Adding upstream version 6.6.15.upstream/6.6.15

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

1 files changed, 3889 insertions, 0 deletions

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
new file mode 100644
index 000000000..51c100c86
--- /dev/null
+++ b/fs/xfs/xfs_log.c
@@ -0,0 +1,3889 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2000-2005 Silicon Graphics, Inc.
+ * All Rights Reserved.
+ */
+#include "xfs.h"
+#include "xfs_fs.h"
+#include "xfs_shared.h"
+#include "xfs_format.h"
+#include "xfs_log_format.h"
+#include "xfs_trans_resv.h"
+#include "xfs_mount.h"
+#include "xfs_errortag.h"
+#include "xfs_error.h"
+#include "xfs_trans.h"
+#include "xfs_trans_priv.h"
+#include "xfs_log.h"
+#include "xfs_log_priv.h"
+#include "xfs_trace.h"
+#include "xfs_sysfs.h"
+#include "xfs_sb.h"
+#include "xfs_health.h"
+
+struct kmem_cache	*xfs_log_ticket_cache;
+
+/* Local miscellaneous function prototypes */
+STATIC struct xlog *
+xlog_alloc_log(
+	struct xfs_mount	*mp,
+	struct xfs_buftarg	*log_target,
+	xfs_daddr_t		blk_offset,
+	int			num_bblks);
+STATIC int
+xlog_space_left(
+	struct xlog		*log,
+	atomic64_t		*head);
+STATIC void
+xlog_dealloc_log(
+	struct xlog		*log);
+
+/* local state machine functions */
+STATIC void xlog_state_done_syncing(
+	struct xlog_in_core	*iclog);
+STATIC void xlog_state_do_callback(
+	struct xlog		*log);
+STATIC int
+xlog_state_get_iclog_space(
+	struct xlog		*log,
+	int			len,
+	struct xlog_in_core	**iclog,
+	struct xlog_ticket	*ticket,
+	int			*logoffsetp);
+STATIC void
+xlog_grant_push_ail(
+	struct xlog		*log,
+	int			need_bytes);
+STATIC void
+xlog_sync(
+	struct xlog		*log,
+	struct xlog_in_core	*iclog,
+	struct xlog_ticket	*ticket);
+#if defined(DEBUG)
+STATIC void
+xlog_verify_grant_tail(
+	struct xlog *log);
+STATIC void
+xlog_verify_iclog(
+	struct xlog		*log,
+	struct xlog_in_core	*iclog,
+	int			count);
+STATIC void
+xlog_verify_tail_lsn(
+	struct xlog		*log,
+	struct xlog_in_core	*iclog);
+#else
+#define xlog_verify_grant_tail(a)
+#define xlog_verify_iclog(a,b,c)
+#define xlog_verify_tail_lsn(a,b)
+#endif
+
+STATIC int
+xlog_iclogs_empty(
+	struct xlog		*log);
+
+static int
+xfs_log_cover(struct xfs_mount *);
+
+/*
+ * We need to make sure the buffer pointer returned is naturally aligned for the
+ * biggest basic data type we put into it. We have already accounted for this
+ * padding when sizing the buffer.
+ *
+ * However, this padding does not get written into the log, and hence we have to
+ * track the space used by the log vectors separately to prevent log space hangs
+ * due to inaccurate accounting (i.e. a leak) of the used log space through the
+ * CIL context ticket.
+ *
+ * We also add space for the xlog_op_header that describes this region in the
+ * log. This prepends the data region we return to the caller to copy their data
+ * into, so do all the static initialisation of the ophdr now. Because the ophdr
+ * is not 8 byte aligned, we have to be careful to ensure that we align the
+ * start of the buffer such that the region we return to the call is 8 byte
+ * aligned and packed against the tail of the ophdr.
+ */
+void *
+xlog_prepare_iovec(
+	struct xfs_log_vec	*lv,
+	struct xfs_log_iovec	**vecp,
+	uint			type)
+{
+	struct xfs_log_iovec	*vec = *vecp;
+	struct xlog_op_header	*oph;
+	uint32_t		len;
+	void			*buf;
+
+	if (vec) {
+		ASSERT(vec - lv->lv_iovecp < lv->lv_niovecs);
+		vec++;
+	} else {
+		vec = &lv->lv_iovecp[0];
+	}
+
+	len = lv->lv_buf_len + sizeof(struct xlog_op_header);
+	if (!IS_ALIGNED(len, sizeof(uint64_t))) {
+		lv->lv_buf_len = round_up(len, sizeof(uint64_t)) -
+					sizeof(struct xlog_op_header);
+	}
+
+	vec->i_type = type;
+	vec->i_addr = lv->lv_buf + lv->lv_buf_len;
+
+	oph = vec->i_addr;
+	oph->oh_clientid = XFS_TRANSACTION;
+	oph->oh_res2 = 0;
+	oph->oh_flags = 0;
+
+	buf = vec->i_addr + sizeof(struct xlog_op_header);
+	ASSERT(IS_ALIGNED((unsigned long)buf, sizeof(uint64_t)));
+
+	*vecp = vec;
+	return buf;
+}
+
+static void
+xlog_grant_sub_space(
+	struct xlog		*log,
+	atomic64_t		*head,
+	int			bytes)
+{
+	int64_t	head_val = atomic64_read(head);
+	int64_t new, old;
+
+	do {
+		int	cycle, space;
+
+		xlog_crack_grant_head_val(head_val, &cycle, &space);
+
+		space -= bytes;
+		if (space < 0) {
+			space += log->l_logsize;
+			cycle--;
+		}
+
+		old = head_val;
+		new = xlog_assign_grant_head_val(cycle, space);
+		head_val = atomic64_cmpxchg(head, old, new);
+	} while (head_val != old);
+}
+
+static void
+xlog_grant_add_space(
+	struct xlog		*log,
+	atomic64_t		*head,
+	int			bytes)
+{
+	int64_t	head_val = atomic64_read(head);
+	int64_t new, old;
+
+	do {
+		int		tmp;
+		int		cycle, space;
+
+		xlog_crack_grant_head_val(head_val, &cycle, &space);
+
+		tmp = log->l_logsize - space;
+		if (tmp > bytes)
+			space += bytes;
+		else {
+			space = bytes - tmp;
+			cycle++;
+		}
+
+		old = head_val;
+		new = xlog_assign_grant_head_val(cycle, space);
+		head_val = atomic64_cmpxchg(head, old, new);
+	} while (head_val != old);
+}
+
+STATIC void
+xlog_grant_head_init(
+	struct xlog_grant_head	*head)
+{
+	xlog_assign_grant_head(&head->grant, 1, 0);
+	INIT_LIST_HEAD(&head->waiters);
+	spin_lock_init(&head->lock);
+}
+
+STATIC void
+xlog_grant_head_wake_all(
+	struct xlog_grant_head	*head)
+{
+	struct xlog_ticket	*tic;
+
+	spin_lock(&head->lock);
+	list_for_each_entry(tic, &head->waiters, t_queue)
+		wake_up_process(tic->t_task);
+	spin_unlock(&head->lock);
+}
+
+static inline int
+xlog_ticket_reservation(
+	struct xlog		*log,
+	struct xlog_grant_head	*head,
+	struct xlog_ticket	*tic)
+{
+	if (head == &log->l_write_head) {
+		ASSERT(tic->t_flags & XLOG_TIC_PERM_RESERV);
+		return tic->t_unit_res;
+	}
+
+	if (tic->t_flags & XLOG_TIC_PERM_RESERV)
+		return tic->t_unit_res * tic->t_cnt;
+
+	return tic->t_unit_res;
+}
+
+STATIC bool
+xlog_grant_head_wake(
+	struct xlog		*log,
+	struct xlog_grant_head	*head,
+	int			*free_bytes)
+{
+	struct xlog_ticket	*tic;
+	int			need_bytes;
+	bool			woken_task = false;
+
+	list_for_each_entry(tic, &head->waiters, t_queue) {
+
+		/*
+		 * There is a chance that the size of the CIL checkpoints in
+		 * progress at the last AIL push target calculation resulted in
+		 * limiting the target to the log head (l_last_sync_lsn) at the
+		 * time. This may not reflect where the log head is now as the
+		 * CIL checkpoints may have completed.
+		 *
+		 * Hence when we are woken here, it may be that the head of the
+		 * log that has moved rather than the tail. As the tail didn't
+		 * move, there still won't be space available for the
+		 * reservation we require.  However, if the AIL has already
+		 * pushed to the target defined by the old log head location, we
+		 * will hang here waiting for something else to update the AIL
+		 * push target.
+		 *
+		 * Therefore, if there isn't space to wake the first waiter on
+		 * the grant head, we need to push the AIL again to ensure the
+		 * target reflects both the current log tail and log head
+		 * position before we wait for the tail to move again.
+		 */
+
+		need_bytes = xlog_ticket_reservation(log, head, tic);
+		if (*free_bytes < need_bytes) {
+			if (!woken_task)
+				xlog_grant_push_ail(log, need_bytes);
+			return false;
+		}
+
+		*free_bytes -= need_bytes;
+		trace_xfs_log_grant_wake_up(log, tic);
+		wake_up_process(tic->t_task);
+		woken_task = true;
+	}
+
+	return true;
+}
+
+STATIC int
+xlog_grant_head_wait(
+	struct xlog		*log,
+	struct xlog_grant_head	*head,
+	struct xlog_ticket	*tic,
+	int			need_bytes) __releases(&head->lock)
+					    __acquires(&head->lock)
+{
+	list_add_tail(&tic->t_queue, &head->waiters);
+
+	do {
+		if (xlog_is_shutdown(log))
+			goto shutdown;
+		xlog_grant_push_ail(log, need_bytes);
+
+		__set_current_state(TASK_UNINTERRUPTIBLE);
+		spin_unlock(&head->lock);
+
+		XFS_STATS_INC(log->l_mp, xs_sleep_logspace);
+
+		trace_xfs_log_grant_sleep(log, tic);
+		schedule();
+		trace_xfs_log_grant_wake(log, tic);
+
+		spin_lock(&head->lock);
+		if (xlog_is_shutdown(log))
+			goto shutdown;
+	} while (xlog_space_left(log, &head->grant) < need_bytes);
+
+	list_del_init(&tic->t_queue);
+	return 0;
+shutdown:
+	list_del_init(&tic->t_queue);
+	return -EIO;
+}
+
+/*
+ * Atomically get the log space required for a log ticket.
+ *
+ * Once a ticket gets put onto head->waiters, it will only return after the
+ * needed reservation is satisfied.
+ *
+ * This function is structured so that it has a lock free fast path. This is
+ * necessary because every new transaction reservation will come through this
+ * path. Hence any lock will be globally hot if we take it unconditionally on
+ * every pass.
+ *
+ * As tickets are only ever moved on and off head->waiters under head->lock, we
+ * only need to take that lock if we are going to add the ticket to the queue
+ * and sleep. We can avoid taking the lock if the ticket was never added to
+ * head->waiters because the t_queue list head will be empty and we hold the
+ * only reference to it so it can safely be checked unlocked.
+ */
+STATIC int
+xlog_grant_head_check(
+	struct xlog		*log,
+	struct xlog_grant_head	*head,
+	struct xlog_ticket	*tic,
+	int			*need_bytes)
+{
+	int			free_bytes;
+	int			error = 0;
+
+	ASSERT(!xlog_in_recovery(log));
+
+	/*
+	 * If there are other waiters on the queue then give them a chance at
+	 * logspace before us.  Wake up the first waiters, if we do not wake
+	 * up all the waiters then go to sleep waiting for more free space,
+	 * otherwise try to get some space for this transaction.
+	 */
+	*need_bytes = xlog_ticket_reservation(log, head, tic);
+	free_bytes = xlog_space_left(log, &head->grant);
+	if (!list_empty_careful(&head->waiters)) {
+		spin_lock(&head->lock);
+		if (!xlog_grant_head_wake(log, head, &free_bytes) ||
+		    free_bytes < *need_bytes) {
+			error = xlog_grant_head_wait(log, head, tic,
+						     *need_bytes);
+		}
+		spin_unlock(&head->lock);
+	} else if (free_bytes < *need_bytes) {
+		spin_lock(&head->lock);
+		error = xlog_grant_head_wait(log, head, tic, *need_bytes);
+		spin_unlock(&head->lock);
+	}
+
+	return error;
+}
+
+bool
+xfs_log_writable(
+	struct xfs_mount	*mp)
+{
+	/*
+	 * Do not write to the log on norecovery mounts, if the data or log
+	 * devices are read-only, or if the filesystem is shutdown. Read-only
+	 * mounts allow internal writes for log recovery and unmount purposes,
+	 * so don't restrict that case.
+	 */
+	if (xfs_has_norecovery(mp))
+		return false;
+	if (xfs_readonly_buftarg(mp->m_ddev_targp))
+		return false;
+	if (xfs_readonly_buftarg(mp->m_log->l_targ))
+		return false;
+	if (xlog_is_shutdown(mp->m_log))
+		return false;
+	return true;
+}
+
+/*
+ * Replenish the byte reservation required by moving the grant write head.
+ */
+int
+xfs_log_regrant(
+	struct xfs_mount	*mp,
+	struct xlog_ticket	*tic)
+{
+	struct xlog		*log = mp->m_log;
+	int			need_bytes;
+	int			error = 0;
+
+	if (xlog_is_shutdown(log))
+		return -EIO;
+
+	XFS_STATS_INC(mp, xs_try_logspace);
+
+	/*
+	 * This is a new transaction on the ticket, so we need to change the
+	 * transaction ID so that the next transaction has a different TID in
+	 * the log. Just add one to the existing tid so that we can see chains
+	 * of rolling transactions in the log easily.
+	 */
+	tic->t_tid++;
+
+	xlog_grant_push_ail(log, tic->t_unit_res);
+
+	tic->t_curr_res = tic->t_unit_res;
+	if (tic->t_cnt > 0)
+		return 0;
+
+	trace_xfs_log_regrant(log, tic);
+
+	error = xlog_grant_head_check(log, &log->l_write_head, tic,
+				      &need_bytes);
+	if (error)
+		goto out_error;
+
+	xlog_grant_add_space(log, &log->l_write_head.grant, need_bytes);
+	trace_xfs_log_regrant_exit(log, tic);
+	xlog_verify_grant_tail(log);
+	return 0;
+
+out_error:
+	/*
+	 * If we are failing, make sure the ticket doesn't have any current
+	 * reservations.  We don't want to add this back when the ticket/
+	 * transaction gets cancelled.
+	 */
+	tic->t_curr_res = 0;
+	tic->t_cnt = 0;	/* ungrant will give back unit_res * t_cnt. */
+	return error;
+}
+
+/*
+ * Reserve log space and return a ticket corresponding to the reservation.
+ *
+ * Each reservation is going to reserve extra space for a log record header.
+ * When writes happen to the on-disk log, we don't subtract the length of the
+ * log record header from any reservation.  By wasting space in each
+ * reservation, we prevent over allocation problems.
+ */
+int
+xfs_log_reserve(
+	struct xfs_mount	*mp,
+	int			unit_bytes,
+	int			cnt,
+	struct xlog_ticket	**ticp,
+	bool			permanent)
+{
+	struct xlog		*log = mp->m_log;
+	struct xlog_ticket	*tic;
+	int			need_bytes;
+	int			error = 0;
+
+	if (xlog_is_shutdown(log))
+		return -EIO;
+
+	XFS_STATS_INC(mp, xs_try_logspace);
+
+	ASSERT(*ticp == NULL);
+	tic = xlog_ticket_alloc(log, unit_bytes, cnt, permanent);
+	*ticp = tic;
+
+	xlog_grant_push_ail(log, tic->t_cnt ? tic->t_unit_res * tic->t_cnt
+					    : tic->t_unit_res);
+
+	trace_xfs_log_reserve(log, tic);
+
+	error = xlog_grant_head_check(log, &log->l_reserve_head, tic,
+				      &need_bytes);
+	if (error)
+		goto out_error;
+
+	xlog_grant_add_space(log, &log->l_reserve_head.grant, need_bytes);
+	xlog_grant_add_space(log, &log->l_write_head.grant, need_bytes);
+	trace_xfs_log_reserve_exit(log, tic);
+	xlog_verify_grant_tail(log);
+	return 0;
+
+out_error:
+	/*
+	 * If we are failing, make sure the ticket doesn't have any current
+	 * reservations.  We don't want to add this back when the ticket/
+	 * transaction gets cancelled.
+	 */
+	tic->t_curr_res = 0;
+	tic->t_cnt = 0;	/* ungrant will give back unit_res * t_cnt. */
+	return error;
+}
+
+/*
+ * Run all the pending iclog callbacks and wake log force waiters and iclog
+ * space waiters so they can process the newly set shutdown state. We really
+ * don't care what order we process callbacks here because the log is shut down
+ * and so state cannot change on disk anymore. However, we cannot wake waiters
+ * until the callbacks have been processed because we may be in unmount and
+ * we must ensure that all AIL operations the callbacks perform have completed
+ * before we tear down the AIL.
+ *
+ * We avoid processing actively referenced iclogs so that we don't run callbacks
+ * while the iclog owner might still be preparing the iclog for IO submssion.
+ * These will be caught by xlog_state_iclog_release() and call this function
+ * again to process any callbacks that may have been added to that iclog.
+ */
+static void
+xlog_state_shutdown_callbacks(
+	struct xlog		*log)
+{
+	struct xlog_in_core	*iclog;
+	LIST_HEAD(cb_list);
+
+	iclog = log->l_iclog;
+	do {
+		if (atomic_read(&iclog->ic_refcnt)) {
+			/* Reference holder will re-run iclog callbacks. */
+			continue;
+		}
+		list_splice_init(&iclog->ic_callbacks, &cb_list);
+		spin_unlock(&log->l_icloglock);
+
+		xlog_cil_process_committed(&cb_list);
+
+		spin_lock(&log->l_icloglock);
+		wake_up_all(&iclog->ic_write_wait);
+		wake_up_all(&iclog->ic_force_wait);
+	} while ((iclog = iclog->ic_next) != log->l_iclog);
+
+	wake_up_all(&log->l_flush_wait);
+}
+
+/*
+ * Flush iclog to disk if this is the last reference to the given iclog and the
+ * it is in the WANT_SYNC state.
+ *
+ * If XLOG_ICL_NEED_FUA is already set on the iclog, we need to ensure that the
+ * log tail is updated correctly. NEED_FUA indicates that the iclog will be
+ * written to stable storage, and implies that a commit record is contained
+ * within the iclog. We need to ensure that the log tail does not move beyond
+ * the tail that the first commit record in the iclog ordered against, otherwise
+ * correct recovery of that checkpoint becomes dependent on future operations
+ * performed on this iclog.
+ *
+ * Hence if NEED_FUA is set and the current iclog tail lsn is empty, write the
+ * current tail into iclog. Once the iclog tail is set, future operations must
+ * not modify it, otherwise they potentially violate ordering constraints for
+ * the checkpoint commit that wrote the initial tail lsn value. The tail lsn in
+ * the iclog will get zeroed on activation of the iclog after sync, so we
+ * always capture the tail lsn on the iclog on the first NEED_FUA release
+ * regardless of the number of active reference counts on this iclog.
+ */
+int
+xlog_state_release_iclog(
+	struct xlog		*log,
+	struct xlog_in_core	*iclog,
+	struct xlog_ticket	*ticket)
+{
+	xfs_lsn_t		tail_lsn;
+	bool			last_ref;
+
+	lockdep_assert_held(&log->l_icloglock);
+
+	trace_xlog_iclog_release(iclog, _RET_IP_);
+	/*
+	 * Grabbing the current log tail needs to be atomic w.r.t. the writing
+	 * of the tail LSN into the iclog so we guarantee that the log tail does
+	 * not move between the first time we know that the iclog needs to be
+	 * made stable and when we eventually submit it.
+	 */
+	if ((iclog->ic_state == XLOG_STATE_WANT_SYNC ||
+	     (iclog->ic_flags & XLOG_ICL_NEED_FUA)) &&
+	    !iclog->ic_header.h_tail_lsn) {
+		tail_lsn = xlog_assign_tail_lsn(log->l_mp);
+		iclog->ic_header.h_tail_lsn = cpu_to_be64(tail_lsn);
+	}
+
+	last_ref = atomic_dec_and_test(&iclog->ic_refcnt);
+
+	if (xlog_is_shutdown(log)) {
+		/*
+		 * If there are no more references to this iclog, process the
+		 * pending iclog callbacks that were waiting on the release of
+		 * this iclog.
+		 */
+		if (last_ref)
+			xlog_state_shutdown_callbacks(log);
+		return -EIO;
+	}
+
+	if (!last_ref)
+		return 0;
+
+	if (iclog->ic_state != XLOG_STATE_WANT_SYNC) {
+		ASSERT(iclog->ic_state == XLOG_STATE_ACTIVE);
+		return 0;
+	}
+
+	iclog->ic_state = XLOG_STATE_SYNCING;
+	xlog_verify_tail_lsn(log, iclog);
+	trace_xlog_iclog_syncing(iclog, _RET_IP_);
+
+	spin_unlock(&log->l_icloglock);
+	xlog_sync(log, iclog, ticket);
+	spin_lock(&log->l_icloglock);
+	return 0;
+}
+
+/*
+ * Mount a log filesystem
+ *
+ * mp		- ubiquitous xfs mount point structure
+ * log_target	- buftarg of on-disk log device
+ * blk_offset	- Start block # where block size is 512 bytes (BBSIZE)
+ * num_bblocks	- Number of BBSIZE blocks in on-disk log
+ *
+ * Return error or zero.
+ */
+int
+xfs_log_mount(
+	xfs_mount_t	*mp,
+	xfs_buftarg_t	*log_target,
+	xfs_daddr_t	blk_offset,
+	int		num_bblks)
+{
+	struct xlog	*log;
+	int		error = 0;
+	int		min_logfsbs;
+
+	if (!xfs_has_norecovery(mp)) {
+		xfs_notice(mp, "Mounting V%d Filesystem %pU",
+			   XFS_SB_VERSION_NUM(&mp->m_sb),
+			   &mp->m_sb.sb_uuid);
+	} else {
+		xfs_notice(mp,
+"Mounting V%d filesystem %pU in no-recovery mode. Filesystem will be inconsistent.",
+			   XFS_SB_VERSION_NUM(&mp->m_sb),
+			   &mp->m_sb.sb_uuid);
+		ASSERT(xfs_is_readonly(mp));
+	}
+
+	log = xlog_alloc_log(mp, log_target, blk_offset, num_bblks);
+	if (IS_ERR(log)) {
+		error = PTR_ERR(log);
+		goto out;
+	}
+	mp->m_log = log;
+
+	/*
+	 * Now that we have set up the log and it's internal geometry
+	 * parameters, we can validate the given log space and drop a critical
+	 * message via syslog if the log size is too small. A log that is too
+	 * small can lead to unexpected situations in transaction log space
+	 * reservation stage. The superblock verifier has already validated all
+	 * the other log geometry constraints, so we don't have to check those
+	 * here.
+	 *
+	 * Note: For v4 filesystems, we can't just reject the mount if the
+	 * validation fails.  This would mean that people would have to
+	 * downgrade their kernel just to remedy the situation as there is no
+	 * way to grow the log (short of black magic surgery with xfs_db).
+	 *
+	 * We can, however, reject mounts for V5 format filesystems, as the
+	 * mkfs binary being used to make the filesystem should never create a
+	 * filesystem with a log that is too small.
+	 */
+	min_logfsbs = xfs_log_calc_minimum_size(mp);
+	if (mp->m_sb.sb_logblocks < min_logfsbs) {
+		xfs_warn(mp,
+		"Log size %d blocks too small, minimum size is %d blocks",
+			 mp->m_sb.sb_logblocks, min_logfsbs);
+
+		/*
+		 * Log check errors are always fatal on v5; or whenever bad
+		 * metadata leads to a crash.
+		 */
+		if (xfs_has_crc(mp)) {
+			xfs_crit(mp, "AAIEEE! Log failed size checks. Abort!");
+			ASSERT(0);
+			error = -EINVAL;
+			goto out_free_log;
+		}
+		xfs_crit(mp, "Log size out of supported range.");
+		xfs_crit(mp,
+"Continuing onwards, but if log hangs are experienced then please report this message in the bug report.");
+	}
+
+	/*
+	 * Initialize the AIL now we have a log.
+	 */
+	error = xfs_trans_ail_init(mp);
+	if (error) {
+		xfs_warn(mp, "AIL initialisation failed: error %d", error);
+		goto out_free_log;
+	}
+	log->l_ailp = mp->m_ail;
+
+	/*
+	 * skip log recovery on a norecovery mount.  pretend it all
+	 * just worked.
+	 */
+	if (!xfs_has_norecovery(mp)) {
+		error = xlog_recover(log);
+		if (error) {
+			xfs_warn(mp, "log mount/recovery failed: error %d",
+				error);
+			xlog_recover_cancel(log);
+			goto out_destroy_ail;
+		}
+	}
+
+	error = xfs_sysfs_init(&log->l_kobj, &xfs_log_ktype, &mp->m_kobj,
+			       "log");
+	if (error)
+		goto out_destroy_ail;
+
+	/* Normal transactions can now occur */
+	clear_bit(XLOG_ACTIVE_RECOVERY, &log->l_opstate);
+
+	/*
+	 * Now the log has been fully initialised and we know were our
+	 * space grant counters are, we can initialise the permanent ticket
+	 * needed for delayed logging to work.
+	 */
+	xlog_cil_init_post_recovery(log);
+
+	return 0;
+
+out_destroy_ail:
+	xfs_trans_ail_destroy(mp);
+out_free_log:
+	xlog_dealloc_log(log);
+out:
+	return error;
+}
+
+/*
+ * Finish the recovery of the file system.  This is separate from the
+ * xfs_log_mount() call, because it depends on the code in xfs_mountfs() to read
+ * in the root and real-time bitmap inodes between calling xfs_log_mount() and
+ * here.
+ *
+ * If we finish recovery successfully, start the background log work. If we are
+ * not doing recovery, then we have a RO filesystem and we don't need to start
+ * it.
+ */
+int
+xfs_log_mount_finish(
+	struct xfs_mount	*mp)
+{
+	struct xlog		*log = mp->m_log;
+	int			error = 0;
+
+	if (xfs_has_norecovery(mp)) {
+		ASSERT(xfs_is_readonly(mp));
+		return 0;
+	}
+
+	/*
+	 * During the second phase of log recovery, we need iget and
+	 * iput to behave like they do for an active filesystem.
+	 * xfs_fs_drop_inode needs to be able to prevent the deletion
+	 * of inodes before we're done replaying log items on those
+	 * inodes.  Turn it off immediately after recovery finishes
+	 * so that we don't leak the quota inodes if subsequent mount
+	 * activities fail.
+	 *
+	 * We let all inodes involved in redo item processing end up on
+	 * the LRU instead of being evicted immediately so that if we do
+	 * something to an unlinked inode, the irele won't cause
+	 * premature truncation and freeing of the inode, which results
+	 * in log recovery failure.  We have to evict the unreferenced
+	 * lru inodes after clearing SB_ACTIVE because we don't
+	 * otherwise clean up the lru if there's a subsequent failure in
+	 * xfs_mountfs, which leads to us leaking the inodes if nothing
+	 * else (e.g. quotacheck) references the inodes before the
+	 * mount failure occurs.
+	 */
+	mp->m_super->s_flags |= SB_ACTIVE;
+	xfs_log_work_queue(mp);
+	if (xlog_recovery_needed(log))
+		error = xlog_recover_finish(log);
+	mp->m_super->s_flags &= ~SB_ACTIVE;
+	evict_inodes(mp->m_super);
+
+	/*
+	 * Drain the buffer LRU after log recovery. This is required for v4
+	 * filesystems to avoid leaving around buffers with NULL verifier ops,
+	 * but we do it unconditionally to make sure we're always in a clean
+	 * cache state after mount.
+	 *
+	 * Don't push in the error case because the AIL may have pending intents
+	 * that aren't removed until recovery is cancelled.
+	 */
+	if (xlog_recovery_needed(log)) {
+		if (!error) {
+			xfs_log_force(mp, XFS_LOG_SYNC);
+			xfs_ail_push_all_sync(mp->m_ail);
+		}
+		xfs_notice(mp, "Ending recovery (logdev: %s)",
+				mp->m_logname ? mp->m_logname : "internal");
+	} else {
+		xfs_info(mp, "Ending clean mount");
+	}
+	xfs_buftarg_drain(mp->m_ddev_targp);
+
+	clear_bit(XLOG_RECOVERY_NEEDED, &log->l_opstate);
+
+	/* Make sure the log is dead if we're returning failure. */
+	ASSERT(!error || xlog_is_shutdown(log));
+
+	return error;
+}
+
+/*
+ * The mount has failed. Cancel the recovery if it hasn't completed and destroy
+ * the log.
+ */
+void
+xfs_log_mount_cancel(
+	struct xfs_mount	*mp)
+{
+	xlog_recover_cancel(mp->m_log);
+	xfs_log_unmount(mp);
+}
+
+/*
+ * Flush out the iclog to disk ensuring that device caches are flushed and
+ * the iclog hits stable storage before any completion waiters are woken.
+ */
+static inline int
+xlog_force_iclog(
+	struct xlog_in_core	*iclog)
+{
+	atomic_inc(&iclog->ic_refcnt);
+	iclog->ic_flags |= XLOG_ICL_NEED_FLUSH | XLOG_ICL_NEED_FUA;
+	if (iclog->ic_state == XLOG_STATE_ACTIVE)
+		xlog_state_switch_iclogs(iclog->ic_log, iclog, 0);
+	return xlog_state_release_iclog(iclog->ic_log, iclog, NULL);
+}
+
+/*
+ * Cycle all the iclogbuf locks to make sure all log IO completion
+ * is done before we tear down these buffers.
+ */
+static void
+xlog_wait_iclog_completion(struct xlog *log)
+{
+	int		i;
+	struct xlog_in_core	*iclog = log->l_iclog;
+
+	for (i = 0; i < log->l_iclog_bufs; i++) {
+		down(&iclog->ic_sema);
+		up(&iclog->ic_sema);
+		iclog = iclog->ic_next;
+	}
+}
+
+/*
+ * Wait for the iclog and all prior iclogs to be written disk as required by the
+ * log force state machine. Waiting on ic_force_wait ensures iclog completions
+ * have been ordered and callbacks run before we are woken here, hence
+ * guaranteeing that all the iclogs up to this one are on stable storage.
+ */
+int
+xlog_wait_on_iclog(
+	struct xlog_in_core	*iclog)
+		__releases(iclog->ic_log->l_icloglock)
+{
+	struct xlog		*log = iclog->ic_log;
+
+	trace_xlog_iclog_wait_on(iclog, _RET_IP_);
+	if (!xlog_is_shutdown(log) &&
+	    iclog->ic_state != XLOG_STATE_ACTIVE &&
+	    iclog->ic_state != XLOG_STATE_DIRTY) {
+		XFS_STATS_INC(log->l_mp, xs_log_force_sleep);
+		xlog_wait(&iclog->ic_force_wait, &log->l_icloglock);
+	} else {
+		spin_unlock(&log->l_icloglock);
+	}
+
+	if (xlog_is_shutdown(log))
+		return -EIO;
+	return 0;
+}
+
+/*
+ * Write out an unmount record using the ticket provided. We have to account for
+ * the data space used in the unmount ticket as this write is not done from a
+ * transaction context that has already done the accounting for us.
+ */
+static int
+xlog_write_unmount_record(
+	struct xlog		*log,
+	struct xlog_ticket	*ticket)
+{
+	struct  {
+		struct xlog_op_header ophdr;
+		struct xfs_unmount_log_format ulf;
+	} unmount_rec = {
+		.ophdr = {
+			.oh_clientid = XFS_LOG,
+			.oh_tid = cpu_to_be32(ticket->t_tid),
+			.oh_flags = XLOG_UNMOUNT_TRANS,
+		},
+		.ulf = {
+			.magic = XLOG_UNMOUNT_TYPE,
+		},
+	};
+	struct xfs_log_iovec reg = {
+		.i_addr = &unmount_rec,
+		.i_len = sizeof(unmount_rec),
+		.i_type = XLOG_REG_TYPE_UNMOUNT,
+	};
+	struct xfs_log_vec vec = {
+		.lv_niovecs = 1,
+		.lv_iovecp = &reg,
+	};
+	LIST_HEAD(lv_chain);
+	list_add(&vec.lv_list, &lv_chain);
+
+	BUILD_BUG_ON((sizeof(struct xlog_op_header) +
+		      sizeof(struct xfs_unmount_log_format)) !=
+							sizeof(unmount_rec));
+
+	/* account for space used by record data */
+	ticket->t_curr_res -= sizeof(unmount_rec);
+
+	return xlog_write(log, NULL, &lv_chain, ticket, reg.i_len);
+}
+
+/*
+ * Mark the filesystem clean by writing an unmount record to the head of the
+ * log.
+ */
+static void
+xlog_unmount_write(
+	struct xlog		*log)
+{
+	struct xfs_mount	*mp = log->l_mp;
+	struct xlog_in_core	*iclog;
+	struct xlog_ticket	*tic = NULL;
+	int			error;
+
+	error = xfs_log_reserve(mp, 600, 1, &tic, 0);
+	if (error)
+		goto out_err;
+
+	error = xlog_write_unmount_record(log, tic);
+	/*
+	 * At this point, we're umounting anyway, so there's no point in
+	 * transitioning log state to shutdown. Just continue...
+	 */
+out_err:
+	if (error)
+		xfs_alert(mp, "%s: unmount record failed", __func__);
+
+	spin_lock(&log->l_icloglock);
+	iclog = log->l_iclog;
+	error = xlog_force_iclog(iclog);
+	xlog_wait_on_iclog(iclog);
+
+	if (tic) {
+		trace_xfs_log_umount_write(log, tic);
+		xfs_log_ticket_ungrant(log, tic);
+	}
+}
+
+static void
+xfs_log_unmount_verify_iclog(
+	struct xlog		*log)
+{
+	struct xlog_in_core	*iclog = log->l_iclog;
+
+	do {
+		ASSERT(iclog->ic_state == XLOG_STATE_ACTIVE);
+		ASSERT(iclog->ic_offset == 0);
+	} while ((iclog = iclog->ic_next) != log->l_iclog);
+}
+
+/*
+ * Unmount record used to have a string "Unmount filesystem--" in the
+ * data section where the "Un" was really a magic number (XLOG_UNMOUNT_TYPE).
+ * We just write the magic number now since that particular field isn't
+ * currently architecture converted and "Unmount" is a bit foo.
+ * As far as I know, there weren't any dependencies on the old behaviour.
+ */
+static void
+xfs_log_unmount_write(
+	struct xfs_mount	*mp)
+{
+	struct xlog		*log = mp->m_log;
+
+	if (!xfs_log_writable(mp))
+		return;
+
+	xfs_log_force(mp, XFS_LOG_SYNC);
+
+	if (xlog_is_shutdown(log))
+		return;
+
+	/*
+	 * If we think the summary counters are bad, avoid writing the unmount
+	 * record to force log recovery at next mount, after which the summary
+	 * counters will be recalculated.  Refer to xlog_check_unmount_rec for
+	 * more details.
+	 */
+	if (XFS_TEST_ERROR(xfs_fs_has_sickness(mp, XFS_SICK_FS_COUNTERS), mp,
+			XFS_ERRTAG_FORCE_SUMMARY_RECALC)) {
+		xfs_alert(mp, "%s: will fix summary counters at next mount",
+				__func__);
+		return;
+	}
+
+	xfs_log_unmount_verify_iclog(log);
+	xlog_unmount_write(log);
+}
+
+/*
+ * Empty the log for unmount/freeze.
+ *
+ * To do this, we first need to shut down the background log work so it is not
+ * trying to cover the log as we clean up. We then need to unpin all objects in
+ * the log so we can then flush them out. Once they have completed their IO and
+ * run the callbacks removing themselves from the AIL, we can cover the log.
+ */
+int
+xfs_log_quiesce(
+	struct xfs_mount	*mp)
+{
+	/*
+	 * Clear log incompat features since we're quiescing the log.  Report
+	 * failures, though it's not fatal to have a higher log feature
+	 * protection level than the log contents actually require.
+	 */
+	if (xfs_clear_incompat_log_features(mp)) {
+		int error;
+
+		error = xfs_sync_sb(mp, false);
+		if (error)
+			xfs_warn(mp,
+	"Failed to clear log incompat features on quiesce");
+	}
+
+	cancel_delayed_work_sync(&mp->m_log->l_work);
+	xfs_log_force(mp, XFS_LOG_SYNC);
+
+	/*
+	 * The superblock buffer is uncached and while xfs_ail_push_all_sync()
+	 * will push it, xfs_buftarg_wait() will not wait for it. Further,
+	 * xfs_buf_iowait() cannot be used because it was pushed with the
+	 * XBF_ASYNC flag set, so we need to use a lock/unlock pair to wait for
+	 * the IO to complete.
+	 */
+	xfs_ail_push_all_sync(mp->m_ail);
+	xfs_buftarg_wait(mp->m_ddev_targp);
+	xfs_buf_lock(mp->m_sb_bp);
+	xfs_buf_unlock(mp->m_sb_bp);
+
+	return xfs_log_cover(mp);
+}
+
+void
+xfs_log_clean(
+	struct xfs_mount	*mp)
+{
+	xfs_log_quiesce(mp);
+	xfs_log_unmount_write(mp);
+}
+
+/*
+ * Shut down and release the AIL and Log.
+ *
+ * During unmount, we need to ensure we flush all the dirty metadata objects
+ * from the AIL so that the log is empty before we write the unmount record to
+ * the log. Once this is done, we can tear down the AIL and the log.
+ */
+void
+xfs_log_unmount(
+	struct xfs_mount	*mp)
+{
+	xfs_log_clean(mp);
+
+	/*
+	 * If shutdown has come from iclog IO context, the log
+	 * cleaning will have been skipped and so we need to wait
+	 * for the iclog to complete shutdown processing before we
+	 * tear anything down.
+	 */
+	xlog_wait_iclog_completion(mp->m_log);
+
+	xfs_buftarg_drain(mp->m_ddev_targp);
+
+	xfs_trans_ail_destroy(mp);
+
+	xfs_sysfs_del(&mp->m_log->l_kobj);
+
+	xlog_dealloc_log(mp->m_log);
+}
+
+void
+xfs_log_item_init(
+	struct xfs_mount	*mp,
+	struct xfs_log_item	*item,
+	int			type,
+	const struct xfs_item_ops *ops)
+{
+	item->li_log = mp->m_log;
+	item->li_ailp = mp->m_ail;
+	item->li_type = type;
+	item->li_ops = ops;
+	item->li_lv = NULL;
+
+	INIT_LIST_HEAD(&item->li_ail);
+	INIT_LIST_HEAD(&item->li_cil);
+	INIT_LIST_HEAD(&item->li_bio_list);
+	INIT_LIST_HEAD(&item->li_trans);
+}
+
+/*
+ * Wake up processes waiting for log space after we have moved the log tail.
+ */
+void
+xfs_log_space_wake(
+	struct xfs_mount	*mp)
+{
+	struct xlog		*log = mp->m_log;
+	int			free_bytes;
+
+	if (xlog_is_shutdown(log))
+		return;
+
+	if (!list_empty_careful(&log->l_write_head.waiters)) {
+		ASSERT(!xlog_in_recovery(log));
+
+		spin_lock(&log->l_write_head.lock);
+		free_bytes = xlog_space_left(log, &log->l_write_head.grant);
+		xlog_grant_head_wake(log, &log->l_write_head, &free_bytes);
+		spin_unlock(&log->l_write_head.lock);
+	}
+
+	if (!list_empty_careful(&log->l_reserve_head.waiters)) {
+		ASSERT(!xlog_in_recovery(log));
+
+		spin_lock(&log->l_reserve_head.lock);
+		free_bytes = xlog_space_left(log, &log->l_reserve_head.grant);
+		xlog_grant_head_wake(log, &log->l_reserve_head, &free_bytes);
+		spin_unlock(&log->l_reserve_head.lock);
+	}
+}
+
+/*
+ * Determine if we have a transaction that has gone to disk that needs to be
+ * covered. To begin the transition to the idle state firstly the log needs to
+ * be idle. That means the CIL, the AIL and the iclogs needs to be empty before
+ * we start attempting to cover the log.
+ *
+ * Only if we are then in a state where covering is needed, the caller is
+ * informed that dummy transactions are required to move the log into the idle
+ * state.
+ *
+ * If there are any items in the AIl or CIL, then we do not want to attempt to
+ * cover the log as we may be in a situation where there isn't log space
+ * available to run a dummy transaction and this can lead to deadlocks when the
+ * tail of the log is pinned by an item that is modified in the CIL.  Hence
+ * there's no point in running a dummy transaction at this point because we
+ * can't start trying to idle the log until both the CIL and AIL are empty.
+ */
+static bool
+xfs_log_need_covered(
+	struct xfs_mount	*mp)
+{
+	struct xlog		*log = mp->m_log;
+	bool			needed = false;
+
+	if (!xlog_cil_empty(log))
+		return false;
+
+	spin_lock(&log->l_icloglock);
+	switch (log->l_covered_state) {
+	case XLOG_STATE_COVER_DONE:
+	case XLOG_STATE_COVER_DONE2:
+	case XLOG_STATE_COVER_IDLE:
+		break;
+	case XLOG_STATE_COVER_NEED:
+	case XLOG_STATE_COVER_NEED2:
+		if (xfs_ail_min_lsn(log->l_ailp))
+			break;
+		if (!xlog_iclogs_empty(log))
+			break;
+
+		needed = true;
+		if (log->l_covered_state == XLOG_STATE_COVER_NEED)
+			log->l_covered_state = XLOG_STATE_COVER_DONE;
+		else
+			log->l_covered_state = XLOG_STATE_COVER_DONE2;
+		break;
+	default:
+		needed = true;
+		break;
+	}
+	spin_unlock(&log->l_icloglock);
+	return needed;
+}
+
+/*
+ * Explicitly cover the log. This is similar to background log covering but
+ * intended for usage in quiesce codepaths. The caller is responsible to ensure
+ * the log is idle and suitable for covering. The CIL, iclog buffers and AIL
+ * must all be empty.
+ */
+static int
+xfs_log_cover(
+	struct xfs_mount	*mp)
+{
+	int			error = 0;
+	bool			need_covered;
+
+	ASSERT((xlog_cil_empty(mp->m_log) && xlog_iclogs_empty(mp->m_log) &&
+	        !xfs_ail_min_lsn(mp->m_log->l_ailp)) ||
+		xlog_is_shutdown(mp->m_log));
+
+	if (!xfs_log_writable(mp))
+		return 0;
+
+	/*
+	 * xfs_log_need_covered() is not idempotent because it progresses the
+	 * state machine if the log requires covering. Therefore, we must call
+	 * this function once and use the result until we've issued an sb sync.
+	 * Do so first to make that abundantly clear.
+	 *
+	 * Fall into the covering sequence if the log needs covering or the
+	 * mount has lazy superblock accounting to sync to disk. The sb sync
+	 * used for covering accumulates the in-core counters, so covering
+	 * handles this for us.
+	 */
+	need_covered = xfs_log_need_covered(mp);
+	if (!need_covered && !xfs_has_lazysbcount(mp))
+		return 0;
+
+	/*
+	 * To cover the log, commit the superblock twice (at most) in
+	 * independent checkpoints. The first serves as a reference for the
+	 * tail pointer. The sync transaction and AIL push empties the AIL and
+	 * updates the in-core tail to the LSN of the first checkpoint. The
+	 * second commit updates the on-disk tail with the in-core LSN,
+	 * covering the log. Push the AIL one more time to leave it empty, as
+	 * we found it.
+	 */
+	do {
+		error = xfs_sync_sb(mp, true);
+		if (error)
+			break;
+		xfs_ail_push_all_sync(mp->m_ail);
+	} while (xfs_log_need_covered(mp));
+
+	return error;
+}
+
+/*
+ * We may be holding the log iclog lock upon entering this routine.
+ */
+xfs_lsn_t
+xlog_assign_tail_lsn_locked(
+	struct xfs_mount	*mp)
+{
+	struct xlog		*log = mp->m_log;
+	struct xfs_log_item	*lip;
+	xfs_lsn_t		tail_lsn;
+
+	assert_spin_locked(&mp->m_ail->ail_lock);
+
+	/*
+	 * To make sure we always have a valid LSN for the log tail we keep
+	 * track of the last LSN which was committed in log->l_last_sync_lsn,
+	 * and use that when the AIL was empty.
+	 */
+	lip = xfs_ail_min(mp->m_ail);
+	if (lip)
+		tail_lsn = lip->li_lsn;
+	else
+		tail_lsn = atomic64_read(&log->l_last_sync_lsn);
+	trace_xfs_log_assign_tail_lsn(log, tail_lsn);
+	atomic64_set(&log->l_tail_lsn, tail_lsn);
+	return tail_lsn;
+}
+
+xfs_lsn_t
+xlog_assign_tail_lsn(
+	struct xfs_mount	*mp)
+{
+	xfs_lsn_t		tail_lsn;
+
+	spin_lock(&mp->m_ail->ail_lock);
+	tail_lsn = xlog_assign_tail_lsn_locked(mp);
+	spin_unlock(&mp->m_ail->ail_lock);
+
+	return tail_lsn;
+}
+
+/*
+ * Return the space in the log between the tail and the head.  The head
+ * is passed in the cycle/bytes formal parms.  In the special case where
+ * the reserve head has wrapped passed the tail, this calculation is no
+ * longer valid.  In this case, just return 0 which means there is no space
+ * in the log.  This works for all places where this function is called
+ * with the reserve head.  Of course, if the write head were to ever
+ * wrap the tail, we should blow up.  Rather than catch this case here,
+ * we depend on other ASSERTions in other parts of the code.   XXXmiken
+ *
+ * If reservation head is behind the tail, we have a problem. Warn about it,
+ * but then treat it as if the log is empty.
+ *
+ * If the log is shut down, the head and tail may be invalid or out of whack, so
+ * shortcut invalidity asserts in this case so that we don't trigger them
+ * falsely.
+ */
+STATIC int
+xlog_space_left(
+	struct xlog	*log,
+	atomic64_t	*head)
+{
+	int		tail_bytes;
+	int		tail_cycle;
+	int		head_cycle;
+	int		head_bytes;
+
+	xlog_crack_grant_head(head, &head_cycle, &head_bytes);
+	xlog_crack_atomic_lsn(&log->l_tail_lsn, &tail_cycle, &tail_bytes);
+	tail_bytes = BBTOB(tail_bytes);
+	if (tail_cycle == head_cycle && head_bytes >= tail_bytes)
+		return log->l_logsize - (head_bytes - tail_bytes);
+	if (tail_cycle + 1 < head_cycle)
+		return 0;
+
+	/* Ignore potential inconsistency when shutdown. */
+	if (xlog_is_shutdown(log))
+		return log->l_logsize;
+
+	if (tail_cycle < head_cycle) {
+		ASSERT(tail_cycle == (head_cycle - 1));
+		return tail_bytes - head_bytes;
+	}
+
+	/*
+	 * The reservation head is behind the tail. In this case we just want to
+	 * return the size of the log as the amount of space left.
+	 */
+	xfs_alert(log->l_mp, "xlog_space_left: head behind tail");
+	xfs_alert(log->l_mp, "  tail_cycle = %d, tail_bytes = %d",
+		  tail_cycle, tail_bytes);
+	xfs_alert(log->l_mp, "  GH   cycle = %d, GH   bytes = %d",
+		  head_cycle, head_bytes);
+	ASSERT(0);
+	return log->l_logsize;
+}
+
+
+static void
+xlog_ioend_work(
+	struct work_struct	*work)
+{
+	struct xlog_in_core     *iclog =
+		container_of(work, struct xlog_in_core, ic_end_io_work);
+	struct xlog		*log = iclog->ic_log;
+	int			error;
+
+	error = blk_status_to_errno(iclog->ic_bio.bi_status);
+#ifdef DEBUG
+	/* treat writes with injected CRC errors as failed */
+	if (iclog->ic_fail_crc)
+		error = -EIO;
+#endif
+
+	/*
+	 * Race to shutdown the filesystem if we see an error.
+	 */
+	if (XFS_TEST_ERROR(error, log->l_mp, XFS_ERRTAG_IODONE_IOERR)) {
+		xfs_alert(log->l_mp, "log I/O error %d", error);
+		xlog_force_shutdown(log, SHUTDOWN_LOG_IO_ERROR);
+	}
+
+	xlog_state_done_syncing(iclog);
+	bio_uninit(&iclog->ic_bio);
+
+	/*
+	 * Drop the lock to signal that we are done. Nothing references the
+	 * iclog after this, so an unmount waiting on this lock can now tear it
+	 * down safely. As such, it is unsafe to reference the iclog after the
+	 * unlock as we could race with it being freed.
+	 */
+	up(&iclog->ic_sema);
+}
+
+/*
+ * Return size of each in-core log record buffer.
+ *
+ * All machines get 8 x 32kB buffers by default, unless tuned otherwise.
+ *
+ * If the filesystem blocksize is too large, we may need to choose a
+ * larger size since the directory code currently logs entire blocks.
+ */
+STATIC void
+xlog_get_iclog_buffer_size(
+	struct xfs_mount	*mp,
+	struct xlog		*log)
+{
+	if (mp->m_logbufs <= 0)
+		mp->m_logbufs = XLOG_MAX_ICLOGS;
+	if (mp->m_logbsize <= 0)
+		mp->m_logbsize = XLOG_BIG_RECORD_BSIZE;
+
+	log->l_iclog_bufs = mp->m_logbufs;
+	log->l_iclog_size = mp->m_logbsize;
+
+	/*
+	 * # headers = size / 32k - one header holds cycles from 32k of data.
+	 */
+	log->l_iclog_heads =
+		DIV_ROUND_UP(mp->m_logbsize, XLOG_HEADER_CYCLE_SIZE);
+	log->l_iclog_hsize = log->l_iclog_heads << BBSHIFT;
+}
+
+void
+xfs_log_work_queue(
+	struct xfs_mount        *mp)
+{
+	queue_delayed_work(mp->m_sync_workqueue, &mp->m_log->l_work,
+				msecs_to_jiffies(xfs_syncd_centisecs * 10));
+}
+
+/*
+ * Clear the log incompat flags if we have the opportunity.
+ *
+ * This only happens if we're about to log the second dummy transaction as part
+ * of covering the log and we can get the log incompat feature usage lock.
+ */
+static inline void
+xlog_clear_incompat(
+	struct xlog		*log)
+{
+	struct xfs_mount	*mp = log->l_mp;
+
+	if (!xfs_sb_has_incompat_log_feature(&mp->m_sb,
+				XFS_SB_FEAT_INCOMPAT_LOG_ALL))
+		return;
+
+	if (log->l_covered_state != XLOG_STATE_COVER_DONE2)
+		return;
+
+	if (!down_write_trylock(&log->l_incompat_users))
+		return;
+
+	xfs_clear_incompat_log_features(mp);
+	up_write(&log->l_incompat_users);
+}
+
+/*
+ * Every sync period we need to unpin all items in the AIL and push them to
+ * disk. If there is nothing dirty, then we might need to cover the log to
+ * indicate that the filesystem is idle.
+ */
+static void
+xfs_log_worker(
+	struct work_struct	*work)
+{
+	struct xlog		*log = container_of(to_delayed_work(work),
+						struct xlog, l_work);
+	struct xfs_mount	*mp = log->l_mp;
+
+	/* dgc: errors ignored - not fatal and nowhere to report them */
+	if (xfs_fs_writable(mp, SB_FREEZE_WRITE) && xfs_log_need_covered(mp)) {
+		/*
+		 * Dump a transaction into the log that contains no real change.
+		 * This is needed to stamp the current tail LSN into the log
+		 * during the covering operation.
+		 *
+		 * We cannot use an inode here for this - that will push dirty
+		 * state back up into the VFS and then periodic inode flushing
+		 * will prevent log covering from making progress. Hence we
+		 * synchronously log the superblock instead to ensure the
+		 * superblock is immediately unpinned and can be written back.
+		 */
+		xlog_clear_incompat(log);
+		xfs_sync_sb(mp, true);
+	} else
+		xfs_log_force(mp, 0);
+
+	/* start pushing all the metadata that is currently dirty */
+	xfs_ail_push_all(mp->m_ail);
+
+	/* queue us up again */
+	xfs_log_work_queue(mp);
+}
+
+/*
+ * This routine initializes some of the log structure for a given mount point.
+ * Its primary purpose is to fill in enough, so recovery can occur.  However,
+ * some other stuff may be filled in too.
+ */
+STATIC struct xlog *
+xlog_alloc_log(
+	struct xfs_mount	*mp,
+	struct xfs_buftarg	*log_target,
+	xfs_daddr_t		blk_offset,
+	int			num_bblks)
+{
+	struct xlog		*log;
+	xlog_rec_header_t	*head;
+	xlog_in_core_t		**iclogp;
+	xlog_in_core_t		*iclog, *prev_iclog=NULL;
+	int			i;
+	int			error = -ENOMEM;
+	uint			log2_size = 0;
+
+	log = kmem_zalloc(sizeof(struct xlog), KM_MAYFAIL);
+	if (!log) {
+		xfs_warn(mp, "Log allocation failed: No memory!");
+		goto out;
+	}
+
+	log->l_mp	   = mp;
+	log->l_targ	   = log_target;
+	log->l_logsize     = BBTOB(num_bblks);
+	log->l_logBBstart  = blk_offset;
+	log->l_logBBsize   = num_bblks;
+	log->l_covered_state = XLOG_STATE_COVER_IDLE;
+	set_bit(XLOG_ACTIVE_RECOVERY, &log->l_opstate);
+	INIT_DELAYED_WORK(&log->l_work, xfs_log_worker);
+
+	log->l_prev_block  = -1;
+	/* log->l_tail_lsn = 0x100000000LL; cycle = 1; current block = 0 */
+	xlog_assign_atomic_lsn(&log->l_tail_lsn, 1, 0);
+	xlog_assign_atomic_lsn(&log->l_last_sync_lsn, 1, 0);
+	log->l_curr_cycle  = 1;	    /* 0 is bad since this is initial value */
+
+	if (xfs_has_logv2(mp) && mp->m_sb.sb_logsunit > 1)
+		log->l_iclog_roundoff = mp->m_sb.sb_logsunit;
+	else
+		log->l_iclog_roundoff = BBSIZE;
+
+	xlog_grant_head_init(&log->l_reserve_head);
+	xlog_grant_head_init(&log->l_write_head);
+
+	error = -EFSCORRUPTED;
+	if (xfs_has_sector(mp)) {
+	        log2_size = mp->m_sb.sb_logsectlog;
+		if (log2_size < BBSHIFT) {
+			xfs_warn(mp, "Log sector size too small (0x%x < 0x%x)",
+				log2_size, BBSHIFT);
+			goto out_free_log;
+		}
+
+	        log2_size -= BBSHIFT;
+		if (log2_size > mp->m_sectbb_log) {
+			xfs_warn(mp, "Log sector size too large (0x%x > 0x%x)",
+				log2_size, mp->m_sectbb_log);
+			goto out_free_log;
+		}
+
+		/* for larger sector sizes, must have v2 or external log */
+		if (log2_size && log->l_logBBstart > 0 &&
+			    !xfs_has_logv2(mp)) {
+			xfs_warn(mp,
+		"log sector size (0x%x) invalid for configuration.",
+				log2_size);
+			goto out_free_log;
+		}
+	}
+	log->l_sectBBsize = 1 << log2_size;
+
+	init_rwsem(&log->l_incompat_users);
+
+	xlog_get_iclog_buffer_size(mp, log);
+
+	spin_lock_init(&log->l_icloglock);
+	init_waitqueue_head(&log->l_flush_wait);
+
+	iclogp = &log->l_iclog;
+	/*
+	 * The amount of memory to allocate for the iclog structure is
+	 * rather funky due to the way the structure is defined.  It is
+	 * done this way so that we can use different sizes for machines
+	 * with different amounts of memory.  See the definition of
+	 * xlog_in_core_t in xfs_log_priv.h for details.
+	 */
+	ASSERT(log->l_iclog_size >= 4096);
+	for (i = 0; i < log->l_iclog_bufs; i++) {
+		size_t bvec_size = howmany(log->l_iclog_size, PAGE_SIZE) *
+				sizeof(struct bio_vec);
+
+		iclog = kmem_zalloc(sizeof(*iclog) + bvec_size, KM_MAYFAIL);
+		if (!iclog)
+			goto out_free_iclog;
+
+		*iclogp = iclog;
+		iclog->ic_prev = prev_iclog;
+		prev_iclog = iclog;
+
+		iclog->ic_data = kvzalloc(log->l_iclog_size,
+				GFP_KERNEL | __GFP_RETRY_MAYFAIL);
+		if (!iclog->ic_data)
+			goto out_free_iclog;
+		head = &iclog->ic_header;
+		memset(head, 0, sizeof(xlog_rec_header_t));
+		head->h_magicno = cpu_to_be32(XLOG_HEADER_MAGIC_NUM);
+		head->h_version = cpu_to_be32(
+			xfs_has_logv2(log->l_mp) ? 2 : 1);
+		head->h_size = cpu_to_be32(log->l_iclog_size);
+		/* new fields */
+		head->h_fmt = cpu_to_be32(XLOG_FMT);
+		memcpy(&head->h_fs_uuid, &mp->m_sb.sb_uuid, sizeof(uuid_t));
+
+		iclog->ic_size = log->l_iclog_size - log->l_iclog_hsize;
+		iclog->ic_state = XLOG_STATE_ACTIVE;
+		iclog->ic_log = log;
+		atomic_set(&iclog->ic_refcnt, 0);
+		INIT_LIST_HEAD(&iclog->ic_callbacks);
+		iclog->ic_datap = (void *)iclog->ic_data + log->l_iclog_hsize;
+
+		init_waitqueue_head(&iclog->ic_force_wait);
+		init_waitqueue_head(&iclog->ic_write_wait);
+		INIT_WORK(&iclog->ic_end_io_work, xlog_ioend_work);
+		sema_init(&iclog->ic_sema, 1);
+
+		iclogp = &iclog->ic_next;
+	}
+	*iclogp = log->l_iclog;			/* complete ring */
+	log->l_iclog->ic_prev = prev_iclog;	/* re-write 1st prev ptr */
+
+	log->l_ioend_workqueue = alloc_workqueue("xfs-log/%s",
+			XFS_WQFLAGS(WQ_FREEZABLE | WQ_MEM_RECLAIM |
+				    WQ_HIGHPRI),
+			0, mp->m_super->s_id);
+	if (!log->l_ioend_workqueue)
+		goto out_free_iclog;
+
+	error = xlog_cil_init(log);
+	if (error)
+		goto out_destroy_workqueue;
+	return log;
+
+out_destroy_workqueue:
+	destroy_workqueue(log->l_ioend_workqueue);
+out_free_iclog:
+	for (iclog = log->l_iclog; iclog; iclog = prev_iclog) {
+		prev_iclog = iclog->ic_next;
+		kmem_free(iclog->ic_data);
+		kmem_free(iclog);
+		if (prev_iclog == log->l_iclog)
+			break;
+	}
+out_free_log:
+	kmem_free(log);
+out:
+	return ERR_PTR(error);
+}	/* xlog_alloc_log */
+
+/*
+ * Compute the LSN that we'd need to push the log tail towards in order to have
+ * (a) enough on-disk log space to log the number of bytes specified, (b) at
+ * least 25% of the log space free, and (c) at least 256 blocks free.  If the
+ * log free space already meets all three thresholds, this function returns
+ * NULLCOMMITLSN.
+ */
+xfs_lsn_t
+xlog_grant_push_threshold(
+	struct xlog	*log,
+	int		need_bytes)
+{
+	xfs_lsn_t	threshold_lsn = 0;
+	xfs_lsn_t	last_sync_lsn;
+	int		free_blocks;
+	int		free_bytes;
+	int		threshold_block;
+	int		threshold_cycle;
+	int		free_threshold;
+
+	ASSERT(BTOBB(need_bytes) < log->l_logBBsize);
+
+	free_bytes = xlog_space_left(log, &log->l_reserve_head.grant);
+	free_blocks = BTOBBT(free_bytes);
+
+	/*
+	 * Set the threshold for the minimum number of free blocks in the
+	 * log to the maximum of what the caller needs, one quarter of the
+	 * log, and 256 blocks.
+	 */
+	free_threshold = BTOBB(need_bytes);
+	free_threshold = max(free_threshold, (log->l_logBBsize >> 2));
+	free_threshold = max(free_threshold, 256);
+	if (free_blocks >= free_threshold)
+		return NULLCOMMITLSN;
+
+	xlog_crack_atomic_lsn(&log->l_tail_lsn, &threshold_cycle,
+						&threshold_block);
+	threshold_block += free_threshold;
+	if (threshold_block >= log->l_logBBsize) {
+		threshold_block -= log->l_logBBsize;
+		threshold_cycle += 1;
+	}
+	threshold_lsn = xlog_assign_lsn(threshold_cycle,
+					threshold_block);
+	/*
+	 * Don't pass in an lsn greater than the lsn of the last
+	 * log record known to be on disk. Use a snapshot of the last sync lsn
+	 * so that it doesn't change between the compare and the set.
+	 */
+	last_sync_lsn = atomic64_read(&log->l_last_sync_lsn);
+	if (XFS_LSN_CMP(threshold_lsn, last_sync_lsn) > 0)
+		threshold_lsn = last_sync_lsn;
+
+	return threshold_lsn;
+}
+
+/*
+ * Push the tail of the log if we need to do so to maintain the free log space
+ * thresholds set out by xlog_grant_push_threshold.  We may need to adopt a
+ * policy which pushes on an lsn which is further along in the log once we
+ * reach the high water mark.  In this manner, we would be creating a low water
+ * mark.
+ */
+STATIC void
+xlog_grant_push_ail(
+	struct xlog	*log,
+	int		need_bytes)
+{
+	xfs_lsn_t	threshold_lsn;
+
+	threshold_lsn = xlog_grant_push_threshold(log, need_bytes);
+	if (threshold_lsn == NULLCOMMITLSN || xlog_is_shutdown(log))
+		return;
+
+	/*
+	 * Get the transaction layer to kick the dirty buffers out to
+	 * disk asynchronously. No point in trying to do this if
+	 * the filesystem is shutting down.
+	 */
+	xfs_ail_push(log->l_ailp, threshold_lsn);
+}
+
+/*
+ * Stamp cycle number in every block
+ */
+STATIC void
+xlog_pack_data(
+	struct xlog		*log,
+	struct xlog_in_core	*iclog,
+	int			roundoff)
+{
+	int			i, j, k;
+	int			size = iclog->ic_offset + roundoff;
+	__be32			cycle_lsn;
+	char			*dp;
+
+	cycle_lsn = CYCLE_LSN_DISK(iclog->ic_header.h_lsn);
+
+	dp = iclog->ic_datap;
+	for (i = 0; i < BTOBB(size); i++) {
+		if (i >= (XLOG_HEADER_CYCLE_SIZE / BBSIZE))
+			break;
+		iclog->ic_header.h_cycle_data[i] = *(__be32 *)dp;
+		*(__be32 *)dp = cycle_lsn;
+		dp += BBSIZE;
+	}
+
+	if (xfs_has_logv2(log->l_mp)) {
+		xlog_in_core_2_t *xhdr = iclog->ic_data;
+
+		for ( ; i < BTOBB(size); i++) {
+			j = i / (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
+			k = i % (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
+			xhdr[j].hic_xheader.xh_cycle_data[k] = *(__be32 *)dp;
+			*(__be32 *)dp = cycle_lsn;
+			dp += BBSIZE;
+		}
+
+		for (i = 1; i < log->l_iclog_heads; i++)
+			xhdr[i].hic_xheader.xh_cycle = cycle_lsn;
+	}
+}
+
+/*
+ * Calculate the checksum for a log buffer.
+ *
+ * This is a little more complicated than it should be because the various
+ * headers and the actual data are non-contiguous.
+ */
+__le32
+xlog_cksum(
+	struct xlog		*log,
+	struct xlog_rec_header	*rhead,
+	char			*dp,
+	int			size)
+{
+	uint32_t		crc;
+
+	/* first generate the crc for the record header ... */
+	crc = xfs_start_cksum_update((char *)rhead,
+			      sizeof(struct xlog_rec_header),
+			      offsetof(struct xlog_rec_header, h_crc));
+
+	/* ... then for additional cycle data for v2 logs ... */
+	if (xfs_has_logv2(log->l_mp)) {
+		union xlog_in_core2 *xhdr = (union xlog_in_core2 *)rhead;
+		int		i;
+		int		xheads;
+
+		xheads = DIV_ROUND_UP(size, XLOG_HEADER_CYCLE_SIZE);
+
+		for (i = 1; i < xheads; i++) {
+			crc = crc32c(crc, &xhdr[i].hic_xheader,
+				     sizeof(struct xlog_rec_ext_header));
+		}
+	}
+
+	/* ... and finally for the payload */
+	crc = crc32c(crc, dp, size);
+
+	return xfs_end_cksum(crc);
+}
+
+static void
+xlog_bio_end_io(
+	struct bio		*bio)
+{
+	struct xlog_in_core	*iclog = bio->bi_private;
+
+	queue_work(iclog->ic_log->l_ioend_workqueue,
+		   &iclog->ic_end_io_work);
+}
+
+static int
+xlog_map_iclog_data(
+	struct bio		*bio,
+	void			*data,
+	size_t			count)
+{
+	do {
+		struct page	*page = kmem_to_page(data);
+		unsigned int	off = offset_in_page(data);
+		size_t		len = min_t(size_t, count, PAGE_SIZE - off);
+
+		if (bio_add_page(bio, page, len, off) != len)
+			return -EIO;
+
+		data += len;
+		count -= len;
+	} while (count);
+
+	return 0;
+}
+
+STATIC void
+xlog_write_iclog(
+	struct xlog		*log,
+	struct xlog_in_core	*iclog,
+	uint64_t		bno,
+	unsigned int		count)
+{
+	ASSERT(bno < log->l_logBBsize);
+	trace_xlog_iclog_write(iclog, _RET_IP_);
+
+	/*
+	 * We lock the iclogbufs here so that we can serialise against I/O
+	 * completion during unmount.  We might be processing a shutdown
+	 * triggered during unmount, and that can occur asynchronously to the
+	 * unmount thread, and hence we need to ensure that completes before
+	 * tearing down the iclogbufs.  Hence we need to hold the buffer lock
+	 * across the log IO to archieve that.
+	 */
+	down(&iclog->ic_sema);
+	if (xlog_is_shutdown(log)) {
+		/*
+		 * It would seem logical to return EIO here, but we rely on
+		 * the log state machine to propagate I/O errors instead of
+		 * doing it here.  We kick of the state machine and unlock
+		 * the buffer manually, the code needs to be kept in sync
+		 * with the I/O completion path.
+		 */
+		xlog_state_done_syncing(iclog);
+		up(&iclog->ic_sema);
+		return;
+	}
+
+	/*
+	 * We use REQ_SYNC | REQ_IDLE here to tell the block layer the are more
+	 * IOs coming immediately after this one. This prevents the block layer
+	 * writeback throttle from throttling log writes behind background
+	 * metadata writeback and causing priority inversions.
+	 */
+	bio_init(&iclog->ic_bio, log->l_targ->bt_bdev, iclog->ic_bvec,
+		 howmany(count, PAGE_SIZE),
+		 REQ_OP_WRITE | REQ_META | REQ_SYNC | REQ_IDLE);
+	iclog->ic_bio.bi_iter.bi_sector = log->l_logBBstart + bno;
+	iclog->ic_bio.bi_end_io = xlog_bio_end_io;
+	iclog->ic_bio.bi_private = iclog;
+
+	if (iclog->ic_flags & XLOG_ICL_NEED_FLUSH) {
+		iclog->ic_bio.bi_opf |= REQ_PREFLUSH;
+		/*
+		 * For external log devices, we also need to flush the data
+		 * device cache first to ensure all metadata writeback covered
+		 * by the LSN in this iclog is on stable storage. This is slow,
+		 * but it *must* complete before we issue the external log IO.
+		 *
+		 * If the flush fails, we cannot conclude that past metadata
+		 * writeback from the log succeeded.  Repeating the flush is
+		 * not possible, hence we must shut down with log IO error to
+		 * avoid shutdown re-entering this path and erroring out again.
+		 */
+		if (log->l_targ != log->l_mp->m_ddev_targp &&
+		    blkdev_issue_flush(log->l_mp->m_ddev_targp->bt_bdev)) {
+			xlog_force_shutdown(log, SHUTDOWN_LOG_IO_ERROR);
+			return;
+		}
+	}
+	if (iclog->ic_flags & XLOG_ICL_NEED_FUA)
+		iclog->ic_bio.bi_opf |= REQ_FUA;
+
+	iclog->ic_flags &= ~(XLOG_ICL_NEED_FLUSH | XLOG_ICL_NEED_FUA);
+
+	if (xlog_map_iclog_data(&iclog->ic_bio, iclog->ic_data, count)) {
+		xlog_force_shutdown(log, SHUTDOWN_LOG_IO_ERROR);
+		return;
+	}
+	if (is_vmalloc_addr(iclog->ic_data))
+		flush_kernel_vmap_range(iclog->ic_data, count);
+
+	/*
+	 * If this log buffer would straddle the end of the log we will have
+	 * to split it up into two bios, so that we can continue at the start.
+	 */
+	if (bno + BTOBB(count) > log->l_logBBsize) {
+		struct bio *split;
+
+		split = bio_split(&iclog->ic_bio, log->l_logBBsize - bno,
+				  GFP_NOIO, &fs_bio_set);
+		bio_chain(split, &iclog->ic_bio);
+		submit_bio(split);
+
+		/* restart at logical offset zero for the remainder */
+		iclog->ic_bio.bi_iter.bi_sector = log->l_logBBstart;
+	}
+
+	submit_bio(&iclog->ic_bio);
+}
+
+/*
+ * We need to bump cycle number for the part of the iclog that is
+ * written to the start of the log. Watch out for the header magic
+ * number case, though.
+ */
+static void
+xlog_split_iclog(
+	struct xlog		*log,
+	void			*data,
+	uint64_t		bno,
+	unsigned int		count)
+{
+	unsigned int		split_offset = BBTOB(log->l_logBBsize - bno);
+	unsigned int		i;
+
+	for (i = split_offset; i < count; i += BBSIZE) {
+		uint32_t cycle = get_unaligned_be32(data + i);
+
+		if (++cycle == XLOG_HEADER_MAGIC_NUM)
+			cycle++;
+		put_unaligned_be32(cycle, data + i);
+	}
+}
+
+static int
+xlog_calc_iclog_size(
+	struct xlog		*log,
+	struct xlog_in_core	*iclog,
+	uint32_t		*roundoff)
+{
+	uint32_t		count_init, count;
+
+	/* Add for LR header */
+	count_init = log->l_iclog_hsize + iclog->ic_offset;
+	count = roundup(count_init, log->l_iclog_roundoff);
+
+	*roundoff = count - count_init;
+
+	ASSERT(count >= count_init);
+	ASSERT(*roundoff < log->l_iclog_roundoff);
+	return count;
+}
+
+/*
+ * Flush out the in-core log (iclog) to the on-disk log in an asynchronous
+ * fashion.  Previously, we should have moved the current iclog
+ * ptr in the log to point to the next available iclog.  This allows further
+ * write to continue while this code syncs out an iclog ready to go.
+ * Before an in-core log can be written out, the data section must be scanned
+ * to save away the 1st word of each BBSIZE block into the header.  We replace
+ * it with the current cycle count.  Each BBSIZE block is tagged with the
+ * cycle count because there in an implicit assumption that drives will
+ * guarantee that entire 512 byte blocks get written at once.  In other words,
+ * we can't have part of a 512 byte block written and part not written.  By
+ * tagging each block, we will know which blocks are valid when recovering
+ * after an unclean shutdown.
+ *
+ * This routine is single threaded on the iclog.  No other thread can be in
+ * this routine with the same iclog.  Changing contents of iclog can there-
+ * fore be done without grabbing the state machine lock.  Updating the global
+ * log will require grabbing the lock though.
+ *
+ * The entire log manager uses a logical block numbering scheme.  Only
+ * xlog_write_iclog knows about the fact that the log may not start with
+ * block zero on a given device.
+ */
+STATIC void
+xlog_sync(
+	struct xlog		*log,
+	struct xlog_in_core	*iclog,
+	struct xlog_ticket	*ticket)
+{
+	unsigned int		count;		/* byte count of bwrite */
+	unsigned int		roundoff;       /* roundoff to BB or stripe */
+	uint64_t		bno;
+	unsigned int		size;
+
+	ASSERT(atomic_read(&iclog->ic_refcnt) == 0);
+	trace_xlog_iclog_sync(iclog, _RET_IP_);
+
+	count = xlog_calc_iclog_size(log, iclog, &roundoff);
+
+	/*
+	 * If we have a ticket, account for the roundoff via the ticket
+	 * reservation to avoid touching the hot grant heads needlessly.
+	 * Otherwise, we have to move grant heads directly.
+	 */
+	if (ticket) {
+		ticket->t_curr_res -= roundoff;
+	} else {
+		xlog_grant_add_space(log, &log->l_reserve_head.grant, roundoff);
+		xlog_grant_add_space(log, &log->l_write_head.grant, roundoff);
+	}
+
+	/* put cycle number in every block */
+	xlog_pack_data(log, iclog, roundoff);
+
+	/* real byte length */
+	size = iclog->ic_offset;
+	if (xfs_has_logv2(log->l_mp))
+		size += roundoff;
+	iclog->ic_header.h_len = cpu_to_be32(size);
+
+	XFS_STATS_INC(log->l_mp, xs_log_writes);
+	XFS_STATS_ADD(log->l_mp, xs_log_blocks, BTOBB(count));
+
+	bno = BLOCK_LSN(be64_to_cpu(iclog->ic_header.h_lsn));
+
+	/* Do we need to split this write into 2 parts? */
+	if (bno + BTOBB(count) > log->l_logBBsize)
+		xlog_split_iclog(log, &iclog->ic_header, bno, count);
+
+	/* calculcate the checksum */
+	iclog->ic_header.h_crc = xlog_cksum(log, &iclog->ic_header,
+					    iclog->ic_datap, size);
+	/*
+	 * Intentionally corrupt the log record CRC based on the error injection
+	 * frequency, if defined. This facilitates testing log recovery in the
+	 * event of torn writes. Hence, set the IOABORT state to abort the log
+	 * write on I/O completion and shutdown the fs. The subsequent mount
+	 * detects the bad CRC and attempts to recover.
+	 */
+#ifdef DEBUG
+	if (XFS_TEST_ERROR(false, log->l_mp, XFS_ERRTAG_LOG_BAD_CRC)) {
+		iclog->ic_header.h_crc &= cpu_to_le32(0xAAAAAAAA);
+		iclog->ic_fail_crc = true;
+		xfs_warn(log->l_mp,
+	"Intentionally corrupted log record at LSN 0x%llx. Shutdown imminent.",
+			 be64_to_cpu(iclog->ic_header.h_lsn));
+	}
+#endif
+	xlog_verify_iclog(log, iclog, count);
+	xlog_write_iclog(log, iclog, bno, count);
+}
+
+/*
+ * Deallocate a log structure
+ */
+STATIC void
+xlog_dealloc_log(
+	struct xlog	*log)
+{
+	xlog_in_core_t	*iclog, *next_iclog;
+	int		i;
+
+	/*
+	 * Destroy the CIL after waiting for iclog IO completion because an
+	 * iclog EIO error will try to shut down the log, which accesses the
+	 * CIL to wake up the waiters.
+	 */
+	xlog_cil_destroy(log);
+
+	iclog = log->l_iclog;
+	for (i = 0; i < log->l_iclog_bufs; i++) {
+		next_iclog = iclog->ic_next;
+		kmem_free(iclog->ic_data);
+		kmem_free(iclog);
+		iclog = next_iclog;
+	}
+
+	log->l_mp->m_log = NULL;
+	destroy_workqueue(log->l_ioend_workqueue);
+	kmem_free(log);
+}
+
+/*
+ * Update counters atomically now that memcpy is done.
+ */
+static inline void
+xlog_state_finish_copy(
+	struct xlog		*log,
+	struct xlog_in_core	*iclog,
+	int			record_cnt,
+	int			copy_bytes)
+{
+	lockdep_assert_held(&log->l_icloglock);
+
+	be32_add_cpu(&iclog->ic_header.h_num_logops, record_cnt);
+	iclog->ic_offset += copy_bytes;
+}
+
+/*
+ * print out info relating to regions written which consume
+ * the reservation
+ */
+void
+xlog_print_tic_res(
+	struct xfs_mount	*mp,
+	struct xlog_ticket	*ticket)
+{
+	xfs_warn(mp, "ticket reservation summary:");
+	xfs_warn(mp, "  unit res    = %d bytes", ticket->t_unit_res);
+	xfs_warn(mp, "  current res = %d bytes", ticket->t_curr_res);
+	xfs_warn(mp, "  original count  = %d", ticket->t_ocnt);
+	xfs_warn(mp, "  remaining count = %d", ticket->t_cnt);
+}
+
+/*
+ * Print a summary of the transaction.
+ */
+void
+xlog_print_trans(
+	struct xfs_trans	*tp)
+{
+	struct xfs_mount	*mp = tp->t_mountp;
+	struct xfs_log_item	*lip;
+
+	/* dump core transaction and ticket info */
+	xfs_warn(mp, "transaction summary:");
+	xfs_warn(mp, "  log res   = %d", tp->t_log_res);
+	xfs_warn(mp, "  log count = %d", tp->t_log_count);
+	xfs_warn(mp, "  flags     = 0x%x", tp->t_flags);
+
+	xlog_print_tic_res(mp, tp->t_ticket);
+
+	/* dump each log item */
+	list_for_each_entry(lip, &tp->t_items, li_trans) {
+		struct xfs_log_vec	*lv = lip->li_lv;
+		struct xfs_log_iovec	*vec;
+		int			i;
+
+		xfs_warn(mp, "log item: ");
+		xfs_warn(mp, "  type	= 0x%x", lip->li_type);
+		xfs_warn(mp, "  flags	= 0x%lx", lip->li_flags);
+		if (!lv)
+			continue;
+		xfs_warn(mp, "  niovecs	= %d", lv->lv_niovecs);
+		xfs_warn(mp, "  size	= %d", lv->lv_size);
+		xfs_warn(mp, "  bytes	= %d", lv->lv_bytes);
+		xfs_warn(mp, "  buf len	= %d", lv->lv_buf_len);
+
+		/* dump each iovec for the log item */
+		vec = lv->lv_iovecp;
+		for (i = 0; i < lv->lv_niovecs; i++) {
+			int dumplen = min(vec->i_len, 32);
+
+			xfs_warn(mp, "  iovec[%d]", i);
+			xfs_warn(mp, "    type	= 0x%x", vec->i_type);
+			xfs_warn(mp, "    len	= %d", vec->i_len);
+			xfs_warn(mp, "    first %d bytes of iovec[%d]:", dumplen, i);
+			xfs_hex_dump(vec->i_addr, dumplen);
+
+			vec++;
+		}
+	}
+}
+
+static inline void
+xlog_write_iovec(
+	struct xlog_in_core	*iclog,
+	uint32_t		*log_offset,
+	void			*data,
+	uint32_t		write_len,
+	int			*bytes_left,
+	uint32_t		*record_cnt,
+	uint32_t		*data_cnt)
+{
+	ASSERT(*log_offset < iclog->ic_log->l_iclog_size);
+	ASSERT(*log_offset % sizeof(int32_t) == 0);
+	ASSERT(write_len % sizeof(int32_t) == 0);
+
+	memcpy(iclog->ic_datap + *log_offset, data, write_len);
+	*log_offset += write_len;
+	*bytes_left -= write_len;
+	(*record_cnt)++;
+	*data_cnt += write_len;
+}
+
+/*
+ * Write log vectors into a single iclog which is guaranteed by the caller
+ * to have enough space to write the entire log vector into.
+ */
+static void
+xlog_write_full(
+	struct xfs_log_vec	*lv,
+	struct xlog_ticket	*ticket,
+	struct xlog_in_core	*iclog,
+	uint32_t		*log_offset,
+	uint32_t		*len,
+	uint32_t		*record_cnt,
+	uint32_t		*data_cnt)
+{
+	int			index;
+
+	ASSERT(*log_offset + *len <= iclog->ic_size ||
+		iclog->ic_state == XLOG_STATE_WANT_SYNC);
+
+	/*
+	 * Ordered log vectors have no regions to write so this
+	 * loop will naturally skip them.
+	 */
+	for (index = 0; index < lv->lv_niovecs; index++) {
+		struct xfs_log_iovec	*reg = &lv->lv_iovecp[index];
+		struct xlog_op_header	*ophdr = reg->i_addr;
+
+		ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
+		xlog_write_iovec(iclog, log_offset, reg->i_addr,
+				reg->i_len, len, record_cnt, data_cnt);
+	}
+}
+
+static int
+xlog_write_get_more_iclog_space(
+	struct xlog_ticket	*ticket,
+	struct xlog_in_core	**iclogp,
+	uint32_t		*log_offset,
+	uint32_t		len,
+	uint32_t		*record_cnt,
+	uint32_t		*data_cnt)
+{
+	struct xlog_in_core	*iclog = *iclogp;
+	struct xlog		*log = iclog->ic_log;
+	int			error;
+
+	spin_lock(&log->l_icloglock);
+	ASSERT(iclog->ic_state == XLOG_STATE_WANT_SYNC);
+	xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
+	error = xlog_state_release_iclog(log, iclog, ticket);
+	spin_unlock(&log->l_icloglock);
+	if (error)
+		return error;
+
+	error = xlog_state_get_iclog_space(log, len, &iclog, ticket,
+					log_offset);
+	if (error)
+		return error;
+	*record_cnt = 0;
+	*data_cnt = 0;
+	*iclogp = iclog;
+	return 0;
+}
+
+/*
+ * Write log vectors into a single iclog which is smaller than the current chain
+ * length. We write until we cannot fit a full record into the remaining space
+ * and then stop. We return the log vector that is to be written that cannot
+ * wholly fit in the iclog.
+ */
+static int
+xlog_write_partial(
+	struct xfs_log_vec	*lv,
+	struct xlog_ticket	*ticket,
+	struct xlog_in_core	**iclogp,
+	uint32_t		*log_offset,
+	uint32_t		*len,
+	uint32_t		*record_cnt,
+	uint32_t		*data_cnt)
+{
+	struct xlog_in_core	*iclog = *iclogp;
+	struct xlog_op_header	*ophdr;
+	int			index = 0;
+	uint32_t		rlen;
+	int			error;
+
+	/* walk the logvec, copying until we run out of space in the iclog */
+	for (index = 0; index < lv->lv_niovecs; index++) {
+		struct xfs_log_iovec	*reg = &lv->lv_iovecp[index];
+		uint32_t		reg_offset = 0;
+
+		/*
+		 * The first region of a continuation must have a non-zero
+		 * length otherwise log recovery will just skip over it and
+		 * start recovering from the next opheader it finds. Because we
+		 * mark the next opheader as a continuation, recovery will then
+		 * incorrectly add the continuation to the previous region and
+		 * that breaks stuff.
+		 *
+		 * Hence if there isn't space for region data after the
+		 * opheader, then we need to start afresh with a new iclog.
+		 */
+		if (iclog->ic_size - *log_offset <=
+					sizeof(struct xlog_op_header)) {
+			error = xlog_write_get_more_iclog_space(ticket,
+					&iclog, log_offset, *len, record_cnt,
+					data_cnt);
+			if (error)
+				return error;
+		}
+
+		ophdr = reg->i_addr;
+		rlen = min_t(uint32_t, reg->i_len, iclog->ic_size - *log_offset);
+
+		ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
+		ophdr->oh_len = cpu_to_be32(rlen - sizeof(struct xlog_op_header));
+		if (rlen != reg->i_len)
+			ophdr->oh_flags |= XLOG_CONTINUE_TRANS;
+
+		xlog_write_iovec(iclog, log_offset, reg->i_addr,
+				rlen, len, record_cnt, data_cnt);
+
+		/* If we wrote the whole region, move to the next. */
+		if (rlen == reg->i_len)
+			continue;
+
+		/*
+		 * We now have a partially written iovec, but it can span
+		 * multiple iclogs so we loop here. First we release the iclog
+		 * we currently have, then we get a new iclog and add a new
+		 * opheader. Then we continue copying from where we were until
+		 * we either complete the iovec or fill the iclog. If we
+		 * complete the iovec, then we increment the index and go right
+		 * back to the top of the outer loop. if we fill the iclog, we
+		 * run the inner loop again.
+		 *
+		 * This is complicated by the tail of a region using all the
+		 * space in an iclog and hence requiring us to release the iclog
+		 * and get a new one before returning to the outer loop. We must
+		 * always guarantee that we exit this inner loop with at least
+		 * space for log transaction opheaders left in the current
+		 * iclog, hence we cannot just terminate the loop at the end
+		 * of the of the continuation. So we loop while there is no
+		 * space left in the current iclog, and check for the end of the
+		 * continuation after getting a new iclog.
+		 */
+		do {
+			/*
+			 * Ensure we include the continuation opheader in the
+			 * space we need in the new iclog by adding that size
+			 * to the length we require. This continuation opheader
+			 * needs to be accounted to the ticket as the space it
+			 * consumes hasn't been accounted to the lv we are
+			 * writing.
+			 */
+			error = xlog_write_get_more_iclog_space(ticket,
+					&iclog, log_offset,
+					*len + sizeof(struct xlog_op_header),
+					record_cnt, data_cnt);
+			if (error)
+				return error;
+
+			ophdr = iclog->ic_datap + *log_offset;
+			ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
+			ophdr->oh_clientid = XFS_TRANSACTION;
+			ophdr->oh_res2 = 0;
+			ophdr->oh_flags = XLOG_WAS_CONT_TRANS;
+
+			ticket->t_curr_res -= sizeof(struct xlog_op_header);
+			*log_offset += sizeof(struct xlog_op_header);
+			*data_cnt += sizeof(struct xlog_op_header);
+
+			/*
+			 * If rlen fits in the iclog, then end the region
+			 * continuation. Otherwise we're going around again.
+			 */
+			reg_offset += rlen;
+			rlen = reg->i_len - reg_offset;
+			if (rlen <= iclog->ic_size - *log_offset)
+				ophdr->oh_flags |= XLOG_END_TRANS;
+			else
+				ophdr->oh_flags |= XLOG_CONTINUE_TRANS;
+
+			rlen = min_t(uint32_t, rlen, iclog->ic_size - *log_offset);
+			ophdr->oh_len = cpu_to_be32(rlen);
+
+			xlog_write_iovec(iclog, log_offset,
+					reg->i_addr + reg_offset,
+					rlen, len, record_cnt, data_cnt);
+
+		} while (ophdr->oh_flags & XLOG_CONTINUE_TRANS);
+	}
+
+	/*
+	 * No more iovecs remain in this logvec so return the next log vec to
+	 * the caller so it can go back to fast path copying.
+	 */
+	*iclogp = iclog;
+	return 0;
+}
+
+/*
+ * Write some region out to in-core log
+ *
+ * This will be called when writing externally provided regions or when
+ * writing out a commit record for a given transaction.
+ *
+ * General algorithm:
+ *	1. Find total length of this write.  This may include adding to the
+ *		lengths passed in.
+ *	2. Check whether we violate the tickets reservation.
+ *	3. While writing to this iclog
+ *	    A. Reserve as much space in this iclog as can get
+ *	    B. If this is first write, save away start lsn
+ *	    C. While writing this region:
+ *		1. If first write of transaction, write start record
+ *		2. Write log operation header (header per region)
+ *		3. Find out if we can fit entire region into this iclog
+ *		4. Potentially, verify destination memcpy ptr
+ *		5. Memcpy (partial) region
+ *		6. If partial copy, release iclog; otherwise, continue
+ *			copying more regions into current iclog
+ *	4. Mark want sync bit (in simulation mode)
+ *	5. Release iclog for potential flush to on-disk log.
+ *
+ * ERRORS:
+ * 1.	Panic if reservation is overrun.  This should never happen since
+ *	reservation amounts are generated internal to the filesystem.
+ * NOTES:
+ * 1. Tickets are single threaded data structures.
+ * 2. The XLOG_END_TRANS & XLOG_CONTINUE_TRANS flags are passed down to the
+ *	syncing routine.  When a single log_write region needs to span
+ *	multiple in-core logs, the XLOG_CONTINUE_TRANS bit should be set
+ *	on all log operation writes which don't contain the end of the
+ *	region.  The XLOG_END_TRANS bit is used for the in-core log
+ *	operation which contains the end of the continued log_write region.
+ * 3. When xlog_state_get_iclog_space() grabs the rest of the current iclog,
+ *	we don't really know exactly how much space will be used.  As a result,
+ *	we don't update ic_offset until the end when we know exactly how many
+ *	bytes have been written out.
+ */
+int
+xlog_write(
+	struct xlog		*log,
+	struct xfs_cil_ctx	*ctx,
+	struct list_head	*lv_chain,
+	struct xlog_ticket	*ticket,
+	uint32_t		len)
+
+{
+	struct xlog_in_core	*iclog = NULL;
+	struct xfs_log_vec	*lv;
+	uint32_t		record_cnt = 0;
+	uint32_t		data_cnt = 0;
+	int			error = 0;
+	int			log_offset;
+
+	if (ticket->t_curr_res < 0) {
+		xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
+		     "ctx ticket reservation ran out. Need to up reservation");
+		xlog_print_tic_res(log->l_mp, ticket);
+		xlog_force_shutdown(log, SHUTDOWN_LOG_IO_ERROR);
+	}
+
+	error = xlog_state_get_iclog_space(log, len, &iclog, ticket,
+					   &log_offset);
+	if (error)
+		return error;
+
+	ASSERT(log_offset <= iclog->ic_size - 1);
+
+	/*
+	 * If we have a context pointer, pass it the first iclog we are
+	 * writing to so it can record state needed for iclog write
+	 * ordering.
+	 */
+	if (ctx)
+		xlog_cil_set_ctx_write_state(ctx, iclog);
+
+	list_for_each_entry(lv, lv_chain, lv_list) {
+		/*
+		 * If the entire log vec does not fit in the iclog, punt it to
+		 * the partial copy loop which can handle this case.
+		 */
+		if (lv->lv_niovecs &&
+		    lv->lv_bytes > iclog->ic_size - log_offset) {
+			error = xlog_write_partial(lv, ticket, &iclog,
+					&log_offset, &len, &record_cnt,
+					&data_cnt);
+			if (error) {
+				/*
+				 * We have no iclog to release, so just return
+				 * the error immediately.
+				 */
+				return error;
+			}
+		} else {
+			xlog_write_full(lv, ticket, iclog, &log_offset,
+					 &len, &record_cnt, &data_cnt);
+		}
+	}
+	ASSERT(len == 0);
+
+	/*
+	 * We've already been guaranteed that the last writes will fit inside
+	 * the current iclog, and hence it will already have the space used by
+	 * those writes accounted to it. Hence we do not need to update the
+	 * iclog with the number of bytes written here.
+	 */
+	spin_lock(&log->l_icloglock);
+	xlog_state_finish_copy(log, iclog, record_cnt, 0);
+	error = xlog_state_release_iclog(log, iclog, ticket);
+	spin_unlock(&log->l_icloglock);
+
+	return error;
+}
+
+static void
+xlog_state_activate_iclog(
+	struct xlog_in_core	*iclog,
+	int			*iclogs_changed)
+{
+	ASSERT(list_empty_careful(&iclog->ic_callbacks));
+	trace_xlog_iclog_activate(iclog, _RET_IP_);
+
+	/*
+	 * If the number of ops in this iclog indicate it just contains the
+	 * dummy transaction, we can change state into IDLE (the second time
+	 * around). Otherwise we should change the state into NEED a dummy.
+	 * We don't need to cover the dummy.
+	 */
+	if (*iclogs_changed == 0 &&
+	    iclog->ic_header.h_num_logops == cpu_to_be32(XLOG_COVER_OPS)) {
+		*iclogs_changed = 1;
+	} else {
+		/*
+		 * We have two dirty iclogs so start over.  This could also be
+		 * num of ops indicating this is not the dummy going out.
+		 */
+		*iclogs_changed = 2;
+	}
+
+	iclog->ic_state	= XLOG_STATE_ACTIVE;
+	iclog->ic_offset = 0;
+	iclog->ic_header.h_num_logops = 0;
+	memset(iclog->ic_header.h_cycle_data, 0,
+		sizeof(iclog->ic_header.h_cycle_data));
+	iclog->ic_header.h_lsn = 0;
+	iclog->ic_header.h_tail_lsn = 0;
+}
+
+/*
+ * Loop through all iclogs and mark all iclogs currently marked DIRTY as
+ * ACTIVE after iclog I/O has completed.
+ */
+static void
+xlog_state_activate_iclogs(
+	struct xlog		*log,
+	int			*iclogs_changed)
+{
+	struct xlog_in_core	*iclog = log->l_iclog;
+
+	do {
+		if (iclog->ic_state == XLOG_STATE_DIRTY)
+			xlog_state_activate_iclog(iclog, iclogs_changed);
+		/*
+		 * The ordering of marking iclogs ACTIVE must be maintained, so
+		 * an iclog doesn't become ACTIVE beyond one that is SYNCING.
+		 */
+		else if (iclog->ic_state != XLOG_STATE_ACTIVE)
+			break;
+	} while ((iclog = iclog->ic_next) != log->l_iclog);
+}
+
+static int
+xlog_covered_state(
+	int			prev_state,
+	int			iclogs_changed)
+{
+	/*
+	 * We go to NEED for any non-covering writes. We go to NEED2 if we just
+	 * wrote the first covering record (DONE). We go to IDLE if we just
+	 * wrote the second covering record (DONE2) and remain in IDLE until a
+	 * non-covering write occurs.
+	 */
+	switch (prev_state) {
+	case XLOG_STATE_COVER_IDLE:
+		if (iclogs_changed == 1)
+			return XLOG_STATE_COVER_IDLE;
+		fallthrough;
+	case XLOG_STATE_COVER_NEED:
+	case XLOG_STATE_COVER_NEED2:
+		break;
+	case XLOG_STATE_COVER_DONE:
+		if (iclogs_changed == 1)
+			return XLOG_STATE_COVER_NEED2;
+		break;
+	case XLOG_STATE_COVER_DONE2:
+		if (iclogs_changed == 1)
+			return XLOG_STATE_COVER_IDLE;
+		break;
+	default:
+		ASSERT(0);
+	}
+
+	return XLOG_STATE_COVER_NEED;
+}
+
+STATIC void
+xlog_state_clean_iclog(
+	struct xlog		*log,
+	struct xlog_in_core	*dirty_iclog)
+{
+	int			iclogs_changed = 0;
+
+	trace_xlog_iclog_clean(dirty_iclog, _RET_IP_);
+
+	dirty_iclog->ic_state = XLOG_STATE_DIRTY;
+
+	xlog_state_activate_iclogs(log, &iclogs_changed);
+	wake_up_all(&dirty_iclog->ic_force_wait);
+
+	if (iclogs_changed) {
+		log->l_covered_state = xlog_covered_state(log->l_covered_state,
+				iclogs_changed);
+	}
+}
+
+STATIC xfs_lsn_t
+xlog_get_lowest_lsn(
+	struct xlog		*log)
+{
+	struct xlog_in_core	*iclog = log->l_iclog;
+	xfs_lsn_t		lowest_lsn = 0, lsn;
+
+	do {
+		if (iclog->ic_state == XLOG_STATE_ACTIVE ||
+		    iclog->ic_state == XLOG_STATE_DIRTY)
+			continue;
+
+		lsn = be64_to_cpu(iclog->ic_header.h_lsn);
+		if ((lsn && !lowest_lsn) || XFS_LSN_CMP(lsn, lowest_lsn) < 0)
+			lowest_lsn = lsn;
+	} while ((iclog = iclog->ic_next) != log->l_iclog);
+
+	return lowest_lsn;
+}
+
+/*
+ * Completion of a iclog IO does not imply that a transaction has completed, as
+ * transactions can be large enough to span many iclogs. We cannot change the
+ * tail of the log half way through a transaction as this may be the only
+ * transaction in the log and moving the tail to point to the middle of it
+ * will prevent recovery from finding the start of the transaction. Hence we
+ * should only update the last_sync_lsn if this iclog contains transaction
+ * completion callbacks on it.
+ *
+ * We have to do this before we drop the icloglock to ensure we are the only one
+ * that can update it.
+ *
+ * If we are moving the last_sync_lsn forwards, we also need to ensure we kick
+ * the reservation grant head pushing. This is due to the fact that the push
+ * target is bound by the current last_sync_lsn value. Hence if we have a large
+ * amount of log space bound up in this committing transaction then the
+ * last_sync_lsn value may be the limiting factor preventing tail pushing from
+ * freeing space in the log. Hence once we've updated the last_sync_lsn we
+ * should push the AIL to ensure the push target (and hence the grant head) is
+ * no longer bound by the old log head location and can move forwards and make
+ * progress again.
+ */
+static void
+xlog_state_set_callback(
+	struct xlog		*log,
+	struct xlog_in_core	*iclog,
+	xfs_lsn_t		header_lsn)
+{
+	trace_xlog_iclog_callback(iclog, _RET_IP_);
+	iclog->ic_state = XLOG_STATE_CALLBACK;
+
+	ASSERT(XFS_LSN_CMP(atomic64_read(&log->l_last_sync_lsn),
+			   header_lsn) <= 0);
+
+	if (list_empty_careful(&iclog->ic_callbacks))
+		return;
+
+	atomic64_set(&log->l_last_sync_lsn, header_lsn);
+	xlog_grant_push_ail(log, 0);
+}
+
+/*
+ * Return true if we need to stop processing, false to continue to the next
+ * iclog. The caller will need to run callbacks if the iclog is returned in the
+ * XLOG_STATE_CALLBACK state.
+ */
+static bool
+xlog_state_iodone_process_iclog(
+	struct xlog		*log,
+	struct xlog_in_core	*iclog)
+{
+	xfs_lsn_t		lowest_lsn;
+	xfs_lsn_t		header_lsn;
+
+	switch (iclog->ic_state) {
+	case XLOG_STATE_ACTIVE:
+	case XLOG_STATE_DIRTY:
+		/*
+		 * Skip all iclogs in the ACTIVE & DIRTY states:
+		 */
+		return false;
+	case XLOG_STATE_DONE_SYNC:
+		/*
+		 * Now that we have an iclog that is in the DONE_SYNC state, do
+		 * one more check here to see if we have chased our tail around.
+		 * If this is not the lowest lsn iclog, then we will leave it
+		 * for another completion to process.
+		 */
+		header_lsn = be64_to_cpu(iclog->ic_header.h_lsn);
+		lowest_lsn = xlog_get_lowest_lsn(log);
+		if (lowest_lsn && XFS_LSN_CMP(lowest_lsn, header_lsn) < 0)
+			return false;
+		xlog_state_set_callback(log, iclog, header_lsn);
+		return false;
+	default:
+		/*
+		 * Can only perform callbacks in order.  Since this iclog is not
+		 * in the DONE_SYNC state, we skip the rest and just try to
+		 * clean up.
+		 */
+		return true;
+	}
+}
+
+/*
+ * Loop over all the iclogs, running attached callbacks on them. Return true if
+ * we ran any callbacks, indicating that we dropped the icloglock. We don't need
+ * to handle transient shutdown state here at all because
+ * xlog_state_shutdown_callbacks() will be run to do the necessary shutdown
+ * cleanup of the callbacks.
+ */
+static bool
+xlog_state_do_iclog_callbacks(
+	struct xlog		*log)
+		__releases(&log->l_icloglock)
+		__acquires(&log->l_icloglock)
+{
+	struct xlog_in_core	*first_iclog = log->l_iclog;
+	struct xlog_in_core	*iclog = first_iclog;
+	bool			ran_callback = false;
+
+	do {
+		LIST_HEAD(cb_list);
+
+		if (xlog_state_iodone_process_iclog(log, iclog))
+			break;
+		if (iclog->ic_state != XLOG_STATE_CALLBACK) {
+			iclog = iclog->ic_next;
+			continue;
+		}
+		list_splice_init(&iclog->ic_callbacks, &cb_list);
+		spin_unlock(&log->l_icloglock);
+
+		trace_xlog_iclog_callbacks_start(iclog, _RET_IP_);
+		xlog_cil_process_committed(&cb_list);
+		trace_xlog_iclog_callbacks_done(iclog, _RET_IP_);
+		ran_callback = true;
+
+		spin_lock(&log->l_icloglock);
+		xlog_state_clean_iclog(log, iclog);
+		iclog = iclog->ic_next;
+	} while (iclog != first_iclog);
+
+	return ran_callback;
+}
+
+
+/*
+ * Loop running iclog completion callbacks until there are no more iclogs in a
+ * state that can run callbacks.
+ */
+STATIC void
+xlog_state_do_callback(
+	struct xlog		*log)
+{
+	int			flushcnt = 0;
+	int			repeats = 0;
+
+	spin_lock(&log->l_icloglock);
+	while (xlog_state_do_iclog_callbacks(log)) {
+		if (xlog_is_shutdown(log))
+			break;
+
+		if (++repeats > 5000) {
+			flushcnt += repeats;
+			repeats = 0;
+			xfs_warn(log->l_mp,
+				"%s: possible infinite loop (%d iterations)",
+				__func__, flushcnt);
+		}
+	}
+
+	if (log->l_iclog->ic_state == XLOG_STATE_ACTIVE)
+		wake_up_all(&log->l_flush_wait);
+
+	spin_unlock(&log->l_icloglock);
+}
+
+
+/*
+ * Finish transitioning this iclog to the dirty state.
+ *
+ * Callbacks could take time, so they are done outside the scope of the
+ * global state machine log lock.
+ */
+STATIC void
+xlog_state_done_syncing(
+	struct xlog_in_core	*iclog)
+{
+	struct xlog		*log = iclog->ic_log;
+
+	spin_lock(&log->l_icloglock);
+	ASSERT(atomic_read(&iclog->ic_refcnt) == 0);
+	trace_xlog_iclog_sync_done(iclog, _RET_IP_);
+
+	/*
+	 * If we got an error, either on the first buffer, or in the case of
+	 * split log writes, on the second, we shut down the file system and
+	 * no iclogs should ever be attempted to be written to disk again.
+	 */
+	if (!xlog_is_shutdown(log)) {
+		ASSERT(iclog->ic_state == XLOG_STATE_SYNCING);
+		iclog->ic_state = XLOG_STATE_DONE_SYNC;
+	}
+
+	/*
+	 * Someone could be sleeping prior to writing out the next
+	 * iclog buffer, we wake them all, one will get to do the
+	 * I/O, the others get to wait for the result.
+	 */
+	wake_up_all(&iclog->ic_write_wait);
+	spin_unlock(&log->l_icloglock);
+	xlog_state_do_callback(log);
+}
+
+/*
+ * If the head of the in-core log ring is not (ACTIVE or DIRTY), then we must
+ * sleep.  We wait on the flush queue on the head iclog as that should be
+ * the first iclog to complete flushing. Hence if all iclogs are syncing,
+ * we will wait here and all new writes will sleep until a sync completes.
+ *
+ * The in-core logs are used in a circular fashion. They are not used
+ * out-of-order even when an iclog past the head is free.
+ *
+ * return:
+ *	* log_offset where xlog_write() can start writing into the in-core
+ *		log's data space.
+ *	* in-core log pointer to which xlog_write() should write.
+ *	* boolean indicating this is a continued write to an in-core log.
+ *		If this is the last write, then the in-core log's offset field
+ *		needs to be incremented, depending on the amount of data which
+ *		is copied.
+ */
+STATIC int
+xlog_state_get_iclog_space(
+	struct xlog		*log,
+	int			len,
+	struct xlog_in_core	**iclogp,
+	struct xlog_ticket	*ticket,
+	int			*logoffsetp)
+{
+	int		  log_offset;
+	xlog_rec_header_t *head;
+	xlog_in_core_t	  *iclog;
+
+restart:
+	spin_lock(&log->l_icloglock);
+	if (xlog_is_shutdown(log)) {
+		spin_unlock(&log->l_icloglock);
+		return -EIO;
+	}
+
+	iclog = log->l_iclog;
+	if (iclog->ic_state != XLOG_STATE_ACTIVE) {
+		XFS_STATS_INC(log->l_mp, xs_log_noiclogs);
+
+		/* Wait for log writes to have flushed */
+		xlog_wait(&log->l_flush_wait, &log->l_icloglock);
+		goto restart;
+	}
+
+	head = &iclog->ic_header;
+
+	atomic_inc(&iclog->ic_refcnt);	/* prevents sync */
+	log_offset = iclog->ic_offset;
+
+	trace_xlog_iclog_get_space(iclog, _RET_IP_);
+
+	/* On the 1st write to an iclog, figure out lsn.  This works
+	 * if iclogs marked XLOG_STATE_WANT_SYNC always write out what they are
+	 * committing to.  If the offset is set, that's how many blocks
+	 * must be written.
+	 */
+	if (log_offset == 0) {
+		ticket->t_curr_res -= log->l_iclog_hsize;
+		head->h_cycle = cpu_to_be32(log->l_curr_cycle);
+		head->h_lsn = cpu_to_be64(
+			xlog_assign_lsn(log->l_curr_cycle, log->l_curr_block));
+		ASSERT(log->l_curr_block >= 0);
+	}
+
+	/* If there is enough room to write everything, then do it.  Otherwise,
+	 * claim the rest of the region and make sure the XLOG_STATE_WANT_SYNC
+	 * bit is on, so this will get flushed out.  Don't update ic_offset
+	 * until you know exactly how many bytes get copied.  Therefore, wait
+	 * until later to update ic_offset.
+	 *
+	 * xlog_write() algorithm assumes that at least 2 xlog_op_header_t's
+	 * can fit into remaining data section.
+	 */
+	if (iclog->ic_size - iclog->ic_offset < 2*sizeof(xlog_op_header_t)) {
+		int		error = 0;
+
+		xlog_state_switch_iclogs(log, iclog, iclog->ic_size);
+
+		/*
+		 * If we are the only one writing to this iclog, sync it to
+		 * disk.  We need to do an atomic compare and decrement here to
+		 * avoid racing with concurrent atomic_dec_and_lock() calls in
+		 * xlog_state_release_iclog() when there is more than one
+		 * reference to the iclog.
+		 */
+		if (!atomic_add_unless(&iclog->ic_refcnt, -1, 1))
+			error = xlog_state_release_iclog(log, iclog, ticket);
+		spin_unlock(&log->l_icloglock);
+		if (error)
+			return error;
+		goto restart;
+	}
+
+	/* Do we have enough room to write the full amount in the remainder
+	 * of this iclog?  Or must we continue a write on the next iclog and
+	 * mark this iclog as completely taken?  In the case where we switch
+	 * iclogs (to mark it taken), this particular iclog will release/sync
+	 * to disk in xlog_write().
+	 */
+	if (len <= iclog->ic_size - iclog->ic_offset)
+		iclog->ic_offset += len;
+	else
+		xlog_state_switch_iclogs(log, iclog, iclog->ic_size);
+	*iclogp = iclog;
+
+	ASSERT(iclog->ic_offset <= iclog->ic_size);
+	spin_unlock(&log->l_icloglock);
+
+	*logoffsetp = log_offset;
+	return 0;
+}
+
+/*
+ * The first cnt-1 times a ticket goes through here we don't need to move the
+ * grant write head because the permanent reservation has reserved cnt times the
+ * unit amount.  Release part of current permanent unit reservation and reset
+ * current reservation to be one units worth.  Also move grant reservation head
+ * forward.
+ */
+void
+xfs_log_ticket_regrant(
+	struct xlog		*log,
+	struct xlog_ticket	*ticket)
+{
+	trace_xfs_log_ticket_regrant(log, ticket);
+
+	if (ticket->t_cnt > 0)
+		ticket->t_cnt--;
+
+	xlog_grant_sub_space(log, &log->l_reserve_head.grant,
+					ticket->t_curr_res);
+	xlog_grant_sub_space(log, &log->l_write_head.grant,
+					ticket->t_curr_res);
+	ticket->t_curr_res = ticket->t_unit_res;
+
+	trace_xfs_log_ticket_regrant_sub(log, ticket);
+
+	/* just return if we still have some of the pre-reserved space */
+	if (!ticket->t_cnt) {
+		xlog_grant_add_space(log, &log->l_reserve_head.grant,
+				     ticket->t_unit_res);
+		trace_xfs_log_ticket_regrant_exit(log, ticket);
+
+		ticket->t_curr_res = ticket->t_unit_res;
+	}
+
+	xfs_log_ticket_put(ticket);
+}
+
+/*
+ * Give back the space left from a reservation.
+ *
+ * All the information we need to make a correct determination of space left
+ * is present.  For non-permanent reservations, things are quite easy.  The
+ * count should have been decremented to zero.  We only need to deal with the
+ * space remaining in the current reservation part of the ticket.  If the
+ * ticket contains a permanent reservation, there may be left over space which
+ * needs to be released.  A count of N means that N-1 refills of the current
+ * reservation can be done before we need to ask for more space.  The first
+ * one goes to fill up the first current reservation.  Once we run out of
+ * space, the count will stay at zero and the only space remaining will be
+ * in the current reservation field.
+ */
+void
+xfs_log_ticket_ungrant(
+	struct xlog		*log,
+	struct xlog_ticket	*ticket)
+{
+	int			bytes;
+
+	trace_xfs_log_ticket_ungrant(log, ticket);
+
+	if (ticket->t_cnt > 0)
+		ticket->t_cnt--;
+
+	trace_xfs_log_ticket_ungrant_sub(log, ticket);
+
+	/*
+	 * If this is a permanent reservation ticket, we may be able to free
+	 * up more space based on the remaining count.
+	 */
+	bytes = ticket->t_curr_res;
+	if (ticket->t_cnt > 0) {
+		ASSERT(ticket->t_flags & XLOG_TIC_PERM_RESERV);
+		bytes += ticket->t_unit_res*ticket->t_cnt;
+	}
+
+	xlog_grant_sub_space(log, &log->l_reserve_head.grant, bytes);
+	xlog_grant_sub_space(log, &log->l_write_head.grant, bytes);
+
+	trace_xfs_log_ticket_ungrant_exit(log, ticket);
+
+	xfs_log_space_wake(log->l_mp);
+	xfs_log_ticket_put(ticket);
+}
+
+/*
+ * This routine will mark the current iclog in the ring as WANT_SYNC and move
+ * the current iclog pointer to the next iclog in the ring.
+ */
+void
+xlog_state_switch_iclogs(
+	struct xlog		*log,
+	struct xlog_in_core	*iclog,
+	int			eventual_size)
+{
+	ASSERT(iclog->ic_state == XLOG_STATE_ACTIVE);
+	assert_spin_locked(&log->l_icloglock);
+	trace_xlog_iclog_switch(iclog, _RET_IP_);
+
+	if (!eventual_size)
+		eventual_size = iclog->ic_offset;
+	iclog->ic_state = XLOG_STATE_WANT_SYNC;
+	iclog->ic_header.h_prev_block = cpu_to_be32(log->l_prev_block);
+	log->l_prev_block = log->l_curr_block;
+	log->l_prev_cycle = log->l_curr_cycle;
+
+	/* roll log?: ic_offset changed later */
+	log->l_curr_block += BTOBB(eventual_size)+BTOBB(log->l_iclog_hsize);
+
+	/* Round up to next log-sunit */
+	if (log->l_iclog_roundoff > BBSIZE) {
+		uint32_t sunit_bb = BTOBB(log->l_iclog_roundoff);
+		log->l_curr_block = roundup(log->l_curr_block, sunit_bb);
+	}
+
+	if (log->l_curr_block >= log->l_logBBsize) {
+		/*
+		 * Rewind the current block before the cycle is bumped to make
+		 * sure that the combined LSN never transiently moves forward
+		 * when the log wraps to the next cycle. This is to support the
+		 * unlocked sample of these fields from xlog_valid_lsn(). Most
+		 * other cases should acquire l_icloglock.
+		 */
+		log->l_curr_block -= log->l_logBBsize;
+		ASSERT(log->l_curr_block >= 0);
+		smp_wmb();
+		log->l_curr_cycle++;
+		if (log->l_curr_cycle == XLOG_HEADER_MAGIC_NUM)
+			log->l_curr_cycle++;
+	}
+	ASSERT(iclog == log->l_iclog);
+	log->l_iclog = iclog->ic_next;
+}
+
+/*
+ * Force the iclog to disk and check if the iclog has been completed before
+ * xlog_force_iclog() returns. This can happen on synchronous (e.g.
+ * pmem) or fast async storage because we drop the icloglock to issue the IO.
+ * If completion has already occurred, tell the caller so that it can avoid an
+ * unnecessary wait on the iclog.
+ */
+static int
+xlog_force_and_check_iclog(
+	struct xlog_in_core	*iclog,
+	bool			*completed)
+{
+	xfs_lsn_t		lsn = be64_to_cpu(iclog->ic_header.h_lsn);
+	int			error;
+
+	*completed = false;
+	error = xlog_force_iclog(iclog);
+	if (error)
+		return error;
+
+	/*
+	 * If the iclog has already been completed and reused the header LSN
+	 * will have been rewritten by completion
+	 */
+	if (be64_to_cpu(iclog->ic_header.h_lsn) != lsn)
+		*completed = true;
+	return 0;
+}
+
+/*
+ * Write out all data in the in-core log as of this exact moment in time.
+ *
+ * Data may be written to the in-core log during this call.  However,
+ * we don't guarantee this data will be written out.  A change from past
+ * implementation means this routine will *not* write out zero length LRs.
+ *
+ * Basically, we try and perform an intelligent scan of the in-core logs.
+ * If we determine there is no flushable data, we just return.  There is no
+ * flushable data if:
+ *
+ *	1. the current iclog is active and has no data; the previous iclog
+ *		is in the active or dirty state.
+ *	2. the current iclog is drity, and the previous iclog is in the
+ *		active or dirty state.
+ *
+ * We may sleep if:
+ *
+ *	1. the current iclog is not in the active nor dirty state.
+ *	2. the current iclog dirty, and the previous iclog is not in the
+ *		active nor dirty state.
+ *	3. the current iclog is active, and there is another thread writing
+ *		to this particular iclog.
+ *	4. a) the current iclog is active and has no other writers
+ *	   b) when we return from flushing out this iclog, it is still
+ *		not in the active nor dirty state.
+ */
+int
+xfs_log_force(
+	struct xfs_mount	*mp,
+	uint			flags)
+{
+	struct xlog		*log = mp->m_log;
+	struct xlog_in_core	*iclog;
+
+	XFS_STATS_INC(mp, xs_log_force);
+	trace_xfs_log_force(mp, 0, _RET_IP_);
+
+	xlog_cil_force(log);
+
+	spin_lock(&log->l_icloglock);
+	if (xlog_is_shutdown(log))
+		goto out_error;
+
+	iclog = log->l_iclog;
+	trace_xlog_iclog_force(iclog, _RET_IP_);
+
+	if (iclog->ic_state == XLOG_STATE_DIRTY ||
+	    (iclog->ic_state == XLOG_STATE_ACTIVE &&
+	     atomic_read(&iclog->ic_refcnt) == 0 && iclog->ic_offset == 0)) {
+		/*
+		 * If the head is dirty or (active and empty), then we need to
+		 * look at the previous iclog.
+		 *
+		 * If the previous iclog is active or dirty we are done.  There
+		 * is nothing to sync out. Otherwise, we attach ourselves to the
+		 * previous iclog and go to sleep.
+		 */
+		iclog = iclog->ic_prev;
+	} else if (iclog->ic_state == XLOG_STATE_ACTIVE) {
+		if (atomic_read(&iclog->ic_refcnt) == 0) {
+			/* We have exclusive access to this iclog. */
+			bool	completed;
+
+			if (xlog_force_and_check_iclog(iclog, &completed))
+				goto out_error;
+
+			if (completed)
+				goto out_unlock;
+		} else {
+			/*
+			 * Someone else is still writing to this iclog, so we
+			 * need to ensure that when they release the iclog it
+			 * gets synced immediately as we may be waiting on it.
+			 */
+			xlog_state_switch_iclogs(log, iclog, 0);
+		}
+	}
+
+	/*
+	 * The iclog we are about to wait on may contain the checkpoint pushed
+	 * by the above xlog_cil_force() call, but it may not have been pushed
+	 * to disk yet. Like the ACTIVE case above, we need to make sure caches
+	 * are flushed when this iclog is written.
+	 */
+	if (iclog->ic_state == XLOG_STATE_WANT_SYNC)
+		iclog->ic_flags |= XLOG_ICL_NEED_FLUSH | XLOG_ICL_NEED_FUA;
+
+	if (flags & XFS_LOG_SYNC)
+		return xlog_wait_on_iclog(iclog);
+out_unlock:
+	spin_unlock(&log->l_icloglock);
+	return 0;
+out_error:
+	spin_unlock(&log->l_icloglock);
+	return -EIO;
+}
+
+/*
+ * Force the log to a specific LSN.
+ *
+ * If an iclog with that lsn can be found:
+ *	If it is in the DIRTY state, just return.
+ *	If it is in the ACTIVE state, move the in-core log into the WANT_SYNC
+ *		state and go to sleep or return.
+ *	If it is in any other state, go to sleep or return.
+ *
+ * Synchronous forces are implemented with a wait queue.  All callers trying
+ * to force a given lsn to disk must wait on the queue attached to the
+ * specific in-core log.  When given in-core log finally completes its write
+ * to disk, that thread will wake up all threads waiting on the queue.
+ */
+static int
+xlog_force_lsn(
+	struct xlog		*log,
+	xfs_lsn_t		lsn,
+	uint			flags,
+	int			*log_flushed,
+	bool			already_slept)
+{
+	struct xlog_in_core	*iclog;
+	bool			completed;
+
+	spin_lock(&log->l_icloglock);
+	if (xlog_is_shutdown(log))
+		goto out_error;
+
+	iclog = log->l_iclog;
+	while (be64_to_cpu(iclog->ic_header.h_lsn) != lsn) {
+		trace_xlog_iclog_force_lsn(iclog, _RET_IP_);
+		iclog = iclog->ic_next;
+		if (iclog == log->l_iclog)
+			goto out_unlock;
+	}
+
+	switch (iclog->ic_state) {
+	case XLOG_STATE_ACTIVE:
+		/*
+		 * We sleep here if we haven't already slept (e.g. this is the
+		 * first time we've looked at the correct iclog buf) and the
+		 * buffer before us is going to be sync'ed.  The reason for this
+		 * is that if we are doing sync transactions here, by waiting
+		 * for the previous I/O to complete, we can allow a few more
+		 * transactions into this iclog before we close it down.
+		 *
+		 * Otherwise, we mark the buffer WANT_SYNC, and bump up the
+		 * refcnt so we can release the log (which drops the ref count).
+		 * The state switch keeps new transaction commits from using
+		 * this buffer.  When the current commits finish writing into
+		 * the buffer, the refcount will drop to zero and the buffer
+		 * will go out then.
+		 */
+		if (!already_slept &&
+		    (iclog->ic_prev->ic_state == XLOG_STATE_WANT_SYNC ||
+		     iclog->ic_prev->ic_state == XLOG_STATE_SYNCING)) {
+			xlog_wait(&iclog->ic_prev->ic_write_wait,
+					&log->l_icloglock);
+			return -EAGAIN;
+		}
+		if (xlog_force_and_check_iclog(iclog, &completed))
+			goto out_error;
+		if (log_flushed)
+			*log_flushed = 1;
+		if (completed)
+			goto out_unlock;
+		break;
+	case XLOG_STATE_WANT_SYNC:
+		/*
+		 * This iclog may contain the checkpoint pushed by the
+		 * xlog_cil_force_seq() call, but there are other writers still
+		 * accessing it so it hasn't been pushed to disk yet. Like the
+		 * ACTIVE case above, we need to make sure caches are flushed
+		 * when this iclog is written.
+		 */
+		iclog->ic_flags |= XLOG_ICL_NEED_FLUSH | XLOG_ICL_NEED_FUA;
+		break;
+	default:
+		/*
+		 * The entire checkpoint was written by the CIL force and is on
+		 * its way to disk already. It will be stable when it
+		 * completes, so we don't need to manipulate caches here at all.
+		 * We just need to wait for completion if necessary.
+		 */
+		break;
+	}
+
+	if (flags & XFS_LOG_SYNC)
+		return xlog_wait_on_iclog(iclog);
+out_unlock:
+	spin_unlock(&log->l_icloglock);
+	return 0;
+out_error:
+	spin_unlock(&log->l_icloglock);
+	return -EIO;
+}
+
+/*
+ * Force the log to a specific checkpoint sequence.
+ *
+ * First force the CIL so that all the required changes have been flushed to the
+ * iclogs. If the CIL force completed it will return a commit LSN that indicates
+ * the iclog that needs to be flushed to stable storage. If the caller needs
+ * a synchronous log force, we will wait on the iclog with the LSN returned by
+ * xlog_cil_force_seq() to be completed.
+ */
+int
+xfs_log_force_seq(
+	struct xfs_mount	*mp,
+	xfs_csn_t		seq,
+	uint			flags,
+	int			*log_flushed)
+{
+	struct xlog		*log = mp->m_log;
+	xfs_lsn_t		lsn;
+	int			ret;
+	ASSERT(seq != 0);
+
+	XFS_STATS_INC(mp, xs_log_force);
+	trace_xfs_log_force(mp, seq, _RET_IP_);
+
+	lsn = xlog_cil_force_seq(log, seq);
+	if (lsn == NULLCOMMITLSN)
+		return 0;
+
+	ret = xlog_force_lsn(log, lsn, flags, log_flushed, false);
+	if (ret == -EAGAIN) {
+		XFS_STATS_INC(mp, xs_log_force_sleep);
+		ret = xlog_force_lsn(log, lsn, flags, log_flushed, true);
+	}
+	return ret;
+}
+
+/*
+ * Free a used ticket when its refcount falls to zero.
+ */
+void
+xfs_log_ticket_put(
+	xlog_ticket_t	*ticket)
+{
+	ASSERT(atomic_read(&ticket->t_ref) > 0);
+	if (atomic_dec_and_test(&ticket->t_ref))
+		kmem_cache_free(xfs_log_ticket_cache, ticket);
+}
+
+xlog_ticket_t *
+xfs_log_ticket_get(
+	xlog_ticket_t	*ticket)
+{
+	ASSERT(atomic_read(&ticket->t_ref) > 0);
+	atomic_inc(&ticket->t_ref);
+	return ticket;
+}
+
+/*
+ * Figure out the total log space unit (in bytes) that would be
+ * required for a log ticket.
+ */
+static int
+xlog_calc_unit_res(
+	struct xlog		*log,
+	int			unit_bytes,
+	int			*niclogs)
+{
+	int			iclog_space;
+	uint			num_headers;
+
+	/*
+	 * Permanent reservations have up to 'cnt'-1 active log operations
+	 * in the log.  A unit in this case is the amount of space for one
+	 * of these log operations.  Normal reservations have a cnt of 1
+	 * and their unit amount is the total amount of space required.
+	 *
+	 * The following lines of code account for non-transaction data
+	 * which occupy space in the on-disk log.
+	 *
+	 * Normal form of a transaction is:
+	 * <oph><trans-hdr><start-oph><reg1-oph><reg1><reg2-oph>...<commit-oph>
+	 * and then there are LR hdrs, split-recs and roundoff at end of syncs.
+	 *
+	 * We need to account for all the leadup data and trailer data
+	 * around the transaction data.
+	 * And then we need to account for the worst case in terms of using
+	 * more space.
+	 * The worst case will happen if:
+	 * - the placement of the transaction happens to be such that the
+	 *   roundoff is at its maximum
+	 * - the transaction data is synced before the commit record is synced
+	 *   i.e. <transaction-data><roundoff> | <commit-rec><roundoff>
+	 *   Therefore the commit record is in its own Log Record.
+	 *   This can happen as the commit record is called with its
+	 *   own region to xlog_write().
+	 *   This then means that in the worst case, roundoff can happen for
+	 *   the commit-rec as well.
+	 *   The commit-rec is smaller than padding in this scenario and so it is
+	 *   not added separately.
+	 */
+
+	/* for trans header */
+	unit_bytes += sizeof(xlog_op_header_t);
+	unit_bytes += sizeof(xfs_trans_header_t);
+
+	/* for start-rec */
+	unit_bytes += sizeof(xlog_op_header_t);
+
+	/*
+	 * for LR headers - the space for data in an iclog is the size minus
+	 * the space used for the headers. If we use the iclog size, then we
+	 * undercalculate the number of headers required.
+	 *
+	 * Furthermore - the addition of op headers for split-recs might
+	 * increase the space required enough to require more log and op
+	 * headers, so take that into account too.
+	 *
+	 * IMPORTANT: This reservation makes the assumption that if this
+	 * transaction is the first in an iclog and hence has the LR headers
+	 * accounted to it, then the remaining space in the iclog is
+	 * exclusively for this transaction.  i.e. if the transaction is larger
+	 * than the iclog, it will be the only thing in that iclog.
+	 * Fundamentally, this means we must pass the entire log vector to
+	 * xlog_write to guarantee this.
+	 */
+	iclog_space = log->l_iclog_size - log->l_iclog_hsize;
+	num_headers = howmany(unit_bytes, iclog_space);
+
+	/* for split-recs - ophdrs added when data split over LRs */
+	unit_bytes += sizeof(xlog_op_header_t) * num_headers;
+
+	/* add extra header reservations if we overrun */
+	while (!num_headers ||
+	       howmany(unit_bytes, iclog_space) > num_headers) {
+		unit_bytes += sizeof(xlog_op_header_t);
+		num_headers++;
+	}
+	unit_bytes += log->l_iclog_hsize * num_headers;
+
+	/* for commit-rec LR header - note: padding will subsume the ophdr */
+	unit_bytes += log->l_iclog_hsize;
+
+	/* roundoff padding for transaction data and one for commit record */
+	unit_bytes += 2 * log->l_iclog_roundoff;
+
+	if (niclogs)
+		*niclogs = num_headers;
+	return unit_bytes;
+}
+
+int
+xfs_log_calc_unit_res(
+	struct xfs_mount	*mp,
+	int			unit_bytes)
+{
+	return xlog_calc_unit_res(mp->m_log, unit_bytes, NULL);
+}
+
+/*
+ * Allocate and initialise a new log ticket.
+ */
+struct xlog_ticket *
+xlog_ticket_alloc(
+	struct xlog		*log,
+	int			unit_bytes,
+	int			cnt,
+	bool			permanent)
+{
+	struct xlog_ticket	*tic;
+	int			unit_res;
+
+	tic = kmem_cache_zalloc(xfs_log_ticket_cache, GFP_NOFS | __GFP_NOFAIL);
+
+	unit_res = xlog_calc_unit_res(log, unit_bytes, &tic->t_iclog_hdrs);
+
+	atomic_set(&tic->t_ref, 1);
+	tic->t_task		= current;
+	INIT_LIST_HEAD(&tic->t_queue);
+	tic->t_unit_res		= unit_res;
+	tic->t_curr_res		= unit_res;
+	tic->t_cnt		= cnt;
+	tic->t_ocnt		= cnt;
+	tic->t_tid		= get_random_u32();
+	if (permanent)
+		tic->t_flags |= XLOG_TIC_PERM_RESERV;
+
+	return tic;
+}
+
+#if defined(DEBUG)
+/*
+ * Check to make sure the grant write head didn't just over lap the tail.  If
+ * the cycles are the same, we can't be overlapping.  Otherwise, make sure that
+ * the cycles differ by exactly one and check the byte count.
+ *
+ * This check is run unlocked, so can give false positives. Rather than assert
+ * on failures, use a warn-once flag and a panic tag to allow the admin to
+ * determine if they want to panic the machine when such an error occurs. For
+ * debug kernels this will have the same effect as using an assert but, unlinke
+ * an assert, it can be turned off at runtime.
+ */
+STATIC void
+xlog_verify_grant_tail(
+	struct xlog	*log)
+{
+	int		tail_cycle, tail_blocks;
+	int		cycle, space;
+
+	xlog_crack_grant_head(&log->l_write_head.grant, &cycle, &space);
+	xlog_crack_atomic_lsn(&log->l_tail_lsn, &tail_cycle, &tail_blocks);
+	if (tail_cycle != cycle) {
+		if (cycle - 1 != tail_cycle &&
+		    !test_and_set_bit(XLOG_TAIL_WARN, &log->l_opstate)) {
+			xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
+				"%s: cycle - 1 != tail_cycle", __func__);
+		}
+
+		if (space > BBTOB(tail_blocks) &&
+		    !test_and_set_bit(XLOG_TAIL_WARN, &log->l_opstate)) {
+			xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
+				"%s: space > BBTOB(tail_blocks)", __func__);
+		}
+	}
+}
+
+/* check if it will fit */
+STATIC void
+xlog_verify_tail_lsn(
+	struct xlog		*log,
+	struct xlog_in_core	*iclog)
+{
+	xfs_lsn_t	tail_lsn = be64_to_cpu(iclog->ic_header.h_tail_lsn);
+	int		blocks;
+
+    if (CYCLE_LSN(tail_lsn) == log->l_prev_cycle) {
+	blocks =
+	    log->l_logBBsize - (log->l_prev_block - BLOCK_LSN(tail_lsn));
+	if (blocks < BTOBB(iclog->ic_offset)+BTOBB(log->l_iclog_hsize))
+		xfs_emerg(log->l_mp, "%s: ran out of log space", __func__);
+    } else {
+	ASSERT(CYCLE_LSN(tail_lsn)+1 == log->l_prev_cycle);
+
+	if (BLOCK_LSN(tail_lsn) == log->l_prev_block)
+		xfs_emerg(log->l_mp, "%s: tail wrapped", __func__);
+
+	blocks = BLOCK_LSN(tail_lsn) - log->l_prev_block;
+	if (blocks < BTOBB(iclog->ic_offset) + 1)
+		xfs_emerg(log->l_mp, "%s: ran out of log space", __func__);
+    }
+}
+
+/*
+ * Perform a number of checks on the iclog before writing to disk.
+ *
+ * 1. Make sure the iclogs are still circular
+ * 2. Make sure we have a good magic number
+ * 3. Make sure we don't have magic numbers in the data
+ * 4. Check fields of each log operation header for:
+ *	A. Valid client identifier
+ *	B. tid ptr value falls in valid ptr space (user space code)
+ *	C. Length in log record header is correct according to the
+ *		individual operation headers within record.
+ * 5. When a bwrite will occur within 5 blocks of the front of the physical
+ *	log, check the preceding blocks of the physical log to make sure all
+ *	the cycle numbers agree with the current cycle number.
+ */
+STATIC void
+xlog_verify_iclog(
+	struct xlog		*log,
+	struct xlog_in_core	*iclog,
+	int			count)
+{
+	xlog_op_header_t	*ophead;
+	xlog_in_core_t		*icptr;
+	xlog_in_core_2_t	*xhdr;
+	void			*base_ptr, *ptr, *p;
+	ptrdiff_t		field_offset;
+	uint8_t			clientid;
+	int			len, i, j, k, op_len;
+	int			idx;
+
+	/* check validity of iclog pointers */
+	spin_lock(&log->l_icloglock);
+	icptr = log->l_iclog;
+	for (i = 0; i < log->l_iclog_bufs; i++, icptr = icptr->ic_next)
+		ASSERT(icptr);
+
+	if (icptr != log->l_iclog)
+		xfs_emerg(log->l_mp, "%s: corrupt iclog ring", __func__);
+	spin_unlock(&log->l_icloglock);
+
+	/* check log magic numbers */
+	if (iclog->ic_header.h_magicno != cpu_to_be32(XLOG_HEADER_MAGIC_NUM))
+		xfs_emerg(log->l_mp, "%s: invalid magic num", __func__);
+
+	base_ptr = ptr = &iclog->ic_header;
+	p = &iclog->ic_header;
+	for (ptr += BBSIZE; ptr < base_ptr + count; ptr += BBSIZE) {
+		if (*(__be32 *)ptr == cpu_to_be32(XLOG_HEADER_MAGIC_NUM))
+			xfs_emerg(log->l_mp, "%s: unexpected magic num",
+				__func__);
+	}
+
+	/* check fields */
+	len = be32_to_cpu(iclog->ic_header.h_num_logops);
+	base_ptr = ptr = iclog->ic_datap;
+	ophead = ptr;
+	xhdr = iclog->ic_data;
+	for (i = 0; i < len; i++) {
+		ophead = ptr;
+
+		/* clientid is only 1 byte */
+		p = &ophead->oh_clientid;
+		field_offset = p - base_ptr;
+		if (field_offset & 0x1ff) {
+			clientid = ophead->oh_clientid;
+		} else {
+			idx = BTOBBT((void *)&ophead->oh_clientid - iclog->ic_datap);
+			if (idx >= (XLOG_HEADER_CYCLE_SIZE / BBSIZE)) {
+				j = idx / (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
+				k = idx % (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
+				clientid = xlog_get_client_id(
+					xhdr[j].hic_xheader.xh_cycle_data[k]);
+			} else {
+				clientid = xlog_get_client_id(
+					iclog->ic_header.h_cycle_data[idx]);
+			}
+		}
+		if (clientid != XFS_TRANSACTION && clientid != XFS_LOG) {
+			xfs_warn(log->l_mp,
+				"%s: op %d invalid clientid %d op "PTR_FMT" offset 0x%lx",
+				__func__, i, clientid, ophead,
+				(unsigned long)field_offset);
+		}
+
+		/* check length */
+		p = &ophead->oh_len;
+		field_offset = p - base_ptr;
+		if (field_offset & 0x1ff) {
+			op_len = be32_to_cpu(ophead->oh_len);
+		} else {
+			idx = BTOBBT((void *)&ophead->oh_len - iclog->ic_datap);
+			if (idx >= (XLOG_HEADER_CYCLE_SIZE / BBSIZE)) {
+				j = idx / (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
+				k = idx % (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
+				op_len = be32_to_cpu(xhdr[j].hic_xheader.xh_cycle_data[k]);
+			} else {
+				op_len = be32_to_cpu(iclog->ic_header.h_cycle_data[idx]);
+			}
+		}
+		ptr += sizeof(xlog_op_header_t) + op_len;
+	}
+}
+#endif
+
+/*
+ * Perform a forced shutdown on the log.
+ *
+ * This can be called from low level log code to trigger a shutdown, or from the
+ * high level mount shutdown code when the mount shuts down.
+ *
+ * Our main objectives here are to make sure that:
+ *	a. if the shutdown was not due to a log IO error, flush the logs to
+ *	   disk. Anything modified after this is ignored.
+ *	b. the log gets atomically marked 'XLOG_IO_ERROR' for all interested
+ *	   parties to find out. Nothing new gets queued after this is done.
+ *	c. Tasks sleeping on log reservations, pinned objects and
+ *	   other resources get woken up.
+ *	d. The mount is also marked as shut down so that log triggered shutdowns
+ *	   still behave the same as if they called xfs_forced_shutdown().
+ *
+ * Return true if the shutdown cause was a log IO error and we actually shut the
+ * log down.
+ */
+bool
+xlog_force_shutdown(
+	struct xlog	*log,
+	uint32_t	shutdown_flags)
+{
+	bool		log_error = (shutdown_flags & SHUTDOWN_LOG_IO_ERROR);
+
+	if (!log)
+		return false;
+
+	/*
+	 * Flush all the completed transactions to disk before marking the log
+	 * being shut down. We need to do this first as shutting down the log
+	 * before the force will prevent the log force from flushing the iclogs
+	 * to disk.
+	 *
+	 * When we are in recovery, there are no transactions to flush, and
+	 * we don't want to touch the log because we don't want to perturb the
+	 * current head/tail for future recovery attempts. Hence we need to
+	 * avoid a log force in this case.
+	 *
+	 * If we are shutting down due to a log IO error, then we must avoid
+	 * trying to write the log as that may just result in more IO errors and
+	 * an endless shutdown/force loop.
+	 */
+	if (!log_error && !xlog_in_recovery(log))
+		xfs_log_force(log->l_mp, XFS_LOG_SYNC);
+
+	/*
+	 * Atomically set the shutdown state. If the shutdown state is already
+	 * set, there someone else is performing the shutdown and so we are done
+	 * here. This should never happen because we should only ever get called
+	 * once by the first shutdown caller.
+	 *
+	 * Much of the log state machine transitions assume that shutdown state
+	 * cannot change once they hold the log->l_icloglock. Hence we need to
+	 * hold that lock here, even though we use the atomic test_and_set_bit()
+	 * operation to set the shutdown state.
+	 */
+	spin_lock(&log->l_icloglock);
+	if (test_and_set_bit(XLOG_IO_ERROR, &log->l_opstate)) {
+		spin_unlock(&log->l_icloglock);
+		return false;
+	}
+	spin_unlock(&log->l_icloglock);
+
+	/*
+	 * If this log shutdown also sets the mount shutdown state, issue a
+	 * shutdown warning message.
+	 */
+	if (!test_and_set_bit(XFS_OPSTATE_SHUTDOWN, &log->l_mp->m_opstate)) {
+		xfs_alert_tag(log->l_mp, XFS_PTAG_SHUTDOWN_LOGERROR,
+"Filesystem has been shut down due to log error (0x%x).",
+				shutdown_flags);
+		xfs_alert(log->l_mp,
+"Please unmount the filesystem and rectify the problem(s).");
+		if (xfs_error_level >= XFS_ERRLEVEL_HIGH)
+			xfs_stack_trace();
+	}
+
+	/*
+	 * We don't want anybody waiting for log reservations after this. That
+	 * means we have to wake up everybody queued up on reserveq as well as
+	 * writeq.  In addition, we make sure in xlog_{re}grant_log_space that
+	 * we don't enqueue anything once the SHUTDOWN flag is set, and this
+	 * action is protected by the grant locks.
+	 */
+	xlog_grant_head_wake_all(&log->l_reserve_head);
+	xlog_grant_head_wake_all(&log->l_write_head);
+
+	/*
+	 * Wake up everybody waiting on xfs_log_force. Wake the CIL push first
+	 * as if the log writes were completed. The abort handling in the log
+	 * item committed callback functions will do this again under lock to
+	 * avoid races.
+	 */
+	spin_lock(&log->l_cilp->xc_push_lock);
+	wake_up_all(&log->l_cilp->xc_start_wait);
+	wake_up_all(&log->l_cilp->xc_commit_wait);
+	spin_unlock(&log->l_cilp->xc_push_lock);
+
+	spin_lock(&log->l_icloglock);
+	xlog_state_shutdown_callbacks(log);
+	spin_unlock(&log->l_icloglock);
+
+	wake_up_var(&log->l_opstate);
+	return log_error;
+}
+
+STATIC int
+xlog_iclogs_empty(
+	struct xlog	*log)
+{
+	xlog_in_core_t	*iclog;
+
+	iclog = log->l_iclog;
+	do {
+		/* endianness does not matter here, zero is zero in
+		 * any language.
+		 */
+		if (iclog->ic_header.h_num_logops)
+			return 0;
+		iclog = iclog->ic_next;
+	} while (iclog != log->l_iclog);
+	return 1;
+}
+
+/*
+ * Verify that an LSN stamped into a piece of metadata is valid. This is
+ * intended for use in read verifiers on v5 superblocks.
+ */
+bool
+xfs_log_check_lsn(
+	struct xfs_mount	*mp,
+	xfs_lsn_t		lsn)
+{
+	struct xlog		*log = mp->m_log;
+	bool			valid;
+
+	/*
+	 * norecovery mode skips mount-time log processing and unconditionally
+	 * resets the in-core LSN. We can't validate in this mode, but
+	 * modifications are not allowed anyways so just return true.
+	 */
+	if (xfs_has_norecovery(mp))
+		return true;
+
+	/*
+	 * Some metadata LSNs are initialized to NULL (e.g., the agfl). This is
+	 * handled by recovery and thus safe to ignore here.
+	 */
+	if (lsn == NULLCOMMITLSN)
+		return true;
+
+	valid = xlog_valid_lsn(mp->m_log, lsn);
+
+	/* warn the user about what's gone wrong before verifier failure */
+	if (!valid) {
+		spin_lock(&log->l_icloglock);
+		xfs_warn(mp,
+"Corruption warning: Metadata has LSN (%d:%d) ahead of current LSN (%d:%d). "
+"Please unmount and run xfs_repair (>= v4.3) to resolve.",
+			 CYCLE_LSN(lsn), BLOCK_LSN(lsn),
+			 log->l_curr_cycle, log->l_curr_block);
+		spin_unlock(&log->l_icloglock);
+	}
+
+	return valid;
+}
+
+/*
+ * Notify the log that we're about to start using a feature that is protected
+ * by a log incompat feature flag.  This will prevent log covering from
+ * clearing those flags.
+ */
+void
+xlog_use_incompat_feat(
+	struct xlog		*log)
+{
+	down_read(&log->l_incompat_users);
+}
+
+/* Notify the log that we've finished using log incompat features. */
+void
+xlog_drop_incompat_feat(
+	struct xlog		*log)
+{
+	up_read(&log->l_incompat_users);
+}