+ *
+ * And dm-thin does not do this (yet), mostly because in general it has
+ * to assume that "skip_block_zeroing" is set.  See also:
+ * https://www.mail-archive.com/dm-devel%40redhat.com/msg07965.html
+ * https://www.redhat.com/archives/dm-devel/2018-January/msg00271.html
+ *
+ * We *may* ignore the discard-zeroes-data setting, if so configured.
+ *
+ * Assumption is that this "discard_zeroes_data=0" is only because the backend
+ * may ignore partial unaligned discards.
+ *
+ * LVM/DM thin as of at least
+ *   LVM version:     2.02.115(2)-RHEL7 (2015-01-28)
+ *   Library version: 1.02.93-RHEL7 (2015-01-28)
+ *   Driver version:  4.29.0
+ * still behaves this way.
+ *
+ * For unaligned (wrt. alignment and granularity) or too small discards,
+ * we zero-out the initial (and/or) trailing unaligned partial chunks,
+ * but discard all the aligned full chunks.
+ *
+ * At least for LVM/DM thin, with skip_block_zeroing=false,
+ * the result is effectively "discard_zeroes_data=1".
+ */
+/* flags: EE_TRIM|EE_ZEROOUT */
+int drbd_issue_discard_or_zero_out(struct drbd_device *device, sector_t start, unsigned int nr_sectors, int flags)
+{
+	struct block_device *bdev = device->ldev->backing_bdev;
+	sector_t tmp, nr;
+	unsigned int max_discard_sectors, granularity;
+	int alignment;
+	int err = 0;
+
+	if ((flags & EE_ZEROOUT) || !(flags & EE_TRIM))
+		goto zero_out;
+
+	/* Zero-sector (unknown) and one-sector granularities are the same.  */
+	granularity = max(bdev_discard_granularity(bdev) >> 9, 1U);
+	alignment = (bdev_discard_alignment(bdev) >> 9) % granularity;
+
+	max_discard_sectors = min(bdev_max_discard_sectors(bdev), (1U << 22));
+	max_discard_sectors -= max_discard_sectors % granularity;
+	if (unlikely(!max_discard_sectors))
+		goto zero_out;
+
+	if (nr_sectors < granularity)
+		goto zero_out;
+
+	tmp = start;
+	if (sector_div(tmp, granularity) != alignment) {
+		if (nr_sectors < 2*granularity)
+			goto zero_out;
+		/* start + gran - (start + gran - align) % gran */
+		tmp = start + granularity - alignment;
+		tmp = start + granularity - sector_div(tmp, granularity);
+
+		nr = tmp - start;
+		/* don't flag BLKDEV_ZERO_NOUNMAP, we don't know how many
+		 * layers are below us, some may have smaller granularity */
+		err |= blkdev_issue_zeroout(bdev, start, nr, GFP_NOIO, 0);
+		nr_sectors -= nr;
+		start = tmp;
+	}
+	while (nr_sectors >= max_discard_sectors) {
+		err |= blkdev_issue_discard(bdev, start, max_discard_sectors,
+					    GFP_NOIO);
+		nr_sectors -= max_discard_sectors;
+		start += max_discard_sectors;
+	}
+	if (nr_sectors) {
+		/* max_discard_sectors is unsigned int (and a multiple of
+		 * granularity, we made sure of that above already);
+		 * nr is < max_discard_sectors;
+		 * I don't need sector_div here, even though nr is sector_t */
+		nr = nr_sectors;
+		nr -= (unsigned int)nr % granularity;
+		if (nr) {
+			err |= blkdev_issue_discard(bdev, start, nr, GFP_NOIO);
+			nr_sectors -= nr;
+			start += nr;
+		}
+	}
+ zero_out:
+	if (nr_sectors) {
+		err |= blkdev_issue_zeroout(bdev, start, nr_sectors, GFP_NOIO,
+				(flags & EE_TRIM) ? 0 : BLKDEV_ZERO_NOUNMAP);
+	}
+	return err != 0;
+}
+
+static bool can_do_reliable_discards(struct drbd_device *device)
+{
+	struct disk_conf *dc;
+	bool can_do;
+
+	if (!bdev_max_discard_sectors(device->ldev->backing_bdev))
+		return false;
+
+	rcu_read_lock();
+	dc = rcu_dereference(device->ldev->disk_conf);
+	can_do = dc->discard_zeroes_if_aligned;
+	rcu_read_unlock();
+	return can_do;
+}
+
+static void drbd_issue_peer_discard_or_zero_out(struct drbd_device *device, struct drbd_peer_request *peer_req)
+{
+	/* If the backend cannot discard, or does not guarantee
+	 * read-back zeroes in discarded ranges, we fall back to
+	 * zero-out.  Unless configuration specifically requested
+	 * otherwise. */
+	if (!can_do_reliable_discards(device))
+		peer_req->flags |= EE_ZEROOUT;
+
+	if (drbd_issue_discard_or_zero_out(device, peer_req->i.sector,
+	    peer_req->i.size >> 9, peer_req->flags & (EE_ZEROOUT|EE_TRIM)))
+		peer_req->flags |= EE_WAS_ERROR;
+	drbd_endio_write_sec_final(peer_req);
+}
+
+static int peer_request_fault_type(struct drbd_peer_request *peer_req)
+{
+	if (peer_req_op(peer_req) == REQ_OP_READ) {
+		return peer_req->flags & EE_APPLICATION ?
+			DRBD_FAULT_DT_RD : DRBD_FAULT_RS_RD;
+	} else {
+		return peer_req->flags & EE_APPLICATION ?
+			DRBD_FAULT_DT_WR : DRBD_FAULT_RS_WR;
+	}
+}
+
+/**
+ * drbd_submit_peer_request()
+ * @peer_req:	peer request
+ *
+ * May spread the pages to multiple bios,
+ * depending on bio_add_page restrictions.
+ *
+ * Returns 0 if all bios have been submitted,
+ * -ENOMEM if we could not allocate enough bios,
+ * -ENOSPC (any better suggestion?) if we have not been able to bio_add_page a
+ *  single page to an empty bio (which should never happen and likely indicates
+ *  that the lower level IO stack is in some way broken). This has been observed
+ *  on certain Xen deployments.
+ */
+/* TODO allocate from our own bio_set. */
+int drbd_submit_peer_request(struct drbd_peer_request *peer_req)
+{
+	struct drbd_device *device = peer_req->peer_device->device;
+	struct bio *bios = NULL;
+	struct bio *bio;
+	struct page *page = peer_req->pages;
+	sector_t sector = peer_req->i.sector;
+	unsigned int data_size = peer_req->i.size;
+	unsigned int n_bios = 0;
+	unsigned int nr_pages = PFN_UP(data_size);
+
+	/* TRIM/DISCARD: for now, always use the helper function
+	 * blkdev_issue_zeroout(..., discard=true).
+	 * It's synchronous, but it does the right thing wrt. bio splitting.
+	 * Correctness first, performance later.  Next step is to code an
+	 * asynchronous variant of the same.
+	 */
+	if (peer_req->flags & (EE_TRIM | EE_ZEROOUT)) {
+		/* wait for all pending IO completions, before we start
+		 * zeroing things out. */
+		conn_wait_active_ee_empty(peer_req->peer_device->connection);
+		/* add it to the active list now,
+		 * so we can find it to present it in debugfs */
+		peer_req->submit_jif = jiffies;
+		peer_req->flags |= EE_SUBMITTED;
+
+		/* If this was a resync request from receive_rs_deallocated(),
+		 * it is already on the sync_ee list */
+		if (list_empty(&peer_req->w.list)) {
+			spin_lock_irq(&device->resource->req_lock);
+			list_add_tail(&peer_req->w.list, &device->active_ee);
+			spin_unlock_irq(&device->resource->req_lock);
+		}
+
+		drbd_issue_peer_discard_or_zero_out(device, peer_req);
+		return 0;
+	}
+
+	/* In most cases, we will only need one bio.  But in case the lower
+	 * level restrictions happen to be different at this offset on this
+	 * side than those of the sending peer, we may need to submit the
+	 * request in more than one bio.
+	 *
+	 * Plain bio_alloc is good enough here, this is no DRBD internally
+	 * generated bio, but a bio allocated on behalf of the peer.
+	 */
+next_bio:
+	/* _DISCARD, _WRITE_ZEROES handled above.
+	 * REQ_OP_FLUSH (empty flush) not expected,
+	 * should have been mapped to a "drbd protocol barrier".
+	 * REQ_OP_SECURE_ERASE: I don't see how we could ever support that.
+	 */
+	if (!(peer_req_op(peer_req) == REQ_OP_WRITE ||
+				peer_req_op(peer_req) == REQ_OP_READ)) {
+		drbd_err(device, "Invalid bio op received: 0x%x\n", peer_req->opf);
+		return -EINVAL;
+	}
+
+	bio = bio_alloc(device->ldev->backing_bdev, nr_pages, peer_req->opf, GFP_NOIO);
+	/* > peer_req->i.sector, unless this is the first bio */
+	bio->bi_iter.bi_sector = sector;
+	bio->bi_private = peer_req;
+	bio->bi_end_io = drbd_peer_request_endio;
+
+	bio->bi_next = bios;
+	bios = bio;
+	++n_bios;
+
+	page_chain_for_each(page) {
+		unsigned len = min_t(unsigned, data_size, PAGE_SIZE);
+		if (!bio_add_page(bio, page, len, 0))
+			goto next_bio;
+		data_size -= len;
+		sector += len >> 9;
+		--nr_pages;
+	}
+	D_ASSERT(device, data_size == 0);
+	D_ASSERT(device, page == NULL);
+
+	atomic_set(&peer_req->pending_bios, n_bios);
+	/* for debugfs: update timestamp, mark as submitted */
+	peer_req->submit_jif = jiffies;
+	peer_req->flags |= EE_SUBMITTED;
+	do {
+		bio = bios;
+		bios = bios->bi_next;
+		bio->bi_next = NULL;
+
+		drbd_submit_bio_noacct(device, peer_request_fault_type(peer_req), bio);
+	} while (bios);
+	return 0;
+}
+
+static void drbd_remove_epoch_entry_interval(struct drbd_device *device,
+					     struct drbd_peer_request *peer_req)
+{
+	struct drbd_interval *i = &peer_req->i;
+
+	drbd_remove_interval(&device->write_requests, i);
+	drbd_clear_interval(i);
+
+	/* Wake up any processes waiting for this peer request to complete.  */
+	if (i->waiting)
+		wake_up(&device->misc_wait);
+}
+
+static void conn_wait_active_ee_empty(struct drbd_connection *connection)
+{
+	struct drbd_peer_device *peer_device;
+	int vnr;
+
+	rcu_read_lock();
+	idr_for_each_entry(&connection->peer_devices, peer_device, vnr) {
+		struct drbd_device *device = peer_device->device;
+
+		kref_get(&device->kref);
+		rcu_read_unlock();
+		drbd_wait_ee_list_empty(device, &device->active_ee);
+		kref_put(&device->kref, drbd_destroy_device);
+		rcu_read_lock();
+	}
+	rcu_read_unlock();
+}
+
+static int receive_Barrier(struct drbd_connection *connection, struct packet_info *pi)
+{
+	int rv;
+	struct p_barrier *p = pi->data;
+	struct drbd_epoch *epoch;
+
+	/* FIXME these are unacked on connection,
+	 * not a specific (peer)device.
+	 */
+	connection->current_epoch->barrier_nr = p->barrier;
+	connection->current_epoch->connection = connection;
+	rv = drbd_may_finish_epoch(connection, connection->current_epoch, EV_GOT_BARRIER_NR);
+
+	/* P_BARRIER_ACK may imply that the corresponding extent is dropped from
+	 * the activity log, which means it would not be resynced in case the
+	 * R_PRIMARY crashes now.
+	 * Therefore we must send the barrier_ack after the barrier request was
+	 * completed. */
+	switch (connection->resource->write_ordering) {
+	case WO_NONE:
+		if (rv == FE_RECYCLED)
+			return 0;
+
+		/* receiver context, in the writeout path of the other node.
+		 * avoid potential distributed deadlock */
+		epoch = kmalloc(sizeof(struct drbd_epoch), GFP_NOIO);
+		if (epoch)
+			break;
+		else
+			drbd_warn(connection, "Allocation of an epoch failed, slowing down\n");
+		fallthrough;
+
+	case WO_BDEV_FLUSH:
+	case WO_DRAIN_IO:
+		conn_wait_active_ee_empty(connection);
+		drbd_flush(connection);
+
+		if (atomic_read(&connection->current_epoch->epoch_size)) {
+			epoch = kmalloc(sizeof(struct drbd_epoch), GFP_NOIO);
+			if (epoch)
+				break;
+		}
+
+		return 0;
+	default:
+		drbd_err(connection, "Strangeness in connection->write_ordering %d\n",
+			 connection->resource->write_ordering);
+		return -EIO;
+	}
+
+	epoch->flags = 0;
+	atomic_set(&epoch->epoch_size, 0);
+	atomic_set(&epoch->active, 0);
+
+	spin_lock(&connection->epoch_lock);
+	if (atomic_read(&connection->current_epoch->epoch_size)) {
+		list_add(&epoch->list, &connection->current_epoch->list);
+		connection->current_epoch = epoch;
+		connection->epochs++;
+	} else {
+		/* The current_epoch got recycled while we allocated this one... */
+		kfree(epoch);
+	}
+	spin_unlock(&connection->epoch_lock);
+
+	return 0;
+}
+
+/* quick wrapper in case payload size != request_size (write same) */
+static void drbd_csum_ee_size(struct crypto_shash *h,
+			      struct drbd_peer_request *r, void *d,
+			      unsigned int payload_size)
+{
+	unsigned int tmp = r->i.size;
+	r->i.size = payload_size;
+	drbd_csum_ee(h, r, d);
+	r->i.size = tmp;
+}
+
+/* used from receive_RSDataReply (recv_resync_read)
+ * and from receive_Data.
+ * data_size: actual payload ("data in")
+ * 	for normal writes that is bi_size.
+ * 	for discards, that is zero.
+ * 	for write same, it is logical_block_size.
+ * both trim and write same have the bi_size ("data len to be affected")
+ * as extra argument in the packet header.
+ */
+static struct drbd_peer_request *
+read_in_block(struct drbd_peer_device *peer_device, u64 id, sector_t sector,
+	      struct packet_info *pi) __must_hold(local)
+{
+	struct drbd_device *device = peer_device->device;
+	const sector_t capacity = get_capacity(device->vdisk);
+	struct drbd_peer_request *peer_req;
+	struct page *page;
+	int digest_size, err;
+	unsigned int data_size = pi->size, ds;
+	void *dig_in = peer_device->connection->int_dig_in;
+	void *dig_vv = peer_device->connection->int_dig_vv;
+	unsigned long *data;
+	struct p_trim *trim = (pi->cmd == P_TRIM) ? pi->data : NULL;
+	struct p_trim *zeroes = (pi->cmd == P_ZEROES) ? pi->data : NULL;
+
+	digest_size = 0;
+	if (!trim && peer_device->connection->peer_integrity_tfm) {
+		digest_size = crypto_shash_digestsize(peer_device->connection->peer_integrity_tfm);
+		/*
+		 * FIXME: Receive the incoming digest into the receive buffer
+		 *	  here, together with its struct p_data?
+		 */
+		err = drbd_recv_all_warn(peer_device->connection, dig_in, digest_size);
+		if (err)
+			return NULL;
+		data_size -= digest_size;
+	}
+
+	/* assume request_size == data_size, but special case trim. */
+	ds = data_size;
+	if (trim) {
+		if (!expect(peer_device, data_size == 0))
+			return NULL;
+		ds = be32_to_cpu(trim->size);
+	} else if (zeroes) {
+		if (!expect(peer_device, data_size == 0))
+			return NULL;
+		ds = be32_to_cpu(zeroes->size);
+	}
+
+	if (!expect(peer_device, IS_ALIGNED(ds, 512)))
+		return NULL;
+	if (trim || zeroes) {
+		if (!expect(peer_device, ds <= (DRBD_MAX_BBIO_SECTORS << 9)))
+			return NULL;
+	} else if (!expect(peer_device, ds <= DRBD_MAX_BIO_SIZE))
+		return NULL;
+
+	/* even though we trust out peer,
+	 * we sometimes have to double check. */
+	if (sector + (ds>>9) > capacity) {
+		drbd_err(device, "request from peer beyond end of local disk: "
+			"capacity: %llus < sector: %llus + size: %u\n",
+			(unsigned long long)capacity,
+			(unsigned long long)sector, ds);
+		return NULL;
+	}
+
+	/* GFP_NOIO, because we must not cause arbitrary write-out: in a DRBD
+	 * "criss-cross" setup, that might cause write-out on some other DRBD,
+	 * which in turn might block on the other node at this very place.  */
+	peer_req = drbd_alloc_peer_req(peer_device, id, sector, ds, data_size, GFP_NOIO);
+	if (!peer_req)
+		return NULL;
+
+	peer_req->flags |= EE_WRITE;
+	if (trim) {
+		peer_req->flags |= EE_TRIM;
+		return peer_req;
+	}
+	if (zeroes) {
+		peer_req->flags |= EE_ZEROOUT;
+		return peer_req;
+	}
+
+	/* receive payload size bytes into page chain */
+	ds = data_size;
+	page = peer_req->pages;
+	page_chain_for_each(page) {
+		unsigned len = min_t(int, ds, PAGE_SIZE);
+		data = kmap(page);
+		err = drbd_recv_all_warn(peer_device->connection, data, len);
+		if (drbd_insert_fault(device, DRBD_FAULT_RECEIVE)) {
+			drbd_err(device, "Fault injection: Corrupting data on receive\n");
+			data[0] = data[0] ^ (unsigned long)-1;
+		}
+		kunmap(page);
+		if (err) {
+			drbd_free_peer_req(device, peer_req);
+			return NULL;
+		}
+		ds -= len;
+	}
+
+	if (digest_size) {
+		drbd_csum_ee_size(peer_device->connection->peer_integrity_tfm, peer_req, dig_vv, data_size);
+		if (memcmp(dig_in, dig_vv, digest_size)) {
+			drbd_err(device, "Digest integrity check FAILED: %llus +%u\n",
+				(unsigned long long)sector, data_size);
+			drbd_free_peer_req(device, peer_req);
+			return NULL;
+		}
+	}
+	device->recv_cnt += data_size >> 9;
+	return peer_req;
+}
+
+/* drbd_drain_block() just takes a data block
+ * out of the socket input buffer, and discards it.
+ */
+static int drbd_drain_block(struct drbd_peer_device *peer_device, int data_size)
+{
+	struct page *page;
+	int err = 0;
+	void *data;
+
+	if (!data_size)
+		return 0;
+
+	page = drbd_alloc_pages(peer_device, 1, 1);
+
+	data = kmap(page);
+	while (data_size) {
+		unsigned int len = min_t(int, data_size, PAGE_SIZE);
+
+		err = drbd_recv_all_warn(peer_device->connection, data, len);
+		if (err)
+			break;
+		data_size -= len;
+	}
+	kunmap(page);
+	drbd_free_pages(peer_device->device, page, 0);
+	return err;
+}
+
+static int recv_dless_read(struct drbd_peer_device *peer_device, struct drbd_request *req,
+			   sector_t sector, int data_size)
+{
+	struct bio_vec bvec;
+	struct bvec_iter iter;
+	struct bio *bio;
+	int digest_size, err, expect;
+	void *dig_in = peer_device->connection->int_dig_in;
+	void *dig_vv = peer_device->connection->int_dig_vv;
+
+	digest_size = 0;
+	if (peer_device->connection->peer_integrity_tfm) {
+		digest_size = crypto_shash_digestsize(peer_device->connection->peer_integrity_tfm);
+		err = drbd_recv_all_warn(peer_device->connection, dig_in, digest_size);
+		if (err)
+			return err;
+		data_size -= digest_size;
+	}
+
+	/* optimistically update recv_cnt.  if receiving fails below,
+	 * we disconnect anyways, and counters will be reset. */
+	peer_device->device->recv_cnt += data_size>>9;
+
+	bio = req->master_bio;
+	D_ASSERT(peer_device->device, sector == bio->bi_iter.bi_sector);
+
+	bio_for_each_segment(bvec, bio, iter) {
+		void *mapped = bvec_kmap_local(&bvec);
+		expect = min_t(int, data_size, bvec.bv_len);
+		err = drbd_recv_all_warn(peer_device->connection, mapped, expect);
+		kunmap_local(mapped);
+		if (err)
+			return err;
+		data_size -= expect;
+	}
+
+	if (digest_size) {
+		drbd_csum_bio(peer_device->connection->peer_integrity_tfm, bio, dig_vv);
+		if (memcmp(dig_in, dig_vv, digest_size)) {
+			drbd_err(peer_device, "Digest integrity check FAILED. Broken NICs?\n");
+			return -EINVAL;
+		}
+	}
+
+	D_ASSERT(peer_device->device, data_size == 0);
+	return 0;
+}
+
+/*
+ * e_end_resync_block() is called in ack_sender context via
+ * drbd_finish_peer_reqs().
+ */
+static int e_end_resync_block(struct drbd_work *w, int unused)
+{
+	struct drbd_peer_request *peer_req =
+		container_of(w, struct drbd_peer_request, w);
+	struct drbd_peer_device *peer_device = peer_req->peer_device;
+	struct drbd_device *device = peer_device->device;
+	sector_t sector = peer_req->i.sector;
+	int err;
+
+	D_ASSERT(device, drbd_interval_empty(&peer_req->i));
+
+	if (likely((peer_req->flags & EE_WAS_ERROR) == 0)) {
+		drbd_set_in_sync(peer_device, sector, peer_req->i.size);
+		err = drbd_send_ack(peer_device, P_RS_WRITE_ACK, peer_req);
+	} else {
+		/* Record failure to sync */
+		drbd_rs_failed_io(peer_device, sector, peer_req->i.size);
+
+		err  = drbd_send_ack(peer_device, P_NEG_ACK, peer_req);
+	}
+	dec_unacked(device);
+
+	return err;
+}
+
+static int recv_resync_read(struct drbd_peer_device *peer_device, sector_t sector,
+			    struct packet_info *pi) __releases(local)
+{
+	struct drbd_device *device = peer_device->device;
+	struct drbd_peer_request *peer_req;
+
+	peer_req = read_in_block(peer_device, ID_SYNCER, sector, pi);
+	if (!peer_req)
+		goto fail;
+
+	dec_rs_pending(peer_device);
+
+	inc_unacked(device);
+	/* corresponding dec_unacked() in e_end_resync_block()
+	 * respective _drbd_clear_done_ee */
+
+	peer_req->w.cb = e_end_resync_block;
+	peer_req->opf = REQ_OP_WRITE;
+	peer_req->submit_jif = jiffies;
+
+	spin_lock_irq(&device->resource->req_lock);
+	list_add_tail(&peer_req->w.list, &device->sync_ee);
+	spin_unlock_irq(&device->resource->req_lock);
+
+	atomic_add(pi->size >> 9, &device->rs_sect_ev);
+	if (drbd_submit_peer_request(peer_req) == 0)
+		return 0;
+
+	/* don't care for the reason here */
+	drbd_err(device, "submit failed, triggering re-connect\n");
+	spin_lock_irq(&device->resource->req_lock);
+	list_del(&peer_req->w.list);
+	spin_unlock_irq(&device->resource->req_lock);
+
+	drbd_free_peer_req(device, peer_req);
+fail:
+	put_ldev(device);
+	return -EIO;
+}
+
+static struct drbd_request *
+find_request(struct drbd_device *device, struct rb_root *root, u64 id,
+	     sector_t sector, bool missing_ok, const char *func)
+{
+	struct drbd_request *req;
+
+	/* Request object according to our peer */
+	req = (struct drbd_request *)(unsigned long)id;
+	if (drbd_contains_interval(root, sector, &req->i) && req->i.local)
+		return req;
+	if (!missing_ok) {
+		drbd_err(device, "%s: failed to find request 0x%lx, sector %llus\n", func,
+			(unsigned long)id, (unsigned long long)sector);
+	}
+	return NULL;
+}
+
+static int receive_DataReply(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct drbd_request *req;
+	sector_t sector;
+	int err;
+	struct p_data *p = pi->data;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+
+	sector = be64_to_cpu(p->sector);
+
+	spin_lock_irq(&device->resource->req_lock);
+	req = find_request(device, &device->read_requests, p->block_id, sector, false, __func__);
+	spin_unlock_irq(&device->resource->req_lock);
+	if (unlikely(!req))
+		return -EIO;
+
+	err = recv_dless_read(peer_device, req, sector, pi->size);
+	if (!err)
+		req_mod(req, DATA_RECEIVED, peer_device);
+	/* else: nothing. handled from drbd_disconnect...
+	 * I don't think we may complete this just yet
+	 * in case we are "on-disconnect: freeze" */
+
+	return err;
+}
+
+static int receive_RSDataReply(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	sector_t sector;
+	int err;
+	struct p_data *p = pi->data;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+
+	sector = be64_to_cpu(p->sector);
+	D_ASSERT(device, p->block_id == ID_SYNCER);
+
+	if (get_ldev(device)) {
+		/* data is submitted to disk within recv_resync_read.
+		 * corresponding put_ldev done below on error,
+		 * or in drbd_peer_request_endio. */
+		err = recv_resync_read(peer_device, sector, pi);
+	} else {
+		if (drbd_ratelimit())
+			drbd_err(device, "Can not write resync data to local disk.\n");
+
+		err = drbd_drain_block(peer_device, pi->size);
+
+		drbd_send_ack_dp(peer_device, P_NEG_ACK, p, pi->size);
+	}
+
+	atomic_add(pi->size >> 9, &device->rs_sect_in);
+
+	return err;
+}
+
+static void restart_conflicting_writes(struct drbd_device *device,
+				       sector_t sector, int size)
+{
+	struct drbd_interval *i;
+	struct drbd_request *req;
+
+	drbd_for_each_overlap(i, &device->write_requests, sector, size) {
+		if (!i->local)
+			continue;
+		req = container_of(i, struct drbd_request, i);
+		if (req->rq_state & RQ_LOCAL_PENDING ||
+		    !(req->rq_state & RQ_POSTPONED))
+			continue;
+		/* as it is RQ_POSTPONED, this will cause it to
+		 * be queued on the retry workqueue. */
+		__req_mod(req, CONFLICT_RESOLVED, NULL, NULL);
+	}
+}
+
+/*
+ * e_end_block() is called in ack_sender context via drbd_finish_peer_reqs().
+ */
+static int e_end_block(struct drbd_work *w, int cancel)
+{
+	struct drbd_peer_request *peer_req =
+		container_of(w, struct drbd_peer_request, w);
+	struct drbd_peer_device *peer_device = peer_req->peer_device;
+	struct drbd_device *device = peer_device->device;
+	sector_t sector = peer_req->i.sector;
+	int err = 0, pcmd;
+
+	if (peer_req->flags & EE_SEND_WRITE_ACK) {
+		if (likely((peer_req->flags & EE_WAS_ERROR) == 0)) {
+			pcmd = (device->state.conn >= C_SYNC_SOURCE &&
+				device->state.conn <= C_PAUSED_SYNC_T &&
+				peer_req->flags & EE_MAY_SET_IN_SYNC) ?
+				P_RS_WRITE_ACK : P_WRITE_ACK;
+			err = drbd_send_ack(peer_device, pcmd, peer_req);
+			if (pcmd == P_RS_WRITE_ACK)
+				drbd_set_in_sync(peer_device, sector, peer_req->i.size);
+		} else {
+			err = drbd_send_ack(peer_device, P_NEG_ACK, peer_req);
+			/* we expect it to be marked out of sync anyways...
+			 * maybe assert this?  */
+		}
+		dec_unacked(device);
+	}
+
+	/* we delete from the conflict detection hash _after_ we sent out the
+	 * P_WRITE_ACK / P_NEG_ACK, to get the sequence number right.  */
+	if (peer_req->flags & EE_IN_INTERVAL_TREE) {
+		spin_lock_irq(&device->resource->req_lock);
+		D_ASSERT(device, !drbd_interval_empty(&peer_req->i));
+		drbd_remove_epoch_entry_interval(device, peer_req);
+		if (peer_req->flags & EE_RESTART_REQUESTS)
+			restart_conflicting_writes(device, sector, peer_req->i.size);
+		spin_unlock_irq(&device->resource->req_lock);
+	} else
+		D_ASSERT(device, drbd_interval_empty(&peer_req->i));
+
+	drbd_may_finish_epoch(peer_device->connection, peer_req->epoch, EV_PUT + (cancel ? EV_CLEANUP : 0));
+
+	return err;
+}
+
+static int e_send_ack(struct drbd_work *w, enum drbd_packet ack)
+{
+	struct drbd_peer_request *peer_req =
+		container_of(w, struct drbd_peer_request, w);
+	struct drbd_peer_device *peer_device = peer_req->peer_device;
+	int err;
+
+	err = drbd_send_ack(peer_device, ack, peer_req);
+	dec_unacked(peer_device->device);
+
+	return err;
+}
+
+static int e_send_superseded(struct drbd_work *w, int unused)
+{
+	return e_send_ack(w, P_SUPERSEDED);
+}
+
+static int e_send_retry_write(struct drbd_work *w, int unused)
+{
+	struct drbd_peer_request *peer_req =
+		container_of(w, struct drbd_peer_request, w);
+	struct drbd_connection *connection = peer_req->peer_device->connection;
+
+	return e_send_ack(w, connection->agreed_pro_version >= 100 ?
+			     P_RETRY_WRITE : P_SUPERSEDED);
+}
+
+static bool seq_greater(u32 a, u32 b)
+{
+	/*
+	 * We assume 32-bit wrap-around here.
+	 * For 24-bit wrap-around, we would have to shift:
+	 *  a <<= 8; b <<= 8;
+	 */
+	return (s32)a - (s32)b > 0;
+}
+
+static u32 seq_max(u32 a, u32 b)
+{
+	return seq_greater(a, b) ? a : b;
+}
+
+static void update_peer_seq(struct drbd_peer_device *peer_device, unsigned int peer_seq)
+{
+	struct drbd_device *device = peer_device->device;
+	unsigned int newest_peer_seq;
+
+	if (test_bit(RESOLVE_CONFLICTS, &peer_device->connection->flags)) {
+		spin_lock(&device->peer_seq_lock);
+		newest_peer_seq = seq_max(device->peer_seq, peer_seq);
+		device->peer_seq = newest_peer_seq;
+		spin_unlock(&device->peer_seq_lock);
+		/* wake up only if we actually changed device->peer_seq */
+		if (peer_seq == newest_peer_seq)
+			wake_up(&device->seq_wait);
+	}
+}
+
+static inline int overlaps(sector_t s1, int l1, sector_t s2, int l2)
+{
+	return !((s1 + (l1>>9) <= s2) || (s1 >= s2 + (l2>>9)));
+}
+
+/* maybe change sync_ee into interval trees as well? */
+static bool overlapping_resync_write(struct drbd_device *device, struct drbd_peer_request *peer_req)
+{
+	struct drbd_peer_request *rs_req;
+	bool rv = false;
+
+	spin_lock_irq(&device->resource->req_lock);
+	list_for_each_entry(rs_req, &device->sync_ee, w.list) {
+		if (overlaps(peer_req->i.sector, peer_req->i.size,
+			     rs_req->i.sector, rs_req->i.size)) {
+			rv = true;
+			break;
+		}
+	}
+	spin_unlock_irq(&device->resource->req_lock);
+
+	return rv;
+}
+
+/* Called from receive_Data.
+ * Synchronize packets on sock with packets on msock.
+ *
+ * This is here so even when a P_DATA packet traveling via sock overtook an Ack
+ * packet traveling on msock, they are still processed in the order they have
+ * been sent.
+ *
+ * Note: we don't care for Ack packets overtaking P_DATA packets.
+ *
+ * In case packet_seq is larger than device->peer_seq number, there are
+ * outstanding packets on the msock. We wait for them to arrive.
+ * In case we are the logically next packet, we update device->peer_seq
+ * ourselves. Correctly handles 32bit wrap around.
+ *
+ * Assume we have a 10 GBit connection, that is about 1<<30 byte per second,
+ * about 1<<21 sectors per second. So "worst" case, we have 1<<3 == 8 seconds
+ * for the 24bit wrap (historical atomic_t guarantee on some archs), and we have
+ * 1<<9 == 512 seconds aka ages for the 32bit wrap around...
+ *
+ * returns 0 if we may process the packet,
+ * -ERESTARTSYS if we were interrupted (by disconnect signal). */
+static int wait_for_and_update_peer_seq(struct drbd_peer_device *peer_device, const u32 peer_seq)
+{
+	struct drbd_device *device = peer_device->device;
+	DEFINE_WAIT(wait);
+	long timeout;
+	int ret = 0, tp;
+
+	if (!test_bit(RESOLVE_CONFLICTS, &peer_device->connection->flags))
+		return 0;
+
+	spin_lock(&device->peer_seq_lock);
+	for (;;) {
+		if (!seq_greater(peer_seq - 1, device->peer_seq)) {
+			device->peer_seq = seq_max(device->peer_seq, peer_seq);
+			break;
+		}
+
+		if (signal_pending(current)) {
+			ret = -ERESTARTSYS;
+			break;
+		}
+
+		rcu_read_lock();
+		tp = rcu_dereference(peer_device->connection->net_conf)->two_primaries;
+		rcu_read_unlock();
+
+		if (!tp)
+			break;
+
+		/* Only need to wait if two_primaries is enabled */
+		prepare_to_wait(&device->seq_wait, &wait, TASK_INTERRUPTIBLE);
+		spin_unlock(&device->peer_seq_lock);
+		rcu_read_lock();
+		timeout = rcu_dereference(peer_device->connection->net_conf)->ping_timeo*HZ/10;
+		rcu_read_unlock();
+		timeout = schedule_timeout(timeout);
+		spin_lock(&device->peer_seq_lock);
+		if (!timeout) {
+			ret = -ETIMEDOUT;
+			drbd_err(device, "Timed out waiting for missing ack packets; disconnecting\n");
+			break;
+		}
+	}
+	spin_unlock(&device->peer_seq_lock);
+	finish_wait(&device->seq_wait, &wait);
+	return ret;
+}
+
+static enum req_op wire_flags_to_bio_op(u32 dpf)
+{
+	if (dpf & DP_ZEROES)
+		return REQ_OP_WRITE_ZEROES;
+	if (dpf & DP_DISCARD)
+		return REQ_OP_DISCARD;
+	else
+		return REQ_OP_WRITE;
+}
+
+/* see also bio_flags_to_wire() */
+static blk_opf_t wire_flags_to_bio(struct drbd_connection *connection, u32 dpf)
+{
+	return wire_flags_to_bio_op(dpf) |
+		(dpf & DP_RW_SYNC ? REQ_SYNC : 0) |
+		(dpf & DP_FUA ? REQ_FUA : 0) |
+		(dpf & DP_FLUSH ? REQ_PREFLUSH : 0);
+}
+
+static void fail_postponed_requests(struct drbd_device *device, sector_t sector,
+				    unsigned int size)
+{
+	struct drbd_peer_device *peer_device = first_peer_device(device);
+	struct drbd_interval *i;
+
+    repeat:
+	drbd_for_each_overlap(i, &device->write_requests, sector, size) {
+		struct drbd_request *req;
+		struct bio_and_error m;
+
+		if (!i->local)
+			continue;
+		req = container_of(i, struct drbd_request, i);
+		if (!(req->rq_state & RQ_POSTPONED))
+			continue;
+		req->rq_state &= ~RQ_POSTPONED;
+		__req_mod(req, NEG_ACKED, peer_device, &m);
+		spin_unlock_irq(&device->resource->req_lock);
+		if (m.bio)
+			complete_master_bio(device, &m);
+		spin_lock_irq(&device->resource->req_lock);
+		goto repeat;
+	}
+}
+
+static int handle_write_conflicts(struct drbd_device *device,
+				  struct drbd_peer_request *peer_req)
+{
+	struct drbd_connection *connection = peer_req->peer_device->connection;
+	bool resolve_conflicts = test_bit(RESOLVE_CONFLICTS, &connection->flags);
+	sector_t sector = peer_req->i.sector;
+	const unsigned int size = peer_req->i.size;
+	struct drbd_interval *i;
+	bool equal;
+	int err;
+
+	/*
+	 * Inserting the peer request into the write_requests tree will prevent
+	 * new conflicting local requests from being added.
+	 */
+	drbd_insert_interval(&device->write_requests, &peer_req->i);
+
+    repeat:
+	drbd_for_each_overlap(i, &device->write_requests, sector, size) {
+		if (i == &peer_req->i)
+			continue;
+		if (i->completed)
+			continue;
+
+		if (!i->local) {
+			/*
+			 * Our peer has sent a conflicting remote request; this
+			 * should not happen in a two-node setup.  Wait for the
+			 * earlier peer request to complete.
+			 */
+			err = drbd_wait_misc(device, i);
+			if (err)
+				goto out;
+			goto repeat;
+		}
+
+		equal = i->sector == sector && i->size == size;
+		if (resolve_conflicts) {
+			/*
+			 * If the peer request is fully contained within the
+			 * overlapping request, it can be considered overwritten
+			 * and thus superseded; otherwise, it will be retried
+			 * once all overlapping requests have completed.
+			 */
+			bool superseded = i->sector <= sector && i->sector +
+				       (i->size >> 9) >= sector + (size >> 9);
+
+			if (!equal)
+				drbd_alert(device, "Concurrent writes detected: "
+					       "local=%llus +%u, remote=%llus +%u, "
+					       "assuming %s came first\n",
+					  (unsigned long long)i->sector, i->size,
+					  (unsigned long long)sector, size,
+					  superseded ? "local" : "remote");
+
+			peer_req->w.cb = superseded ? e_send_superseded :
+						   e_send_retry_write;
+			list_add_tail(&peer_req->w.list, &device->done_ee);
+			queue_work(connection->ack_sender, &peer_req->peer_device->send_acks_work);
+
+			err = -ENOENT;
+			goto out;
+		} else {
+			struct drbd_request *req =
+				container_of(i, struct drbd_request, i);
+
+			if (!equal)
+				drbd_alert(device, "Concurrent writes detected: "
+					       "local=%llus +%u, remote=%llus +%u\n",
+					  (unsigned long long)i->sector, i->size,
+					  (unsigned long long)sector, size);
+
+			if (req->rq_state & RQ_LOCAL_PENDING ||
+			    !(req->rq_state & RQ_POSTPONED)) {
+				/*
+				 * Wait for the node with the discard flag to
+				 * decide if this request has been superseded
+				 * or needs to be retried.
+				 * Requests that have been superseded will
+				 * disappear from the write_requests tree.
+				 *
+				 * In addition, wait for the conflicting
+				 * request to finish locally before submitting
+				 * the conflicting peer request.
+				 */
+				err = drbd_wait_misc(device, &req->i);
+				if (err) {
+					_conn_request_state(connection, NS(conn, C_TIMEOUT), CS_HARD);
+					fail_postponed_requests(device, sector, size);
+					goto out;
+				}
+				goto repeat;
+			}
+			/*
+			 * Remember to restart the conflicting requests after
+			 * the new peer request has completed.
+			 */
+			peer_req->flags |= EE_RESTART_REQUESTS;
+		}
+	}
+	err = 0;
+
+    out:
+	if (err)
+		drbd_remove_epoch_entry_interval(device, peer_req);
+	return err;
+}
+
+/* mirrored write */
+static int receive_Data(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct net_conf *nc;
+	sector_t sector;
+	struct drbd_peer_request *peer_req;
+	struct p_data *p = pi->data;
+	u32 peer_seq = be32_to_cpu(p->seq_num);
+	u32 dp_flags;
+	int err, tp;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+
+	if (!get_ldev(device)) {
+		int err2;
+
+		err = wait_for_and_update_peer_seq(peer_device, peer_seq);
+		drbd_send_ack_dp(peer_device, P_NEG_ACK, p, pi->size);
+		atomic_inc(&connection->current_epoch->epoch_size);
+		err2 = drbd_drain_block(peer_device, pi->size);
+		if (!err)
+			err = err2;
+		return err;
+	}
+
+	/*
+	 * Corresponding put_ldev done either below (on various errors), or in
+	 * drbd_peer_request_endio, if we successfully submit the data at the
+	 * end of this function.
+	 */
+
+	sector = be64_to_cpu(p->sector);
+	peer_req = read_in_block(peer_device, p->block_id, sector, pi);
+	if (!peer_req) {
+		put_ldev(device);
+		return -EIO;
+	}
+
+	peer_req->w.cb = e_end_block;
+	peer_req->submit_jif = jiffies;
+	peer_req->flags |= EE_APPLICATION;
+
+	dp_flags = be32_to_cpu(p->dp_flags);
+	peer_req->opf = wire_flags_to_bio(connection, dp_flags);
+	if (pi->cmd == P_TRIM) {
+		D_ASSERT(peer_device, peer_req->i.size > 0);
+		D_ASSERT(peer_device, peer_req_op(peer_req) == REQ_OP_DISCARD);
+		D_ASSERT(peer_device, peer_req->pages == NULL);
+		/* need to play safe: an older DRBD sender
+		 * may mean zero-out while sending P_TRIM. */
+		if (0 == (connection->agreed_features & DRBD_FF_WZEROES))
+			peer_req->flags |= EE_ZEROOUT;
+	} else if (pi->cmd == P_ZEROES) {
+		D_ASSERT(peer_device, peer_req->i.size > 0);
+		D_ASSERT(peer_device, peer_req_op(peer_req) == REQ_OP_WRITE_ZEROES);
+		D_ASSERT(peer_device, peer_req->pages == NULL);
+		/* Do (not) pass down BLKDEV_ZERO_NOUNMAP? */
+		if (dp_flags & DP_DISCARD)
+			peer_req->flags |= EE_TRIM;
+	} else if (peer_req->pages == NULL) {
+		D_ASSERT(device, peer_req->i.size == 0);
+		D_ASSERT(device, dp_flags & DP_FLUSH);
+	}
+
+	if (dp_flags & DP_MAY_SET_IN_SYNC)
+		peer_req->flags |= EE_MAY_SET_IN_SYNC;
+
+	spin_lock(&connection->epoch_lock);
+	peer_req->epoch = connection->current_epoch;
+	atomic_inc(&peer_req->epoch->epoch_size);
+	atomic_inc(&peer_req->epoch->active);
+	spin_unlock(&connection->epoch_lock);
+
+	rcu_read_lock();
+	nc = rcu_dereference(peer_device->connection->net_conf);
+	tp = nc->two_primaries;
+	if (peer_device->connection->agreed_pro_version < 100) {
+		switch (nc->wire_protocol) {
+		case DRBD_PROT_C:
+			dp_flags |= DP_SEND_WRITE_ACK;
+			break;
+		case DRBD_PROT_B:
+			dp_flags |= DP_SEND_RECEIVE_ACK;
+			break;
+		}
+	}
+	rcu_read_unlock();
+
+	if (dp_flags & DP_SEND_WRITE_ACK) {
+		peer_req->flags |= EE_SEND_WRITE_ACK;
+		inc_unacked(device);
+		/* corresponding dec_unacked() in e_end_block()
+		 * respective _drbd_clear_done_ee */
+	}
+
+	if (dp_flags & DP_SEND_RECEIVE_ACK) {
+		/* I really don't like it that the receiver thread
+		 * sends on the msock, but anyways */
+		drbd_send_ack(peer_device, P_RECV_ACK, peer_req);
+	}
+
+	if (tp) {
+		/* two primaries implies protocol C */
+		D_ASSERT(device, dp_flags & DP_SEND_WRITE_ACK);
+		peer_req->flags |= EE_IN_INTERVAL_TREE;
+		err = wait_for_and_update_peer_seq(peer_device, peer_seq);
+		if (err)
+			goto out_interrupted;
+		spin_lock_irq(&device->resource->req_lock);
+		err = handle_write_conflicts(device, peer_req);
+		if (err) {
+			spin_unlock_irq(&device->resource->req_lock);
+			if (err == -ENOENT) {
+				put_ldev(device);
+				return 0;
+			}
+			goto out_interrupted;
+		}
+	} else {
+		update_peer_seq(peer_device, peer_seq);
+		spin_lock_irq(&device->resource->req_lock);
+	}
+	/* TRIM and is processed synchronously,
+	 * we wait for all pending requests, respectively wait for
+	 * active_ee to become empty in drbd_submit_peer_request();
+	 * better not add ourselves here. */
+	if ((peer_req->flags & (EE_TRIM | EE_ZEROOUT)) == 0)
+		list_add_tail(&peer_req->w.list, &device->active_ee);
+	spin_unlock_irq(&device->resource->req_lock);
+
+	if (device->state.conn == C_SYNC_TARGET)
+		wait_event(device->ee_wait, !overlapping_resync_write(device, peer_req));
+
+	if (device->state.pdsk < D_INCONSISTENT) {
+		/* In case we have the only disk of the cluster, */
+		drbd_set_out_of_sync(peer_device, peer_req->i.sector, peer_req->i.size);
+		peer_req->flags &= ~EE_MAY_SET_IN_SYNC;
+		drbd_al_begin_io(device, &peer_req->i);
+		peer_req->flags |= EE_CALL_AL_COMPLETE_IO;
+	}
+
+	err = drbd_submit_peer_request(peer_req);
+	if (!err)
+		return 0;
+
+	/* don't care for the reason here */
+	drbd_err(device, "submit failed, triggering re-connect\n");
+	spin_lock_irq(&device->resource->req_lock);
+	list_del(&peer_req->w.list);
+	drbd_remove_epoch_entry_interval(device, peer_req);
+	spin_unlock_irq(&device->resource->req_lock);
+	if (peer_req->flags & EE_CALL_AL_COMPLETE_IO) {
+		peer_req->flags &= ~EE_CALL_AL_COMPLETE_IO;
+		drbd_al_complete_io(device, &peer_req->i);
+	}
+
+out_interrupted:
+	drbd_may_finish_epoch(connection, peer_req->epoch, EV_PUT | EV_CLEANUP);
+	put_ldev(device);
+	drbd_free_peer_req(device, peer_req);
+	return err;
+}
+
+/* We may throttle resync, if the lower device seems to be busy,
+ * and current sync rate is above c_min_rate.
+ *
+ * To decide whether or not the lower device is busy, we use a scheme similar
+ * to MD RAID is_mddev_idle(): if the partition stats reveal "significant"
+ * (more than 64 sectors) of activity we cannot account for with our own resync
+ * activity, it obviously is "busy".
+ *
+ * The current sync rate used here uses only the most recent two step marks,
+ * to have a short time average so we can react faster.
+ */
+bool drbd_rs_should_slow_down(struct drbd_peer_device *peer_device, sector_t sector,
+		bool throttle_if_app_is_waiting)
+{
+	struct drbd_device *device = peer_device->device;
+	struct lc_element *tmp;
+	bool throttle = drbd_rs_c_min_rate_throttle(device);
+
+	if (!throttle || throttle_if_app_is_waiting)
+		return throttle;
+
+	spin_lock_irq(&device->al_lock);
+	tmp = lc_find(device->resync, BM_SECT_TO_EXT(sector));
+	if (tmp) {
+		struct bm_extent *bm_ext = lc_entry(tmp, struct bm_extent, lce);
+		if (test_bit(BME_PRIORITY, &bm_ext->flags))
+			throttle = false;
+		/* Do not slow down if app IO is already waiting for this extent,
+		 * and our progress is necessary for application IO to complete. */
+	}
+	spin_unlock_irq(&device->al_lock);
+
+	return throttle;
+}
+
+bool drbd_rs_c_min_rate_throttle(struct drbd_device *device)
+{
+	struct gendisk *disk = device->ldev->backing_bdev->bd_disk;
+	unsigned long db, dt, dbdt;
+	unsigned int c_min_rate;
+	int curr_events;
+
+	rcu_read_lock();
+	c_min_rate = rcu_dereference(device->ldev->disk_conf)->c_min_rate;
+	rcu_read_unlock();
+
+	/* feature disabled? */
+	if (c_min_rate == 0)
+		return false;
+
+	curr_events = (int)part_stat_read_accum(disk->part0, sectors) -
+			atomic_read(&device->rs_sect_ev);
+
+	if (atomic_read(&device->ap_actlog_cnt)
+	    || curr_events - device->rs_last_events > 64) {
+		unsigned long rs_left;
+		int i;
+
+		device->rs_last_events = curr_events;
+
+		/* sync speed average over the last 2*DRBD_SYNC_MARK_STEP,
+		 * approx. */
+		i = (device->rs_last_mark + DRBD_SYNC_MARKS-1) % DRBD_SYNC_MARKS;
+
+		if (device->state.conn == C_VERIFY_S || device->state.conn == C_VERIFY_T)
+			rs_left = device->ov_left;
+		else
+			rs_left = drbd_bm_total_weight(device) - device->rs_failed;
+
+		dt = ((long)jiffies - (long)device->rs_mark_time[i]) / HZ;
+		if (!dt)
+			dt++;
+		db = device->rs_mark_left[i] - rs_left;
+		dbdt = Bit2KB(db/dt);
+
+		if (dbdt > c_min_rate)
+			return true;
+	}
+	return false;
+}
+
+static int receive_DataRequest(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	sector_t sector;
+	sector_t capacity;
+	struct drbd_peer_request *peer_req;
+	struct digest_info *di = NULL;
+	int size, verb;
+	struct p_block_req *p =	pi->data;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+	capacity = get_capacity(device->vdisk);
+
+	sector = be64_to_cpu(p->sector);
+	size   = be32_to_cpu(p->blksize);
+
+	if (size <= 0 || !IS_ALIGNED(size, 512) || size > DRBD_MAX_BIO_SIZE) {
+		drbd_err(device, "%s:%d: sector: %llus, size: %u\n", __FILE__, __LINE__,
+				(unsigned long long)sector, size);
+		return -EINVAL;
+	}
+	if (sector + (size>>9) > capacity) {
+		drbd_err(device, "%s:%d: sector: %llus, size: %u\n", __FILE__, __LINE__,
+				(unsigned long long)sector, size);
+		return -EINVAL;
+	}
+
+	if (!get_ldev_if_state(device, D_UP_TO_DATE)) {
+		verb = 1;
+		switch (pi->cmd) {
+		case P_DATA_REQUEST:
+			drbd_send_ack_rp(peer_device, P_NEG_DREPLY, p);
+			break;
+		case P_RS_THIN_REQ:
+		case P_RS_DATA_REQUEST:
+		case P_CSUM_RS_REQUEST:
+		case P_OV_REQUEST:
+			drbd_send_ack_rp(peer_device, P_NEG_RS_DREPLY , p);
+			break;
+		case P_OV_REPLY:
+			verb = 0;
+			dec_rs_pending(peer_device);
+			drbd_send_ack_ex(peer_device, P_OV_RESULT, sector, size, ID_IN_SYNC);
+			break;
+		default:
+			BUG();
+		}
+		if (verb && drbd_ratelimit())
+			drbd_err(device, "Can not satisfy peer's read request, "
+			    "no local data.\n");
+
+		/* drain possibly payload */
+		return drbd_drain_block(peer_device, pi->size);
+	}
+
+	/* GFP_NOIO, because we must not cause arbitrary write-out: in a DRBD
+	 * "criss-cross" setup, that might cause write-out on some other DRBD,
+	 * which in turn might block on the other node at this very place.  */
+	peer_req = drbd_alloc_peer_req(peer_device, p->block_id, sector, size,
+			size, GFP_NOIO);
+	if (!peer_req) {
+		put_ldev(device);
+		return -ENOMEM;
+	}
+	peer_req->opf = REQ_OP_READ;
+
+	switch (pi->cmd) {
+	case P_DATA_REQUEST:
+		peer_req->w.cb = w_e_end_data_req;
+		/* application IO, don't drbd_rs_begin_io */
+		peer_req->flags |= EE_APPLICATION;
+		goto submit;
+
+	case P_RS_THIN_REQ:
+		/* If at some point in the future we have a smart way to
+		   find out if this data block is completely deallocated,
+		   then we would do something smarter here than reading
+		   the block... */
+		peer_req->flags |= EE_RS_THIN_REQ;
+		fallthrough;
+	case P_RS_DATA_REQUEST:
+		peer_req->w.cb = w_e_end_rsdata_req;
+		/* used in the sector offset progress display */
+		device->bm_resync_fo = BM_SECT_TO_BIT(sector);
+		break;
+
+	case P_OV_REPLY:
+	case P_CSUM_RS_REQUEST:
+		di = kmalloc(sizeof(*di) + pi->size, GFP_NOIO);
+		if (!di)
+			goto out_free_e;
+
+		di->digest_size = pi->size;
+		di->digest = (((char *)di)+sizeof(struct digest_info));
+
+		peer_req->digest = di;
+		peer_req->flags |= EE_HAS_DIGEST;
+
+		if (drbd_recv_all(peer_device->connection, di->digest, pi->size))
+			goto out_free_e;
+
+		if (pi->cmd == P_CSUM_RS_REQUEST) {
+			D_ASSERT(device, peer_device->connection->agreed_pro_version >= 89);
+			peer_req->w.cb = w_e_end_csum_rs_req;
+			/* used in the sector offset progress display */
+			device->bm_resync_fo = BM_SECT_TO_BIT(sector);
+			/* remember to report stats in drbd_resync_finished */
+			device->use_csums = true;
+		} else if (pi->cmd == P_OV_REPLY) {
+			/* track progress, we may need to throttle */
+			atomic_add(size >> 9, &device->rs_sect_in);
+			peer_req->w.cb = w_e_end_ov_reply;
+			dec_rs_pending(peer_device);
+			/* drbd_rs_begin_io done when we sent this request,
+			 * but accounting still needs to be done. */
+			goto submit_for_resync;
+		}
+		break;
+
+	case P_OV_REQUEST:
+		if (device->ov_start_sector == ~(sector_t)0 &&
+		    peer_device->connection->agreed_pro_version >= 90) {
+			unsigned long now = jiffies;
+			int i;
+			device->ov_start_sector = sector;
+			device->ov_position = sector;
+			device->ov_left = drbd_bm_bits(device) - BM_SECT_TO_BIT(sector);
+			device->rs_total = device->ov_left;
+			for (i = 0; i < DRBD_SYNC_MARKS; i++) {
+				device->rs_mark_left[i] = device->ov_left;
+				device->rs_mark_time[i] = now;
+			}
+			drbd_info(device, "Online Verify start sector: %llu\n",
+					(unsigned long long)sector);
+		}
+		peer_req->w.cb = w_e_end_ov_req;
+		break;
+
+	default:
+		BUG();
+	}
+
+	/* Throttle, drbd_rs_begin_io and submit should become asynchronous
+	 * wrt the receiver, but it is not as straightforward as it may seem.
+	 * Various places in the resync start and stop logic assume resync
+	 * requests are processed in order, requeuing this on the worker thread
+	 * introduces a bunch of new code for synchronization between threads.
+	 *
+	 * Unlimited throttling before drbd_rs_begin_io may stall the resync
+	 * "forever", throttling after drbd_rs_begin_io will lock that extent
+	 * for application writes for the same time.  For now, just throttle
+	 * here, where the rest of the code expects the receiver to sleep for
+	 * a while, anyways.
+	 */
+
+	/* Throttle before drbd_rs_begin_io, as that locks out application IO;
+	 * this defers syncer requests for some time, before letting at least
+	 * on request through.  The resync controller on the receiving side
+	 * will adapt to the incoming rate accordingly.
+	 *
+	 * We cannot throttle here if remote is Primary/SyncTarget:
+	 * we would also throttle its application reads.
+	 * In that case, throttling is done on the SyncTarget only.
+	 */
+
+	/* Even though this may be a resync request, we do add to "read_ee";
+	 * "sync_ee" is only used for resync WRITEs.
+	 * Add to list early, so debugfs can find this request
+	 * even if we have to sleep below. */
+	spin_lock_irq(&device->resource->req_lock);
+	list_add_tail(&peer_req->w.list, &device->read_ee);
+	spin_unlock_irq(&device->resource->req_lock);
+
+	update_receiver_timing_details(connection, drbd_rs_should_slow_down);
+	if (device->state.peer != R_PRIMARY
+	&& drbd_rs_should_slow_down(peer_device, sector, false))
+		schedule_timeout_uninterruptible(HZ/10);
+	update_receiver_timing_details(connection, drbd_rs_begin_io);
+	if (drbd_rs_begin_io(device, sector))
+		goto out_free_e;
+
+submit_for_resync:
+	atomic_add(size >> 9, &device->rs_sect_ev);
+
+submit:
+	update_receiver_timing_details(connection, drbd_submit_peer_request);
+	inc_unacked(device);
+	if (drbd_submit_peer_request(peer_req) == 0)
+		return 0;
+
+	/* don't care for the reason here */
+	drbd_err(device, "submit failed, triggering re-connect\n");
+
+out_free_e:
+	spin_lock_irq(&device->resource->req_lock);
+	list_del(&peer_req->w.list);
+	spin_unlock_irq(&device->resource->req_lock);
+	/* no drbd_rs_complete_io(), we are dropping the connection anyways */
+
+	put_ldev(device);
+	drbd_free_peer_req(device, peer_req);
+	return -EIO;
+}
+
+/*
+ * drbd_asb_recover_0p  -  Recover after split-brain with no remaining primaries
+ */
+static int drbd_asb_recover_0p(struct drbd_peer_device *peer_device) __must_hold(local)
+{
+	struct drbd_device *device = peer_device->device;
+	int self, peer, rv = -100;
+	unsigned long ch_self, ch_peer;
+	enum drbd_after_sb_p after_sb_0p;
+
+	self = device->ldev->md.uuid[UI_BITMAP] & 1;
+	peer = device->p_uuid[UI_BITMAP] & 1;
+
+	ch_peer = device->p_uuid[UI_SIZE];
+	ch_self = device->comm_bm_set;
+
+	rcu_read_lock();
+	after_sb_0p = rcu_dereference(peer_device->connection->net_conf)->after_sb_0p;
+	rcu_read_unlock();
+	switch (after_sb_0p) {
+	case ASB_CONSENSUS:
+	case ASB_DISCARD_SECONDARY:
+	case ASB_CALL_HELPER:
+	case ASB_VIOLENTLY:
+		drbd_err(device, "Configuration error.\n");
+		break;
+	case ASB_DISCONNECT:
+		break;
+	case ASB_DISCARD_YOUNGER_PRI:
+		if (self == 0 && peer == 1) {
+			rv = -1;
+			break;
+		}
+		if (self == 1 && peer == 0) {
+			rv =  1;
+			break;
+		}
+		fallthrough;	/* to one of the other strategies */
+	case ASB_DISCARD_OLDER_PRI:
+		if (self == 0 && peer == 1) {
+			rv = 1;
+			break;
+		}
+		if (self == 1 && peer == 0) {
+			rv = -1;
+			break;
+		}
+		/* Else fall through to one of the other strategies... */
+		drbd_warn(device, "Discard younger/older primary did not find a decision\n"
+		     "Using discard-least-changes instead\n");
+		fallthrough;
+	case ASB_DISCARD_ZERO_CHG:
+		if (ch_peer == 0 && ch_self == 0) {
+			rv = test_bit(RESOLVE_CONFLICTS, &peer_device->connection->flags)
+				? -1 : 1;
+			break;
+		} else {
+			if (ch_peer == 0) { rv =  1; break; }
+			if (ch_self == 0) { rv = -1; break; }
+		}
+		if (after_sb_0p == ASB_DISCARD_ZERO_CHG)
+			break;
+		fallthrough;
+	case ASB_DISCARD_LEAST_CHG:
+		if	(ch_self < ch_peer)
+			rv = -1;
+		else if (ch_self > ch_peer)
+			rv =  1;
+		else /* ( ch_self == ch_peer ) */
+		     /* Well, then use something else. */
+			rv = test_bit(RESOLVE_CONFLICTS, &peer_device->connection->flags)
+				? -1 : 1;
+		break;
+	case ASB_DISCARD_LOCAL:
+		rv = -1;
+		break;
+	case ASB_DISCARD_REMOTE:
+		rv =  1;
+	}
+
+	return rv;
+}
+
+/*
+ * drbd_asb_recover_1p  -  Recover after split-brain with one remaining primary
+ */
+static int drbd_asb_recover_1p(struct drbd_peer_device *peer_device) __must_hold(local)
+{
+	struct drbd_device *device = peer_device->device;
+	int hg, rv = -100;
+	enum drbd_after_sb_p after_sb_1p;
+
+	rcu_read_lock();
+	after_sb_1p = rcu_dereference(peer_device->connection->net_conf)->after_sb_1p;
+	rcu_read_unlock();
+	switch (after_sb_1p) {
+	case ASB_DISCARD_YOUNGER_PRI:
+	case ASB_DISCARD_OLDER_PRI:
+	case ASB_DISCARD_LEAST_CHG:
+	case ASB_DISCARD_LOCAL:
+	case ASB_DISCARD_REMOTE:
+	case ASB_DISCARD_ZERO_CHG:
+		drbd_err(device, "Configuration error.\n");
+		break;
+	case ASB_DISCONNECT:
+		break;
+	case ASB_CONSENSUS:
+		hg = drbd_asb_recover_0p(peer_device);
+		if (hg == -1 && device->state.role == R_SECONDARY)
+			rv = hg;
+		if (hg == 1  && device->state.role == R_PRIMARY)
+			rv = hg;
+		break;
+	case ASB_VIOLENTLY:
+		rv = drbd_asb_recover_0p(peer_device);
+		break;
+	case ASB_DISCARD_SECONDARY:
+		return device->state.role == R_PRIMARY ? 1 : -1;
+	case ASB_CALL_HELPER:
+		hg = drbd_asb_recover_0p(peer_device);
+		if (hg == -1 && device->state.role == R_PRIMARY) {
+			enum drbd_state_rv rv2;
+
+			 /* drbd_change_state() does not sleep while in SS_IN_TRANSIENT_STATE,
+			  * we might be here in C_WF_REPORT_PARAMS which is transient.
+			  * we do not need to wait for the after state change work either. */
+			rv2 = drbd_change_state(device, CS_VERBOSE, NS(role, R_SECONDARY));
+			if (rv2 != SS_SUCCESS) {
+				drbd_khelper(device, "pri-lost-after-sb");
+			} else {
+				drbd_warn(device, "Successfully gave up primary role.\n");
+				rv = hg;
+			}
+		} else
+			rv = hg;
+	}
+
+	return rv;
+}
+
+/*
+ * drbd_asb_recover_2p  -  Recover after split-brain with two remaining primaries
+ */
+static int drbd_asb_recover_2p(struct drbd_peer_device *peer_device) __must_hold(local)
+{
+	struct drbd_device *device = peer_device->device;
+	int hg, rv = -100;
+	enum drbd_after_sb_p after_sb_2p;
+
+	rcu_read_lock();
+	after_sb_2p = rcu_dereference(peer_device->connection->net_conf)->after_sb_2p;
+	rcu_read_unlock();
+	switch (after_sb_2p) {
+	case ASB_DISCARD_YOUNGER_PRI:
+	case ASB_DISCARD_OLDER_PRI:
+	case ASB_DISCARD_LEAST_CHG:
+	case ASB_DISCARD_LOCAL:
+	case ASB_DISCARD_REMOTE:
+	case ASB_CONSENSUS:
+	case ASB_DISCARD_SECONDARY:
+	case ASB_DISCARD_ZERO_CHG:
+		drbd_err(device, "Configuration error.\n");
+		break;
+	case ASB_VIOLENTLY:
+		rv = drbd_asb_recover_0p(peer_device);
+		break;
+	case ASB_DISCONNECT:
+		break;
+	case ASB_CALL_HELPER:
+		hg = drbd_asb_recover_0p(peer_device);
+		if (hg == -1) {
+			enum drbd_state_rv rv2;
+
+			 /* drbd_change_state() does not sleep while in SS_IN_TRANSIENT_STATE,
+			  * we might be here in C_WF_REPORT_PARAMS which is transient.
+			  * we do not need to wait for the after state change work either. */
+			rv2 = drbd_change_state(device, CS_VERBOSE, NS(role, R_SECONDARY));
+			if (rv2 != SS_SUCCESS) {
+				drbd_khelper(device, "pri-lost-after-sb");
+			} else {
+				drbd_warn(device, "Successfully gave up primary role.\n");
+				rv = hg;
+			}
+		} else
+			rv = hg;
+	}
+
+	return rv;
+}
+
+static void drbd_uuid_dump(struct drbd_device *device, char *text, u64 *uuid,
+			   u64 bits, u64 flags)
+{
+	if (!uuid) {
+		drbd_info(device, "%s uuid info vanished while I was looking!\n", text);
+		return;
+	}
+	drbd_info(device, "%s %016llX:%016llX:%016llX:%016llX bits:%llu flags:%llX\n",
+	     text,
+	     (unsigned long long)uuid[UI_CURRENT],
+	     (unsigned long long)uuid[UI_BITMAP],
+	     (unsigned long long)uuid[UI_HISTORY_START],
+	     (unsigned long long)uuid[UI_HISTORY_END],
+	     (unsigned long long)bits,
+	     (unsigned long long)flags);
+}
+
+/*
+  100	after split brain try auto recover
+    2	C_SYNC_SOURCE set BitMap
+    1	C_SYNC_SOURCE use BitMap
+    0	no Sync
+   -1	C_SYNC_TARGET use BitMap
+   -2	C_SYNC_TARGET set BitMap
+ -100	after split brain, disconnect
+-1000	unrelated data
+-1091   requires proto 91
+-1096   requires proto 96
+ */
+
+static int drbd_uuid_compare(struct drbd_peer_device *const peer_device,
+		enum drbd_role const peer_role, int *rule_nr) __must_hold(local)
+{
+	struct drbd_connection *const connection = peer_device->connection;
+	struct drbd_device *device = peer_device->device;
+	u64 self, peer;
+	int i, j;
+
+	self = device->ldev->md.uuid[UI_CURRENT] & ~((u64)1);
+	peer = device->p_uuid[UI_CURRENT] & ~((u64)1);
+
+	*rule_nr = 10;
+	if (self == UUID_JUST_CREATED && peer == UUID_JUST_CREATED)
+		return 0;
+
+	*rule_nr = 20;
+	if ((self == UUID_JUST_CREATED || self == (u64)0) &&
+	     peer != UUID_JUST_CREATED)
+		return -2;
+
+	*rule_nr = 30;
+	if (self != UUID_JUST_CREATED &&
+	    (peer == UUID_JUST_CREATED || peer == (u64)0))
+		return 2;
+
+	if (self == peer) {
+		int rct, dc; /* roles at crash time */
+
+		if (device->p_uuid[UI_BITMAP] == (u64)0 && device->ldev->md.uuid[UI_BITMAP] != (u64)0) {
+
+			if (connection->agreed_pro_version < 91)
+				return -1091;
+
+			if ((device->ldev->md.uuid[UI_BITMAP] & ~((u64)1)) == (device->p_uuid[UI_HISTORY_START] & ~((u64)1)) &&
+			    (device->ldev->md.uuid[UI_HISTORY_START] & ~((u64)1)) == (device->p_uuid[UI_HISTORY_START + 1] & ~((u64)1))) {
+				drbd_info(device, "was SyncSource, missed the resync finished event, corrected myself:\n");
+				drbd_uuid_move_history(device);
+				device->ldev->md.uuid[UI_HISTORY_START] = device->ldev->md.uuid[UI_BITMAP];
+				device->ldev->md.uuid[UI_BITMAP] = 0;
+
+				drbd_uuid_dump(device, "self", device->ldev->md.uuid,
+					       device->state.disk >= D_NEGOTIATING ? drbd_bm_total_weight(device) : 0, 0);
+				*rule_nr = 34;
+			} else {
+				drbd_info(device, "was SyncSource (peer failed to write sync_uuid)\n");
+				*rule_nr = 36;
+			}
+
+			return 1;
+		}
+
+		if (device->ldev->md.uuid[UI_BITMAP] == (u64)0 && device->p_uuid[UI_BITMAP] != (u64)0) {
+
+			if (connection->agreed_pro_version < 91)
+				return -1091;
+
+			if ((device->ldev->md.uuid[UI_HISTORY_START] & ~((u64)1)) == (device->p_uuid[UI_BITMAP] & ~((u64)1)) &&
+			    (device->ldev->md.uuid[UI_HISTORY_START + 1] & ~((u64)1)) == (device->p_uuid[UI_HISTORY_START] & ~((u64)1))) {
+				drbd_info(device, "was SyncTarget, peer missed the resync finished event, corrected peer:\n");
+
+				device->p_uuid[UI_HISTORY_START + 1] = device->p_uuid[UI_HISTORY_START];
+				device->p_uuid[UI_HISTORY_START] = device->p_uuid[UI_BITMAP];
+				device->p_uuid[UI_BITMAP] = 0UL;
+
+				drbd_uuid_dump(device, "peer", device->p_uuid, device->p_uuid[UI_SIZE], device->p_uuid[UI_FLAGS]);
+				*rule_nr = 35;
+			} else {
+				drbd_info(device, "was SyncTarget (failed to write sync_uuid)\n");
+				*rule_nr = 37;
+			}
+
+			return -1;
+		}
+
+		/* Common power [off|failure] */
+		rct = (test_bit(CRASHED_PRIMARY, &device->flags) ? 1 : 0) +
+			(device->p_uuid[UI_FLAGS] & 2);
+		/* lowest bit is set when we were primary,
+		 * next bit (weight 2) is set when peer was primary */
+		*rule_nr = 40;
+
+		/* Neither has the "crashed primary" flag set,
+		 * only a replication link hickup. */
+		if (rct == 0)
+			return 0;
+
+		/* Current UUID equal and no bitmap uuid; does not necessarily
+		 * mean this was a "simultaneous hard crash", maybe IO was
+		 * frozen, so no UUID-bump happened.
+		 * This is a protocol change, overload DRBD_FF_WSAME as flag
+		 * for "new-enough" peer DRBD version. */
+		if (device->state.role == R_PRIMARY || peer_role == R_PRIMARY) {
+			*rule_nr = 41;
+			if (!(connection->agreed_features & DRBD_FF_WSAME)) {
+				drbd_warn(peer_device, "Equivalent unrotated UUIDs, but current primary present.\n");
+				return -(0x10000 | PRO_VERSION_MAX | (DRBD_FF_WSAME << 8));
+			}
+			if (device->state.role == R_PRIMARY && peer_role == R_PRIMARY) {
+				/* At least one has the "crashed primary" bit set,
+				 * both are primary now, but neither has rotated its UUIDs?
+				 * "Can not happen." */
+				drbd_err(peer_device, "Equivalent unrotated UUIDs, but both are primary. Can not resolve this.\n");
+				return -100;
+			}
+			if (device->state.role == R_PRIMARY)
+				return 1;
+			return -1;
+		}
+
+		/* Both are secondary.
+		 * Really looks like recovery from simultaneous hard crash.
+		 * Check which had been primary before, and arbitrate. */
+		switch (rct) {
+		case 0: /* !self_pri && !peer_pri */ return 0; /* already handled */
+		case 1: /*  self_pri && !peer_pri */ return 1;
+		case 2: /* !self_pri &&  peer_pri */ return -1;
+		case 3: /*  self_pri &&  peer_pri */
+			dc = test_bit(RESOLVE_CONFLICTS, &connection->flags);
+			return dc ? -1 : 1;
+		}
+	}
+
+	*rule_nr = 50;
+	peer = device->p_uuid[UI_BITMAP] & ~((u64)1);
+	if (self == peer)
+		return -1;
+
+	*rule_nr = 51;
+	peer = device->p_uuid[UI_HISTORY_START] & ~((u64)1);
+	if (self == peer) {
+		if (connection->agreed_pro_version < 96 ?
+		    (device->ldev->md.uuid[UI_HISTORY_START] & ~((u64)1)) ==
+		    (device->p_uuid[UI_HISTORY_START + 1] & ~((u64)1)) :
+		    peer + UUID_NEW_BM_OFFSET == (device->p_uuid[UI_BITMAP] & ~((u64)1))) {
+			/* The last P_SYNC_UUID did not get though. Undo the last start of
+			   resync as sync source modifications of the peer's UUIDs. */
+
+			if (connection->agreed_pro_version < 91)
+				return -1091;
+
+			device->p_uuid[UI_BITMAP] = device->p_uuid[UI_HISTORY_START];
+			device->p_uuid[UI_HISTORY_START] = device->p_uuid[UI_HISTORY_START + 1];
+
+			drbd_info(device, "Lost last syncUUID packet, corrected:\n");
+			drbd_uuid_dump(device, "peer", device->p_uuid, device->p_uuid[UI_SIZE], device->p_uuid[UI_FLAGS]);
+
+			return -1;
+		}
+	}
+
+	*rule_nr = 60;
+	self = device->ldev->md.uuid[UI_CURRENT] & ~((u64)1);
+	for (i = UI_HISTORY_START; i <= UI_HISTORY_END; i++) {
+		peer = device->p_uuid[i] & ~((u64)1);
+		if (self == peer)
+			return -2;
+	}
+
+	*rule_nr = 70;
+	self = device->ldev->md.uuid[UI_BITMAP] & ~((u64)1);
+	peer = device->p_uuid[UI_CURRENT] & ~((u64)1);
+	if (self == peer)
+		return 1;
+
+	*rule_nr = 71;
+	self = device->ldev->md.uuid[UI_HISTORY_START] & ~((u64)1);
+	if (self == peer) {
+		if (connection->agreed_pro_version < 96 ?
+		    (device->ldev->md.uuid[UI_HISTORY_START + 1] & ~((u64)1)) ==
+		    (device->p_uuid[UI_HISTORY_START] & ~((u64)1)) :
+		    self + UUID_NEW_BM_OFFSET == (device->ldev->md.uuid[UI_BITMAP] & ~((u64)1))) {
+			/* The last P_SYNC_UUID did not get though. Undo the last start of
+			   resync as sync source modifications of our UUIDs. */
+
+			if (connection->agreed_pro_version < 91)
+				return -1091;
+
+			__drbd_uuid_set(device, UI_BITMAP, device->ldev->md.uuid[UI_HISTORY_START]);
+			__drbd_uuid_set(device, UI_HISTORY_START, device->ldev->md.uuid[UI_HISTORY_START + 1]);
+
+			drbd_info(device, "Last syncUUID did not get through, corrected:\n");
+			drbd_uuid_dump(device, "self", device->ldev->md.uuid,
+				       device->state.disk >= D_NEGOTIATING ? drbd_bm_total_weight(device) : 0, 0);
+
+			return 1;
+		}
+	}
+
+
+	*rule_nr = 80;
+	peer = device->p_uuid[UI_CURRENT] & ~((u64)1);
+	for (i = UI_HISTORY_START; i <= UI_HISTORY_END; i++) {
+		self = device->ldev->md.uuid[i] & ~((u64)1);
+		if (self == peer)
+			return 2;
+	}
+
+	*rule_nr = 90;
+	self = device->ldev->md.uuid[UI_BITMAP] & ~((u64)1);
+	peer = device->p_uuid[UI_BITMAP] & ~((u64)1);
+	if (self == peer && self != ((u64)0))
+		return 100;
+
+	*rule_nr = 100;
+	for (i = UI_HISTORY_START; i <= UI_HISTORY_END; i++) {
+		self = device->ldev->md.uuid[i] & ~((u64)1);
+		for (j = UI_HISTORY_START; j <= UI_HISTORY_END; j++) {
+			peer = device->p_uuid[j] & ~((u64)1);
+			if (self == peer)
+				return -100;
+		}
+	}
+
+	return -1000;
+}
+
+/* drbd_sync_handshake() returns the new conn state on success, or
+   CONN_MASK (-1) on failure.
+ */
+static enum drbd_conns drbd_sync_handshake(struct drbd_peer_device *peer_device,
+					   enum drbd_role peer_role,
+					   enum drbd_disk_state peer_disk) __must_hold(local)
+{
+	struct drbd_device *device = peer_device->device;
+	enum drbd_conns rv = C_MASK;
+	enum drbd_disk_state mydisk;
+	struct net_conf *nc;
+	int hg, rule_nr, rr_conflict, tentative, always_asbp;
+
+	mydisk = device->state.disk;
+	if (mydisk == D_NEGOTIATING)
+		mydisk = device->new_state_tmp.disk;
+
+	drbd_info(device, "drbd_sync_handshake:\n");
+
+	spin_lock_irq(&device->ldev->md.uuid_lock);
+	drbd_uuid_dump(device, "self", device->ldev->md.uuid, device->comm_bm_set, 0);
+	drbd_uuid_dump(device, "peer", device->p_uuid,
+		       device->p_uuid[UI_SIZE], device->p_uuid[UI_FLAGS]);
+
+	hg = drbd_uuid_compare(peer_device, peer_role, &rule_nr);
+	spin_unlock_irq(&device->ldev->md.uuid_lock);
+
+	drbd_info(device, "uuid_compare()=%d by rule %d\n", hg, rule_nr);
+
+	if (hg == -1000) {
+		drbd_alert(device, "Unrelated data, aborting!\n");
+		return C_MASK;
+	}
+	if (hg < -0x10000) {
+		int proto, fflags;
+		hg = -hg;
+		proto = hg & 0xff;
+		fflags = (hg >> 8) & 0xff;
+		drbd_alert(device, "To resolve this both sides have to support at least protocol %d and feature flags 0x%x\n",
+					proto, fflags);
+		return C_MASK;
+	}
+	if (hg < -1000) {
+		drbd_alert(device, "To resolve this both sides have to support at least protocol %d\n", -hg - 1000);
+		return C_MASK;
+	}
+
+	if    ((mydisk == D_INCONSISTENT && peer_disk > D_INCONSISTENT) ||
+	    (peer_disk == D_INCONSISTENT && mydisk    > D_INCONSISTENT)) {
+		int f = (hg == -100) || abs(hg) == 2;
+		hg = mydisk > D_INCONSISTENT ? 1 : -1;
+		if (f)
+			hg = hg*2;
+		drbd_info(device, "Becoming sync %s due to disk states.\n",
+		     hg > 0 ? "source" : "target");
+	}
+
+	if (abs(hg) == 100)
+		drbd_khelper(device, "initial-split-brain");
+
+	rcu_read_lock();
+	nc = rcu_dereference(peer_device->connection->net_conf);
+	always_asbp = nc->always_asbp;
+	rr_conflict = nc->rr_conflict;
+	tentative = nc->tentative;
+	rcu_read_unlock();
+
+	if (hg == 100 || (hg == -100 && always_asbp)) {
+		int pcount = (device->state.role == R_PRIMARY)
+			   + (peer_role == R_PRIMARY);
+		int forced = (hg == -100);
+
+		switch (pcount) {
+		case 0:
+			hg = drbd_asb_recover_0p(peer_device);
+			break;
+		case 1:
+			hg = drbd_asb_recover_1p(peer_device);
+			break;
+		case 2:
+			hg = drbd_asb_recover_2p(peer_device);
+			break;
+		}
+		if (abs(hg) < 100) {
+			drbd_warn(device, "Split-Brain detected, %d primaries, "
+			     "automatically solved. Sync from %s node\n",
+			     pcount, (hg < 0) ? "peer" : "this");
+			if (forced) {
+				drbd_warn(device, "Doing a full sync, since"
+				     " UUIDs where ambiguous.\n");
+				hg = hg*2;
+			}
+		}
+	}
+
+	if (hg == -100) {
+		if (test_bit(DISCARD_MY_DATA, &device->flags) && !(device->p_uuid[UI_FLAGS]&1))
+			hg = -1;
+		if (!test_bit(DISCARD_MY_DATA, &device->flags) && (device->p_uuid[UI_FLAGS]&1))
+			hg = 1;
+
+		if (abs(hg) < 100)
+			drbd_warn(device, "Split-Brain detected, manually solved. "
+			     "Sync from %s node\n",
+			     (hg < 0) ? "peer" : "this");
+	}
+
+	if (hg == -100) {
+		/* FIXME this log message is not correct if we end up here
+		 * after an attempted attach on a diskless node.
+		 * We just refuse to attach -- well, we drop the "connection"
+		 * to that disk, in a way... */
+		drbd_alert(device, "Split-Brain detected but unresolved, dropping connection!\n");
+		drbd_khelper(device, "split-brain");
+		return C_MASK;
+	}
+
+	if (hg > 0 && mydisk <= D_INCONSISTENT) {
+		drbd_err(device, "I shall become SyncSource, but I am inconsistent!\n");
+		return C_MASK;
+	}
+
+	if (hg < 0 && /* by intention we do not use mydisk here. */
+	    device->state.role == R_PRIMARY && device->state.disk >= D_CONSISTENT) {
+		switch (rr_conflict) {
+		case ASB_CALL_HELPER:
+			drbd_khelper(device, "pri-lost");
+			fallthrough;
+		case ASB_DISCONNECT:
+			drbd_err(device, "I shall become SyncTarget, but I am primary!\n");
+			return C_MASK;
+		case ASB_VIOLENTLY:
+			drbd_warn(device, "Becoming SyncTarget, violating the stable-data"
+			     "assumption\n");
+		}
+	}
+
+	if (tentative || test_bit(CONN_DRY_RUN, &peer_device->connection->flags)) {
+		if (hg == 0)
+			drbd_info(device, "dry-run connect: No resync, would become Connected immediately.\n");
+		else
+			drbd_info(device, "dry-run connect: Would become %s, doing a %s resync.",
+				 drbd_conn_str(hg > 0 ? C_SYNC_SOURCE : C_SYNC_TARGET),
+				 abs(hg) >= 2 ? "full" : "bit-map based");
+		return C_MASK;
+	}
+
+	if (abs(hg) >= 2) {
+		drbd_info(device, "Writing the whole bitmap, full sync required after drbd_sync_handshake.\n");
+		if (drbd_bitmap_io(device, &drbd_bmio_set_n_write, "set_n_write from sync_handshake",
+					BM_LOCKED_SET_ALLOWED, NULL))
+			return C_MASK;
+	}
+
+	if (hg > 0) { /* become sync source. */
+		rv = C_WF_BITMAP_S;
+	} else if (hg < 0) { /* become sync target */
+		rv = C_WF_BITMAP_T;
+	} else {
+		rv = C_CONNECTED;
+		if (drbd_bm_total_weight(device)) {
+			drbd_info(device, "No resync, but %lu bits in bitmap!\n",
+			     drbd_bm_total_weight(device));
+		}
+	}
+
+	return rv;
+}
+
+static enum drbd_after_sb_p convert_after_sb(enum drbd_after_sb_p peer)
+{
+	/* ASB_DISCARD_REMOTE - ASB_DISCARD_LOCAL is valid */
+	if (peer == ASB_DISCARD_REMOTE)
+		return ASB_DISCARD_LOCAL;
+
+	/* any other things with ASB_DISCARD_REMOTE or ASB_DISCARD_LOCAL are invalid */
+	if (peer == ASB_DISCARD_LOCAL)
+		return ASB_DISCARD_REMOTE;
+
+	/* everything else is valid if they are equal on both sides. */
+	return peer;
+}
+
+static int receive_protocol(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct p_protocol *p = pi->data;
+	enum drbd_after_sb_p p_after_sb_0p, p_after_sb_1p, p_after_sb_2p;
+	int p_proto, p_discard_my_data, p_two_primaries, cf;
+	struct net_conf *nc, *old_net_conf, *new_net_conf = NULL;
+	char integrity_alg[SHARED_SECRET_MAX] = "";
+	struct crypto_shash *peer_integrity_tfm = NULL;
+	void *int_dig_in = NULL, *int_dig_vv = NULL;
+
+	p_proto		= be32_to_cpu(p->protocol);
+	p_after_sb_0p	= be32_to_cpu(p->after_sb_0p);
+	p_after_sb_1p	= be32_to_cpu(p->after_sb_1p);
+	p_after_sb_2p	= be32_to_cpu(p->after_sb_2p);
+	p_two_primaries = be32_to_cpu(p->two_primaries);
+	cf		= be32_to_cpu(p->conn_flags);
+	p_discard_my_data = cf & CF_DISCARD_MY_DATA;
+
+	if (connection->agreed_pro_version >= 87) {
+		int err;
+
+		if (pi->size > sizeof(integrity_alg))
+			return -EIO;
+		err = drbd_recv_all(connection, integrity_alg, pi->size);
+		if (err)
+			return err;
+		integrity_alg[SHARED_SECRET_MAX - 1] = 0;
+	}
+
+	if (pi->cmd != P_PROTOCOL_UPDATE) {
+		clear_bit(CONN_DRY_RUN, &connection->flags);
+
+		if (cf & CF_DRY_RUN)
+			set_bit(CONN_DRY_RUN, &connection->flags);
+
+		rcu_read_lock();
+		nc = rcu_dereference(connection->net_conf);
+
+		if (p_proto != nc->wire_protocol) {
+			drbd_err(connection, "incompatible %s settings\n", "protocol");
+			goto disconnect_rcu_unlock;
+		}
+
+		if (convert_after_sb(p_after_sb_0p) != nc->after_sb_0p) {
+			drbd_err(connection, "incompatible %s settings\n", "after-sb-0pri");
+			goto disconnect_rcu_unlock;
+		}
+
+		if (convert_after_sb(p_after_sb_1p) != nc->after_sb_1p) {
+			drbd_err(connection, "incompatible %s settings\n", "after-sb-1pri");
+			goto disconnect_rcu_unlock;
+		}
+
+		if (convert_after_sb(p_after_sb_2p) != nc->after_sb_2p) {
+			drbd_err(connection, "incompatible %s settings\n", "after-sb-2pri");
+			goto disconnect_rcu_unlock;
+		}
+
+		if (p_discard_my_data && nc->discard_my_data) {
+			drbd_err(connection, "incompatible %s settings\n", "discard-my-data");
+			goto disconnect_rcu_unlock;
+		}
+
+		if (p_two_primaries != nc->two_primaries) {
+			drbd_err(connection, "incompatible %s settings\n", "allow-two-primaries");
+			goto disconnect_rcu_unlock;
+		}
+
+		if (strcmp(integrity_alg, nc->integrity_alg)) {
+			drbd_err(connection, "incompatible %s settings\n", "data-integrity-alg");
+			goto disconnect_rcu_unlock;
+		}
+
+		rcu_read_unlock();
+	}
+
+	if (integrity_alg[0]) {
+		int hash_size;
+
+		/*
+		 * We can only change the peer data integrity algorithm
+		 * here.  Changing our own data integrity algorithm
+		 * requires that we send a P_PROTOCOL_UPDATE packet at
+		 * the same time; otherwise, the peer has no way to
+		 * tell between which packets the algorithm should
+		 * change.
+		 */
+
+		peer_integrity_tfm = crypto_alloc_shash(integrity_alg, 0, 0);
+		if (IS_ERR(peer_integrity_tfm)) {
+			peer_integrity_tfm = NULL;
+			drbd_err(connection, "peer data-integrity-alg %s not supported\n",
+				 integrity_alg);
+			goto disconnect;
+		}
+
+		hash_size = crypto_shash_digestsize(peer_integrity_tfm);
+		int_dig_in = kmalloc(hash_size, GFP_KERNEL);
+		int_dig_vv = kmalloc(hash_size, GFP_KERNEL);
+		if (!(int_dig_in && int_dig_vv)) {
+			drbd_err(connection, "Allocation of buffers for data integrity checking failed\n");
+			goto disconnect;
+		}
+	}
+
+	new_net_conf = kmalloc(sizeof(struct net_conf), GFP_KERNEL);
+	if (!new_net_conf)
+		goto disconnect;
+
+	mutex_lock(&connection->data.mutex);
+	mutex_lock(&connection->resource->conf_update);
+	old_net_conf = connection->net_conf;
+	*new_net_conf = *old_net_conf;
+
+	new_net_conf->wire_protocol = p_proto;
+	new_net_conf->after_sb_0p = convert_after_sb(p_after_sb_0p);
+	new_net_conf->after_sb_1p = convert_after_sb(p_after_sb_1p);
+	new_net_conf->after_sb_2p = convert_after_sb(p_after_sb_2p);
+	new_net_conf->two_primaries = p_two_primaries;
+
+	rcu_assign_pointer(connection->net_conf, new_net_conf);
+	mutex_unlock(&connection->resource->conf_update);
+	mutex_unlock(&connection->data.mutex);
+
+	crypto_free_shash(connection->peer_integrity_tfm);
+	kfree(connection->int_dig_in);
+	kfree(connection->int_dig_vv);
+	connection->peer_integrity_tfm = peer_integrity_tfm;
+	connection->int_dig_in = int_dig_in;
+	connection->int_dig_vv = int_dig_vv;
+
+	if (strcmp(old_net_conf->integrity_alg, integrity_alg))
+		drbd_info(connection, "peer data-integrity-alg: %s\n",
+			  integrity_alg[0] ? integrity_alg : "(none)");
+
+	kvfree_rcu_mightsleep(old_net_conf);
+	return 0;
+
+disconnect_rcu_unlock:
+	rcu_read_unlock();
+disconnect:
+	crypto_free_shash(peer_integrity_tfm);
+	kfree(int_dig_in);
+	kfree(int_dig_vv);
+	conn_request_state(connection, NS(conn, C_DISCONNECTING), CS_HARD);
+	return -EIO;
+}
+
+/* helper function
+ * input: alg name, feature name
+ * return: NULL (alg name was "")
+ *         ERR_PTR(error) if something goes wrong
+ *         or the crypto hash ptr, if it worked out ok. */
+static struct crypto_shash *drbd_crypto_alloc_digest_safe(
+		const struct drbd_device *device,
+		const char *alg, const char *name)
+{
+	struct crypto_shash *tfm;
+
+	if (!alg[0])
+		return NULL;
+
+	tfm = crypto_alloc_shash(alg, 0, 0);
+	if (IS_ERR(tfm)) {
+		drbd_err(device, "Can not allocate \"%s\" as %s (reason: %ld)\n",
+			alg, name, PTR_ERR(tfm));
+		return tfm;
+	}
+	return tfm;
+}
+
+static int ignore_remaining_packet(struct drbd_connection *connection, struct packet_info *pi)
+{
+	void *buffer = connection->data.rbuf;
+	int size = pi->size;
+
+	while (size) {
+		int s = min_t(int, size, DRBD_SOCKET_BUFFER_SIZE);
+		s = drbd_recv(connection, buffer, s);
+		if (s <= 0) {
+			if (s < 0)
+				return s;
+			break;
+		}
+		size -= s;
+	}
+	if (size)
+		return -EIO;
+	return 0;
+}
+
+/*
+ * config_unknown_volume  -  device configuration command for unknown volume
+ *
+ * When a device is added to an existing connection, the node on which the
+ * device is added first will send configuration commands to its peer but the
+ * peer will not know about the device yet.  It will warn and ignore these
+ * commands.  Once the device is added on the second node, the second node will
+ * send the same device configuration commands, but in the other direction.
+ *
+ * (We can also end up here if drbd is misconfigured.)
+ */
+static int config_unknown_volume(struct drbd_connection *connection, struct packet_info *pi)
+{
+	drbd_warn(connection, "%s packet received for volume %u, which is not configured locally\n",
+		  cmdname(pi->cmd), pi->vnr);
+	return ignore_remaining_packet(connection, pi);
+}
+
+static int receive_SyncParam(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct p_rs_param_95 *p;
+	unsigned int header_size, data_size, exp_max_sz;
+	struct crypto_shash *verify_tfm = NULL;
+	struct crypto_shash *csums_tfm = NULL;
+	struct net_conf *old_net_conf, *new_net_conf = NULL;
+	struct disk_conf *old_disk_conf = NULL, *new_disk_conf = NULL;
+	const int apv = connection->agreed_pro_version;
+	struct fifo_buffer *old_plan = NULL, *new_plan = NULL;
+	unsigned int fifo_size = 0;
+	int err;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return config_unknown_volume(connection, pi);
+	device = peer_device->device;
+
+	exp_max_sz  = apv <= 87 ? sizeof(struct p_rs_param)
+		    : apv == 88 ? sizeof(struct p_rs_param)
+					+ SHARED_SECRET_MAX
+		    : apv <= 94 ? sizeof(struct p_rs_param_89)
+		    : /* apv >= 95 */ sizeof(struct p_rs_param_95);
+
+	if (pi->size > exp_max_sz) {
+		drbd_err(device, "SyncParam packet too long: received %u, expected <= %u bytes\n",
+		    pi->size, exp_max_sz);
+		return -EIO;
+	}
+
+	if (apv <= 88) {
+		header_size = sizeof(struct p_rs_param);
+		data_size = pi->size - header_size;
+	} else if (apv <= 94) {
+		header_size = sizeof(struct p_rs_param_89);
+		data_size = pi->size - header_size;
+		D_ASSERT(device, data_size == 0);
+	} else {
+		header_size = sizeof(struct p_rs_param_95);
+		data_size = pi->size - header_size;
+		D_ASSERT(device, data_size == 0);
+	}
+
+	/* initialize verify_alg and csums_alg */
+	p = pi->data;
+	BUILD_BUG_ON(sizeof(p->algs) != 2 * SHARED_SECRET_MAX);
+	memset(&p->algs, 0, sizeof(p->algs));
+
+	err = drbd_recv_all(peer_device->connection, p, header_size);
+	if (err)
+		return err;
+
+	mutex_lock(&connection->resource->conf_update);
+	old_net_conf = peer_device->connection->net_conf;
+	if (get_ldev(device)) {
+		new_disk_conf = kzalloc(sizeof(struct disk_conf), GFP_KERNEL);
+		if (!new_disk_conf) {
+			put_ldev(device);
+			mutex_unlock(&connection->resource->conf_update);
+			drbd_err(device, "Allocation of new disk_conf failed\n");
+			return -ENOMEM;
+		}
+
+		old_disk_conf = device->ldev->disk_conf;
+		*new_disk_conf = *old_disk_conf;
+
+		new_disk_conf->resync_rate = be32_to_cpu(p->resync_rate);
+	}
+
+	if (apv >= 88) {
+		if (apv == 88) {
+			if (data_size > SHARED_SECRET_MAX || data_size == 0) {
+				drbd_err(device, "verify-alg of wrong size, "
+					"peer wants %u, accepting only up to %u byte\n",
+					data_size, SHARED_SECRET_MAX);
+				goto reconnect;
+			}
+
+			err = drbd_recv_all(peer_device->connection, p->verify_alg, data_size);
+			if (err)
+				goto reconnect;
+			/* we expect NUL terminated string */
+			/* but just in case someone tries to be evil */
+			D_ASSERT(device, p->verify_alg[data_size-1] == 0);
+			p->verify_alg[data_size-1] = 0;
+
+		} else /* apv >= 89 */ {
+			/* we still expect NUL terminated strings */
+			/* but just in case someone tries to be evil */
+			D_ASSERT(device, p->verify_alg[SHARED_SECRET_MAX-1] == 0);
+			D_ASSERT(device, p->csums_alg[SHARED_SECRET_MAX-1] == 0);
+			p->verify_alg[SHARED_SECRET_MAX-1] = 0;
+			p->csums_alg[SHARED_SECRET_MAX-1] = 0;
+		}
+
+		if (strcmp(old_net_conf->verify_alg, p->verify_alg)) {
+			if (device->state.conn == C_WF_REPORT_PARAMS) {
+				drbd_err(device, "Different verify-alg settings. me=\"%s\" peer=\"%s\"\n",
+				    old_net_conf->verify_alg, p->verify_alg);
+				goto disconnect;
+			}
+			verify_tfm = drbd_crypto_alloc_digest_safe(device,
+					p->verify_alg, "verify-alg");
+			if (IS_ERR(verify_tfm)) {
+				verify_tfm = NULL;
+				goto disconnect;
+			}
+		}
+
+		if (apv >= 89 && strcmp(old_net_conf->csums_alg, p->csums_alg)) {
+			if (device->state.conn == C_WF_REPORT_PARAMS) {
+				drbd_err(device, "Different csums-alg settings. me=\"%s\" peer=\"%s\"\n",
+				    old_net_conf->csums_alg, p->csums_alg);
+				goto disconnect;
+			}
+			csums_tfm = drbd_crypto_alloc_digest_safe(device,
+					p->csums_alg, "csums-alg");
+			if (IS_ERR(csums_tfm)) {
+				csums_tfm = NULL;
+				goto disconnect;
+			}
+		}
+
+		if (apv > 94 && new_disk_conf) {
+			new_disk_conf->c_plan_ahead = be32_to_cpu(p->c_plan_ahead);
+			new_disk_conf->c_delay_target = be32_to_cpu(p->c_delay_target);
+			new_disk_conf->c_fill_target = be32_to_cpu(p->c_fill_target);
+			new_disk_conf->c_max_rate = be32_to_cpu(p->c_max_rate);
+
+			fifo_size = (new_disk_conf->c_plan_ahead * 10 * SLEEP_TIME) / HZ;
+			if (fifo_size != device->rs_plan_s->size) {
+				new_plan = fifo_alloc(fifo_size);
+				if (!new_plan) {
+					drbd_err(device, "kmalloc of fifo_buffer failed");
+					put_ldev(device);
+					goto disconnect;
+				}
+			}
+		}
+
+		if (verify_tfm || csums_tfm) {
+			new_net_conf = kzalloc(sizeof(struct net_conf), GFP_KERNEL);
+			if (!new_net_conf)
+				goto disconnect;
+
+			*new_net_conf = *old_net_conf;
+
+			if (verify_tfm) {
+				strcpy(new_net_conf->verify_alg, p->verify_alg);
+				new_net_conf->verify_alg_len = strlen(p->verify_alg) + 1;
+				crypto_free_shash(peer_device->connection->verify_tfm);
+				peer_device->connection->verify_tfm = verify_tfm;
+				drbd_info(device, "using verify-alg: \"%s\"\n", p->verify_alg);
+			}
+			if (csums_tfm) {
+				strcpy(new_net_conf->csums_alg, p->csums_alg);
+				new_net_conf->csums_alg_len = strlen(p->csums_alg) + 1;
+				crypto_free_shash(peer_device->connection->csums_tfm);
+				peer_device->connection->csums_tfm = csums_tfm;
+				drbd_info(device, "using csums-alg: \"%s\"\n", p->csums_alg);
+			}
+			rcu_assign_pointer(connection->net_conf, new_net_conf);
+		}
+	}
+
+	if (new_disk_conf) {
+		rcu_assign_pointer(device->ldev->disk_conf, new_disk_conf);
+		put_ldev(device);
+	}
+
+	if (new_plan) {
+		old_plan = device->rs_plan_s;
+		rcu_assign_pointer(device->rs_plan_s, new_plan);
+	}
+
+	mutex_unlock(&connection->resource->conf_update);
+	synchronize_rcu();
+	if (new_net_conf)
+		kfree(old_net_conf);
+	kfree(old_disk_conf);
+	kfree(old_plan);
+
+	return 0;
+
+reconnect:
+	if (new_disk_conf) {
+		put_ldev(device);
+		kfree(new_disk_conf);
+	}
+	mutex_unlock(&connection->resource->conf_update);
+	return -EIO;
+
+disconnect:
+	kfree(new_plan);
+	if (new_disk_conf) {
+		put_ldev(device);
+		kfree(new_disk_conf);
+	}
+	mutex_unlock(&connection->resource->conf_update);
+	/* just for completeness: actually not needed,
+	 * as this is not reached if csums_tfm was ok. */
+	crypto_free_shash(csums_tfm);
+	/* but free the verify_tfm again, if csums_tfm did not work out */
+	crypto_free_shash(verify_tfm);
+	conn_request_state(peer_device->connection, NS(conn, C_DISCONNECTING), CS_HARD);
+	return -EIO;
+}
+
+/* warn if the arguments differ by more than 12.5% */
+static void warn_if_differ_considerably(struct drbd_device *device,
+	const char *s, sector_t a, sector_t b)
+{
+	sector_t d;
+	if (a == 0 || b == 0)
+		return;
+	d = (a > b) ? (a - b) : (b - a);
+	if (d > (a>>3) || d > (b>>3))
+		drbd_warn(device, "Considerable difference in %s: %llus vs. %llus\n", s,
+		     (unsigned long long)a, (unsigned long long)b);
+}
+
+static int receive_sizes(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct p_sizes *p = pi->data;
+	struct o_qlim *o = (connection->agreed_features & DRBD_FF_WSAME) ? p->qlim : NULL;
+	enum determine_dev_size dd = DS_UNCHANGED;
+	sector_t p_size, p_usize, p_csize, my_usize;
+	sector_t new_size, cur_size;
+	int ldsc = 0; /* local disk size changed */
+	enum dds_flags ddsf;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return config_unknown_volume(connection, pi);
+	device = peer_device->device;
+	cur_size = get_capacity(device->vdisk);
+
+	p_size = be64_to_cpu(p->d_size);
+	p_usize = be64_to_cpu(p->u_size);
+	p_csize = be64_to_cpu(p->c_size);
+
+	/* just store the peer's disk size for now.
+	 * we still need to figure out whether we accept that. */
+	device->p_size = p_size;
+
+	if (get_ldev(device)) {
+		rcu_read_lock();
+		my_usize = rcu_dereference(device->ldev->disk_conf)->disk_size;
+		rcu_read_unlock();
+
+		warn_if_differ_considerably(device, "lower level device sizes",
+			   p_size, drbd_get_max_capacity(device->ldev));
+		warn_if_differ_considerably(device, "user requested size",
+					    p_usize, my_usize);
+
+		/* if this is the first connect, or an otherwise expected
+		 * param exchange, choose the minimum */
+		if (device->state.conn == C_WF_REPORT_PARAMS)
+			p_usize = min_not_zero(my_usize, p_usize);
+
+		/* Never shrink a device with usable data during connect,
+		 * or "attach" on the peer.
+		 * But allow online shrinking if we are connected. */
+		new_size = drbd_new_dev_size(device, device->ldev, p_usize, 0);
+		if (new_size < cur_size &&
+		    device->state.disk >= D_OUTDATED &&
+		    (device->state.conn < C_CONNECTED || device->state.pdsk == D_DISKLESS)) {
+			drbd_err(device, "The peer's disk size is too small! (%llu < %llu sectors)\n",
+					(unsigned long long)new_size, (unsigned long long)cur_size);
+			conn_request_state(peer_device->connection, NS(conn, C_DISCONNECTING), CS_HARD);
+			put_ldev(device);
+			return -EIO;
+		}
+
+		if (my_usize != p_usize) {
+			struct disk_conf *old_disk_conf, *new_disk_conf = NULL;
+
+			new_disk_conf = kzalloc(sizeof(struct disk_conf), GFP_KERNEL);
+			if (!new_disk_conf) {
+				put_ldev(device);
+				return -ENOMEM;
+			}
+
+			mutex_lock(&connection->resource->conf_update);
+			old_disk_conf = device->ldev->disk_conf;
+			*new_disk_conf = *old_disk_conf;
+			new_disk_conf->disk_size = p_usize;
+
+			rcu_assign_pointer(device->ldev->disk_conf, new_disk_conf);
+			mutex_unlock(&connection->resource->conf_update);
+			kvfree_rcu_mightsleep(old_disk_conf);
+
+			drbd_info(device, "Peer sets u_size to %lu sectors (old: %lu)\n",
+				 (unsigned long)p_usize, (unsigned long)my_usize);
+		}
+
+		put_ldev(device);
+	}
+
+	device->peer_max_bio_size = be32_to_cpu(p->max_bio_size);
+	/* Leave drbd_reconsider_queue_parameters() before drbd_determine_dev_size().
+	   In case we cleared the QUEUE_FLAG_DISCARD from our queue in
+	   drbd_reconsider_queue_parameters(), we can be sure that after
+	   drbd_determine_dev_size() no REQ_DISCARDs are in the queue. */
+
+	ddsf = be16_to_cpu(p->dds_flags);
+	if (get_ldev(device)) {
+		drbd_reconsider_queue_parameters(device, device->ldev, o);
+		dd = drbd_determine_dev_size(device, ddsf, NULL);
+		put_ldev(device);
+		if (dd == DS_ERROR)
+			return -EIO;
+		drbd_md_sync(device);
+	} else {
+		/*
+		 * I am diskless, need to accept the peer's *current* size.
+		 * I must NOT accept the peers backing disk size,
+		 * it may have been larger than mine all along...
+		 *
+		 * At this point, the peer knows more about my disk, or at
+		 * least about what we last agreed upon, than myself.
+		 * So if his c_size is less than his d_size, the most likely
+		 * reason is that *my* d_size was smaller last time we checked.
+		 *
+		 * However, if he sends a zero current size,
+		 * take his (user-capped or) backing disk size anyways.
+		 *
+		 * Unless of course he does not have a disk himself.
+		 * In which case we ignore this completely.
+		 */
+		sector_t new_size = p_csize ?: p_usize ?: p_size;
+		drbd_reconsider_queue_parameters(device, NULL, o);
+		if (new_size == 0) {
+			/* Ignore, peer does not know nothing. */
+		} else if (new_size == cur_size) {
+			/* nothing to do */
+		} else if (cur_size != 0 && p_size == 0) {
+			drbd_warn(device, "Ignored diskless peer device size (peer:%llu != me:%llu sectors)!\n",
+					(unsigned long long)new_size, (unsigned long long)cur_size);
+		} else if (new_size < cur_size && device->state.role == R_PRIMARY) {
+			drbd_err(device, "The peer's device size is too small! (%llu < %llu sectors); demote me first!\n",
+					(unsigned long long)new_size, (unsigned long long)cur_size);
+			conn_request_state(peer_device->connection, NS(conn, C_DISCONNECTING), CS_HARD);
+			return -EIO;
+		} else {
+			/* I believe the peer, if
+			 *  - I don't have a current size myself
+			 *  - we agree on the size anyways
+			 *  - I do have a current size, am Secondary,
+			 *    and he has the only disk
+			 *  - I do have a current size, am Primary,
+			 *    and he has the only disk,
+			 *    which is larger than my current size
+			 */
+			drbd_set_my_capacity(device, new_size);
+		}
+	}
+
+	if (get_ldev(device)) {
+		if (device->ldev->known_size != drbd_get_capacity(device->ldev->backing_bdev)) {
+			device->ldev->known_size = drbd_get_capacity(device->ldev->backing_bdev);
+			ldsc = 1;
+		}
+
+		put_ldev(device);
+	}
+
+	if (device->state.conn > C_WF_REPORT_PARAMS) {
+		if (be64_to_cpu(p->c_size) != get_capacity(device->vdisk) ||
+		    ldsc) {
+			/* we have different sizes, probably peer
+			 * needs to know my new size... */
+			drbd_send_sizes(peer_device, 0, ddsf);
+		}
+		if (test_and_clear_bit(RESIZE_PENDING, &device->flags) ||
+		    (dd == DS_GREW && device->state.conn == C_CONNECTED)) {
+			if (device->state.pdsk >= D_INCONSISTENT &&
+			    device->state.disk >= D_INCONSISTENT) {
+				if (ddsf & DDSF_NO_RESYNC)
+					drbd_info(device, "Resync of new storage suppressed with --assume-clean\n");
+				else
+					resync_after_online_grow(device);
+			} else
+				set_bit(RESYNC_AFTER_NEG, &device->flags);
+		}
+	}
+
+	return 0;
+}
+
+static int receive_uuids(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct p_uuids *p = pi->data;
+	u64 *p_uuid;
+	int i, updated_uuids = 0;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return config_unknown_volume(connection, pi);
+	device = peer_device->device;
+
+	p_uuid = kmalloc_array(UI_EXTENDED_SIZE, sizeof(*p_uuid), GFP_NOIO);
+	if (!p_uuid)
+		return false;
+
+	for (i = UI_CURRENT; i < UI_EXTENDED_SIZE; i++)
+		p_uuid[i] = be64_to_cpu(p->uuid[i]);
+
+	kfree(device->p_uuid);
+	device->p_uuid = p_uuid;
+
+	if ((device->state.conn < C_CONNECTED || device->state.pdsk == D_DISKLESS) &&
+	    device->state.disk < D_INCONSISTENT &&
+	    device->state.role == R_PRIMARY &&
+	    (device->ed_uuid & ~((u64)1)) != (p_uuid[UI_CURRENT] & ~((u64)1))) {
+		drbd_err(device, "Can only connect to data with current UUID=%016llX\n",
+		    (unsigned long long)device->ed_uuid);
+		conn_request_state(peer_device->connection, NS(conn, C_DISCONNECTING), CS_HARD);
+		return -EIO;
+	}
+
+	if (get_ldev(device)) {
+		int skip_initial_sync =
+			device->state.conn == C_CONNECTED &&
+			peer_device->connection->agreed_pro_version >= 90 &&
+			device->ldev->md.uuid[UI_CURRENT] == UUID_JUST_CREATED &&
+			(p_uuid[UI_FLAGS] & 8);
+		if (skip_initial_sync) {
+			drbd_info(device, "Accepted new current UUID, preparing to skip initial sync\n");
+			drbd_bitmap_io(device, &drbd_bmio_clear_n_write,
+					"clear_n_write from receive_uuids",
+					BM_LOCKED_TEST_ALLOWED, NULL);
+			_drbd_uuid_set(device, UI_CURRENT, p_uuid[UI_CURRENT]);
+			_drbd_uuid_set(device, UI_BITMAP, 0);
+			_drbd_set_state(_NS2(device, disk, D_UP_TO_DATE, pdsk, D_UP_TO_DATE),
+					CS_VERBOSE, NULL);
+			drbd_md_sync(device);
+			updated_uuids = 1;
+		}
+		put_ldev(device);
+	} else if (device->state.disk < D_INCONSISTENT &&
+		   device->state.role == R_PRIMARY) {
+		/* I am a diskless primary, the peer just created a new current UUID
+		   for me. */
+		updated_uuids = drbd_set_ed_uuid(device, p_uuid[UI_CURRENT]);
+	}
+
+	/* Before we test for the disk state, we should wait until an eventually
+	   ongoing cluster wide state change is finished. That is important if
+	   we are primary and are detaching from our disk. We need to see the
+	   new disk state... */
+	mutex_lock(device->state_mutex);
+	mutex_unlock(device->state_mutex);
+	if (device->state.conn >= C_CONNECTED && device->state.disk < D_INCONSISTENT)
+		updated_uuids |= drbd_set_ed_uuid(device, p_uuid[UI_CURRENT]);
+
+	if (updated_uuids)
+		drbd_print_uuids(device, "receiver updated UUIDs to");
+
+	return 0;
+}
+
+/**
+ * convert_state() - Converts the peer's view of the cluster state to our point of view
+ * @ps:		The state as seen by the peer.
+ */
+static union drbd_state convert_state(union drbd_state ps)
+{
+	union drbd_state ms;
+
+	static enum drbd_conns c_tab[] = {
+		[C_WF_REPORT_PARAMS] = C_WF_REPORT_PARAMS,
+		[C_CONNECTED] = C_CONNECTED,
+
+		[C_STARTING_SYNC_S] = C_STARTING_SYNC_T,
+		[C_STARTING_SYNC_T] = C_STARTING_SYNC_S,
+		[C_DISCONNECTING] = C_TEAR_DOWN, /* C_NETWORK_FAILURE, */
+		[C_VERIFY_S]       = C_VERIFY_T,
+		[C_MASK]   = C_MASK,
+	};
+
+	ms.i = ps.i;
+
+	ms.conn = c_tab[ps.conn];
+	ms.peer = ps.role;
+	ms.role = ps.peer;
+	ms.pdsk = ps.disk;
+	ms.disk = ps.pdsk;
+	ms.peer_isp = (ps.aftr_isp | ps.user_isp);
+
+	return ms;
+}
+
+static int receive_req_state(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct p_req_state *p = pi->data;
+	union drbd_state mask, val;
+	enum drbd_state_rv rv;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+
+	mask.i = be32_to_cpu(p->mask);
+	val.i = be32_to_cpu(p->val);
+
+	if (test_bit(RESOLVE_CONFLICTS, &peer_device->connection->flags) &&
+	    mutex_is_locked(device->state_mutex)) {
+		drbd_send_sr_reply(peer_device, SS_CONCURRENT_ST_CHG);
+		return 0;
+	}
+
+	mask = convert_state(mask);
+	val = convert_state(val);
+
+	rv = drbd_change_state(device, CS_VERBOSE, mask, val);
+	drbd_send_sr_reply(peer_device, rv);
+
+	drbd_md_sync(device);
+
+	return 0;
+}
+
+static int receive_req_conn_state(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct p_req_state *p = pi->data;
+	union drbd_state mask, val;
+	enum drbd_state_rv rv;
+
+	mask.i = be32_to_cpu(p->mask);
+	val.i = be32_to_cpu(p->val);
+
+	if (test_bit(RESOLVE_CONFLICTS, &connection->flags) &&
+	    mutex_is_locked(&connection->cstate_mutex)) {
+		conn_send_sr_reply(connection, SS_CONCURRENT_ST_CHG);
+		return 0;
+	}
+
+	mask = convert_state(mask);
+	val = convert_state(val);
+
+	rv = conn_request_state(connection, mask, val, CS_VERBOSE | CS_LOCAL_ONLY | CS_IGN_OUTD_FAIL);
+	conn_send_sr_reply(connection, rv);
+
+	return 0;
+}
+
+static int receive_state(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct p_state *p = pi->data;
+	union drbd_state os, ns, peer_state;
+	enum drbd_disk_state real_peer_disk;
+	enum chg_state_flags cs_flags;
+	int rv;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return config_unknown_volume(connection, pi);
+	device = peer_device->device;
+
+	peer_state.i = be32_to_cpu(p->state);
+
+	real_peer_disk = peer_state.disk;
+	if (peer_state.disk == D_NEGOTIATING) {
+		real_peer_disk = device->p_uuid[UI_FLAGS] & 4 ? D_INCONSISTENT : D_CONSISTENT;
+		drbd_info(device, "real peer disk state = %s\n", drbd_disk_str(real_peer_disk));
+	}
+
+	spin_lock_irq(&device->resource->req_lock);
+ retry:
+	os = ns = drbd_read_state(device);
+	spin_unlock_irq(&device->resource->req_lock);
+
+	/* If some other part of the code (ack_receiver thread, timeout)
+	 * already decided to close the connection again,
+	 * we must not "re-establish" it here. */
+	if (os.conn <= C_TEAR_DOWN)
+		return -ECONNRESET;
+
+	/* If this is the "end of sync" confirmation, usually the peer disk
+	 * transitions from D_INCONSISTENT to D_UP_TO_DATE. For empty (0 bits
+	 * set) resync started in PausedSyncT, or if the timing of pause-/
+	 * unpause-sync events has been "just right", the peer disk may
+	 * transition from D_CONSISTENT to D_UP_TO_DATE as well.
+	 */
+	if ((os.pdsk == D_INCONSISTENT || os.pdsk == D_CONSISTENT) &&
+	    real_peer_disk == D_UP_TO_DATE &&
+	    os.conn > C_CONNECTED && os.disk == D_UP_TO_DATE) {
+		/* If we are (becoming) SyncSource, but peer is still in sync
+		 * preparation, ignore its uptodate-ness to avoid flapping, it
+		 * will change to inconsistent once the peer reaches active
+		 * syncing states.
+		 * It may have changed syncer-paused flags, however, so we
+		 * cannot ignore this completely. */
+		if (peer_state.conn > C_CONNECTED &&
+		    peer_state.conn < C_SYNC_SOURCE)
+			real_peer_disk = D_INCONSISTENT;
+
+		/* if peer_state changes to connected at the same time,
+		 * it explicitly notifies us that it finished resync.
+		 * Maybe we should finish it up, too? */
+		else if (os.conn >= C_SYNC_SOURCE &&
+			 peer_state.conn == C_CONNECTED) {
+			if (drbd_bm_total_weight(device) <= device->rs_failed)
+				drbd_resync_finished(peer_device);
+			return 0;
+		}
+	}
+
+	/* explicit verify finished notification, stop sector reached. */
+	if (os.conn == C_VERIFY_T && os.disk == D_UP_TO_DATE &&
+	    peer_state.conn == C_CONNECTED && real_peer_disk == D_UP_TO_DATE) {
+		ov_out_of_sync_print(peer_device);
+		drbd_resync_finished(peer_device);
+		return 0;
+	}
+
+	/* peer says his disk is inconsistent, while we think it is uptodate,
+	 * and this happens while the peer still thinks we have a sync going on,
+	 * but we think we are already done with the sync.
+	 * We ignore this to avoid flapping pdsk.
+	 * This should not happen, if the peer is a recent version of drbd. */
+	if (os.pdsk == D_UP_TO_DATE && real_peer_disk == D_INCONSISTENT &&
+	    os.conn == C_CONNECTED && peer_state.conn > C_SYNC_SOURCE)
+		real_peer_disk = D_UP_TO_DATE;
+
+	if (ns.conn == C_WF_REPORT_PARAMS)
+		ns.conn = C_CONNECTED;
+
+	if (peer_state.conn == C_AHEAD)
+		ns.conn = C_BEHIND;
+
+	/* TODO:
+	 * if (primary and diskless and peer uuid != effective uuid)
+	 *     abort attach on peer;
+	 *
+	 * If this node does not have good data, was already connected, but
+	 * the peer did a late attach only now, trying to "negotiate" with me,
+	 * AND I am currently Primary, possibly frozen, with some specific
+	 * "effective" uuid, this should never be reached, really, because
+	 * we first send the uuids, then the current state.
+	 *
+	 * In this scenario, we already dropped the connection hard
+	 * when we received the unsuitable uuids (receive_uuids().
+	 *
+	 * Should we want to change this, that is: not drop the connection in
+	 * receive_uuids() already, then we would need to add a branch here
+	 * that aborts the attach of "unsuitable uuids" on the peer in case
+	 * this node is currently Diskless Primary.
+	 */
+
+	if (device->p_uuid && peer_state.disk >= D_NEGOTIATING &&
+	    get_ldev_if_state(device, D_NEGOTIATING)) {
+		int cr; /* consider resync */
+
+		/* if we established a new connection */
+		cr  = (os.conn < C_CONNECTED);
+		/* if we had an established connection
+		 * and one of the nodes newly attaches a disk */
+		cr |= (os.conn == C_CONNECTED &&
+		       (peer_state.disk == D_NEGOTIATING ||
+			os.disk == D_NEGOTIATING));
+		/* if we have both been inconsistent, and the peer has been
+		 * forced to be UpToDate with --force */
+		cr |= test_bit(CONSIDER_RESYNC, &device->flags);
+		/* if we had been plain connected, and the admin requested to
+		 * start a sync by "invalidate" or "invalidate-remote" */
+		cr |= (os.conn == C_CONNECTED &&
+				(peer_state.conn >= C_STARTING_SYNC_S &&
+				 peer_state.conn <= C_WF_BITMAP_T));
+
+		if (cr)
+			ns.conn = drbd_sync_handshake(peer_device, peer_state.role, real_peer_disk);
+
+		put_ldev(device);
+		if (ns.conn == C_MASK) {
+			ns.conn = C_CONNECTED;
+			if (device->state.disk == D_NEGOTIATING) {
+				drbd_force_state(device, NS(disk, D_FAILED));
+			} else if (peer_state.disk == D_NEGOTIATING) {
+				drbd_err(device, "Disk attach process on the peer node was aborted.\n");
+				peer_state.disk = D_DISKLESS;
+				real_peer_disk = D_DISKLESS;
+			} else {
+				if (test_and_clear_bit(CONN_DRY_RUN, &peer_device->connection->flags))
+					return -EIO;
+				D_ASSERT(device, os.conn == C_WF_REPORT_PARAMS);
+				conn_request_state(peer_device->connection, NS(conn, C_DISCONNECTING), CS_HARD);
+				return -EIO;
+			}
+		}
+	}
+
+	spin_lock_irq(&device->resource->req_lock);
+	if (os.i != drbd_read_state(device).i)
+		goto retry;
+	clear_bit(CONSIDER_RESYNC, &device->flags);
+	ns.peer = peer_state.role;
+	ns.pdsk = real_peer_disk;
+	ns.peer_isp = (peer_state.aftr_isp | peer_state.user_isp);
+	if ((ns.conn == C_CONNECTED || ns.conn == C_WF_BITMAP_S) && ns.disk == D_NEGOTIATING)
+		ns.disk = device->new_state_tmp.disk;
+	cs_flags = CS_VERBOSE + (os.conn < C_CONNECTED && ns.conn >= C_CONNECTED ? 0 : CS_HARD);
+	if (ns.pdsk == D_CONSISTENT && drbd_suspended(device) && ns.conn == C_CONNECTED && os.conn < C_CONNECTED &&
+	    test_bit(NEW_CUR_UUID, &device->flags)) {
+		/* Do not allow tl_restart(RESEND) for a rebooted peer. We can only allow this
+		   for temporal network outages! */
+		spin_unlock_irq(&device->resource->req_lock);
+		drbd_err(device, "Aborting Connect, can not thaw IO with an only Consistent peer\n");
+		tl_clear(peer_device->connection);
+		drbd_uuid_new_current(device);
+		clear_bit(NEW_CUR_UUID, &device->flags);
+		conn_request_state(peer_device->connection, NS2(conn, C_PROTOCOL_ERROR, susp, 0), CS_HARD);
+		return -EIO;
+	}
+	rv = _drbd_set_state(device, ns, cs_flags, NULL);
+	ns = drbd_read_state(device);
+	spin_unlock_irq(&device->resource->req_lock);
+
+	if (rv < SS_SUCCESS) {
+		conn_request_state(peer_device->connection, NS(conn, C_DISCONNECTING), CS_HARD);
+		return -EIO;
+	}
+
+	if (os.conn > C_WF_REPORT_PARAMS) {
+		if (ns.conn > C_CONNECTED && peer_state.conn <= C_CONNECTED &&
+		    peer_state.disk != D_NEGOTIATING ) {
+			/* we want resync, peer has not yet decided to sync... */
+			/* Nowadays only used when forcing a node into primary role and
+			   setting its disk to UpToDate with that */
+			drbd_send_uuids(peer_device);
+			drbd_send_current_state(peer_device);
+		}
+	}
+
+	clear_bit(DISCARD_MY_DATA, &device->flags);
+
+	drbd_md_sync(device); /* update connected indicator, la_size_sect, ... */
+
+	return 0;
+}
+
+static int receive_sync_uuid(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct p_rs_uuid *p = pi->data;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+
+	wait_event(device->misc_wait,
+		   device->state.conn == C_WF_SYNC_UUID ||
+		   device->state.conn == C_BEHIND ||
+		   device->state.conn < C_CONNECTED ||
+		   device->state.disk < D_NEGOTIATING);
+
+	/* D_ASSERT(device,  device->state.conn == C_WF_SYNC_UUID ); */
+
+	/* Here the _drbd_uuid_ functions are right, current should
+	   _not_ be rotated into the history */
+	if (get_ldev_if_state(device, D_NEGOTIATING)) {
+		_drbd_uuid_set(device, UI_CURRENT, be64_to_cpu(p->uuid));
+		_drbd_uuid_set(device, UI_BITMAP, 0UL);
+
+		drbd_print_uuids(device, "updated sync uuid");
+		drbd_start_resync(device, C_SYNC_TARGET);
+
+		put_ldev(device);
+	} else
+		drbd_err(device, "Ignoring SyncUUID packet!\n");
+
+	return 0;
+}
+
+/*
+ * receive_bitmap_plain
+ *
+ * Return 0 when done, 1 when another iteration is needed, and a negative error
+ * code upon failure.
+ */
+static int
+receive_bitmap_plain(struct drbd_peer_device *peer_device, unsigned int size,
+		     unsigned long *p, struct bm_xfer_ctx *c)
+{
+	unsigned int data_size = DRBD_SOCKET_BUFFER_SIZE -
+				 drbd_header_size(peer_device->connection);
+	unsigned int num_words = min_t(size_t, data_size / sizeof(*p),
+				       c->bm_words - c->word_offset);
+	unsigned int want = num_words * sizeof(*p);
+	int err;
+
+	if (want != size) {
+		drbd_err(peer_device, "%s:want (%u) != size (%u)\n", __func__, want, size);
+		return -EIO;
+	}
+	if (want == 0)
+		return 0;
+	err = drbd_recv_all(peer_device->connection, p, want);
+	if (err)
+		return err;
+
+	drbd_bm_merge_lel(peer_device->device, c->word_offset, num_words, p);
+
+	c->word_offset += num_words;
+	c->bit_offset = c->word_offset * BITS_PER_LONG;
+	if (c->bit_offset > c->bm_bits)
+		c->bit_offset = c->bm_bits;
+
+	return 1;
+}
+
+static enum drbd_bitmap_code dcbp_get_code(struct p_compressed_bm *p)
+{
+	return (enum drbd_bitmap_code)(p->encoding & 0x0f);
+}
+
+static int dcbp_get_start(struct p_compressed_bm *p)
+{
+	return (p->encoding & 0x80) != 0;
+}
+
+static int dcbp_get_pad_bits(struct p_compressed_bm *p)
+{
+	return (p->encoding >> 4) & 0x7;
+}
+
+/*
+ * recv_bm_rle_bits
+ *
+ * Return 0 when done, 1 when another iteration is needed, and a negative error
+ * code upon failure.
+ */
+static int
+recv_bm_rle_bits(struct drbd_peer_device *peer_device,
+		struct p_compressed_bm *p,
+		 struct bm_xfer_ctx *c,
+		 unsigned int len)
+{
+	struct bitstream bs;
+	u64 look_ahead;
+	u64 rl;
+	u64 tmp;
+	unsigned long s = c->bit_offset;
+	unsigned long e;
+	int toggle = dcbp_get_start(p);
+	int have;
+	int bits;
+
+	bitstream_init(&bs, p->code, len, dcbp_get_pad_bits(p));
+
+	bits = bitstream_get_bits(&bs, &look_ahead, 64);
+	if (bits < 0)
+		return -EIO;
+
+	for (have = bits; have > 0; s += rl, toggle = !toggle) {
+		bits = vli_decode_bits(&rl, look_ahead);
+		if (bits <= 0)
+			return -EIO;
+
+		if (toggle) {
+			e = s + rl -1;
+			if (e >= c->bm_bits) {
+				drbd_err(peer_device, "bitmap overflow (e:%lu) while decoding bm RLE packet\n", e);
+				return -EIO;
+			}
+			_drbd_bm_set_bits(peer_device->device, s, e);
+		}
+
+		if (have < bits) {
+			drbd_err(peer_device, "bitmap decoding error: h:%d b:%d la:0x%08llx l:%u/%u\n",
+				have, bits, look_ahead,
+				(unsigned int)(bs.cur.b - p->code),
+				(unsigned int)bs.buf_len);
+			return -EIO;
+		}
+		/* if we consumed all 64 bits, assign 0; >> 64 is "undefined"; */
+		if (likely(bits < 64))
+			look_ahead >>= bits;
+		else
+			look_ahead = 0;
+		have -= bits;
+
+		bits = bitstream_get_bits(&bs, &tmp, 64 - have);
+		if (bits < 0)
+			return -EIO;
+		look_ahead |= tmp << have;
+		have += bits;
+	}
+
+	c->bit_offset = s;
+	bm_xfer_ctx_bit_to_word_offset(c);
+
+	return (s != c->bm_bits);
+}
+
+/*
+ * decode_bitmap_c
+ *
+ * Return 0 when done, 1 when another iteration is needed, and a negative error
+ * code upon failure.
+ */
+static int
+decode_bitmap_c(struct drbd_peer_device *peer_device,
+		struct p_compressed_bm *p,
+		struct bm_xfer_ctx *c,
+		unsigned int len)
+{
+	if (dcbp_get_code(p) == RLE_VLI_Bits)
+		return recv_bm_rle_bits(peer_device, p, c, len - sizeof(*p));
+
+	/* other variants had been implemented for evaluation,
+	 * but have been dropped as this one turned out to be "best"
+	 * during all our tests. */
+
+	drbd_err(peer_device, "receive_bitmap_c: unknown encoding %u\n", p->encoding);
+	conn_request_state(peer_device->connection, NS(conn, C_PROTOCOL_ERROR), CS_HARD);
+	return -EIO;
+}
+
+void INFO_bm_xfer_stats(struct drbd_peer_device *peer_device,
+		const char *direction, struct bm_xfer_ctx *c)
+{
+	/* what would it take to transfer it "plaintext" */
+	unsigned int header_size = drbd_header_size(peer_device->connection);
+	unsigned int data_size = DRBD_SOCKET_BUFFER_SIZE - header_size;
+	unsigned int plain =
+		header_size * (DIV_ROUND_UP(c->bm_words, data_size) + 1) +
+		c->bm_words * sizeof(unsigned long);
+	unsigned int total = c->bytes[0] + c->bytes[1];
+	unsigned int r;
+
+	/* total can not be zero. but just in case: */
+	if (total == 0)
+		return;
+
+	/* don't report if not compressed */
+	if (total >= plain)
+		return;
+
+	/* total < plain. check for overflow, still */
+	r = (total > UINT_MAX/1000) ? (total / (plain/1000))
+		                    : (1000 * total / plain);
+
+	if (r > 1000)
+		r = 1000;
+
+	r = 1000 - r;
+	drbd_info(peer_device, "%s bitmap stats [Bytes(packets)]: plain %u(%u), RLE %u(%u), "
+	     "total %u; compression: %u.%u%%\n",
+			direction,
+			c->bytes[1], c->packets[1],
+			c->bytes[0], c->packets[0],
+			total, r/10, r % 10);
+}
+
+/* Since we are processing the bitfield from lower addresses to higher,
+   it does not matter if the process it in 32 bit chunks or 64 bit
+   chunks as long as it is little endian. (Understand it as byte stream,
+   beginning with the lowest byte...) If we would use big endian
+   we would need to process it from the highest address to the lowest,
+   in order to be agnostic to the 32 vs 64 bits issue.
+
+   returns 0 on failure, 1 if we successfully received it. */
+static int receive_bitmap(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct bm_xfer_ctx c;
+	int err;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+
+	drbd_bm_lock(device, "receive bitmap", BM_LOCKED_SET_ALLOWED);
+	/* you are supposed to send additional out-of-sync information
+	 * if you actually set bits during this phase */
+
+	c = (struct bm_xfer_ctx) {
+		.bm_bits = drbd_bm_bits(device),
+		.bm_words = drbd_bm_words(device),
+	};
+
+	for(;;) {
+		if (pi->cmd == P_BITMAP)
+			err = receive_bitmap_plain(peer_device, pi->size, pi->data, &c);
+		else if (pi->cmd == P_COMPRESSED_BITMAP) {
+			/* MAYBE: sanity check that we speak proto >= 90,
+			 * and the feature is enabled! */
+			struct p_compressed_bm *p = pi->data;
+
+			if (pi->size > DRBD_SOCKET_BUFFER_SIZE - drbd_header_size(connection)) {
+				drbd_err(device, "ReportCBitmap packet too large\n");
+				err = -EIO;
+				goto out;
+			}
+			if (pi->size <= sizeof(*p)) {
+				drbd_err(device, "ReportCBitmap packet too small (l:%u)\n", pi->size);
+				err = -EIO;
+				goto out;
+			}
+			err = drbd_recv_all(peer_device->connection, p, pi->size);
+			if (err)
+			       goto out;
+			err = decode_bitmap_c(peer_device, p, &c, pi->size);
+		} else {
+			drbd_warn(device, "receive_bitmap: cmd neither ReportBitMap nor ReportCBitMap (is 0x%x)", pi->cmd);
+			err = -EIO;
+			goto out;
+		}
+
+		c.packets[pi->cmd == P_BITMAP]++;
+		c.bytes[pi->cmd == P_BITMAP] += drbd_header_size(connection) + pi->size;
+
+		if (err <= 0) {
+			if (err < 0)
+				goto out;
+			break;
+		}
+		err = drbd_recv_header(peer_device->connection, pi);
+		if (err)
+			goto out;
+	}
+
+	INFO_bm_xfer_stats(peer_device, "receive", &c);
+
+	if (device->state.conn == C_WF_BITMAP_T) {
+		enum drbd_state_rv rv;
+
+		err = drbd_send_bitmap(device, peer_device);
+		if (err)
+			goto out;
+		/* Omit CS_ORDERED with this state transition to avoid deadlocks. */
+		rv = _drbd_request_state(device, NS(conn, C_WF_SYNC_UUID), CS_VERBOSE);
+		D_ASSERT(device, rv == SS_SUCCESS);
+	} else if (device->state.conn != C_WF_BITMAP_S) {
+		/* admin may have requested C_DISCONNECTING,
+		 * other threads may have noticed network errors */
+		drbd_info(device, "unexpected cstate (%s) in receive_bitmap\n",
+		    drbd_conn_str(device->state.conn));
+	}
+	err = 0;
+
+ out:
+	drbd_bm_unlock(device);
+	if (!err && device->state.conn == C_WF_BITMAP_S)
+		drbd_start_resync(device, C_SYNC_SOURCE);
+	return err;
+}
+
+static int receive_skip(struct drbd_connection *connection, struct packet_info *pi)
+{
+	drbd_warn(connection, "skipping unknown optional packet type %d, l: %d!\n",
+		 pi->cmd, pi->size);
+
+	return ignore_remaining_packet(connection, pi);
+}
+
+static int receive_UnplugRemote(struct drbd_connection *connection, struct packet_info *pi)
+{
+	/* Make sure we've acked all the TCP data associated
+	 * with the data requests being unplugged */
+	tcp_sock_set_quickack(connection->data.socket->sk, 2);
+	return 0;
+}
+
+static int receive_out_of_sync(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct p_block_desc *p = pi->data;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+
+	switch (device->state.conn) {
+	case C_WF_SYNC_UUID:
+	case C_WF_BITMAP_T:
+	case C_BEHIND:
+			break;
+	default:
+		drbd_err(device, "ASSERT FAILED cstate = %s, expected: WFSyncUUID|WFBitMapT|Behind\n",
+				drbd_conn_str(device->state.conn));
+	}
+
+	drbd_set_out_of_sync(peer_device, be64_to_cpu(p->sector), be32_to_cpu(p->blksize));
+
+	return 0;
+}
+
+static int receive_rs_deallocated(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct p_block_desc *p = pi->data;
+	struct drbd_device *device;
+	sector_t sector;
+	int size, err = 0;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+
+	sector = be64_to_cpu(p->sector);
+	size = be32_to_cpu(p->blksize);
+
+	dec_rs_pending(peer_device);
+
+	if (get_ldev(device)) {
+		struct drbd_peer_request *peer_req;
+
+		peer_req = drbd_alloc_peer_req(peer_device, ID_SYNCER, sector,
+					       size, 0, GFP_NOIO);
+		if (!peer_req) {
+			put_ldev(device);
+			return -ENOMEM;
+		}
+
+		peer_req->w.cb = e_end_resync_block;
+		peer_req->opf = REQ_OP_DISCARD;
+		peer_req->submit_jif = jiffies;
+		peer_req->flags |= EE_TRIM;
+
+		spin_lock_irq(&device->resource->req_lock);
+		list_add_tail(&peer_req->w.list, &device->sync_ee);
+		spin_unlock_irq(&device->resource->req_lock);
+
+		atomic_add(pi->size >> 9, &device->rs_sect_ev);
+		err = drbd_submit_peer_request(peer_req);
+
+		if (err) {
+			spin_lock_irq(&device->resource->req_lock);
+			list_del(&peer_req->w.list);
+			spin_unlock_irq(&device->resource->req_lock);
+
+			drbd_free_peer_req(device, peer_req);
+			put_ldev(device);
+			err = 0;
+			goto fail;
+		}
+
+		inc_unacked(device);
+
+		/* No put_ldev() here. Gets called in drbd_endio_write_sec_final(),
+		   as well as drbd_rs_complete_io() */
+	} else {
+	fail:
+		drbd_rs_complete_io(device, sector);
+		drbd_send_ack_ex(peer_device, P_NEG_ACK, sector, size, ID_SYNCER);
+	}
+
+	atomic_add(size >> 9, &device->rs_sect_in);
+
+	return err;
+}
+
+struct data_cmd {
+	int expect_payload;
+	unsigned int pkt_size;
+	int (*fn)(struct drbd_connection *, struct packet_info *);
+};
+
+static struct data_cmd drbd_cmd_handler[] = {
+	[P_DATA]	    = { 1, sizeof(struct p_data), receive_Data },
+	[P_DATA_REPLY]	    = { 1, sizeof(struct p_data), receive_DataReply },
+	[P_RS_DATA_REPLY]   = { 1, sizeof(struct p_data), receive_RSDataReply } ,
+	[P_BARRIER]	    = { 0, sizeof(struct p_barrier), receive_Barrier } ,
+	[P_BITMAP]	    = { 1, 0, receive_bitmap } ,
+	[P_COMPRESSED_BITMAP] = { 1, 0, receive_bitmap } ,
+	[P_UNPLUG_REMOTE]   = { 0, 0, receive_UnplugRemote },
+	[P_DATA_REQUEST]    = { 0, sizeof(struct p_block_req), receive_DataRequest },
+	[P_RS_DATA_REQUEST] = { 0, sizeof(struct p_block_req), receive_DataRequest },
+	[P_SYNC_PARAM]	    = { 1, 0, receive_SyncParam },
+	[P_SYNC_PARAM89]    = { 1, 0, receive_SyncParam },
+	[P_PROTOCOL]        = { 1, sizeof(struct p_protocol), receive_protocol },
+	[P_UUIDS]	    = { 0, sizeof(struct p_uuids), receive_uuids },
+	[P_SIZES]	    = { 0, sizeof(struct p_sizes), receive_sizes },
+	[P_STATE]	    = { 0, sizeof(struct p_state), receive_state },
+	[P_STATE_CHG_REQ]   = { 0, sizeof(struct p_req_state), receive_req_state },
+	[P_SYNC_UUID]       = { 0, sizeof(struct p_rs_uuid), receive_sync_uuid },
+	[P_OV_REQUEST]      = { 0, sizeof(struct p_block_req), receive_DataRequest },
+	[P_OV_REPLY]        = { 1, sizeof(struct p_block_req), receive_DataRequest },
+	[P_CSUM_RS_REQUEST] = { 1, sizeof(struct p_block_req), receive_DataRequest },
+	[P_RS_THIN_REQ]     = { 0, sizeof(struct p_block_req), receive_DataRequest },
+	[P_DELAY_PROBE]     = { 0, sizeof(struct p_delay_probe93), receive_skip },
+	[P_OUT_OF_SYNC]     = { 0, sizeof(struct p_block_desc), receive_out_of_sync },
+	[P_CONN_ST_CHG_REQ] = { 0, sizeof(struct p_req_state), receive_req_conn_state },
+	[P_PROTOCOL_UPDATE] = { 1, sizeof(struct p_protocol), receive_protocol },
+	[P_TRIM]	    = { 0, sizeof(struct p_trim), receive_Data },
+	[P_ZEROES]	    = { 0, sizeof(struct p_trim), receive_Data },
+	[P_RS_DEALLOCATED]  = { 0, sizeof(struct p_block_desc), receive_rs_deallocated },
+};
+
+static void drbdd(struct drbd_connection *connection)
+{
+	struct packet_info pi;
+	size_t shs; /* sub header size */
+	int err;
+
+	while (get_t_state(&connection->receiver) == RUNNING) {
+		struct data_cmd const *cmd;
+
+		drbd_thread_current_set_cpu(&connection->receiver);
+		update_receiver_timing_details(connection, drbd_recv_header_maybe_unplug);
+		if (drbd_recv_header_maybe_unplug(connection, &pi))
+			goto err_out;
+
+		cmd = &drbd_cmd_handler[pi.cmd];
+		if (unlikely(pi.cmd >= ARRAY_SIZE(drbd_cmd_handler) || !cmd->fn)) {
+			drbd_err(connection, "Unexpected data packet %s (0x%04x)",
+				 cmdname(pi.cmd), pi.cmd);
+			goto err_out;
+		}
+
+		shs = cmd->pkt_size;
+		if (pi.cmd == P_SIZES && connection->agreed_features & DRBD_FF_WSAME)
+			shs += sizeof(struct o_qlim);
+		if (pi.size > shs && !cmd->expect_payload) {
+			drbd_err(connection, "No payload expected %s l:%d\n",
+				 cmdname(pi.cmd), pi.size);
+			goto err_out;
+		}
+		if (pi.size < shs) {
+			drbd_err(connection, "%s: unexpected packet size, expected:%d received:%d\n",
+				 cmdname(pi.cmd), (int)shs, pi.size);
+			goto err_out;
+		}
+
+		if (shs) {
+			update_receiver_timing_details(connection, drbd_recv_all_warn);
+			err = drbd_recv_all_warn(connection, pi.data, shs);
+			if (err)
+				goto err_out;
+			pi.size -= shs;
+		}
+
+		update_receiver_timing_details(connection, cmd->fn);
+		err = cmd->fn(connection, &pi);
+		if (err) {
+			drbd_err(connection, "error receiving %s, e: %d l: %d!\n",
+				 cmdname(pi.cmd), err, pi.size);
+			goto err_out;
+		}
+	}
+	return;
+
+    err_out:
+	conn_request_state(connection, NS(conn, C_PROTOCOL_ERROR), CS_HARD);
+}
+
+static void conn_disconnect(struct drbd_connection *connection)
+{
+	struct drbd_peer_device *peer_device;
+	enum drbd_conns oc;
+	int vnr;
+
+	if (connection->cstate == C_STANDALONE)
+		return;
+
+	/* We are about to start the cleanup after connection loss.
+	 * Make sure drbd_make_request knows about that.
+	 * Usually we should be in some network failure state already,
+	 * but just in case we are not, we fix it up here.
+	 */
+	conn_request_state(connection, NS(conn, C_NETWORK_FAILURE), CS_HARD);
+
+	/* ack_receiver does not clean up anything. it must not interfere, either */
+	drbd_thread_stop(&connection->ack_receiver);
+	if (connection->ack_sender) {
+		destroy_workqueue(connection->ack_sender);
+		connection->ack_sender = NULL;
+	}
+	drbd_free_sock(connection);
+
+	rcu_read_lock();
+	idr_for_each_entry(&connection->peer_devices, peer_device, vnr) {
+		struct drbd_device *device = peer_device->device;
+		kref_get(&device->kref);
+		rcu_read_unlock();
+		drbd_disconnected(peer_device);
+		kref_put(&device->kref, drbd_destroy_device);
+		rcu_read_lock();
+	}
+	rcu_read_unlock();
+
+	if (!list_empty(&connection->current_epoch->list))
+		drbd_err(connection, "ASSERTION FAILED: connection->current_epoch->list not empty\n");
+	/* ok, no more ee's on the fly, it is safe to reset the epoch_size */
+	atomic_set(&connection->current_epoch->epoch_size, 0);
+	connection->send.seen_any_write_yet = false;
+
+	drbd_info(connection, "Connection closed\n");
+
+	if (conn_highest_role(connection) == R_PRIMARY && conn_highest_pdsk(connection) >= D_UNKNOWN)
+		conn_try_outdate_peer_async(connection);
+
+	spin_lock_irq(&connection->resource->req_lock);
+	oc = connection->cstate;
+	if (oc >= C_UNCONNECTED)
+		_conn_request_state(connection, NS(conn, C_UNCONNECTED), CS_VERBOSE);
+
+	spin_unlock_irq(&connection->resource->req_lock);
+
+	if (oc == C_DISCONNECTING)
+		conn_request_state(connection, NS(conn, C_STANDALONE), CS_VERBOSE | CS_HARD);
+}
+
+static int drbd_disconnected(struct drbd_peer_device *peer_device)
+{
+	struct drbd_device *device = peer_device->device;
+	unsigned int i;
+
+	/* wait for current activity to cease. */
+	spin_lock_irq(&device->resource->req_lock);
+	_drbd_wait_ee_list_empty(device, &device->active_ee);
+	_drbd_wait_ee_list_empty(device, &device->sync_ee);
+	_drbd_wait_ee_list_empty(device, &device->read_ee);
+	spin_unlock_irq(&device->resource->req_lock);
+
+	/* We do not have data structures that would allow us to
+	 * get the rs_pending_cnt down to 0 again.
+	 *  * On C_SYNC_TARGET we do not have any data structures describing
+	 *    the pending RSDataRequest's we have sent.
+	 *  * On C_SYNC_SOURCE there is no data structure that tracks
+	 *    the P_RS_DATA_REPLY blocks that we sent to the SyncTarget.
+	 *  And no, it is not the sum of the reference counts in the
+	 *  resync_LRU. The resync_LRU tracks the whole operation including
+	 *  the disk-IO, while the rs_pending_cnt only tracks the blocks
+	 *  on the fly. */
+	drbd_rs_cancel_all(device);
+	device->rs_total = 0;
+	device->rs_failed = 0;
+	atomic_set(&device->rs_pending_cnt, 0);
+	wake_up(&device->misc_wait);
+
+	del_timer_sync(&device->resync_timer);
+	resync_timer_fn(&device->resync_timer);
+
+	/* wait for all w_e_end_data_req, w_e_end_rsdata_req, w_send_barrier,
+	 * w_make_resync_request etc. which may still be on the worker queue
+	 * to be "canceled" */
+	drbd_flush_workqueue(&peer_device->connection->sender_work);
+
+	drbd_finish_peer_reqs(device);
+
+	/* This second workqueue flush is necessary, since drbd_finish_peer_reqs()
+	   might have issued a work again. The one before drbd_finish_peer_reqs() is
+	   necessary to reclain net_ee in drbd_finish_peer_reqs(). */
+	drbd_flush_workqueue(&peer_device->connection->sender_work);
+
+	/* need to do it again, drbd_finish_peer_reqs() may have populated it
+	 * again via drbd_try_clear_on_disk_bm(). */
+	drbd_rs_cancel_all(device);
+
+	kfree(device->p_uuid);
+	device->p_uuid = NULL;
+
+	if (!drbd_suspended(device))
+		tl_clear(peer_device->connection);
+
+	drbd_md_sync(device);
+
+	if (get_ldev(device)) {
+		drbd_bitmap_io(device, &drbd_bm_write_copy_pages,
+				"write from disconnected", BM_LOCKED_CHANGE_ALLOWED, NULL);
+		put_ldev(device);
+	}
+
+	/* tcp_close and release of sendpage pages can be deferred.  I don't
+	 * want to use SO_LINGER, because apparently it can be deferred for
+	 * more than 20 seconds (longest time I checked).
+	 *
+	 * Actually we don't care for exactly when the network stack does its
+	 * put_page(), but release our reference on these pages right here.
+	 */
+	i = drbd_free_peer_reqs(device, &device->net_ee);
+	if (i)
+		drbd_info(device, "net_ee not empty, killed %u entries\n", i);
+	i = atomic_read(&device->pp_in_use_by_net);
+	if (i)
+		drbd_info(device, "pp_in_use_by_net = %d, expected 0\n", i);
+	i = atomic_read(&device->pp_in_use);
+	if (i)
+		drbd_info(device, "pp_in_use = %d, expected 0\n", i);
+
+	D_ASSERT(device, list_empty(&device->read_ee));
+	D_ASSERT(device, list_empty(&device->active_ee));
+	D_ASSERT(device, list_empty(&device->sync_ee));
+	D_ASSERT(device, list_empty(&device->done_ee));
+
+	return 0;
+}
+
+/*
+ * We support PRO_VERSION_MIN to PRO_VERSION_MAX. The protocol version
+ * we can agree on is stored in agreed_pro_version.
+ *
+ * feature flags and the reserved array should be enough room for future
+ * enhancements of the handshake protocol, and possible plugins...
+ *
+ * for now, they are expected to be zero, but ignored.
+ */
+static int drbd_send_features(struct drbd_connection *connection)
+{
+	struct drbd_socket *sock;
+	struct p_connection_features *p;
+
+	sock = &connection->data;
+	p = conn_prepare_command(connection, sock);
+	if (!p)
+		return -EIO;
+	memset(p, 0, sizeof(*p));
+	p->protocol_min = cpu_to_be32(PRO_VERSION_MIN);
+	p->protocol_max = cpu_to_be32(PRO_VERSION_MAX);
+	p->feature_flags = cpu_to_be32(PRO_FEATURES);
+	return conn_send_command(connection, sock, P_CONNECTION_FEATURES, sizeof(*p), NULL, 0);
+}
+
+/*
+ * return values:
+ *   1 yes, we have a valid connection
+ *   0 oops, did not work out, please try again
+ *  -1 peer talks different language,
+ *     no point in trying again, please go standalone.
+ */
+static int drbd_do_features(struct drbd_connection *connection)
+{
+	/* ASSERT current == connection->receiver ... */
+	struct p_connection_features *p;
+	const int expect = sizeof(struct p_connection_features);
+	struct packet_info pi;
+	int err;
+
+	err = drbd_send_features(connection);
+	if (err)
+		return 0;
+
+	err = drbd_recv_header(connection, &pi);
+	if (err)
+		return 0;
+
+	if (pi.cmd != P_CONNECTION_FEATURES) {
+		drbd_err(connection, "expected ConnectionFeatures packet, received: %s (0x%04x)\n",
+			 cmdname(pi.cmd), pi.cmd);
+		return -1;
+	}
+
+	if (pi.size != expect) {
+		drbd_err(connection, "expected ConnectionFeatures length: %u, received: %u\n",
+		     expect, pi.size);
+		return -1;
+	}
+
+	p = pi.data;
+	err = drbd_recv_all_warn(connection, p, expect);
+	if (err)
+		return 0;
+
+	p->protocol_min = be32_to_cpu(p->protocol_min);
+	p->protocol_max = be32_to_cpu(p->protocol_max);
+	if (p->protocol_max == 0)
+		p->protocol_max = p->protocol_min;
+
+	if (PRO_VERSION_MAX < p->protocol_min ||
+	    PRO_VERSION_MIN > p->protocol_max)
+		goto incompat;
+
+	connection->agreed_pro_version = min_t(int, PRO_VERSION_MAX, p->protocol_max);
+	connection->agreed_features = PRO_FEATURES & be32_to_cpu(p->feature_flags);
+
+	drbd_info(connection, "Handshake successful: "
+	     "Agreed network protocol version %d\n", connection->agreed_pro_version);
+
+	drbd_info(connection, "Feature flags enabled on protocol level: 0x%x%s%s%s%s.\n",
+		  connection->agreed_features,
+		  connection->agreed_features & DRBD_FF_TRIM ? " TRIM" : "",
+		  connection->agreed_features & DRBD_FF_THIN_RESYNC ? " THIN_RESYNC" : "",
+		  connection->agreed_features & DRBD_FF_WSAME ? " WRITE_SAME" : "",
+		  connection->agreed_features & DRBD_FF_WZEROES ? " WRITE_ZEROES" :
+		  connection->agreed_features ? "" : " none");
+
+	return 1;
+
+ incompat:
+	drbd_err(connection, "incompatible DRBD dialects: "
+	    "I support %d-%d, peer supports %d-%d\n",
+	    PRO_VERSION_MIN, PRO_VERSION_MAX,
+	    p->protocol_min, p->protocol_max);
+	return -1;
+}
+
+#if !defined(CONFIG_CRYPTO_HMAC) && !defined(CONFIG_CRYPTO_HMAC_MODULE)
+static int drbd_do_auth(struct drbd_connection *connection)
+{
+	drbd_err(connection, "This kernel was build without CONFIG_CRYPTO_HMAC.\n");
+	drbd_err(connection, "You need to disable 'cram-hmac-alg' in drbd.conf.\n");
+	return -1;
+}
+#else
+#define CHALLENGE_LEN 64
+
+/* Return value:
+	1 - auth succeeded,
+	0 - failed, try again (network error),
+	-1 - auth failed, don't try again.
+*/
+
+static int drbd_do_auth(struct drbd_connection *connection)
+{
+	struct drbd_socket *sock;
+	char my_challenge[CHALLENGE_LEN];  /* 64 Bytes... */
+	char *response = NULL;
+	char *right_response = NULL;
+	char *peers_ch = NULL;
+	unsigned int key_len;
+	char secret[SHARED_SECRET_MAX]; /* 64 byte */
+	unsigned int resp_size;
+	struct shash_desc *desc;
+	struct packet_info pi;
+	struct net_conf *nc;
+	int err, rv;
+
+	/* FIXME: Put the challenge/response into the preallocated socket buffer.  */
+
+	rcu_read_lock();
+	nc = rcu_dereference(connection->net_conf);
+	key_len = strlen(nc->shared_secret);
+	memcpy(secret, nc->shared_secret, key_len);
+	rcu_read_unlock();
+
+	desc = kmalloc(sizeof(struct shash_desc) +
+		       crypto_shash_descsize(connection->cram_hmac_tfm),
+		       GFP_KERNEL);
+	if (!desc) {
+		rv = -1;
+		goto fail;
+	}
+	desc->tfm = connection->cram_hmac_tfm;
+
+	rv = crypto_shash_setkey(connection->cram_hmac_tfm, (u8 *)secret, key_len);
+	if (rv) {
+		drbd_err(connection, "crypto_shash_setkey() failed with %d\n", rv);
+		rv = -1;
+		goto fail;
+	}
+
+	get_random_bytes(my_challenge, CHALLENGE_LEN);
+
+	sock = &connection->data;
+	if (!conn_prepare_command(connection, sock)) {
+		rv = 0;
+		goto fail;
+	}
+	rv = !conn_send_command(connection, sock, P_AUTH_CHALLENGE, 0,
+				my_challenge, CHALLENGE_LEN);
+	if (!rv)
+		goto fail;
+
+	err = drbd_recv_header(connection, &pi);
+	if (err) {
+		rv = 0;
+		goto fail;
+	}
+
+	if (pi.cmd != P_AUTH_CHALLENGE) {
+		drbd_err(connection, "expected AuthChallenge packet, received: %s (0x%04x)\n",
+			 cmdname(pi.cmd), pi.cmd);
+		rv = -1;
+		goto fail;
+	}
+
+	if (pi.size > CHALLENGE_LEN * 2) {
+		drbd_err(connection, "expected AuthChallenge payload too big.\n");
+		rv = -1;
+		goto fail;
+	}
+
+	if (pi.size < CHALLENGE_LEN) {
+		drbd_err(connection, "AuthChallenge payload too small.\n");
+		rv = -1;
+		goto fail;
+	}
+
+	peers_ch = kmalloc(pi.size, GFP_NOIO);
+	if (!peers_ch) {
+		rv = -1;
+		goto fail;
+	}
+
+	err = drbd_recv_all_warn(connection, peers_ch, pi.size);
+	if (err) {
+		rv = 0;
+		goto fail;
+	}
+
+	if (!memcmp(my_challenge, peers_ch, CHALLENGE_LEN)) {
+		drbd_err(connection, "Peer presented the same challenge!\n");
+		rv = -1;
+		goto fail;
+	}
+
+	resp_size = crypto_shash_digestsize(connection->cram_hmac_tfm);
+	response = kmalloc(resp_size, GFP_NOIO);
+	if (!response) {
+		rv = -1;
+		goto fail;
+	}
+
+	rv = crypto_shash_digest(desc, peers_ch, pi.size, response);
+	if (rv) {
+		drbd_err(connection, "crypto_hash_digest() failed with %d\n", rv);
+		rv = -1;
+		goto fail;
+	}
+
+	if (!conn_prepare_command(connection, sock)) {
+		rv = 0;
+		goto fail;
+	}
+	rv = !conn_send_command(connection, sock, P_AUTH_RESPONSE, 0,
+				response, resp_size);
+	if (!rv)
+		goto fail;
+
+	err = drbd_recv_header(connection, &pi);
+	if (err) {
+		rv = 0;
+		goto fail;
+	}
+
+	if (pi.cmd != P_AUTH_RESPONSE) {
+		drbd_err(connection, "expected AuthResponse packet, received: %s (0x%04x)\n",
+			 cmdname(pi.cmd), pi.cmd);
+		rv = 0;
+		goto fail;
+	}
+
+	if (pi.size != resp_size) {
+		drbd_err(connection, "expected AuthResponse payload of wrong size\n");
+		rv = 0;
+		goto fail;
+	}
+
+	err = drbd_recv_all_warn(connection, response , resp_size);
+	if (err) {
+		rv = 0;
+		goto fail;
+	}
+
+	right_response = kmalloc(resp_size, GFP_NOIO);
+	if (!right_response) {
+		rv = -1;
+		goto fail;
+	}
+
+	rv = crypto_shash_digest(desc, my_challenge, CHALLENGE_LEN,
+				 right_response);
+	if (rv) {
+		drbd_err(connection, "crypto_hash_digest() failed with %d\n", rv);
+		rv = -1;
+		goto fail;
+	}
+
+	rv = !memcmp(response, right_response, resp_size);
+
+	if (rv)
+		drbd_info(connection, "Peer authenticated using %d bytes HMAC\n",
+		     resp_size);
+	else
+		rv = -1;
+
+ fail:
+	kfree(peers_ch);
+	kfree(response);
+	kfree(right_response);
+	if (desc) {
+		shash_desc_zero(desc);
+		kfree(desc);
+	}
+
+	return rv;
+}
+#endif
+
+int drbd_receiver(struct drbd_thread *thi)
+{
+	struct drbd_connection *connection = thi->connection;
+	int h;
+
+	drbd_info(connection, "receiver (re)started\n");
+
+	do {
+		h = conn_connect(connection);
+		if (h == 0) {
+			conn_disconnect(connection);
+			schedule_timeout_interruptible(HZ);
+		}
+		if (h == -1) {
+			drbd_warn(connection, "Discarding network configuration.\n");
+			conn_request_state(connection, NS(conn, C_DISCONNECTING), CS_HARD);
+		}
+	} while (h == 0);
+
+	if (h > 0) {
+		blk_start_plug(&connection->receiver_plug);
+		drbdd(connection);
+		blk_finish_plug(&connection->receiver_plug);
+	}
+
+	conn_disconnect(connection);
+
+	drbd_info(connection, "receiver terminated\n");
+	return 0;
+}
+
+/* ********* acknowledge sender ******** */
+
+static int got_conn_RqSReply(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct p_req_state_reply *p = pi->data;
+	int retcode = be32_to_cpu(p->retcode);
+
+	if (retcode >= SS_SUCCESS) {
+		set_bit(CONN_WD_ST_CHG_OKAY, &connection->flags);
+	} else {
+		set_bit(CONN_WD_ST_CHG_FAIL, &connection->flags);
+		drbd_err(connection, "Requested state change failed by peer: %s (%d)\n",
+			 drbd_set_st_err_str(retcode), retcode);
+	}
+	wake_up(&connection->ping_wait);
+
+	return 0;
+}
+
+static int got_RqSReply(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct p_req_state_reply *p = pi->data;
+	int retcode = be32_to_cpu(p->retcode);
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+
+	if (test_bit(CONN_WD_ST_CHG_REQ, &connection->flags)) {
+		D_ASSERT(device, connection->agreed_pro_version < 100);
+		return got_conn_RqSReply(connection, pi);
+	}
+
+	if (retcode >= SS_SUCCESS) {
+		set_bit(CL_ST_CHG_SUCCESS, &device->flags);
+	} else {
+		set_bit(CL_ST_CHG_FAIL, &device->flags);
+		drbd_err(device, "Requested state change failed by peer: %s (%d)\n",
+			drbd_set_st_err_str(retcode), retcode);
+	}
+	wake_up(&device->state_wait);
+
+	return 0;
+}
+
+static int got_Ping(struct drbd_connection *connection, struct packet_info *pi)
+{
+	return drbd_send_ping_ack(connection);
+
+}
+
+static int got_PingAck(struct drbd_connection *connection, struct packet_info *pi)
+{
+	/* restore idle timeout */
+	connection->meta.socket->sk->sk_rcvtimeo = connection->net_conf->ping_int*HZ;
+	if (!test_and_set_bit(GOT_PING_ACK, &connection->flags))
+		wake_up(&connection->ping_wait);
+
+	return 0;
+}
+
+static int got_IsInSync(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct p_block_ack *p = pi->data;
+	sector_t sector = be64_to_cpu(p->sector);
+	int blksize = be32_to_cpu(p->blksize);
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+
+	D_ASSERT(device, peer_device->connection->agreed_pro_version >= 89);
+
+	update_peer_seq(peer_device, be32_to_cpu(p->seq_num));
+
+	if (get_ldev(device)) {
+		drbd_rs_complete_io(device, sector);
+		drbd_set_in_sync(peer_device, sector, blksize);
+		/* rs_same_csums is supposed to count in units of BM_BLOCK_SIZE */
+		device->rs_same_csum += (blksize >> BM_BLOCK_SHIFT);
+		put_ldev(device);
+	}
+	dec_rs_pending(peer_device);
+	atomic_add(blksize >> 9, &device->rs_sect_in);
+
+	return 0;
+}
+
+static int
+validate_req_change_req_state(struct drbd_peer_device *peer_device, u64 id, sector_t sector,
+			      struct rb_root *root, const char *func,
+			      enum drbd_req_event what, bool missing_ok)
+{
+	struct drbd_device *device = peer_device->device;
+	struct drbd_request *req;
+	struct bio_and_error m;
+
+	spin_lock_irq(&device->resource->req_lock);
+	req = find_request(device, root, id, sector, missing_ok, func);
+	if (unlikely(!req)) {
+		spin_unlock_irq(&device->resource->req_lock);
+		return -EIO;
+	}
+	__req_mod(req, what, peer_device, &m);
+	spin_unlock_irq(&device->resource->req_lock);
+
+	if (m.bio)
+		complete_master_bio(device, &m);
+	return 0;
+}
+
+static int got_BlockAck(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct p_block_ack *p = pi->data;
+	sector_t sector = be64_to_cpu(p->sector);
+	int blksize = be32_to_cpu(p->blksize);
+	enum drbd_req_event what;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+
+	update_peer_seq(peer_device, be32_to_cpu(p->seq_num));
+
+	if (p->block_id == ID_SYNCER) {
+		drbd_set_in_sync(peer_device, sector, blksize);
+		dec_rs_pending(peer_device);
+		return 0;
+	}
+	switch (pi->cmd) {
+	case P_RS_WRITE_ACK:
+		what = WRITE_ACKED_BY_PEER_AND_SIS;
+		break;
+	case P_WRITE_ACK:
+		what = WRITE_ACKED_BY_PEER;
+		break;
+	case P_RECV_ACK:
+		what = RECV_ACKED_BY_PEER;
+		break;
+	case P_SUPERSEDED:
+		what = CONFLICT_RESOLVED;
+		break;
+	case P_RETRY_WRITE:
+		what = POSTPONE_WRITE;
+		break;
+	default:
+		BUG();
+	}
+
+	return validate_req_change_req_state(peer_device, p->block_id, sector,
+					     &device->write_requests, __func__,
+					     what, false);
+}
+
+static int got_NegAck(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct p_block_ack *p = pi->data;
+	sector_t sector = be64_to_cpu(p->sector);
+	int size = be32_to_cpu(p->blksize);
+	int err;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+
+	update_peer_seq(peer_device, be32_to_cpu(p->seq_num));
+
+	if (p->block_id == ID_SYNCER) {
+		dec_rs_pending(peer_device);
+		drbd_rs_failed_io(peer_device, sector, size);
+		return 0;
+	}
+
+	err = validate_req_change_req_state(peer_device, p->block_id, sector,
+					    &device->write_requests, __func__,
+					    NEG_ACKED, true);
+	if (err) {
+		/* Protocol A has no P_WRITE_ACKs, but has P_NEG_ACKs.
+		   The master bio might already be completed, therefore the
+		   request is no longer in the collision hash. */
+		/* In Protocol B we might already have got a P_RECV_ACK
+		   but then get a P_NEG_ACK afterwards. */
+		drbd_set_out_of_sync(peer_device, sector, size);
+	}
+	return 0;
+}
+
+static int got_NegDReply(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct p_block_ack *p = pi->data;
+	sector_t sector = be64_to_cpu(p->sector);
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+
+	update_peer_seq(peer_device, be32_to_cpu(p->seq_num));
+
+	drbd_err(device, "Got NegDReply; Sector %llus, len %u.\n",
+	    (unsigned long long)sector, be32_to_cpu(p->blksize));
+
+	return validate_req_change_req_state(peer_device, p->block_id, sector,
+					     &device->read_requests, __func__,
+					     NEG_ACKED, false);
+}
+
+static int got_NegRSDReply(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	sector_t sector;
+	int size;
+	struct p_block_ack *p = pi->data;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+
+	sector = be64_to_cpu(p->sector);
+	size = be32_to_cpu(p->blksize);
+
+	update_peer_seq(peer_device, be32_to_cpu(p->seq_num));
+
+	dec_rs_pending(peer_device);
+
+	if (get_ldev_if_state(device, D_FAILED)) {
+		drbd_rs_complete_io(device, sector);
+		switch (pi->cmd) {
+		case P_NEG_RS_DREPLY:
+			drbd_rs_failed_io(peer_device, sector, size);
+			break;
+		case P_RS_CANCEL:
+			break;
+		default:
+			BUG();
+		}
+		put_ldev(device);
+	}
+
+	return 0;
+}
+
+static int got_BarrierAck(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct p_barrier_ack *p = pi->data;
+	struct drbd_peer_device *peer_device;
+	int vnr;
+
+	tl_release(connection, p->barrier, be32_to_cpu(p->set_size));
+
+	rcu_read_lock();
+	idr_for_each_entry(&connection->peer_devices, peer_device, vnr) {
+		struct drbd_device *device = peer_device->device;
+
+		if (device->state.conn == C_AHEAD &&
+		    atomic_read(&device->ap_in_flight) == 0 &&
+		    !test_and_set_bit(AHEAD_TO_SYNC_SOURCE, &device->flags)) {
+			device->start_resync_timer.expires = jiffies + HZ;
+			add_timer(&device->start_resync_timer);
+		}
+	}
+	rcu_read_unlock();
+
+	return 0;
+}
+
+static int got_OVResult(struct drbd_connection *connection, struct packet_info *pi)
+{
+	struct drbd_peer_device *peer_device;
+	struct drbd_device *device;
+	struct p_block_ack *p = pi->data;
+	struct drbd_device_work *dw;
+	sector_t sector;
+	int size;
+
+	peer_device = conn_peer_device(connection, pi->vnr);
+	if (!peer_device)
+		return -EIO;
+	device = peer_device->device;
+
+	sector = be64_to_cpu(p->sector);
+	size = be32_to_cpu(p->blksize);
+
+	update_peer_seq(peer_device, be32_to_cpu(p->seq_num));
+
+	if (be64_to_cpu(p->block_id) == ID_OUT_OF_SYNC)
+		drbd_ov_out_of_sync_found(peer_device, sector, size);
+	else
+		ov_out_of_sync_print(peer_device);
+
+	if (!get_ldev(device))
+		return 0;
+
+	drbd_rs_complete_io(device, sector);
+	dec_rs_pending(peer_device);
+
+	--device->ov_left;
+
+	/* let's advance progress step marks only for every other megabyte */
+	if ((device->ov_left & 0x200) == 0x200)
+		drbd_advance_rs_marks(peer_device, device->ov_left);
+
+	if (device->ov_left == 0) {
+		dw = kmalloc(sizeof(*dw), GFP_NOIO);
+		if (dw) {
+			dw->w.cb = w_ov_finished;
+			dw->device = device;
+			drbd_queue_work(&peer_device->connection->sender_work, &dw->w);
+		} else {
+			drbd_err(device, "kmalloc(dw) failed.");
+			ov_out_of_sync_print(peer_device);
+			drbd_resync_finished(peer_device);
+		}
+	}
+	put_ldev(device);
+	return 0;
+}
+
+static int got_skip(struct drbd_connection *connection, struct packet_info *pi)
+{
+	return 0;
+}
+
+struct meta_sock_cmd {
+	size_t pkt_size;
+	int (*fn)(struct drbd_connection *connection, struct packet_info *);
+};
+
+static void set_rcvtimeo(struct drbd_connection *connection, bool ping_timeout)
+{
+	long t;
+	struct net_conf *nc;
+
+	rcu_read_lock();
+	nc = rcu_dereference(connection->net_conf);
+	t = ping_timeout ? nc->ping_timeo : nc->ping_int;
+	rcu_read_unlock();
+
+	t *= HZ;
+	if (ping_timeout)
+		t /= 10;
+
+	connection->meta.socket->sk->sk_rcvtimeo = t;
+}
+
+static void set_ping_timeout(struct drbd_connection *connection)
+{
+	set_rcvtimeo(connection, 1);
+}
+
+static void set_idle_timeout(struct drbd_connection *connection)
+{
+	set_rcvtimeo(connection, 0);
+}
+
+static struct meta_sock_cmd ack_receiver_tbl[] = {
+	[P_PING]	    = { 0, got_Ping },
+	[P_PING_ACK]	    = { 0, got_PingAck },
+	[P_RECV_ACK]	    = { sizeof(struct p_block_ack), got_BlockAck },
+	[P_WRITE_ACK]	    = { sizeof(struct p_block_ack), got_BlockAck },
+	[P_RS_WRITE_ACK]    = { sizeof(struct p_block_ack), got_BlockAck },
+	[P_SUPERSEDED]   = { sizeof(struct p_block_ack), got_BlockAck },
+	[P_NEG_ACK]	    = { sizeof(struct p_block_ack), got_NegAck },
+	[P_NEG_DREPLY]	    = { sizeof(struct p_block_ack), got_NegDReply },
+	[P_NEG_RS_DREPLY]   = { sizeof(struct p_block_ack), got_NegRSDReply },
+	[P_OV_RESULT]	    = { sizeof(struct p_block_ack), got_OVResult },
+	[P_BARRIER_ACK]	    = { sizeof(struct p_barrier_ack), got_BarrierAck },
+	[P_STATE_CHG_REPLY] = { sizeof(struct p_req_state_reply), got_RqSReply },
+	[P_RS_IS_IN_SYNC]   = { sizeof(struct p_block_ack), got_IsInSync },
+	[P_DELAY_PROBE]     = { sizeof(struct p_delay_probe93), got_skip },
+	[P_RS_CANCEL]       = { sizeof(struct p_block_ack), got_NegRSDReply },
+	[P_CONN_ST_CHG_REPLY]={ sizeof(struct p_req_state_reply), got_conn_RqSReply },
+	[P_RETRY_WRITE]	    = { sizeof(struct p_block_ack), got_BlockAck },
+};
+
+int drbd_ack_receiver(struct drbd_thread *thi)
+{
+	struct drbd_connection *connection = thi->connection;
+	struct meta_sock_cmd *cmd = NULL;
+	struct packet_info pi;
+	unsigned long pre_recv_jif;
+	int rv;
+	void *buf    = connection->meta.rbuf;
+	int received = 0;
+	unsigned int header_size = drbd_header_size(connection);
+	int expect   = header_size;
+	bool ping_timeout_active = false;
+
+	sched_set_fifo_low(current);
+
+	while (get_t_state(thi) == RUNNING) {
+		drbd_thread_current_set_cpu(thi);
+
+		conn_reclaim_net_peer_reqs(connection);
+
+		if (test_and_clear_bit(SEND_PING, &connection->flags)) {
+			if (drbd_send_ping(connection)) {
+				drbd_err(connection, "drbd_send_ping has failed\n");
+				goto reconnect;
+			}
+			set_ping_timeout(connection);
+			ping_timeout_active = true;
+		}
+
+		pre_recv_jif = jiffies;
+		rv = drbd_recv_short(connection->meta.socket, buf, expect-received, 0);
+
+		/* Note:
+		 * -EINTR	 (on meta) we got a signal
+		 * -EAGAIN	 (on meta) rcvtimeo expired
+		 * -ECONNRESET	 other side closed the connection
+		 * -ERESTARTSYS  (on data) we got a signal
+		 * rv <  0	 other than above: unexpected error!
+		 * rv == expected: full header or command
+		 * rv <  expected: "woken" by signal during receive
+		 * rv == 0	 : "connection shut down by peer"
+		 */
+		if (likely(rv > 0)) {
+			received += rv;
+			buf	 += rv;
+		} else if (rv == 0) {
+			if (test_bit(DISCONNECT_SENT, &connection->flags)) {
+				long t;
+				rcu_read_lock();
+				t = rcu_dereference(connection->net_conf)->ping_timeo * HZ/10;
+				rcu_read_unlock();
+
+				t = wait_event_timeout(connection->ping_wait,
+						       connection->cstate < C_WF_REPORT_PARAMS,
+						       t);
+				if (t)
+					break;
+			}
+			drbd_err(connection, "meta connection shut down by peer.\n");
+			goto reconnect;
+		} else if (rv == -EAGAIN) {
+			/* If the data socket received something meanwhile,
+			 * that is good enough: peer is still alive. */
+			if (time_after(connection->last_received, pre_recv_jif))
+				continue;
+			if (ping_timeout_active) {
+				drbd_err(connection, "PingAck did not arrive in time.\n");
+				goto reconnect;
+			}
+			set_bit(SEND_PING, &connection->flags);
+			continue;
+		} else if (rv == -EINTR) {
+			/* maybe drbd_thread_stop(): the while condition will notice.
+			 * maybe woken for send_ping: we'll send a ping above,
+			 * and change the rcvtimeo */
+			flush_signals(current);
+			continue;
+		} else {
+			drbd_err(connection, "sock_recvmsg returned %d\n", rv);
+			goto reconnect;
+		}
+
+		if (received == expect && cmd == NULL) {
+			if (decode_header(connection, connection->meta.rbuf, &pi))
+				goto reconnect;
+			cmd = &ack_receiver_tbl[pi.cmd];
+			if (pi.cmd >= ARRAY_SIZE(ack_receiver_tbl) || !cmd->fn) {
+				drbd_err(connection, "Unexpected meta packet %s (0x%04x)\n",
+					 cmdname(pi.cmd), pi.cmd);
+				goto disconnect;
+			}
+			expect = header_size + cmd->pkt_size;
+			if (pi.size != expect - header_size) {
+				drbd_err(connection, "Wrong packet size on meta (c: %d, l: %d)\n",
+					pi.cmd, pi.size);
+				goto reconnect;
+			}
+		}
+		if (received == expect) {
+			bool err;
+
+			err = cmd->fn(connection, &pi);
+			if (err) {
+				drbd_err(connection, "%ps failed\n", cmd->fn);
+				goto reconnect;
+			}
+
+			connection->last_received = jiffies;
+
+			if (cmd == &ack_receiver_tbl[P_PING_ACK]) {
+				set_idle_timeout(connection);
+				ping_timeout_active = false;
+			}
+
+			buf	 = connection->meta.rbuf;
+			received = 0;
+			expect	 = header_size;
+			cmd	 = NULL;
+		}
+	}
+
+	if (0) {
+reconnect:
+		conn_request_state(connection, NS(conn, C_NETWORK_FAILURE), CS_HARD);
+		conn_md_sync(connection);
+	}
+	if (0) {
+disconnect:
+		conn_request_state(connection, NS(conn, C_DISCONNECTING), CS_HARD);
+	}
+
+	drbd_info(connection, "ack_receiver terminated\n");
+
+	return 0;
+}
+
+void drbd_send_acks_wf(struct work_struct *ws)
+{
+	struct drbd_peer_device *peer_device =
+		container_of(ws, struct drbd_peer_device, send_acks_work);
+	struct drbd_connection *connection = peer_device->connection;
+	struct drbd_device *device = peer_device->device;
+	struct net_conf *nc;
+	int tcp_cork, err;
+
+	rcu_read_lock();
+	nc = rcu_dereference(connection->net_conf);
+	tcp_cork = nc->tcp_cork;
+	rcu_read_unlock();
+
+	if (tcp_cork)
+		tcp_sock_set_cork(connection->meta.socket->sk, true);
+
+	err = drbd_finish_peer_reqs(device);
+	kref_put(&device->kref, drbd_destroy_device);
+	/* get is in drbd_endio_write_sec_final(). That is necessary to keep the
+	   struct work_struct send_acks_work alive, which is in the peer_device object */
+
+	if (err) {
+		conn_request_state(connection, NS(conn, C_NETWORK_FAILURE), CS_HARD);
+		return;
+	}
+
+	if (tcp_cork)
+		tcp_sock_set_cork(connection->meta.socket->sk, false);
+
+	return;
+}