Adding upstream version 6.6.15.upstream/6.6.15

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

1 files changed, 2630 insertions, 0 deletions

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
new file mode 100644
index 0000000000..aa65313aab
--- /dev/null
+++ b/drivers/block/nbd.c
@@ -0,0 +1,2630 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Network block device - make block devices work over TCP
+ *
+ * Note that you can not swap over this thing, yet. Seems to work but
+ * deadlocks sometimes - you can not swap over TCP in general.
+ * 
+ * Copyright 1997-2000, 2008 Pavel Machek <pavel@ucw.cz>
+ * Parts copyright 2001 Steven Whitehouse <steve@chygwyn.com>
+ *
+ * (part of code stolen from loop.c)
+ */
+
+#define pr_fmt(fmt) "nbd: " fmt
+
+#include <linux/major.h>
+
+#include <linux/blkdev.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/sched/mm.h>
+#include <linux/fs.h>
+#include <linux/bio.h>
+#include <linux/stat.h>
+#include <linux/errno.h>
+#include <linux/file.h>
+#include <linux/ioctl.h>
+#include <linux/mutex.h>
+#include <linux/compiler.h>
+#include <linux/completion.h>
+#include <linux/err.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <net/sock.h>
+#include <linux/net.h>
+#include <linux/kthread.h>
+#include <linux/types.h>
+#include <linux/debugfs.h>
+#include <linux/blk-mq.h>
+
+#include <linux/uaccess.h>
+#include <asm/types.h>
+
+#include <linux/nbd.h>
+#include <linux/nbd-netlink.h>
+#include <net/genetlink.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/nbd.h>
+
+static DEFINE_IDR(nbd_index_idr);
+static DEFINE_MUTEX(nbd_index_mutex);
+static struct workqueue_struct *nbd_del_wq;
+static int nbd_total_devices = 0;
+
+struct nbd_sock {
+	struct socket *sock;
+	struct mutex tx_lock;
+	struct request *pending;
+	int sent;
+	bool dead;
+	int fallback_index;
+	int cookie;
+};
+
+struct recv_thread_args {
+	struct work_struct work;
+	struct nbd_device *nbd;
+	struct nbd_sock *nsock;
+	int index;
+};
+
+struct link_dead_args {
+	struct work_struct work;
+	int index;
+};
+
+#define NBD_RT_TIMEDOUT			0
+#define NBD_RT_DISCONNECT_REQUESTED	1
+#define NBD_RT_DISCONNECTED		2
+#define NBD_RT_HAS_PID_FILE		3
+#define NBD_RT_HAS_CONFIG_REF		4
+#define NBD_RT_BOUND			5
+#define NBD_RT_DISCONNECT_ON_CLOSE	6
+#define NBD_RT_HAS_BACKEND_FILE		7
+
+#define NBD_DESTROY_ON_DISCONNECT	0
+#define NBD_DISCONNECT_REQUESTED	1
+
+struct nbd_config {
+	u32 flags;
+	unsigned long runtime_flags;
+	u64 dead_conn_timeout;
+
+	struct nbd_sock **socks;
+	int num_connections;
+	atomic_t live_connections;
+	wait_queue_head_t conn_wait;
+
+	atomic_t recv_threads;
+	wait_queue_head_t recv_wq;
+	unsigned int blksize_bits;
+	loff_t bytesize;
+#if IS_ENABLED(CONFIG_DEBUG_FS)
+	struct dentry *dbg_dir;
+#endif
+};
+
+static inline unsigned int nbd_blksize(struct nbd_config *config)
+{
+	return 1u << config->blksize_bits;
+}
+
+struct nbd_device {
+	struct blk_mq_tag_set tag_set;
+
+	int index;
+	refcount_t config_refs;
+	refcount_t refs;
+	struct nbd_config *config;
+	struct mutex config_lock;
+	struct gendisk *disk;
+	struct workqueue_struct *recv_workq;
+	struct work_struct remove_work;
+
+	struct list_head list;
+	struct task_struct *task_setup;
+
+	unsigned long flags;
+	pid_t pid; /* pid of nbd-client, if attached */
+
+	char *backend;
+};
+
+#define NBD_CMD_REQUEUED	1
+/*
+ * This flag will be set if nbd_queue_rq() succeed, and will be checked and
+ * cleared in completion. Both setting and clearing of the flag are protected
+ * by cmd->lock.
+ */
+#define NBD_CMD_INFLIGHT	2
+
+struct nbd_cmd {
+	struct nbd_device *nbd;
+	struct mutex lock;
+	int index;
+	int cookie;
+	int retries;
+	blk_status_t status;
+	unsigned long flags;
+	u32 cmd_cookie;
+};
+
+#if IS_ENABLED(CONFIG_DEBUG_FS)
+static struct dentry *nbd_dbg_dir;
+#endif
+
+#define nbd_name(nbd) ((nbd)->disk->disk_name)
+
+#define NBD_DEF_BLKSIZE_BITS 10
+
+static unsigned int nbds_max = 16;
+static int max_part = 16;
+static int part_shift;
+
+static int nbd_dev_dbg_init(struct nbd_device *nbd);
+static void nbd_dev_dbg_close(struct nbd_device *nbd);
+static void nbd_config_put(struct nbd_device *nbd);
+static void nbd_connect_reply(struct genl_info *info, int index);
+static int nbd_genl_status(struct sk_buff *skb, struct genl_info *info);
+static void nbd_dead_link_work(struct work_struct *work);
+static void nbd_disconnect_and_put(struct nbd_device *nbd);
+
+static inline struct device *nbd_to_dev(struct nbd_device *nbd)
+{
+	return disk_to_dev(nbd->disk);
+}
+
+static void nbd_requeue_cmd(struct nbd_cmd *cmd)
+{
+	struct request *req = blk_mq_rq_from_pdu(cmd);
+
+	if (!test_and_set_bit(NBD_CMD_REQUEUED, &cmd->flags))
+		blk_mq_requeue_request(req, true);
+}
+
+#define NBD_COOKIE_BITS 32
+
+static u64 nbd_cmd_handle(struct nbd_cmd *cmd)
+{
+	struct request *req = blk_mq_rq_from_pdu(cmd);
+	u32 tag = blk_mq_unique_tag(req);
+	u64 cookie = cmd->cmd_cookie;
+
+	return (cookie << NBD_COOKIE_BITS) | tag;
+}
+
+static u32 nbd_handle_to_tag(u64 handle)
+{
+	return (u32)handle;
+}
+
+static u32 nbd_handle_to_cookie(u64 handle)
+{
+	return (u32)(handle >> NBD_COOKIE_BITS);
+}
+
+static const char *nbdcmd_to_ascii(int cmd)
+{
+	switch (cmd) {
+	case  NBD_CMD_READ: return "read";
+	case NBD_CMD_WRITE: return "write";
+	case  NBD_CMD_DISC: return "disconnect";
+	case NBD_CMD_FLUSH: return "flush";
+	case  NBD_CMD_TRIM: return "trim/discard";
+	}
+	return "invalid";
+}
+
+static ssize_t pid_show(struct device *dev,
+			struct device_attribute *attr, char *buf)
+{
+	struct gendisk *disk = dev_to_disk(dev);
+	struct nbd_device *nbd = (struct nbd_device *)disk->private_data;
+
+	return sprintf(buf, "%d\n", nbd->pid);
+}
+
+static const struct device_attribute pid_attr = {
+	.attr = { .name = "pid", .mode = 0444},
+	.show = pid_show,
+};
+
+static ssize_t backend_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct gendisk *disk = dev_to_disk(dev);
+	struct nbd_device *nbd = (struct nbd_device *)disk->private_data;
+
+	return sprintf(buf, "%s\n", nbd->backend ?: "");
+}
+
+static const struct device_attribute backend_attr = {
+	.attr = { .name = "backend", .mode = 0444},
+	.show = backend_show,
+};
+
+static void nbd_dev_remove(struct nbd_device *nbd)
+{
+	struct gendisk *disk = nbd->disk;
+
+	del_gendisk(disk);
+	blk_mq_free_tag_set(&nbd->tag_set);
+
+	/*
+	 * Remove from idr after del_gendisk() completes, so if the same ID is
+	 * reused, the following add_disk() will succeed.
+	 */
+	mutex_lock(&nbd_index_mutex);
+	idr_remove(&nbd_index_idr, nbd->index);
+	mutex_unlock(&nbd_index_mutex);
+	destroy_workqueue(nbd->recv_workq);
+	put_disk(disk);
+}
+
+static void nbd_dev_remove_work(struct work_struct *work)
+{
+	nbd_dev_remove(container_of(work, struct nbd_device, remove_work));
+}
+
+static void nbd_put(struct nbd_device *nbd)
+{
+	if (!refcount_dec_and_test(&nbd->refs))
+		return;
+
+	/* Call del_gendisk() asynchrounously to prevent deadlock */
+	if (test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags))
+		queue_work(nbd_del_wq, &nbd->remove_work);
+	else
+		nbd_dev_remove(nbd);
+}
+
+static int nbd_disconnected(struct nbd_config *config)
+{
+	return test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags) ||
+		test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags);
+}
+
+static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock,
+				int notify)
+{
+	if (!nsock->dead && notify && !nbd_disconnected(nbd->config)) {
+		struct link_dead_args *args;
+		args = kmalloc(sizeof(struct link_dead_args), GFP_NOIO);
+		if (args) {
+			INIT_WORK(&args->work, nbd_dead_link_work);
+			args->index = nbd->index;
+			queue_work(system_wq, &args->work);
+		}
+	}
+	if (!nsock->dead) {
+		kernel_sock_shutdown(nsock->sock, SHUT_RDWR);
+		if (atomic_dec_return(&nbd->config->live_connections) == 0) {
+			if (test_and_clear_bit(NBD_RT_DISCONNECT_REQUESTED,
+					       &nbd->config->runtime_flags)) {
+				set_bit(NBD_RT_DISCONNECTED,
+					&nbd->config->runtime_flags);
+				dev_info(nbd_to_dev(nbd),
+					"Disconnected due to user request.\n");
+			}
+		}
+	}
+	nsock->dead = true;
+	nsock->pending = NULL;
+	nsock->sent = 0;
+}
+
+static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize,
+		loff_t blksize)
+{
+	if (!blksize)
+		blksize = 1u << NBD_DEF_BLKSIZE_BITS;
+
+	if (blk_validate_block_size(blksize))
+		return -EINVAL;
+
+	if (bytesize < 0)
+		return -EINVAL;
+
+	nbd->config->bytesize = bytesize;
+	nbd->config->blksize_bits = __ffs(blksize);
+
+	if (!nbd->pid)
+		return 0;
+
+	if (nbd->config->flags & NBD_FLAG_SEND_TRIM) {
+		nbd->disk->queue->limits.discard_granularity = blksize;
+		blk_queue_max_discard_sectors(nbd->disk->queue, UINT_MAX);
+	}
+	blk_queue_logical_block_size(nbd->disk->queue, blksize);
+	blk_queue_physical_block_size(nbd->disk->queue, blksize);
+
+	if (max_part)
+		set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
+	if (!set_capacity_and_notify(nbd->disk, bytesize >> 9))
+		kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
+	return 0;
+}
+
+static void nbd_complete_rq(struct request *req)
+{
+	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);
+
+	dev_dbg(nbd_to_dev(cmd->nbd), "request %p: %s\n", req,
+		cmd->status ? "failed" : "done");
+
+	blk_mq_end_request(req, cmd->status);
+}
+
+/*
+ * Forcibly shutdown the socket causing all listeners to error
+ */
+static void sock_shutdown(struct nbd_device *nbd)
+{
+	struct nbd_config *config = nbd->config;
+	int i;
+
+	if (config->num_connections == 0)
+		return;
+	if (test_and_set_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
+		return;
+
+	for (i = 0; i < config->num_connections; i++) {
+		struct nbd_sock *nsock = config->socks[i];
+		mutex_lock(&nsock->tx_lock);
+		nbd_mark_nsock_dead(nbd, nsock, 0);
+		mutex_unlock(&nsock->tx_lock);
+	}
+	dev_warn(disk_to_dev(nbd->disk), "shutting down sockets\n");
+}
+
+static u32 req_to_nbd_cmd_type(struct request *req)
+{
+	switch (req_op(req)) {
+	case REQ_OP_DISCARD:
+		return NBD_CMD_TRIM;
+	case REQ_OP_FLUSH:
+		return NBD_CMD_FLUSH;
+	case REQ_OP_WRITE:
+		return NBD_CMD_WRITE;
+	case REQ_OP_READ:
+		return NBD_CMD_READ;
+	default:
+		return U32_MAX;
+	}
+}
+
+static struct nbd_config *nbd_get_config_unlocked(struct nbd_device *nbd)
+{
+	if (refcount_inc_not_zero(&nbd->config_refs)) {
+		/*
+		 * Add smp_mb__after_atomic to ensure that reading nbd->config_refs
+		 * and reading nbd->config is ordered. The pair is the barrier in
+		 * nbd_alloc_and_init_config(), avoid nbd->config_refs is set
+		 * before nbd->config.
+		 */
+		smp_mb__after_atomic();
+		return nbd->config;
+	}
+
+	return NULL;
+}
+
+static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req)
+{
+	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);
+	struct nbd_device *nbd = cmd->nbd;
+	struct nbd_config *config;
+
+	if (!mutex_trylock(&cmd->lock))
+		return BLK_EH_RESET_TIMER;
+
+	if (!test_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
+		mutex_unlock(&cmd->lock);
+		return BLK_EH_DONE;
+	}
+
+	config = nbd_get_config_unlocked(nbd);
+	if (!config) {
+		cmd->status = BLK_STS_TIMEOUT;
+		__clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);
+		mutex_unlock(&cmd->lock);
+		goto done;
+	}
+
+	if (config->num_connections > 1 ||
+	    (config->num_connections == 1 && nbd->tag_set.timeout)) {
+		dev_err_ratelimited(nbd_to_dev(nbd),
+				    "Connection timed out, retrying (%d/%d alive)\n",
+				    atomic_read(&config->live_connections),
+				    config->num_connections);
+		/*
+		 * Hooray we have more connections, requeue this IO, the submit
+		 * path will put it on a real connection. Or if only one
+		 * connection is configured, the submit path will wait util
+		 * a new connection is reconfigured or util dead timeout.
+		 */
+		if (config->socks) {
+			if (cmd->index < config->num_connections) {
+				struct nbd_sock *nsock =
+					config->socks[cmd->index];
+				mutex_lock(&nsock->tx_lock);
+				/* We can have multiple outstanding requests, so
+				 * we don't want to mark the nsock dead if we've
+				 * already reconnected with a new socket, so
+				 * only mark it dead if its the same socket we
+				 * were sent out on.
+				 */
+				if (cmd->cookie == nsock->cookie)
+					nbd_mark_nsock_dead(nbd, nsock, 1);
+				mutex_unlock(&nsock->tx_lock);
+			}
+			mutex_unlock(&cmd->lock);
+			nbd_requeue_cmd(cmd);
+			nbd_config_put(nbd);
+			return BLK_EH_DONE;
+		}
+	}
+
+	if (!nbd->tag_set.timeout) {
+		/*
+		 * Userspace sets timeout=0 to disable socket disconnection,
+		 * so just warn and reset the timer.
+		 */
+		struct nbd_sock *nsock = config->socks[cmd->index];
+		cmd->retries++;
+		dev_info(nbd_to_dev(nbd), "Possible stuck request %p: control (%s@%llu,%uB). Runtime %u seconds\n",
+			req, nbdcmd_to_ascii(req_to_nbd_cmd_type(req)),
+			(unsigned long long)blk_rq_pos(req) << 9,
+			blk_rq_bytes(req), (req->timeout / HZ) * cmd->retries);
+
+		mutex_lock(&nsock->tx_lock);
+		if (cmd->cookie != nsock->cookie) {
+			nbd_requeue_cmd(cmd);
+			mutex_unlock(&nsock->tx_lock);
+			mutex_unlock(&cmd->lock);
+			nbd_config_put(nbd);
+			return BLK_EH_DONE;
+		}
+		mutex_unlock(&nsock->tx_lock);
+		mutex_unlock(&cmd->lock);
+		nbd_config_put(nbd);
+		return BLK_EH_RESET_TIMER;
+	}
+
+	dev_err_ratelimited(nbd_to_dev(nbd), "Connection timed out\n");
+	set_bit(NBD_RT_TIMEDOUT, &config->runtime_flags);
+	cmd->status = BLK_STS_IOERR;
+	__clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);
+	mutex_unlock(&cmd->lock);
+	sock_shutdown(nbd);
+	nbd_config_put(nbd);
+done:
+	blk_mq_complete_request(req);
+	return BLK_EH_DONE;
+}
+
+static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
+		       struct iov_iter *iter, int msg_flags, int *sent)
+{
+	int result;
+	struct msghdr msg = {} ;
+	unsigned int noreclaim_flag;
+
+	if (unlikely(!sock)) {
+		dev_err_ratelimited(disk_to_dev(nbd->disk),
+			"Attempted %s on closed socket in sock_xmit\n",
+			(send ? "send" : "recv"));
+		return -EINVAL;
+	}
+
+	msg.msg_iter = *iter;
+
+	noreclaim_flag = memalloc_noreclaim_save();
+	do {
+		sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
+		sock->sk->sk_use_task_frag = false;
+		msg.msg_flags = msg_flags | MSG_NOSIGNAL;
+
+		if (send)
+			result = sock_sendmsg(sock, &msg);
+		else
+			result = sock_recvmsg(sock, &msg, msg.msg_flags);
+
+		if (result <= 0) {
+			if (result == 0)
+				result = -EPIPE; /* short read */
+			break;
+		}
+		if (sent)
+			*sent += result;
+	} while (msg_data_left(&msg));
+
+	memalloc_noreclaim_restore(noreclaim_flag);
+
+	return result;
+}
+
+/*
+ *  Send or receive packet. Return a positive value on success and
+ *  negtive value on failure, and never return 0.
+ */
+static int sock_xmit(struct nbd_device *nbd, int index, int send,
+		     struct iov_iter *iter, int msg_flags, int *sent)
+{
+	struct nbd_config *config = nbd->config;
+	struct socket *sock = config->socks[index]->sock;
+
+	return __sock_xmit(nbd, sock, send, iter, msg_flags, sent);
+}
+
+/*
+ * Different settings for sk->sk_sndtimeo can result in different return values
+ * if there is a signal pending when we enter sendmsg, because reasons?
+ */
+static inline int was_interrupted(int result)
+{
+	return result == -ERESTARTSYS || result == -EINTR;
+}
+
+/* always call with the tx_lock held */
+static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
+{
+	struct request *req = blk_mq_rq_from_pdu(cmd);
+	struct nbd_config *config = nbd->config;
+	struct nbd_sock *nsock = config->socks[index];
+	int result;
+	struct nbd_request request = {.magic = htonl(NBD_REQUEST_MAGIC)};
+	struct kvec iov = {.iov_base = &request, .iov_len = sizeof(request)};
+	struct iov_iter from;
+	unsigned long size = blk_rq_bytes(req);
+	struct bio *bio;
+	u64 handle;
+	u32 type;
+	u32 nbd_cmd_flags = 0;
+	int sent = nsock->sent, skip = 0;
+
+	iov_iter_kvec(&from, ITER_SOURCE, &iov, 1, sizeof(request));
+
+	type = req_to_nbd_cmd_type(req);
+	if (type == U32_MAX)
+		return -EIO;
+
+	if (rq_data_dir(req) == WRITE &&
+	    (config->flags & NBD_FLAG_READ_ONLY)) {
+		dev_err_ratelimited(disk_to_dev(nbd->disk),
+				    "Write on read-only\n");
+		return -EIO;
+	}
+
+	if (req->cmd_flags & REQ_FUA)
+		nbd_cmd_flags |= NBD_CMD_FLAG_FUA;
+
+	/* We did a partial send previously, and we at least sent the whole
+	 * request struct, so just go and send the rest of the pages in the
+	 * request.
+	 */
+	if (sent) {
+		if (sent >= sizeof(request)) {
+			skip = sent - sizeof(request);
+
+			/* initialize handle for tracing purposes */
+			handle = nbd_cmd_handle(cmd);
+
+			goto send_pages;
+		}
+		iov_iter_advance(&from, sent);
+	} else {
+		cmd->cmd_cookie++;
+	}
+	cmd->index = index;
+	cmd->cookie = nsock->cookie;
+	cmd->retries = 0;
+	request.type = htonl(type | nbd_cmd_flags);
+	if (type != NBD_CMD_FLUSH) {
+		request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
+		request.len = htonl(size);
+	}
+	handle = nbd_cmd_handle(cmd);
+	request.cookie = cpu_to_be64(handle);
+
+	trace_nbd_send_request(&request, nbd->index, blk_mq_rq_from_pdu(cmd));
+
+	dev_dbg(nbd_to_dev(nbd), "request %p: sending control (%s@%llu,%uB)\n",
+		req, nbdcmd_to_ascii(type),
+		(unsigned long long)blk_rq_pos(req) << 9, blk_rq_bytes(req));
+	result = sock_xmit(nbd, index, 1, &from,
+			(type == NBD_CMD_WRITE) ? MSG_MORE : 0, &sent);
+	trace_nbd_header_sent(req, handle);
+	if (result < 0) {
+		if (was_interrupted(result)) {
+			/* If we haven't sent anything we can just return BUSY,
+			 * however if we have sent something we need to make
+			 * sure we only allow this req to be sent until we are
+			 * completely done.
+			 */
+			if (sent) {
+				nsock->pending = req;
+				nsock->sent = sent;
+			}
+			set_bit(NBD_CMD_REQUEUED, &cmd->flags);
+			return BLK_STS_RESOURCE;
+		}
+		dev_err_ratelimited(disk_to_dev(nbd->disk),
+			"Send control failed (result %d)\n", result);
+		return -EAGAIN;
+	}
+send_pages:
+	if (type != NBD_CMD_WRITE)
+		goto out;
+
+	bio = req->bio;
+	while (bio) {
+		struct bio *next = bio->bi_next;
+		struct bvec_iter iter;
+		struct bio_vec bvec;
+
+		bio_for_each_segment(bvec, bio, iter) {
+			bool is_last = !next && bio_iter_last(bvec, iter);
+			int flags = is_last ? 0 : MSG_MORE;
+
+			dev_dbg(nbd_to_dev(nbd), "request %p: sending %d bytes data\n",
+				req, bvec.bv_len);
+			iov_iter_bvec(&from, ITER_SOURCE, &bvec, 1, bvec.bv_len);
+			if (skip) {
+				if (skip >= iov_iter_count(&from)) {
+					skip -= iov_iter_count(&from);
+					continue;
+				}
+				iov_iter_advance(&from, skip);
+				skip = 0;
+			}
+			result = sock_xmit(nbd, index, 1, &from, flags, &sent);
+			if (result < 0) {
+				if (was_interrupted(result)) {
+					/* We've already sent the header, we
+					 * have no choice but to set pending and
+					 * return BUSY.
+					 */
+					nsock->pending = req;
+					nsock->sent = sent;
+					set_bit(NBD_CMD_REQUEUED, &cmd->flags);
+					return BLK_STS_RESOURCE;
+				}
+				dev_err(disk_to_dev(nbd->disk),
+					"Send data failed (result %d)\n",
+					result);
+				return -EAGAIN;
+			}
+			/*
+			 * The completion might already have come in,
+			 * so break for the last one instead of letting
+			 * the iterator do it. This prevents use-after-free
+			 * of the bio.
+			 */
+			if (is_last)
+				break;
+		}
+		bio = next;
+	}
+out:
+	trace_nbd_payload_sent(req, handle);
+	nsock->pending = NULL;
+	nsock->sent = 0;
+	return 0;
+}
+
+static int nbd_read_reply(struct nbd_device *nbd, struct socket *sock,
+			  struct nbd_reply *reply)
+{
+	struct kvec iov = {.iov_base = reply, .iov_len = sizeof(*reply)};
+	struct iov_iter to;
+	int result;
+
+	reply->magic = 0;
+	iov_iter_kvec(&to, ITER_DEST, &iov, 1, sizeof(*reply));
+	result = __sock_xmit(nbd, sock, 0, &to, MSG_WAITALL, NULL);
+	if (result < 0) {
+		if (!nbd_disconnected(nbd->config))
+			dev_err(disk_to_dev(nbd->disk),
+				"Receive control failed (result %d)\n", result);
+		return result;
+	}
+
+	if (ntohl(reply->magic) != NBD_REPLY_MAGIC) {
+		dev_err(disk_to_dev(nbd->disk), "Wrong magic (0x%lx)\n",
+				(unsigned long)ntohl(reply->magic));
+		return -EPROTO;
+	}
+
+	return 0;
+}
+
+/* NULL returned = something went wrong, inform userspace */
+static struct nbd_cmd *nbd_handle_reply(struct nbd_device *nbd, int index,
+					struct nbd_reply *reply)
+{
+	int result;
+	struct nbd_cmd *cmd;
+	struct request *req = NULL;
+	u64 handle;
+	u16 hwq;
+	u32 tag;
+	int ret = 0;
+
+	handle = be64_to_cpu(reply->cookie);
+	tag = nbd_handle_to_tag(handle);
+	hwq = blk_mq_unique_tag_to_hwq(tag);
+	if (hwq < nbd->tag_set.nr_hw_queues)
+		req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq],
+				       blk_mq_unique_tag_to_tag(tag));
+	if (!req || !blk_mq_request_started(req)) {
+		dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n",
+			tag, req);
+		return ERR_PTR(-ENOENT);
+	}
+	trace_nbd_header_received(req, handle);
+	cmd = blk_mq_rq_to_pdu(req);
+
+	mutex_lock(&cmd->lock);
+	if (!test_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
+		dev_err(disk_to_dev(nbd->disk), "Suspicious reply %d (status %u flags %lu)",
+			tag, cmd->status, cmd->flags);
+		ret = -ENOENT;
+		goto out;
+	}
+	if (cmd->index != index) {
+		dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d from different sock %d (expected %d)",
+			tag, index, cmd->index);
+		ret = -ENOENT;
+		goto out;
+	}
+	if (cmd->cmd_cookie != nbd_handle_to_cookie(handle)) {
+		dev_err(disk_to_dev(nbd->disk), "Double reply on req %p, cmd_cookie %u, handle cookie %u\n",
+			req, cmd->cmd_cookie, nbd_handle_to_cookie(handle));
+		ret = -ENOENT;
+		goto out;
+	}
+	if (cmd->status != BLK_STS_OK) {
+		dev_err(disk_to_dev(nbd->disk), "Command already handled %p\n",
+			req);
+		ret = -ENOENT;
+		goto out;
+	}
+	if (test_bit(NBD_CMD_REQUEUED, &cmd->flags)) {
+		dev_err(disk_to_dev(nbd->disk), "Raced with timeout on req %p\n",
+			req);
+		ret = -ENOENT;
+		goto out;
+	}
+	if (ntohl(reply->error)) {
+		dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)\n",
+			ntohl(reply->error));
+		cmd->status = BLK_STS_IOERR;
+		goto out;
+	}
+
+	dev_dbg(nbd_to_dev(nbd), "request %p: got reply\n", req);
+	if (rq_data_dir(req) != WRITE) {
+		struct req_iterator iter;
+		struct bio_vec bvec;
+		struct iov_iter to;
+
+		rq_for_each_segment(bvec, req, iter) {
+			iov_iter_bvec(&to, ITER_DEST, &bvec, 1, bvec.bv_len);
+			result = sock_xmit(nbd, index, 0, &to, MSG_WAITALL, NULL);
+			if (result < 0) {
+				dev_err(disk_to_dev(nbd->disk), "Receive data failed (result %d)\n",
+					result);
+				/*
+				 * If we've disconnected, we need to make sure we
+				 * complete this request, otherwise error out
+				 * and let the timeout stuff handle resubmitting
+				 * this request onto another connection.
+				 */
+				if (nbd_disconnected(nbd->config)) {
+					cmd->status = BLK_STS_IOERR;
+					goto out;
+				}
+				ret = -EIO;
+				goto out;
+			}
+			dev_dbg(nbd_to_dev(nbd), "request %p: got %d bytes data\n",
+				req, bvec.bv_len);
+		}
+	}
+out:
+	trace_nbd_payload_received(req, handle);
+	mutex_unlock(&cmd->lock);
+	return ret ? ERR_PTR(ret) : cmd;
+}
+
+static void recv_work(struct work_struct *work)
+{
+	struct recv_thread_args *args = container_of(work,
+						     struct recv_thread_args,
+						     work);
+	struct nbd_device *nbd = args->nbd;
+	struct nbd_config *config = nbd->config;
+	struct request_queue *q = nbd->disk->queue;
+	struct nbd_sock *nsock = args->nsock;
+	struct nbd_cmd *cmd;
+	struct request *rq;
+
+	while (1) {
+		struct nbd_reply reply;
+
+		if (nbd_read_reply(nbd, nsock->sock, &reply))
+			break;
+
+		/*
+		 * Grab .q_usage_counter so request pool won't go away, then no
+		 * request use-after-free is possible during nbd_handle_reply().
+		 * If queue is frozen, there won't be any inflight requests, we
+		 * needn't to handle the incoming garbage message.
+		 */
+		if (!percpu_ref_tryget(&q->q_usage_counter)) {
+			dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n",
+				__func__);
+			break;
+		}
+
+		cmd = nbd_handle_reply(nbd, args->index, &reply);
+		if (IS_ERR(cmd)) {
+			percpu_ref_put(&q->q_usage_counter);
+			break;
+		}
+
+		rq = blk_mq_rq_from_pdu(cmd);
+		if (likely(!blk_should_fake_timeout(rq->q))) {
+			bool complete;
+
+			mutex_lock(&cmd->lock);
+			complete = __test_and_clear_bit(NBD_CMD_INFLIGHT,
+							&cmd->flags);
+			mutex_unlock(&cmd->lock);
+			if (complete)
+				blk_mq_complete_request(rq);
+		}
+		percpu_ref_put(&q->q_usage_counter);
+	}
+
+	mutex_lock(&nsock->tx_lock);
+	nbd_mark_nsock_dead(nbd, nsock, 1);
+	mutex_unlock(&nsock->tx_lock);
+
+	nbd_config_put(nbd);
+	atomic_dec(&config->recv_threads);
+	wake_up(&config->recv_wq);
+	kfree(args);
+}
+
+static bool nbd_clear_req(struct request *req, void *data)
+{
+	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);
+
+	/* don't abort one completed request */
+	if (blk_mq_request_completed(req))
+		return true;
+
+	mutex_lock(&cmd->lock);
+	if (!__test_and_clear_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
+		mutex_unlock(&cmd->lock);
+		return true;
+	}
+	cmd->status = BLK_STS_IOERR;
+	mutex_unlock(&cmd->lock);
+
+	blk_mq_complete_request(req);
+	return true;
+}
+
+static void nbd_clear_que(struct nbd_device *nbd)
+{
+	blk_mq_quiesce_queue(nbd->disk->queue);
+	blk_mq_tagset_busy_iter(&nbd->tag_set, nbd_clear_req, NULL);
+	blk_mq_unquiesce_queue(nbd->disk->queue);
+	dev_dbg(disk_to_dev(nbd->disk), "queue cleared\n");
+}
+
+static int find_fallback(struct nbd_device *nbd, int index)
+{
+	struct nbd_config *config = nbd->config;
+	int new_index = -1;
+	struct nbd_sock *nsock = config->socks[index];
+	int fallback = nsock->fallback_index;
+
+	if (test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
+		return new_index;
+
+	if (config->num_connections <= 1) {
+		dev_err_ratelimited(disk_to_dev(nbd->disk),
+				    "Dead connection, failed to find a fallback\n");
+		return new_index;
+	}
+
+	if (fallback >= 0 && fallback < config->num_connections &&
+	    !config->socks[fallback]->dead)
+		return fallback;
+
+	if (nsock->fallback_index < 0 ||
+	    nsock->fallback_index >= config->num_connections ||
+	    config->socks[nsock->fallback_index]->dead) {
+		int i;
+		for (i = 0; i < config->num_connections; i++) {
+			if (i == index)
+				continue;
+			if (!config->socks[i]->dead) {
+				new_index = i;
+				break;
+			}
+		}
+		nsock->fallback_index = new_index;
+		if (new_index < 0) {
+			dev_err_ratelimited(disk_to_dev(nbd->disk),
+					    "Dead connection, failed to find a fallback\n");
+			return new_index;
+		}
+	}
+	new_index = nsock->fallback_index;
+	return new_index;
+}
+
+static int wait_for_reconnect(struct nbd_device *nbd)
+{
+	struct nbd_config *config = nbd->config;
+	if (!config->dead_conn_timeout)
+		return 0;
+
+	if (!wait_event_timeout(config->conn_wait,
+				test_bit(NBD_RT_DISCONNECTED,
+					 &config->runtime_flags) ||
+				atomic_read(&config->live_connections) > 0,
+				config->dead_conn_timeout))
+		return 0;
+
+	return !test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);
+}
+
+static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)
+{
+	struct request *req = blk_mq_rq_from_pdu(cmd);
+	struct nbd_device *nbd = cmd->nbd;
+	struct nbd_config *config;
+	struct nbd_sock *nsock;
+	int ret;
+
+	config = nbd_get_config_unlocked(nbd);
+	if (!config) {
+		dev_err_ratelimited(disk_to_dev(nbd->disk),
+				    "Socks array is empty\n");
+		return -EINVAL;
+	}
+
+	if (index >= config->num_connections) {
+		dev_err_ratelimited(disk_to_dev(nbd->disk),
+				    "Attempted send on invalid socket\n");
+		nbd_config_put(nbd);
+		return -EINVAL;
+	}
+	cmd->status = BLK_STS_OK;
+again:
+	nsock = config->socks[index];
+	mutex_lock(&nsock->tx_lock);
+	if (nsock->dead) {
+		int old_index = index;
+		index = find_fallback(nbd, index);
+		mutex_unlock(&nsock->tx_lock);
+		if (index < 0) {
+			if (wait_for_reconnect(nbd)) {
+				index = old_index;
+				goto again;
+			}
+			/* All the sockets should already be down at this point,
+			 * we just want to make sure that DISCONNECTED is set so
+			 * any requests that come in that were queue'ed waiting
+			 * for the reconnect timer don't trigger the timer again
+			 * and instead just error out.
+			 */
+			sock_shutdown(nbd);
+			nbd_config_put(nbd);
+			return -EIO;
+		}
+		goto again;
+	}
+
+	/* Handle the case that we have a pending request that was partially
+	 * transmitted that _has_ to be serviced first.  We need to call requeue
+	 * here so that it gets put _after_ the request that is already on the
+	 * dispatch list.
+	 */
+	blk_mq_start_request(req);
+	if (unlikely(nsock->pending && nsock->pending != req)) {
+		nbd_requeue_cmd(cmd);
+		ret = 0;
+		goto out;
+	}
+	/*
+	 * Some failures are related to the link going down, so anything that
+	 * returns EAGAIN can be retried on a different socket.
+	 */
+	ret = nbd_send_cmd(nbd, cmd, index);
+	/*
+	 * Access to this flag is protected by cmd->lock, thus it's safe to set
+	 * the flag after nbd_send_cmd() succeed to send request to server.
+	 */
+	if (!ret)
+		__set_bit(NBD_CMD_INFLIGHT, &cmd->flags);
+	else if (ret == -EAGAIN) {
+		dev_err_ratelimited(disk_to_dev(nbd->disk),
+				    "Request send failed, requeueing\n");
+		nbd_mark_nsock_dead(nbd, nsock, 1);
+		nbd_requeue_cmd(cmd);
+		ret = 0;
+	}
+out:
+	mutex_unlock(&nsock->tx_lock);
+	nbd_config_put(nbd);
+	return ret;
+}
+
+static blk_status_t nbd_queue_rq(struct blk_mq_hw_ctx *hctx,
+			const struct blk_mq_queue_data *bd)
+{
+	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
+	int ret;
+
+	/*
+	 * Since we look at the bio's to send the request over the network we
+	 * need to make sure the completion work doesn't mark this request done
+	 * before we are done doing our send.  This keeps us from dereferencing
+	 * freed data if we have particularly fast completions (ie we get the
+	 * completion before we exit sock_xmit on the last bvec) or in the case
+	 * that the server is misbehaving (or there was an error) before we're
+	 * done sending everything over the wire.
+	 */
+	mutex_lock(&cmd->lock);
+	clear_bit(NBD_CMD_REQUEUED, &cmd->flags);
+
+	/* We can be called directly from the user space process, which means we
+	 * could possibly have signals pending so our sendmsg will fail.  In
+	 * this case we need to return that we are busy, otherwise error out as
+	 * appropriate.
+	 */
+	ret = nbd_handle_cmd(cmd, hctx->queue_num);
+	if (ret < 0)
+		ret = BLK_STS_IOERR;
+	else if (!ret)
+		ret = BLK_STS_OK;
+	mutex_unlock(&cmd->lock);
+
+	return ret;
+}
+
+static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
+				     int *err)
+{
+	struct socket *sock;
+
+	*err = 0;
+	sock = sockfd_lookup(fd, err);
+	if (!sock)
+		return NULL;
+
+	if (sock->ops->shutdown == sock_no_shutdown) {
+		dev_err(disk_to_dev(nbd->disk), "Unsupported socket: shutdown callout must be supported.\n");
+		*err = -EINVAL;
+		sockfd_put(sock);
+		return NULL;
+	}
+
+	return sock;
+}
+
+static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
+			  bool netlink)
+{
+	struct nbd_config *config = nbd->config;
+	struct socket *sock;
+	struct nbd_sock **socks;
+	struct nbd_sock *nsock;
+	int err;
+
+	/* Arg will be cast to int, check it to avoid overflow */
+	if (arg > INT_MAX)
+		return -EINVAL;
+	sock = nbd_get_socket(nbd, arg, &err);
+	if (!sock)
+		return err;
+
+	/*
+	 * We need to make sure we don't get any errant requests while we're
+	 * reallocating the ->socks array.
+	 */
+	blk_mq_freeze_queue(nbd->disk->queue);
+
+	if (!netlink && !nbd->task_setup &&
+	    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
+		nbd->task_setup = current;
+
+	if (!netlink &&
+	    (nbd->task_setup != current ||
+	     test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
+		dev_err(disk_to_dev(nbd->disk),
+			"Device being setup by another task");
+		err = -EBUSY;
+		goto put_socket;
+	}
+
+	nsock = kzalloc(sizeof(*nsock), GFP_KERNEL);
+	if (!nsock) {
+		err = -ENOMEM;
+		goto put_socket;
+	}
+
+	socks = krealloc(config->socks, (config->num_connections + 1) *
+			 sizeof(struct nbd_sock *), GFP_KERNEL);
+	if (!socks) {
+		kfree(nsock);
+		err = -ENOMEM;
+		goto put_socket;
+	}
+
+	config->socks = socks;
+
+	nsock->fallback_index = -1;
+	nsock->dead = false;
+	mutex_init(&nsock->tx_lock);
+	nsock->sock = sock;
+	nsock->pending = NULL;
+	nsock->sent = 0;
+	nsock->cookie = 0;
+	socks[config->num_connections++] = nsock;
+	atomic_inc(&config->live_connections);
+	blk_mq_unfreeze_queue(nbd->disk->queue);
+
+	return 0;
+
+put_socket:
+	blk_mq_unfreeze_queue(nbd->disk->queue);
+	sockfd_put(sock);
+	return err;
+}
+
+static int nbd_reconnect_socket(struct nbd_device *nbd, unsigned long arg)
+{
+	struct nbd_config *config = nbd->config;
+	struct socket *sock, *old;
+	struct recv_thread_args *args;
+	int i;
+	int err;
+
+	sock = nbd_get_socket(nbd, arg, &err);
+	if (!sock)
+		return err;
+
+	args = kzalloc(sizeof(*args), GFP_KERNEL);
+	if (!args) {
+		sockfd_put(sock);
+		return -ENOMEM;
+	}
+
+	for (i = 0; i < config->num_connections; i++) {
+		struct nbd_sock *nsock = config->socks[i];
+
+		if (!nsock->dead)
+			continue;
+
+		mutex_lock(&nsock->tx_lock);
+		if (!nsock->dead) {
+			mutex_unlock(&nsock->tx_lock);
+			continue;
+		}
+		sk_set_memalloc(sock->sk);
+		if (nbd->tag_set.timeout)
+			sock->sk->sk_sndtimeo = nbd->tag_set.timeout;
+		atomic_inc(&config->recv_threads);
+		refcount_inc(&nbd->config_refs);
+		old = nsock->sock;
+		nsock->fallback_index = -1;
+		nsock->sock = sock;
+		nsock->dead = false;
+		INIT_WORK(&args->work, recv_work);
+		args->index = i;
+		args->nbd = nbd;
+		args->nsock = nsock;
+		nsock->cookie++;
+		mutex_unlock(&nsock->tx_lock);
+		sockfd_put(old);
+
+		clear_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);
+
+		/* We take the tx_mutex in an error path in the recv_work, so we
+		 * need to queue_work outside of the tx_mutex.
+		 */
+		queue_work(nbd->recv_workq, &args->work);
+
+		atomic_inc(&config->live_connections);
+		wake_up(&config->conn_wait);
+		return 0;
+	}
+	sockfd_put(sock);
+	kfree(args);
+	return -ENOSPC;
+}
+
+static void nbd_bdev_reset(struct nbd_device *nbd)
+{
+	if (disk_openers(nbd->disk) > 1)
+		return;
+	set_capacity(nbd->disk, 0);
+}
+
+static void nbd_parse_flags(struct nbd_device *nbd)
+{
+	struct nbd_config *config = nbd->config;
+	if (config->flags & NBD_FLAG_READ_ONLY)
+		set_disk_ro(nbd->disk, true);
+	else
+		set_disk_ro(nbd->disk, false);
+	if (config->flags & NBD_FLAG_SEND_FLUSH) {
+		if (config->flags & NBD_FLAG_SEND_FUA)
+			blk_queue_write_cache(nbd->disk->queue, true, true);
+		else
+			blk_queue_write_cache(nbd->disk->queue, true, false);
+	}
+	else
+		blk_queue_write_cache(nbd->disk->queue, false, false);
+}
+
+static void send_disconnects(struct nbd_device *nbd)
+{
+	struct nbd_config *config = nbd->config;
+	struct nbd_request request = {
+		.magic = htonl(NBD_REQUEST_MAGIC),
+		.type = htonl(NBD_CMD_DISC),
+	};
+	struct kvec iov = {.iov_base = &request, .iov_len = sizeof(request)};
+	struct iov_iter from;
+	int i, ret;
+
+	for (i = 0; i < config->num_connections; i++) {
+		struct nbd_sock *nsock = config->socks[i];
+
+		iov_iter_kvec(&from, ITER_SOURCE, &iov, 1, sizeof(request));
+		mutex_lock(&nsock->tx_lock);
+		ret = sock_xmit(nbd, i, 1, &from, 0, NULL);
+		if (ret < 0)
+			dev_err(disk_to_dev(nbd->disk),
+				"Send disconnect failed %d\n", ret);
+		mutex_unlock(&nsock->tx_lock);
+	}
+}
+
+static int nbd_disconnect(struct nbd_device *nbd)
+{
+	struct nbd_config *config = nbd->config;
+
+	dev_info(disk_to_dev(nbd->disk), "NBD_DISCONNECT\n");
+	set_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags);
+	set_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags);
+	send_disconnects(nbd);
+	return 0;
+}
+
+static void nbd_clear_sock(struct nbd_device *nbd)
+{
+	sock_shutdown(nbd);
+	nbd_clear_que(nbd);
+	nbd->task_setup = NULL;
+}
+
+static void nbd_config_put(struct nbd_device *nbd)
+{
+	if (refcount_dec_and_mutex_lock(&nbd->config_refs,
+					&nbd->config_lock)) {
+		struct nbd_config *config = nbd->config;
+		nbd_dev_dbg_close(nbd);
+		invalidate_disk(nbd->disk);
+		if (nbd->config->bytesize)
+			kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
+		if (test_and_clear_bit(NBD_RT_HAS_PID_FILE,
+				       &config->runtime_flags))
+			device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
+		nbd->pid = 0;
+		if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE,
+				       &config->runtime_flags)) {
+			device_remove_file(disk_to_dev(nbd->disk), &backend_attr);
+			kfree(nbd->backend);
+			nbd->backend = NULL;
+		}
+		nbd_clear_sock(nbd);
+		if (config->num_connections) {
+			int i;
+			for (i = 0; i < config->num_connections; i++) {
+				sockfd_put(config->socks[i]->sock);
+				kfree(config->socks[i]);
+			}
+			kfree(config->socks);
+		}
+		kfree(nbd->config);
+		nbd->config = NULL;
+
+		nbd->tag_set.timeout = 0;
+		nbd->disk->queue->limits.discard_granularity = 0;
+		blk_queue_max_discard_sectors(nbd->disk->queue, 0);
+
+		mutex_unlock(&nbd->config_lock);
+		nbd_put(nbd);
+		module_put(THIS_MODULE);
+	}
+}
+
+static int nbd_start_device(struct nbd_device *nbd)
+{
+	struct nbd_config *config = nbd->config;
+	int num_connections = config->num_connections;
+	int error = 0, i;
+
+	if (nbd->pid)
+		return -EBUSY;
+	if (!config->socks)
+		return -EINVAL;
+	if (num_connections > 1 &&
+	    !(config->flags & NBD_FLAG_CAN_MULTI_CONN)) {
+		dev_err(disk_to_dev(nbd->disk), "server does not support multiple connections per device.\n");
+		return -EINVAL;
+	}
+
+	blk_mq_update_nr_hw_queues(&nbd->tag_set, config->num_connections);
+	nbd->pid = task_pid_nr(current);
+
+	nbd_parse_flags(nbd);
+
+	error = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
+	if (error) {
+		dev_err(disk_to_dev(nbd->disk), "device_create_file failed for pid!\n");
+		return error;
+	}
+	set_bit(NBD_RT_HAS_PID_FILE, &config->runtime_flags);
+
+	nbd_dev_dbg_init(nbd);
+	for (i = 0; i < num_connections; i++) {
+		struct recv_thread_args *args;
+
+		args = kzalloc(sizeof(*args), GFP_KERNEL);
+		if (!args) {
+			sock_shutdown(nbd);
+			/*
+			 * If num_connections is m (2 < m),
+			 * and NO.1 ~ NO.n(1 < n < m) kzallocs are successful.
+			 * But NO.(n + 1) failed. We still have n recv threads.
+			 * So, add flush_workqueue here to prevent recv threads
+			 * dropping the last config_refs and trying to destroy
+			 * the workqueue from inside the workqueue.
+			 */
+			if (i)
+				flush_workqueue(nbd->recv_workq);
+			return -ENOMEM;
+		}
+		sk_set_memalloc(config->socks[i]->sock->sk);
+		if (nbd->tag_set.timeout)
+			config->socks[i]->sock->sk->sk_sndtimeo =
+				nbd->tag_set.timeout;
+		atomic_inc(&config->recv_threads);
+		refcount_inc(&nbd->config_refs);
+		INIT_WORK(&args->work, recv_work);
+		args->nbd = nbd;
+		args->nsock = config->socks[i];
+		args->index = i;
+		queue_work(nbd->recv_workq, &args->work);
+	}
+	return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
+}
+
+static int nbd_start_device_ioctl(struct nbd_device *nbd)
+{
+	struct nbd_config *config = nbd->config;
+	int ret;
+
+	ret = nbd_start_device(nbd);
+	if (ret)
+		return ret;
+
+	if (max_part)
+		set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
+	mutex_unlock(&nbd->config_lock);
+	ret = wait_event_interruptible(config->recv_wq,
+					 atomic_read(&config->recv_threads) == 0);
+	if (ret) {
+		sock_shutdown(nbd);
+		nbd_clear_que(nbd);
+	}
+
+	flush_workqueue(nbd->recv_workq);
+	mutex_lock(&nbd->config_lock);
+	nbd_bdev_reset(nbd);
+	/* user requested, ignore socket errors */
+	if (test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags))
+		ret = 0;
+	if (test_bit(NBD_RT_TIMEDOUT, &config->runtime_flags))
+		ret = -ETIMEDOUT;
+	return ret;
+}
+
+static void nbd_clear_sock_ioctl(struct nbd_device *nbd)
+{
+	nbd_clear_sock(nbd);
+	disk_force_media_change(nbd->disk);
+	nbd_bdev_reset(nbd);
+	if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,
+			       &nbd->config->runtime_flags))
+		nbd_config_put(nbd);
+}
+
+static void nbd_set_cmd_timeout(struct nbd_device *nbd, u64 timeout)
+{
+	nbd->tag_set.timeout = timeout * HZ;
+	if (timeout)
+		blk_queue_rq_timeout(nbd->disk->queue, timeout * HZ);
+	else
+		blk_queue_rq_timeout(nbd->disk->queue, 30 * HZ);
+}
+
+/* Must be called with config_lock held */
+static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
+		       unsigned int cmd, unsigned long arg)
+{
+	struct nbd_config *config = nbd->config;
+	loff_t bytesize;
+
+	switch (cmd) {
+	case NBD_DISCONNECT:
+		return nbd_disconnect(nbd);
+	case NBD_CLEAR_SOCK:
+		nbd_clear_sock_ioctl(nbd);
+		return 0;
+	case NBD_SET_SOCK:
+		return nbd_add_socket(nbd, arg, false);
+	case NBD_SET_BLKSIZE:
+		return nbd_set_size(nbd, config->bytesize, arg);
+	case NBD_SET_SIZE:
+		return nbd_set_size(nbd, arg, nbd_blksize(config));
+	case NBD_SET_SIZE_BLOCKS:
+		if (check_shl_overflow(arg, config->blksize_bits, &bytesize))
+			return -EINVAL;
+		return nbd_set_size(nbd, bytesize, nbd_blksize(config));
+	case NBD_SET_TIMEOUT:
+		nbd_set_cmd_timeout(nbd, arg);
+		return 0;
+
+	case NBD_SET_FLAGS:
+		config->flags = arg;
+		return 0;
+	case NBD_DO_IT:
+		return nbd_start_device_ioctl(nbd);
+	case NBD_CLEAR_QUE:
+		/*
+		 * This is for compatibility only.  The queue is always cleared
+		 * by NBD_DO_IT or NBD_CLEAR_SOCK.
+		 */
+		return 0;
+	case NBD_PRINT_DEBUG:
+		/*
+		 * For compatibility only, we no longer keep a list of
+		 * outstanding requests.
+		 */
+		return 0;
+	}
+	return -ENOTTY;
+}
+
+static int nbd_ioctl(struct block_device *bdev, blk_mode_t mode,
+		     unsigned int cmd, unsigned long arg)
+{
+	struct nbd_device *nbd = bdev->bd_disk->private_data;
+	struct nbd_config *config = nbd->config;
+	int error = -EINVAL;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	/* The block layer will pass back some non-nbd ioctls in case we have
+	 * special handling for them, but we don't so just return an error.
+	 */
+	if (_IOC_TYPE(cmd) != 0xab)
+		return -EINVAL;
+
+	mutex_lock(&nbd->config_lock);
+
+	/* Don't allow ioctl operations on a nbd device that was created with
+	 * netlink, unless it's DISCONNECT or CLEAR_SOCK, which are fine.
+	 */
+	if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
+	    (cmd == NBD_DISCONNECT || cmd == NBD_CLEAR_SOCK))
+		error = __nbd_ioctl(bdev, nbd, cmd, arg);
+	else
+		dev_err(nbd_to_dev(nbd), "Cannot use ioctl interface on a netlink controlled device.\n");
+	mutex_unlock(&nbd->config_lock);
+	return error;
+}
+
+static int nbd_alloc_and_init_config(struct nbd_device *nbd)
+{
+	struct nbd_config *config;
+
+	if (WARN_ON(nbd->config))
+		return -EINVAL;
+
+	if (!try_module_get(THIS_MODULE))
+		return -ENODEV;
+
+	config = kzalloc(sizeof(struct nbd_config), GFP_NOFS);
+	if (!config) {
+		module_put(THIS_MODULE);
+		return -ENOMEM;
+	}
+
+	atomic_set(&config->recv_threads, 0);
+	init_waitqueue_head(&config->recv_wq);
+	init_waitqueue_head(&config->conn_wait);
+	config->blksize_bits = NBD_DEF_BLKSIZE_BITS;
+	atomic_set(&config->live_connections, 0);
+
+	nbd->config = config;
+	/*
+	 * Order refcount_set(&nbd->config_refs, 1) and nbd->config assignment,
+	 * its pair is the barrier in nbd_get_config_unlocked().
+	 * So nbd_get_config_unlocked() won't see nbd->config as null after
+	 * refcount_inc_not_zero() succeed.
+	 */
+	smp_mb__before_atomic();
+	refcount_set(&nbd->config_refs, 1);
+
+	return 0;
+}
+
+static int nbd_open(struct gendisk *disk, blk_mode_t mode)
+{
+	struct nbd_device *nbd;
+	struct nbd_config *config;
+	int ret = 0;
+
+	mutex_lock(&nbd_index_mutex);
+	nbd = disk->private_data;
+	if (!nbd) {
+		ret = -ENXIO;
+		goto out;
+	}
+	if (!refcount_inc_not_zero(&nbd->refs)) {
+		ret = -ENXIO;
+		goto out;
+	}
+
+	config = nbd_get_config_unlocked(nbd);
+	if (!config) {
+		mutex_lock(&nbd->config_lock);
+		if (refcount_inc_not_zero(&nbd->config_refs)) {
+			mutex_unlock(&nbd->config_lock);
+			goto out;
+		}
+		ret = nbd_alloc_and_init_config(nbd);
+		if (ret) {
+			mutex_unlock(&nbd->config_lock);
+			goto out;
+		}
+
+		refcount_inc(&nbd->refs);
+		mutex_unlock(&nbd->config_lock);
+		if (max_part)
+			set_bit(GD_NEED_PART_SCAN, &disk->state);
+	} else if (nbd_disconnected(config)) {
+		if (max_part)
+			set_bit(GD_NEED_PART_SCAN, &disk->state);
+	}
+out:
+	mutex_unlock(&nbd_index_mutex);
+	return ret;
+}
+
+static void nbd_release(struct gendisk *disk)
+{
+	struct nbd_device *nbd = disk->private_data;
+
+	if (test_bit(NBD_RT_DISCONNECT_ON_CLOSE, &nbd->config->runtime_flags) &&
+			disk_openers(disk) == 0)
+		nbd_disconnect_and_put(nbd);
+
+	nbd_config_put(nbd);
+	nbd_put(nbd);
+}
+
+static void nbd_free_disk(struct gendisk *disk)
+{
+	struct nbd_device *nbd = disk->private_data;
+
+	kfree(nbd);
+}
+
+static const struct block_device_operations nbd_fops =
+{
+	.owner =	THIS_MODULE,
+	.open =		nbd_open,
+	.release =	nbd_release,
+	.ioctl =	nbd_ioctl,
+	.compat_ioctl =	nbd_ioctl,
+	.free_disk =	nbd_free_disk,
+};
+
+#if IS_ENABLED(CONFIG_DEBUG_FS)
+
+static int nbd_dbg_tasks_show(struct seq_file *s, void *unused)
+{
+	struct nbd_device *nbd = s->private;
+
+	if (nbd->pid)
+		seq_printf(s, "recv: %d\n", nbd->pid);
+
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(nbd_dbg_tasks);
+
+static int nbd_dbg_flags_show(struct seq_file *s, void *unused)
+{
+	struct nbd_device *nbd = s->private;
+	u32 flags = nbd->config->flags;
+
+	seq_printf(s, "Hex: 0x%08x\n\n", flags);
+
+	seq_puts(s, "Known flags:\n");
+
+	if (flags & NBD_FLAG_HAS_FLAGS)
+		seq_puts(s, "NBD_FLAG_HAS_FLAGS\n");
+	if (flags & NBD_FLAG_READ_ONLY)
+		seq_puts(s, "NBD_FLAG_READ_ONLY\n");
+	if (flags & NBD_FLAG_SEND_FLUSH)
+		seq_puts(s, "NBD_FLAG_SEND_FLUSH\n");
+	if (flags & NBD_FLAG_SEND_FUA)
+		seq_puts(s, "NBD_FLAG_SEND_FUA\n");
+	if (flags & NBD_FLAG_SEND_TRIM)
+		seq_puts(s, "NBD_FLAG_SEND_TRIM\n");
+
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(nbd_dbg_flags);
+
+static int nbd_dev_dbg_init(struct nbd_device *nbd)
+{
+	struct dentry *dir;
+	struct nbd_config *config = nbd->config;
+
+	if (!nbd_dbg_dir)
+		return -EIO;
+
+	dir = debugfs_create_dir(nbd_name(nbd), nbd_dbg_dir);
+	if (IS_ERR(dir)) {
+		dev_err(nbd_to_dev(nbd), "Failed to create debugfs dir for '%s'\n",
+			nbd_name(nbd));
+		return -EIO;
+	}
+	config->dbg_dir = dir;
+
+	debugfs_create_file("tasks", 0444, dir, nbd, &nbd_dbg_tasks_fops);
+	debugfs_create_u64("size_bytes", 0444, dir, &config->bytesize);
+	debugfs_create_u32("timeout", 0444, dir, &nbd->tag_set.timeout);
+	debugfs_create_u32("blocksize_bits", 0444, dir, &config->blksize_bits);
+	debugfs_create_file("flags", 0444, dir, nbd, &nbd_dbg_flags_fops);
+
+	return 0;
+}
+
+static void nbd_dev_dbg_close(struct nbd_device *nbd)
+{
+	debugfs_remove_recursive(nbd->config->dbg_dir);
+}
+
+static int nbd_dbg_init(void)
+{
+	struct dentry *dbg_dir;
+
+	dbg_dir = debugfs_create_dir("nbd", NULL);
+	if (IS_ERR(dbg_dir))
+		return -EIO;
+
+	nbd_dbg_dir = dbg_dir;
+
+	return 0;
+}
+
+static void nbd_dbg_close(void)
+{
+	debugfs_remove_recursive(nbd_dbg_dir);
+}
+
+#else  /* IS_ENABLED(CONFIG_DEBUG_FS) */
+
+static int nbd_dev_dbg_init(struct nbd_device *nbd)
+{
+	return 0;
+}
+
+static void nbd_dev_dbg_close(struct nbd_device *nbd)
+{
+}
+
+static int nbd_dbg_init(void)
+{
+	return 0;
+}
+
+static void nbd_dbg_close(void)
+{
+}
+
+#endif
+
+static int nbd_init_request(struct blk_mq_tag_set *set, struct request *rq,
+			    unsigned int hctx_idx, unsigned int numa_node)
+{
+	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(rq);
+	cmd->nbd = set->driver_data;
+	cmd->flags = 0;
+	mutex_init(&cmd->lock);
+	return 0;
+}
+
+static const struct blk_mq_ops nbd_mq_ops = {
+	.queue_rq	= nbd_queue_rq,
+	.complete	= nbd_complete_rq,
+	.init_request	= nbd_init_request,
+	.timeout	= nbd_xmit_timeout,
+};
+
+static struct nbd_device *nbd_dev_add(int index, unsigned int refs)
+{
+	struct nbd_device *nbd;
+	struct gendisk *disk;
+	int err = -ENOMEM;
+
+	nbd = kzalloc(sizeof(struct nbd_device), GFP_KERNEL);
+	if (!nbd)
+		goto out;
+
+	nbd->tag_set.ops = &nbd_mq_ops;
+	nbd->tag_set.nr_hw_queues = 1;
+	nbd->tag_set.queue_depth = 128;
+	nbd->tag_set.numa_node = NUMA_NO_NODE;
+	nbd->tag_set.cmd_size = sizeof(struct nbd_cmd);
+	nbd->tag_set.flags = BLK_MQ_F_SHOULD_MERGE |
+		BLK_MQ_F_BLOCKING;
+	nbd->tag_set.driver_data = nbd;
+	INIT_WORK(&nbd->remove_work, nbd_dev_remove_work);
+	nbd->backend = NULL;
+
+	err = blk_mq_alloc_tag_set(&nbd->tag_set);
+	if (err)
+		goto out_free_nbd;
+
+	mutex_lock(&nbd_index_mutex);
+	if (index >= 0) {
+		err = idr_alloc(&nbd_index_idr, nbd, index, index + 1,
+				GFP_KERNEL);
+		if (err == -ENOSPC)
+			err = -EEXIST;
+	} else {
+		err = idr_alloc(&nbd_index_idr, nbd, 0,
+				(MINORMASK >> part_shift) + 1, GFP_KERNEL);
+		if (err >= 0)
+			index = err;
+	}
+	nbd->index = index;
+	mutex_unlock(&nbd_index_mutex);
+	if (err < 0)
+		goto out_free_tags;
+
+	disk = blk_mq_alloc_disk(&nbd->tag_set, NULL);
+	if (IS_ERR(disk)) {
+		err = PTR_ERR(disk);
+		goto out_free_idr;
+	}
+	nbd->disk = disk;
+
+	nbd->recv_workq = alloc_workqueue("nbd%d-recv",
+					  WQ_MEM_RECLAIM | WQ_HIGHPRI |
+					  WQ_UNBOUND, 0, nbd->index);
+	if (!nbd->recv_workq) {
+		dev_err(disk_to_dev(nbd->disk), "Could not allocate knbd recv work queue.\n");
+		err = -ENOMEM;
+		goto out_err_disk;
+	}
+
+	/*
+	 * Tell the block layer that we are not a rotational device
+	 */
+	blk_queue_flag_set(QUEUE_FLAG_NONROT, disk->queue);
+	disk->queue->limits.discard_granularity = 0;
+	blk_queue_max_discard_sectors(disk->queue, 0);
+	blk_queue_max_segment_size(disk->queue, UINT_MAX);
+	blk_queue_max_segments(disk->queue, USHRT_MAX);
+	blk_queue_max_hw_sectors(disk->queue, 65536);
+	disk->queue->limits.max_sectors = 256;
+
+	mutex_init(&nbd->config_lock);
+	refcount_set(&nbd->config_refs, 0);
+	/*
+	 * Start out with a zero references to keep other threads from using
+	 * this device until it is fully initialized.
+	 */
+	refcount_set(&nbd->refs, 0);
+	INIT_LIST_HEAD(&nbd->list);
+	disk->major = NBD_MAJOR;
+	disk->first_minor = index << part_shift;
+	disk->minors = 1 << part_shift;
+	disk->fops = &nbd_fops;
+	disk->private_data = nbd;
+	sprintf(disk->disk_name, "nbd%d", index);
+	err = add_disk(disk);
+	if (err)
+		goto out_free_work;
+
+	/*
+	 * Now publish the device.
+	 */
+	refcount_set(&nbd->refs, refs);
+	nbd_total_devices++;
+	return nbd;
+
+out_free_work:
+	destroy_workqueue(nbd->recv_workq);
+out_err_disk:
+	put_disk(disk);
+out_free_idr:
+	mutex_lock(&nbd_index_mutex);
+	idr_remove(&nbd_index_idr, index);
+	mutex_unlock(&nbd_index_mutex);
+out_free_tags:
+	blk_mq_free_tag_set(&nbd->tag_set);
+out_free_nbd:
+	kfree(nbd);
+out:
+	return ERR_PTR(err);
+}
+
+static struct nbd_device *nbd_find_get_unused(void)
+{
+	struct nbd_device *nbd;
+	int id;
+
+	lockdep_assert_held(&nbd_index_mutex);
+
+	idr_for_each_entry(&nbd_index_idr, nbd, id) {
+		if (refcount_read(&nbd->config_refs) ||
+		    test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags))
+			continue;
+		if (refcount_inc_not_zero(&nbd->refs))
+			return nbd;
+	}
+
+	return NULL;
+}
+
+/* Netlink interface. */
+static const struct nla_policy nbd_attr_policy[NBD_ATTR_MAX + 1] = {
+	[NBD_ATTR_INDEX]		=	{ .type = NLA_U32 },
+	[NBD_ATTR_SIZE_BYTES]		=	{ .type = NLA_U64 },
+	[NBD_ATTR_BLOCK_SIZE_BYTES]	=	{ .type = NLA_U64 },
+	[NBD_ATTR_TIMEOUT]		=	{ .type = NLA_U64 },
+	[NBD_ATTR_SERVER_FLAGS]		=	{ .type = NLA_U64 },
+	[NBD_ATTR_CLIENT_FLAGS]		=	{ .type = NLA_U64 },
+	[NBD_ATTR_SOCKETS]		=	{ .type = NLA_NESTED},
+	[NBD_ATTR_DEAD_CONN_TIMEOUT]	=	{ .type = NLA_U64 },
+	[NBD_ATTR_DEVICE_LIST]		=	{ .type = NLA_NESTED},
+	[NBD_ATTR_BACKEND_IDENTIFIER]	=	{ .type = NLA_STRING},
+};
+
+static const struct nla_policy nbd_sock_policy[NBD_SOCK_MAX + 1] = {
+	[NBD_SOCK_FD]			=	{ .type = NLA_U32 },
+};
+
+/* We don't use this right now since we don't parse the incoming list, but we
+ * still want it here so userspace knows what to expect.
+ */
+static const struct nla_policy __attribute__((unused))
+nbd_device_policy[NBD_DEVICE_ATTR_MAX + 1] = {
+	[NBD_DEVICE_INDEX]		=	{ .type = NLA_U32 },
+	[NBD_DEVICE_CONNECTED]		=	{ .type = NLA_U8 },
+};
+
+static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd)
+{
+	struct nbd_config *config = nbd->config;
+	u64 bsize = nbd_blksize(config);
+	u64 bytes = config->bytesize;
+
+	if (info->attrs[NBD_ATTR_SIZE_BYTES])
+		bytes = nla_get_u64(info->attrs[NBD_ATTR_SIZE_BYTES]);
+
+	if (info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES])
+		bsize = nla_get_u64(info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES]);
+
+	if (bytes != config->bytesize || bsize != nbd_blksize(config))
+		return nbd_set_size(nbd, bytes, bsize);
+	return 0;
+}
+
+static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
+{
+	struct nbd_device *nbd;
+	struct nbd_config *config;
+	int index = -1;
+	int ret;
+	bool put_dev = false;
+
+	if (!netlink_capable(skb, CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (info->attrs[NBD_ATTR_INDEX]) {
+		index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
+
+		/*
+		 * Too big first_minor can cause duplicate creation of
+		 * sysfs files/links, since index << part_shift might overflow, or
+		 * MKDEV() expect that the max bits of first_minor is 20.
+		 */
+		if (index < 0 || index > MINORMASK >> part_shift) {
+			pr_err("illegal input index %d\n", index);
+			return -EINVAL;
+		}
+	}
+	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SOCKETS)) {
+		pr_err("must specify at least one socket\n");
+		return -EINVAL;
+	}
+	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SIZE_BYTES)) {
+		pr_err("must specify a size in bytes for the device\n");
+		return -EINVAL;
+	}
+again:
+	mutex_lock(&nbd_index_mutex);
+	if (index == -1) {
+		nbd = nbd_find_get_unused();
+	} else {
+		nbd = idr_find(&nbd_index_idr, index);
+		if (nbd) {
+			if ((test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) &&
+			     test_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags)) ||
+			    !refcount_inc_not_zero(&nbd->refs)) {
+				mutex_unlock(&nbd_index_mutex);
+				pr_err("device at index %d is going down\n",
+					index);
+				return -EINVAL;
+			}
+		}
+	}
+	mutex_unlock(&nbd_index_mutex);
+
+	if (!nbd) {
+		nbd = nbd_dev_add(index, 2);
+		if (IS_ERR(nbd)) {
+			pr_err("failed to add new device\n");
+			return PTR_ERR(nbd);
+		}
+	}
+
+	mutex_lock(&nbd->config_lock);
+	if (refcount_read(&nbd->config_refs)) {
+		mutex_unlock(&nbd->config_lock);
+		nbd_put(nbd);
+		if (index == -1)
+			goto again;
+		pr_err("nbd%d already in use\n", index);
+		return -EBUSY;
+	}
+
+	ret = nbd_alloc_and_init_config(nbd);
+	if (ret) {
+		mutex_unlock(&nbd->config_lock);
+		nbd_put(nbd);
+		pr_err("couldn't allocate config\n");
+		return ret;
+	}
+
+	config = nbd->config;
+	set_bit(NBD_RT_BOUND, &config->runtime_flags);
+	ret = nbd_genl_size_set(info, nbd);
+	if (ret)
+		goto out;
+
+	if (info->attrs[NBD_ATTR_TIMEOUT])
+		nbd_set_cmd_timeout(nbd,
+				    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
+	if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
+		config->dead_conn_timeout =
+			nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
+		config->dead_conn_timeout *= HZ;
+	}
+	if (info->attrs[NBD_ATTR_SERVER_FLAGS])
+		config->flags =
+			nla_get_u64(info->attrs[NBD_ATTR_SERVER_FLAGS]);
+	if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
+		u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
+		if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
+			/*
+			 * We have 1 ref to keep the device around, and then 1
+			 * ref for our current operation here, which will be
+			 * inherited by the config.  If we already have
+			 * DESTROY_ON_DISCONNECT set then we know we don't have
+			 * that extra ref already held so we don't need the
+			 * put_dev.
+			 */
+			if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
+					      &nbd->flags))
+				put_dev = true;
+		} else {
+			if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
+					       &nbd->flags))
+				refcount_inc(&nbd->refs);
+		}
+		if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
+			set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
+				&config->runtime_flags);
+		}
+	}
+
+	if (info->attrs[NBD_ATTR_SOCKETS]) {
+		struct nlattr *attr;
+		int rem, fd;
+
+		nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
+				    rem) {
+			struct nlattr *socks[NBD_SOCK_MAX+1];
+
+			if (nla_type(attr) != NBD_SOCK_ITEM) {
+				pr_err("socks must be embedded in a SOCK_ITEM attr\n");
+				ret = -EINVAL;
+				goto out;
+			}
+			ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
+							  attr,
+							  nbd_sock_policy,
+							  info->extack);
+			if (ret != 0) {
+				pr_err("error processing sock list\n");
+				ret = -EINVAL;
+				goto out;
+			}
+			if (!socks[NBD_SOCK_FD])
+				continue;
+			fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
+			ret = nbd_add_socket(nbd, fd, true);
+			if (ret)
+				goto out;
+		}
+	}
+	ret = nbd_start_device(nbd);
+	if (ret)
+		goto out;
+	if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
+		nbd->backend = nla_strdup(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
+					  GFP_KERNEL);
+		if (!nbd->backend) {
+			ret = -ENOMEM;
+			goto out;
+		}
+	}
+	ret = device_create_file(disk_to_dev(nbd->disk), &backend_attr);
+	if (ret) {
+		dev_err(disk_to_dev(nbd->disk),
+			"device_create_file failed for backend!\n");
+		goto out;
+	}
+	set_bit(NBD_RT_HAS_BACKEND_FILE, &config->runtime_flags);
+out:
+	mutex_unlock(&nbd->config_lock);
+	if (!ret) {
+		set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
+		refcount_inc(&nbd->config_refs);
+		nbd_connect_reply(info, nbd->index);
+	}
+	nbd_config_put(nbd);
+	if (put_dev)
+		nbd_put(nbd);
+	return ret;
+}
+
+static void nbd_disconnect_and_put(struct nbd_device *nbd)
+{
+	mutex_lock(&nbd->config_lock);
+	nbd_disconnect(nbd);
+	sock_shutdown(nbd);
+	wake_up(&nbd->config->conn_wait);
+	/*
+	 * Make sure recv thread has finished, we can safely call nbd_clear_que()
+	 * to cancel the inflight I/Os.
+	 */
+	flush_workqueue(nbd->recv_workq);
+	nbd_clear_que(nbd);
+	nbd->task_setup = NULL;
+	mutex_unlock(&nbd->config_lock);
+
+	if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,
+			       &nbd->config->runtime_flags))
+		nbd_config_put(nbd);
+}
+
+static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info)
+{
+	struct nbd_device *nbd;
+	int index;
+
+	if (!netlink_capable(skb, CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
+		pr_err("must specify an index to disconnect\n");
+		return -EINVAL;
+	}
+	index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
+	mutex_lock(&nbd_index_mutex);
+	nbd = idr_find(&nbd_index_idr, index);
+	if (!nbd) {
+		mutex_unlock(&nbd_index_mutex);
+		pr_err("couldn't find device at index %d\n", index);
+		return -EINVAL;
+	}
+	if (!refcount_inc_not_zero(&nbd->refs)) {
+		mutex_unlock(&nbd_index_mutex);
+		pr_err("device at index %d is going down\n", index);
+		return -EINVAL;
+	}
+	mutex_unlock(&nbd_index_mutex);
+	if (!refcount_inc_not_zero(&nbd->config_refs))
+		goto put_nbd;
+	nbd_disconnect_and_put(nbd);
+	nbd_config_put(nbd);
+put_nbd:
+	nbd_put(nbd);
+	return 0;
+}
+
+static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
+{
+	struct nbd_device *nbd = NULL;
+	struct nbd_config *config;
+	int index;
+	int ret = 0;
+	bool put_dev = false;
+
+	if (!netlink_capable(skb, CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
+		pr_err("must specify a device to reconfigure\n");
+		return -EINVAL;
+	}
+	index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
+	mutex_lock(&nbd_index_mutex);
+	nbd = idr_find(&nbd_index_idr, index);
+	if (!nbd) {
+		mutex_unlock(&nbd_index_mutex);
+		pr_err("couldn't find a device at index %d\n", index);
+		return -EINVAL;
+	}
+	if (nbd->backend) {
+		if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
+			if (nla_strcmp(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
+				       nbd->backend)) {
+				mutex_unlock(&nbd_index_mutex);
+				dev_err(nbd_to_dev(nbd),
+					"backend image doesn't match with %s\n",
+					nbd->backend);
+				return -EINVAL;
+			}
+		} else {
+			mutex_unlock(&nbd_index_mutex);
+			dev_err(nbd_to_dev(nbd), "must specify backend\n");
+			return -EINVAL;
+		}
+	}
+	if (!refcount_inc_not_zero(&nbd->refs)) {
+		mutex_unlock(&nbd_index_mutex);
+		pr_err("device at index %d is going down\n", index);
+		return -EINVAL;
+	}
+	mutex_unlock(&nbd_index_mutex);
+
+	config = nbd_get_config_unlocked(nbd);
+	if (!config) {
+		dev_err(nbd_to_dev(nbd),
+			"not configured, cannot reconfigure\n");
+		nbd_put(nbd);
+		return -EINVAL;
+	}
+
+	mutex_lock(&nbd->config_lock);
+	if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
+	    !nbd->pid) {
+		dev_err(nbd_to_dev(nbd),
+			"not configured, cannot reconfigure\n");
+		ret = -EINVAL;
+		goto out;
+	}
+
+	ret = nbd_genl_size_set(info, nbd);
+	if (ret)
+		goto out;
+
+	if (info->attrs[NBD_ATTR_TIMEOUT])
+		nbd_set_cmd_timeout(nbd,
+				    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
+	if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
+		config->dead_conn_timeout =
+			nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
+		config->dead_conn_timeout *= HZ;
+	}
+	if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
+		u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
+		if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
+			if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
+					      &nbd->flags))
+				put_dev = true;
+		} else {
+			if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
+					       &nbd->flags))
+				refcount_inc(&nbd->refs);
+		}
+
+		if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
+			set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
+					&config->runtime_flags);
+		} else {
+			clear_bit(NBD_RT_DISCONNECT_ON_CLOSE,
+					&config->runtime_flags);
+		}
+	}
+
+	if (info->attrs[NBD_ATTR_SOCKETS]) {
+		struct nlattr *attr;
+		int rem, fd;
+
+		nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
+				    rem) {
+			struct nlattr *socks[NBD_SOCK_MAX+1];
+
+			if (nla_type(attr) != NBD_SOCK_ITEM) {
+				pr_err("socks must be embedded in a SOCK_ITEM attr\n");
+				ret = -EINVAL;
+				goto out;
+			}
+			ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
+							  attr,
+							  nbd_sock_policy,
+							  info->extack);
+			if (ret != 0) {
+				pr_err("error processing sock list\n");
+				ret = -EINVAL;
+				goto out;
+			}
+			if (!socks[NBD_SOCK_FD])
+				continue;
+			fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
+			ret = nbd_reconnect_socket(nbd, fd);
+			if (ret) {
+				if (ret == -ENOSPC)
+					ret = 0;
+				goto out;
+			}
+			dev_info(nbd_to_dev(nbd), "reconnected socket\n");
+		}
+	}
+out:
+	mutex_unlock(&nbd->config_lock);
+	nbd_config_put(nbd);
+	nbd_put(nbd);
+	if (put_dev)
+		nbd_put(nbd);
+	return ret;
+}
+
+static const struct genl_small_ops nbd_connect_genl_ops[] = {
+	{
+		.cmd	= NBD_CMD_CONNECT,
+		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
+		.doit	= nbd_genl_connect,
+	},
+	{
+		.cmd	= NBD_CMD_DISCONNECT,
+		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
+		.doit	= nbd_genl_disconnect,
+	},
+	{
+		.cmd	= NBD_CMD_RECONFIGURE,
+		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
+		.doit	= nbd_genl_reconfigure,
+	},
+	{
+		.cmd	= NBD_CMD_STATUS,
+		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
+		.doit	= nbd_genl_status,
+	},
+};
+
+static const struct genl_multicast_group nbd_mcast_grps[] = {
+	{ .name = NBD_GENL_MCAST_GROUP_NAME, },
+};
+
+static struct genl_family nbd_genl_family __ro_after_init = {
+	.hdrsize	= 0,
+	.name		= NBD_GENL_FAMILY_NAME,
+	.version	= NBD_GENL_VERSION,
+	.module		= THIS_MODULE,
+	.small_ops	= nbd_connect_genl_ops,
+	.n_small_ops	= ARRAY_SIZE(nbd_connect_genl_ops),
+	.resv_start_op	= NBD_CMD_STATUS + 1,
+	.maxattr	= NBD_ATTR_MAX,
+	.netnsok	= 1,
+	.policy = nbd_attr_policy,
+	.mcgrps		= nbd_mcast_grps,
+	.n_mcgrps	= ARRAY_SIZE(nbd_mcast_grps),
+};
+MODULE_ALIAS_GENL_FAMILY(NBD_GENL_FAMILY_NAME);
+
+static int populate_nbd_status(struct nbd_device *nbd, struct sk_buff *reply)
+{
+	struct nlattr *dev_opt;
+	u8 connected = 0;
+	int ret;
+
+	/* This is a little racey, but for status it's ok.  The
+	 * reason we don't take a ref here is because we can't
+	 * take a ref in the index == -1 case as we would need
+	 * to put under the nbd_index_mutex, which could
+	 * deadlock if we are configured to remove ourselves
+	 * once we're disconnected.
+	 */
+	if (refcount_read(&nbd->config_refs))
+		connected = 1;
+	dev_opt = nla_nest_start_noflag(reply, NBD_DEVICE_ITEM);
+	if (!dev_opt)
+		return -EMSGSIZE;
+	ret = nla_put_u32(reply, NBD_DEVICE_INDEX, nbd->index);
+	if (ret)
+		return -EMSGSIZE;
+	ret = nla_put_u8(reply, NBD_DEVICE_CONNECTED,
+			 connected);
+	if (ret)
+		return -EMSGSIZE;
+	nla_nest_end(reply, dev_opt);
+	return 0;
+}
+
+static int status_cb(int id, void *ptr, void *data)
+{
+	struct nbd_device *nbd = ptr;
+	return populate_nbd_status(nbd, (struct sk_buff *)data);
+}
+
+static int nbd_genl_status(struct sk_buff *skb, struct genl_info *info)
+{
+	struct nlattr *dev_list;
+	struct sk_buff *reply;
+	void *reply_head;
+	size_t msg_size;
+	int index = -1;
+	int ret = -ENOMEM;
+
+	if (info->attrs[NBD_ATTR_INDEX])
+		index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
+
+	mutex_lock(&nbd_index_mutex);
+
+	msg_size = nla_total_size(nla_attr_size(sizeof(u32)) +
+				  nla_attr_size(sizeof(u8)));
+	msg_size *= (index == -1) ? nbd_total_devices : 1;
+
+	reply = genlmsg_new(msg_size, GFP_KERNEL);
+	if (!reply)
+		goto out;
+	reply_head = genlmsg_put_reply(reply, info, &nbd_genl_family, 0,
+				       NBD_CMD_STATUS);
+	if (!reply_head) {
+		nlmsg_free(reply);
+		goto out;
+	}
+
+	dev_list = nla_nest_start_noflag(reply, NBD_ATTR_DEVICE_LIST);
+	if (index == -1) {
+		ret = idr_for_each(&nbd_index_idr, &status_cb, reply);
+		if (ret) {
+			nlmsg_free(reply);
+			goto out;
+		}
+	} else {
+		struct nbd_device *nbd;
+		nbd = idr_find(&nbd_index_idr, index);
+		if (nbd) {
+			ret = populate_nbd_status(nbd, reply);
+			if (ret) {
+				nlmsg_free(reply);
+				goto out;
+			}
+		}
+	}
+	nla_nest_end(reply, dev_list);
+	genlmsg_end(reply, reply_head);
+	ret = genlmsg_reply(reply, info);
+out:
+	mutex_unlock(&nbd_index_mutex);
+	return ret;
+}
+
+static void nbd_connect_reply(struct genl_info *info, int index)
+{
+	struct sk_buff *skb;
+	void *msg_head;
+	int ret;
+
+	skb = genlmsg_new(nla_total_size(sizeof(u32)), GFP_KERNEL);
+	if (!skb)
+		return;
+	msg_head = genlmsg_put_reply(skb, info, &nbd_genl_family, 0,
+				     NBD_CMD_CONNECT);
+	if (!msg_head) {
+		nlmsg_free(skb);
+		return;
+	}
+	ret = nla_put_u32(skb, NBD_ATTR_INDEX, index);
+	if (ret) {
+		nlmsg_free(skb);
+		return;
+	}
+	genlmsg_end(skb, msg_head);
+	genlmsg_reply(skb, info);
+}
+
+static void nbd_mcast_index(int index)
+{
+	struct sk_buff *skb;
+	void *msg_head;
+	int ret;
+
+	skb = genlmsg_new(nla_total_size(sizeof(u32)), GFP_KERNEL);
+	if (!skb)
+		return;
+	msg_head = genlmsg_put(skb, 0, 0, &nbd_genl_family, 0,
+				     NBD_CMD_LINK_DEAD);
+	if (!msg_head) {
+		nlmsg_free(skb);
+		return;
+	}
+	ret = nla_put_u32(skb, NBD_ATTR_INDEX, index);
+	if (ret) {
+		nlmsg_free(skb);
+		return;
+	}
+	genlmsg_end(skb, msg_head);
+	genlmsg_multicast(&nbd_genl_family, skb, 0, 0, GFP_KERNEL);
+}
+
+static void nbd_dead_link_work(struct work_struct *work)
+{
+	struct link_dead_args *args = container_of(work, struct link_dead_args,
+						   work);
+	nbd_mcast_index(args->index);
+	kfree(args);
+}
+
+static int __init nbd_init(void)
+{
+	int i;
+
+	BUILD_BUG_ON(sizeof(struct nbd_request) != 28);
+
+	if (max_part < 0) {
+		pr_err("max_part must be >= 0\n");
+		return -EINVAL;
+	}
+
+	part_shift = 0;
+	if (max_part > 0) {
+		part_shift = fls(max_part);
+
+		/*
+		 * Adjust max_part according to part_shift as it is exported
+		 * to user space so that user can know the max number of
+		 * partition kernel should be able to manage.
+		 *
+		 * Note that -1 is required because partition 0 is reserved
+		 * for the whole disk.
+		 */
+		max_part = (1UL << part_shift) - 1;
+	}
+
+	if ((1UL << part_shift) > DISK_MAX_PARTS)
+		return -EINVAL;
+
+	if (nbds_max > 1UL << (MINORBITS - part_shift))
+		return -EINVAL;
+
+	if (register_blkdev(NBD_MAJOR, "nbd"))
+		return -EIO;
+
+	nbd_del_wq = alloc_workqueue("nbd-del", WQ_UNBOUND, 0);
+	if (!nbd_del_wq) {
+		unregister_blkdev(NBD_MAJOR, "nbd");
+		return -ENOMEM;
+	}
+
+	if (genl_register_family(&nbd_genl_family)) {
+		destroy_workqueue(nbd_del_wq);
+		unregister_blkdev(NBD_MAJOR, "nbd");
+		return -EINVAL;
+	}
+	nbd_dbg_init();
+
+	for (i = 0; i < nbds_max; i++)
+		nbd_dev_add(i, 1);
+	return 0;
+}
+
+static int nbd_exit_cb(int id, void *ptr, void *data)
+{
+	struct list_head *list = (struct list_head *)data;
+	struct nbd_device *nbd = ptr;
+
+	/* Skip nbd that is being removed asynchronously */
+	if (refcount_read(&nbd->refs))
+		list_add_tail(&nbd->list, list);
+
+	return 0;
+}
+
+static void __exit nbd_cleanup(void)
+{
+	struct nbd_device *nbd;
+	LIST_HEAD(del_list);
+
+	/*
+	 * Unregister netlink interface prior to waiting
+	 * for the completion of netlink commands.
+	 */
+	genl_unregister_family(&nbd_genl_family);
+
+	nbd_dbg_close();
+
+	mutex_lock(&nbd_index_mutex);
+	idr_for_each(&nbd_index_idr, &nbd_exit_cb, &del_list);
+	mutex_unlock(&nbd_index_mutex);
+
+	while (!list_empty(&del_list)) {
+		nbd = list_first_entry(&del_list, struct nbd_device, list);
+		list_del_init(&nbd->list);
+		if (refcount_read(&nbd->config_refs))
+			pr_err("possibly leaking nbd_config (ref %d)\n",
+					refcount_read(&nbd->config_refs));
+		if (refcount_read(&nbd->refs) != 1)
+			pr_err("possibly leaking a device\n");
+		nbd_put(nbd);
+	}
+
+	/* Also wait for nbd_dev_remove_work() completes */
+	destroy_workqueue(nbd_del_wq);
+
+	idr_destroy(&nbd_index_idr);
+	unregister_blkdev(NBD_MAJOR, "nbd");
+}
+
+module_init(nbd_init);
+module_exit(nbd_cleanup);
+
+MODULE_DESCRIPTION("Network Block Device");
+MODULE_LICENSE("GPL");
+
+module_param(nbds_max, int, 0444);
+MODULE_PARM_DESC(nbds_max, "number of network block devices to initialize (default: 16)");
+module_param(max_part, int, 0444);
+MODULE_PARM_DESC(max_part, "number of partitions per device (default: 16)");