text: // 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"
  
  kmem_zone_t	*xfs_log_ticket_zone;
  
  /* 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 int
  xlog_state_get_iclog_space(
  	struct xlog		*log,
  	int			len,
  	struct xlog_in_core	**iclog,
  	struct xlog_ticket	*ticket,
  	int			*continued_write,
  	int			*logoffsetp);
  STATIC void
  xlog_state_switch_iclogs(
  	struct xlog		*log,
  	struct xlog_in_core	*iclog,
  	int			eventual_size);
  STATIC void
  xlog_grant_push_ail(
  	struct xlog		*log,
  	int			need_bytes);
  STATIC void
  xlog_sync(
  	struct xlog		*log,
  	struct xlog_in_core	*iclog);
  #if defined(DEBUG)
  STATIC void
  xlog_verify_dest_ptr(
  	struct xlog		*log,
  	void			*ptr);
  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,
  	xfs_lsn_t		tail_lsn);
  #else
  #define xlog_verify_dest_ptr(a,b)
  #define xlog_verify_grant_tail(a)
  #define xlog_verify_iclog(a,b,c)
  #define xlog_verify_tail_lsn(a,b,c)
  #endif
  
  STATIC int
  xlog_iclogs_empty(
  	struct xlog		*log);
  
  static int
  xfs_log_cover(struct xfs_mount *);
  
  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;
  	} else {
  		if (tic->t_flags & XLOG_TIC_PERM_RESERV)
  			return tic->t_unit_res * tic->t_cnt;
  		else
  			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_FORCED_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_FORCED_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(!(log->l_flags & XLOG_ACTIVE_RECOVERY));
  
  	/*
  	 * 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;
  }
  
  static void
  xlog_tic_reset_res(xlog_ticket_t *tic)
  {
  	tic->t_res_num = 0;
  	tic->t_res_arr_sum = 0;
  	tic->t_res_num_ophdrs = 0;
  }
  
  static void
  xlog_tic_add_region(xlog_ticket_t *tic, uint len, uint type)
  {
  	if (tic->t_res_num == XLOG_TIC_LEN_MAX) {
  		/* add to overflow and start again */
  		tic->t_res_o_flow += tic->t_res_arr_sum;
  		tic->t_res_num = 0;
  		tic->t_res_arr_sum = 0;
  	}
  
  	tic->t_res_arr[tic->t_res_num].r_len = len;
  	tic->t_res_arr[tic->t_res_num].r_type = type;
  	tic->t_res_arr_sum += len;
  	tic->t_res_num++;
  }
  
  bool
  xfs_log_writable(
  	struct xfs_mount	*mp)
  {
  	/*
  	 * Never write to the log on norecovery mounts, if the block device is
  	 * read-only, or if the filesystem is shutdown. Read-only mounts still
  	 * allow internal writes for log recovery and unmount purposes, so don't
  	 * restrict that case here.
  	 */
  	if (mp->m_flags & XFS_MOUNT_NORECOVERY)
  		return false;
  	if (xfs_readonly_buftarg(mp->m_log->l_targ))
  		return false;
  	if (XFS_FORCED_SHUTDOWN(mp))
  		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_FORCED_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;
  	xlog_tic_reset_res(tic);
  
  	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,
  	uint8_t		 	client,
  	bool			permanent)
  {
  	struct xlog		*log = mp->m_log;
  	struct xlog_ticket	*tic;
  	int			need_bytes;
  	int			error = 0;
  
  	ASSERT(client == XFS_TRANSACTION || client == XFS_LOG);
  
  	if (XLOG_FORCED_SHUTDOWN(log))
  		return -EIO;
  
  	XFS_STATS_INC(mp, xs_try_logspace);
  
  	ASSERT(*ticp == NULL);
  	tic = xlog_ticket_alloc(log, unit_bytes, cnt, client, 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;
  }
  
  static bool
  __xlog_state_release_iclog(
  	struct xlog		*log,
  	struct xlog_in_core	*iclog)
  {
  	lockdep_assert_held(&log->l_icloglock);
  
  	if (iclog->ic_state == XLOG_STATE_WANT_SYNC) {
  		/* update tail before writing to iclog */
  		xfs_lsn_t tail_lsn = xlog_assign_tail_lsn(log->l_mp);
  
  		iclog->ic_state = XLOG_STATE_SYNCING;
  		iclog->ic_header.h_tail_lsn = cpu_to_be64(tail_lsn);
  		xlog_verify_tail_lsn(log, iclog, tail_lsn);
  		/* cycle incremented when incrementing curr_block */
  		return true;
  	}
  
  	ASSERT(iclog->ic_state == XLOG_STATE_ACTIVE);
  	return false;
  }
  
  /*
   * Flush iclog to disk if this is the last reference to the given iclog and the
   * it is in the WANT_SYNC state.
   */
  static int
  xlog_state_release_iclog(
  	struct xlog		*log,
  	struct xlog_in_core	*iclog)
  {
  	lockdep_assert_held(&log->l_icloglock);
  
  	if (iclog->ic_state == XLOG_STATE_IOERROR)
  		return -EIO;
  
  	if (atomic_dec_and_test(&iclog->ic_refcnt) &&
  	    __xlog_state_release_iclog(log, iclog)) {
  		spin_unlock(&log->l_icloglock);
  		xlog_sync(log, iclog);
  		spin_lock(&log->l_icloglock);
  	}
  
  	return 0;
  }
  
  void
  xfs_log_release_iclog(
  	struct xlog_in_core	*iclog)
  {
  	struct xlog		*log = iclog->ic_log;
  	bool			sync = false;
  
  	if (atomic_dec_and_lock(&iclog->ic_refcnt, &log->l_icloglock)) {
  		if (iclog->ic_state != XLOG_STATE_IOERROR)
  			sync = __xlog_state_release_iclog(log, iclog);
  		spin_unlock(&log->l_icloglock);
  	}
  
  	if (sync)
  		xlog_sync(log, iclog);
  }
  
  /*
   * 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)
  {
  	bool		fatal = xfs_sb_version_hascrc(&mp->m_sb);
  	int		error = 0;
  	int		min_logfsbs;
  
  	if (!(mp->m_flags & XFS_MOUNT_NORECOVERY)) {
  		xfs_notice(mp, "Mounting V%d Filesystem",
  			   XFS_SB_VERSION_NUM(&mp->m_sb));
  	} else {
  		xfs_notice(mp,
  "Mounting V%d filesystem in no-recovery mode. Filesystem will be inconsistent.",
  			   XFS_SB_VERSION_NUM(&mp->m_sb));
  		ASSERT(mp->m_flags & XFS_MOUNT_RDONLY);
  	}
  
  	mp->m_log = xlog_alloc_log(mp, log_target, blk_offset, num_bblks);
  	if (IS_ERR(mp->m_log)) {
  		error = PTR_ERR(mp->m_log);
  		goto out;
  	}
  
  	/*
  	 * Validate the given log space and drop a critical message via syslog
  	 * if the log size is too small that would lead to some unexpected
  	 * situations in transaction log space reservation stage.
  	 *
  	 * Note: 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 CRC 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);
  		error = -EINVAL;
  	} else if (mp->m_sb.sb_logblocks > XFS_MAX_LOG_BLOCKS) {
  		xfs_warn(mp,
  		"Log size %d blocks too large, maximum size is %lld blocks",
  			 mp->m_sb.sb_logblocks, XFS_MAX_LOG_BLOCKS);
  		error = -EINVAL;
  	} else if (XFS_FSB_TO_B(mp, mp->m_sb.sb_logblocks) > XFS_MAX_LOG_BYTES) {
  		xfs_warn(mp,
  		"log size %lld bytes too large, maximum size is %lld bytes",
  			 XFS_FSB_TO_B(mp, mp->m_sb.sb_logblocks),
  			 XFS_MAX_LOG_BYTES);
  		error = -EINVAL;
  	} else if (mp->m_sb.sb_logsunit > 1 &&
  		   mp->m_sb.sb_logsunit % mp->m_sb.sb_blocksize) {
  		xfs_warn(mp,
  		"log stripe unit %u bytes must be a multiple of block size",
  			 mp->m_sb.sb_logsunit);
  		error = -EINVAL;
  		fatal = true;
  	}
  	if (error) {
  		/*
  		 * Log check errors are always fatal on v5; or whenever bad
  		 * metadata leads to a crash.
  		 */
  		if (fatal) {
  			xfs_crit(mp, "AAIEEE! Log failed size checks. Abort!");
  			ASSERT(0);
  			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;
  	}
  	mp->m_log->l_ailp = mp->m_ail;
  
  	/*
  	 * skip log recovery on a norecovery mount.  pretend it all
  	 * just worked.
  	 */
  	if (!(mp->m_flags & XFS_MOUNT_NORECOVERY)) {
  		int	readonly = (mp->m_flags & XFS_MOUNT_RDONLY);
  
  		if (readonly)
  			mp->m_flags &= ~XFS_MOUNT_RDONLY;
  
  		error = xlog_recover(mp->m_log);
  
  		if (readonly)
  			mp->m_flags |= XFS_MOUNT_RDONLY;
  		if (error) {
  			xfs_warn(mp, "log mount/recovery failed: error %d",
  				error);
  			xlog_recover_cancel(mp->m_log);
  			goto out_destroy_ail;
  		}
  	}
  
  	error = xfs_sysfs_init(&mp->m_log->l_kobj, &xfs_log_ktype, &mp->m_kobj,
  			       "log");
  	if (error)
  		goto out_destroy_ail;
  
  	/* Normal transactions can now occur */
  	mp->m_log->l_flags &= ~XLOG_ACTIVE_RECOVERY;
  
  	/*
  	 * 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(mp->m_log);
  
  	return 0;
  
  out_destroy_ail:
  	xfs_trans_ail_destroy(mp);
  out_free_log:
  	xlog_dealloc_log(mp->m_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)
  {
  	int	error = 0;
  	bool	readonly = (mp->m_flags & XFS_MOUNT_RDONLY);
  	bool	recovered = mp->m_log->l_flags & XLOG_RECOVERY_NEEDED;
  
  	if (mp->m_flags & XFS_MOUNT_NORECOVERY) {
  		ASSERT(mp->m_flags & XFS_MOUNT_RDONLY);
  		return 0;
  	} else if (readonly) {
  		/* Allow unlinked processing to proceed */
  		mp->m_flags &= ~XFS_MOUNT_RDONLY;
  	}
  
  	/*
  	 * 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;
  	error = xlog_recover_finish(mp->m_log);
  	if (!error)
  		xfs_log_work_queue(mp);
  	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 (!error && recovered) {
  		xfs_log_force(mp, XFS_LOG_SYNC);
  		xfs_ail_push_all_sync(mp->m_ail);
  	}
  	xfs_buftarg_drain(mp->m_ddev_targp);
  
  	if (readonly)
  		mp->m_flags |= XFS_MOUNT_RDONLY;
  
  	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);
  }
  
  /*
   * Wait for the iclog to be written disk, or return an error if the log has been
   * shut down.
   */
  static int
  xlog_wait_on_iclog(
  	struct xlog_in_core	*iclog)
  		__releases(iclog->ic_log->l_icloglock)
  {
  	struct xlog		*log = iclog->ic_log;
  
  	if (!XLOG_FORCED_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_FORCED_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,
  	xfs_lsn_t		*lsn,
  	uint			flags)
  {
  	struct xfs_unmount_log_format ulf = {
  		.magic = XLOG_UNMOUNT_TYPE,
  	};
  	struct xfs_log_iovec reg = {
  		.i_addr = &ulf,
  		.i_len = sizeof(ulf),
  		.i_type = XLOG_REG_TYPE_UNMOUNT,
  	};
  	struct xfs_log_vec vec = {
  		.lv_niovecs = 1,
  		.lv_iovecp = &reg,
  	};
  
  	/* account for space used by record data */
  	ticket->t_curr_res -= sizeof(ulf);
  	return xlog_write(log, &vec, ticket, lsn, NULL, flags, false);
  }
  
  /*
   * 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;
  	xfs_lsn_t		lsn;
  	uint			flags = XLOG_UNMOUNT_TRANS;
  	int			error;
  
  	error = xfs_log_reserve(mp, 600, 1, &tic, XFS_LOG, 0);
  	if (error)
  		goto out_err;
  
  	error = xlog_write_unmount_record(log, tic, &lsn, flags);
  	/*
  	 * At this point, we're umounting anyway, so there's no point in
  	 * transitioning log state to IOERROR. Just continue...
  	 */
  out_err:
  	if (error)
  		xfs_alert(mp, "%s: unmount record failed", __func__);
  
  	spin_lock(&log->l_icloglock);
  	iclog = log->l_iclog;
  	atomic_inc(&iclog->ic_refcnt);
  	if (iclog->ic_state == XLOG_STATE_ACTIVE)
  		xlog_state_switch_iclogs(log, iclog, 0);
  	else
  		ASSERT(iclog->ic_state == XLOG_STATE_WANT_SYNC ||
  		       iclog->ic_state == XLOG_STATE_IOERROR);
  	error = xlog_state_release_iclog(log, 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_FORCED_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)
  {
  	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);
  
  	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_mountp = mp;
  	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_FORCED_SHUTDOWN(log))
  		return;
  
  	if (!list_empty_careful(&log->l_write_head.waiters)) {
  		ASSERT(!(log->l_flags & XLOG_ACTIVE_RECOVERY));
  
  		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(!(log->l_flags & XLOG_ACTIVE_RECOVERY));
  
  		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)) ||
  	       XFS_FORCED_SHUTDOWN(mp));
  
  	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_sb_version_haslazysbcount(&mp->m_sb))
  		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
   *
   * This code also handles the case where the reservation head is behind
   * the tail.  The details of this case are described below, but the end
   * result is that we return the size of the log as the amount of space left.
   */
  STATIC int
  xlog_space_left(
  	struct xlog	*log,
  	atomic64_t	*head)
  {
  	int		free_bytes;
  	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)
  		free_bytes = log->l_logsize - (head_bytes - tail_bytes);
  	else if (tail_cycle + 1 < head_cycle)
  		return 0;
  	else if (tail_cycle < head_cycle) {
  		ASSERT(tail_cycle == (head_cycle - 1));
  		free_bytes = tail_bytes - head_bytes;
  	} else {
  		/*
  		 * 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);
  		free_bytes = log->l_logsize;
  	}
  	return free_bytes;
  }
  
  
  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);
  		xfs_force_shutdown(log->l_mp, 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));
  }
  
  /*
   * 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.
  		 */
  		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;
  	log->l_flags	   |= XLOG_ACTIVE_RECOVERY;
  	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 */
  
  	xlog_grant_head_init(&log->l_reserve_head);
  	xlog_grant_head_init(&log->l_write_head);
  
  	error = -EFSCORRUPTED;
  	if (xfs_sb_version_hassector(&mp->m_sb)) {
  	        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_sb_version_haslogv2(&mp->m_sb)) {
  			xfs_warn(mp,
  		"log sector size (0x%x) invalid for configuration.",
  				log2_size);
  			goto out_free_log;
  		}
  	}
  	log->l_sectBBsize = 1 << log2_size;
  
  	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++) {
  		int align_mask = xfs_buftarg_dma_alignment(mp->m_logdev_targp);
  		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 = kmem_alloc_io(log->l_iclog_size, align_mask,
  						KM_MAYFAIL | KM_ZERO);
  		if (!iclog->ic_data)
  			goto out_free_iclog;
  #ifdef DEBUG
  		log->l_iclog_bak[i] = &iclog->ic_header;
  #endif
  		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_sb_version_haslogv2(&log->l_mp->m_sb) ? 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);
  		spin_lock_init(&iclog->ic_callback_lock);
  		INIT_LIST_HEAD(&iclog->ic_callbacks);
  		iclog->ic_datap = (char *)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 */
  
  /*
   * Write out the commit record of a transaction associated with the given
   * ticket to close off a running log write. Return the lsn of the commit record.
   */
  int
  xlog_commit_record(
  	struct xlog		*log,
  	struct xlog_ticket	*ticket,
  	struct xlog_in_core	**iclog,
  	xfs_lsn_t		*lsn)
  {
  	struct xfs_log_iovec reg = {
  		.i_addr = NULL,
  		.i_len = 0,
  		.i_type = XLOG_REG_TYPE_COMMIT,
  	};
  	struct xfs_log_vec vec = {
  		.lv_niovecs = 1,
  		.lv_iovecp = &reg,
  	};
  	int	error;
  
  	if (XLOG_FORCED_SHUTDOWN(log))
  		return -EIO;
  
  	error = xlog_write(log, &vec, ticket, lsn, iclog, XLOG_COMMIT_TRANS,
  			   false);
  	if (error)
  		xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR);
  	return error;
  }
  
  /*
   * 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_FORCED_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_sb_version_haslogv2(&log->l_mp->m_sb)) {
  		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_sb_version_haslogv2(&log->l_mp->m_sb)) {
  		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,
  	bool			need_flush)
  {
  	ASSERT(bno < log->l_logBBsize);
  
  	/*
  	 * 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 (unlikely(iclog->ic_state == XLOG_STATE_IOERROR)) {
  		/*
  		 * 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;
  	}
  
  	bio_init(&iclog->ic_bio, iclog->ic_bvec, howmany(count, PAGE_SIZE));
  	bio_set_dev(&iclog->ic_bio, log->l_targ->bt_bdev);
  	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;
  
  	/*
  	 * 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.
  	 */
  	iclog->ic_bio.bi_opf = REQ_OP_WRITE | REQ_META | REQ_SYNC |
  				REQ_IDLE | REQ_FUA;
  	if (need_flush)
  		iclog->ic_bio.bi_opf |= REQ_PREFLUSH;
  
  	if (xlog_map_iclog_data(&iclog->ic_bio, iclog->ic_data, count)) {
  		xfs_force_shutdown(log->l_mp, 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;
  	bool			use_lsunit;
  
  	use_lsunit = xfs_sb_version_haslogv2(&log->l_mp->m_sb) &&
  			log->l_mp->m_sb.sb_logsunit > 1;
  
  	/* Add for LR header */
  	count_init = log->l_iclog_hsize + iclog->ic_offset;
  
  	/* Round out the log write size */
  	if (use_lsunit) {
  		/* we have a v2 stripe unit to use */
  		count = XLOG_LSUNITTOB(log, XLOG_BTOLSUNIT(log, count_init));
  	} else {
  		count = BBTOB(BTOBB(count_init));
  	}
  
  	ASSERT(count >= count_init);
  	*roundoff = count - count_init;
  
  	if (use_lsunit)
  		ASSERT(*roundoff < log->l_mp->m_sb.sb_logsunit);
  	else
  		ASSERT(*roundoff < BBTOB(1));
  	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)
  {
  	unsigned int		count;		/* byte count of bwrite */
  	unsigned int		roundoff;       /* roundoff to BB or stripe */
  	uint64_t		bno;
  	unsigned int		size;
  	bool			need_flush = true, split = false;
  
  	ASSERT(atomic_read(&iclog->ic_refcnt) == 0);
  
  	count = xlog_calc_iclog_size(log, iclog, &roundoff);
  
  	/* move grant heads by roundoff in sync */
  	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_sb_version_haslogv2(&log->l_mp->m_sb))
  		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);
  		split = true;
  	}
  
  	/* 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
  
  	/*
  	 * Flush the data device before flushing the log to make sure all meta
  	 * data written back from the AIL actually made it to disk before
  	 * stamping the new log tail LSN into the log buffer.  For an external
  	 * log we need to issue the flush explicitly, and unfortunately
  	 * synchronously here; for an internal log we can simply use the block
  	 * layer state machine for preflushes.
  	 */
  	if (log->l_targ != log->l_mp->m_ddev_targp || split) {
  		xfs_blkdev_issue_flush(log->l_mp->m_ddev_targp);
  		need_flush = false;
  	}
  
  	xlog_verify_iclog(log, iclog, count);
  	xlog_write_iclog(log, iclog, bno, count, need_flush);
  }
  
  /*
   * Deallocate a log structure
   */
  STATIC void
  xlog_dealloc_log(
  	struct xlog	*log)
  {
  	xlog_in_core_t	*iclog, *next_iclog;
  	int		i;
  
  	xlog_cil_destroy(log);
  
  	/*
  	 * Cycle all the iclogbuf locks to make sure all log IO completion
  	 * is done before we tear down these buffers.
  	 */
  	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;
  	}
  
  	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)
  {
  	uint i;
  	uint ophdr_spc = ticket->t_res_num_ophdrs * (uint)sizeof(xlog_op_header_t);
  
  	/* match with XLOG_REG_TYPE_* in xfs_log.h */
  #define REG_TYPE_STR(type, str)	[XLOG_REG_TYPE_##type] = str
  	static char *res_type_str[] = {
  	    REG_TYPE_STR(BFORMAT, "bformat"),
  	    REG_TYPE_STR(BCHUNK, "bchunk"),
  	    REG_TYPE_STR(EFI_FORMAT, "efi_format"),
  	    REG_TYPE_STR(EFD_FORMAT, "efd_format"),
  	    REG_TYPE_STR(IFORMAT, "iformat"),
  	    REG_TYPE_STR(ICORE, "icore"),
  	    REG_TYPE_STR(IEXT, "iext"),
  	    REG_TYPE_STR(IBROOT, "ibroot"),
  	    REG_TYPE_STR(ILOCAL, "ilocal"),
  	    REG_TYPE_STR(IATTR_EXT, "iattr_ext"),
  	    REG_TYPE_STR(IATTR_BROOT, "iattr_broot"),
  	    REG_TYPE_STR(IATTR_LOCAL, "iattr_local"),
  	    REG_TYPE_STR(QFORMAT, "qformat"),
  	    REG_TYPE_STR(DQUOT, "dquot"),
  	    REG_TYPE_STR(QUOTAOFF, "quotaoff"),
  	    REG_TYPE_STR(LRHEADER, "LR header"),
  	    REG_TYPE_STR(UNMOUNT, "unmount"),
  	    REG_TYPE_STR(COMMIT, "commit"),
  	    REG_TYPE_STR(TRANSHDR, "trans header"),
  	    REG_TYPE_STR(ICREATE, "inode create"),
  	    REG_TYPE_STR(RUI_FORMAT, "rui_format"),
  	    REG_TYPE_STR(RUD_FORMAT, "rud_format"),
  	    REG_TYPE_STR(CUI_FORMAT, "cui_format"),
  	    REG_TYPE_STR(CUD_FORMAT, "cud_format"),
  	    REG_TYPE_STR(BUI_FORMAT, "bui_format"),
  	    REG_TYPE_STR(BUD_FORMAT, "bud_format"),
  	};
  	BUILD_BUG_ON(ARRAY_SIZE(res_type_str) != XLOG_REG_TYPE_MAX + 1);
  #undef REG_TYPE_STR
  
  	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, "  total reg   = %u bytes (o/flow = %u bytes)",
  		 ticket->t_res_arr_sum, ticket->t_res_o_flow);
  	xfs_warn(mp, "  ophdrs      = %u (ophdr space = %u bytes)",
  		 ticket->t_res_num_ophdrs, ophdr_spc);
  	xfs_warn(mp, "  ophdr + reg = %u bytes",
  		 ticket->t_res_arr_sum + ticket->t_res_o_flow + ophdr_spc);
  	xfs_warn(mp, "  num regions = %u",
  		 ticket->t_res_num);
  
  	for (i = 0; i < ticket->t_res_num; i++) {
  		uint r_type = ticket->t_res_arr[i].r_type;
  		xfs_warn(mp, "region[%u]: %s - %u bytes", i,
  			    ((r_type <= 0 || r_type > XLOG_REG_TYPE_MAX) ?
  			    "bad-rtype" : res_type_str[r_type]),
  			    ticket->t_res_arr[i].r_len);
  	}
  }
  
  /*
   * 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++;
  		}
  	}
  }
  
  /*
   * Calculate the potential space needed by the log vector.  We may need a start
   * record, and each region gets its own struct xlog_op_header and may need to be
   * double word aligned.
   */
  static int
  xlog_write_calc_vec_length(
  	struct xlog_ticket	*ticket,
  	struct xfs_log_vec	*log_vector,
  	bool			need_start_rec)
  {
  	struct xfs_log_vec	*lv;
  	int			headers = need_start_rec ? 1 : 0;
  	int			len = 0;
  	int			i;
  
  	for (lv = log_vector; lv; lv = lv->lv_next) {
  		/* we don't write ordered log vectors */
  		if (lv->lv_buf_len == XFS_LOG_VEC_ORDERED)
  			continue;
  
  		headers += lv->lv_niovecs;
  
  		for (i = 0; i < lv->lv_niovecs; i++) {
  			struct xfs_log_iovec	*vecp = &lv->lv_iovecp[i];
  
  			len += vecp->i_len;
  			xlog_tic_add_region(ticket, vecp->i_len, vecp->i_type);
  		}
  	}
  
  	ticket->t_res_num_ophdrs += headers;
  	len += headers * sizeof(struct xlog_op_header);
  
  	return len;
  }
  
  static void
  xlog_write_start_rec(
  	struct xlog_op_header	*ophdr,
  	struct xlog_ticket	*ticket)
  {
  	ophdr->oh_tid	= cpu_to_be32(ticket->t_tid);
  	ophdr->oh_clientid = ticket->t_clientid;
  	ophdr->oh_len = 0;
  	ophdr->oh_flags = XLOG_START_TRANS;
  	ophdr->oh_res2 = 0;
  }
  
  static xlog_op_header_t *
  xlog_write_setup_ophdr(
  	struct xlog		*log,
  	struct xlog_op_header	*ophdr,
  	struct xlog_ticket	*ticket,
  	uint			flags)
  {
  	ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
  	ophdr->oh_clientid = ticket->t_clientid;
  	ophdr->oh_res2 = 0;
  
  	/* are we copying a commit or unmount record? */
  	ophdr->oh_flags = flags;
  
  	/*
  	 * We've seen logs corrupted with bad transaction client ids.  This
  	 * makes sure that XFS doesn't generate them on.  Turn this into an EIO
  	 * and shut down the filesystem.
  	 */
  	switch (ophdr->oh_clientid)  {
  	case XFS_TRANSACTION:
  	case XFS_VOLUME:
  	case XFS_LOG:
  		break;
  	default:
  		xfs_warn(log->l_mp,
  			"Bad XFS transaction clientid 0x%x in ticket "PTR_FMT,
  			ophdr->oh_clientid, ticket);
  		return NULL;
  	}
  
  	return ophdr;
  }
  
  /*
   * Set up the parameters of the region copy into the log. This has
   * to handle region write split across multiple log buffers - this
   * state is kept external to this function so that this code can
   * be written in an obvious, self documenting manner.
   */
  static int
  xlog_write_setup_copy(
  	struct xlog_ticket	*ticket,
  	struct xlog_op_header	*ophdr,
  	int			space_available,
  	int			space_required,
  	int			*copy_off,
  	int			*copy_len,
  	int			*last_was_partial_copy,
  	int			*bytes_consumed)
  {
  	int			still_to_copy;
  
  	still_to_copy = space_required - *bytes_consumed;
  	*copy_off = *bytes_consumed;
  
  	if (still_to_copy <= space_available) {
  		/* write of region completes here */
  		*copy_len = still_to_copy;
  		ophdr->oh_len = cpu_to_be32(*copy_len);
  		if (*last_was_partial_copy)
  			ophdr->oh_flags |= (XLOG_END_TRANS|XLOG_WAS_CONT_TRANS);
  		*last_was_partial_copy = 0;
  		*bytes_consumed = 0;
  		return 0;
  	}
  
  	/* partial write of region, needs extra log op header reservation */
  	*copy_len = space_available;
  	ophdr->oh_len = cpu_to_be32(*copy_len);
  	ophdr->oh_flags |= XLOG_CONTINUE_TRANS;
  	if (*last_was_partial_copy)
  		ophdr->oh_flags |= XLOG_WAS_CONT_TRANS;
  	*bytes_consumed += *copy_len;
  	(*last_was_partial_copy)++;
  
  	/* account for new log op header */
  	ticket->t_curr_res -= sizeof(struct xlog_op_header);
  	ticket->t_res_num_ophdrs++;
  
  	return sizeof(struct xlog_op_header);
  }
  
  static int
  xlog_write_copy_finish(
  	struct xlog		*log,
  	struct xlog_in_core	*iclog,
  	uint			flags,
  	int			*record_cnt,
  	int			*data_cnt,
  	int			*partial_copy,
  	int			*partial_copy_len,
  	int			log_offset,
  	struct xlog_in_core	**commit_iclog)
  {
  	int			error;
  
  	if (*partial_copy) {
  		/*
  		 * This iclog has already been marked WANT_SYNC by
  		 * xlog_state_get_iclog_space.
  		 */
  		spin_lock(&log->l_icloglock);
  		xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
  		*record_cnt = 0;
  		*data_cnt = 0;
  		goto release_iclog;
  	}
  
  	*partial_copy = 0;
  	*partial_copy_len = 0;
  
  	if (iclog->ic_size - log_offset <= sizeof(xlog_op_header_t)) {
  		/* no more space in this iclog - push it. */
  		spin_lock(&log->l_icloglock);
  		xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
  		*record_cnt = 0;
  		*data_cnt = 0;
  
  		if (iclog->ic_state == XLOG_STATE_ACTIVE)
  			xlog_state_switch_iclogs(log, iclog, 0);
  		else
  			ASSERT(iclog->ic_state == XLOG_STATE_WANT_SYNC ||
  			       iclog->ic_state == XLOG_STATE_IOERROR);
  		if (!commit_iclog)
  			goto release_iclog;
  		spin_unlock(&log->l_icloglock);
  		ASSERT(flags & XLOG_COMMIT_TRANS);
  		*commit_iclog = iclog;
  	}
  
  	return 0;
  
  release_iclog:
  	error = xlog_state_release_iclog(log, iclog);
  	spin_unlock(&log->l_icloglock);
  	return error;
  }
  
  /*
   * 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_log_vec	*log_vector,
  	struct xlog_ticket	*ticket,
  	xfs_lsn_t		*start_lsn,
  	struct xlog_in_core	**commit_iclog,
  	uint			flags,
  	bool			need_start_rec)
  {
  	struct xlog_in_core	*iclog = NULL;
  	struct xfs_log_vec	*lv = log_vector;
  	struct xfs_log_iovec	*vecp = lv->lv_iovecp;
  	int			index = 0;
  	int			len;
  	int			partial_copy = 0;
  	int			partial_copy_len = 0;
  	int			contwr = 0;
  	int			record_cnt = 0;
  	int			data_cnt = 0;
  	int			error = 0;
  
  	/*
  	 * If this is a commit or unmount transaction, we don't need a start
  	 * record to be written.  We do, however, have to account for the
  	 * commit or unmount header that gets written. Hence we always have
  	 * to account for an extra xlog_op_header here.
  	 */
  	ticket->t_curr_res -= sizeof(struct xlog_op_header);
  	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);
  		xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR);
  	}
  
  	len = xlog_write_calc_vec_length(ticket, log_vector, need_start_rec);
  	*start_lsn = 0;
  	while (lv && (!lv->lv_niovecs || index < lv->lv_niovecs)) {
  		void		*ptr;
  		int		log_offset;
  
  		error = xlog_state_get_iclog_space(log, len, &iclog, ticket,
  						   &contwr, &log_offset);
  		if (error)
  			return error;
  
  		ASSERT(log_offset <= iclog->ic_size - 1);
  		ptr = iclog->ic_datap + log_offset;
  
  		/* start_lsn is the first lsn written to. That's all we need. */
  		if (!*start_lsn)
  			*start_lsn = be64_to_cpu(iclog->ic_header.h_lsn);
  
  		/*
  		 * This loop writes out as many regions as can fit in the amount
  		 * of space which was allocated by xlog_state_get_iclog_space().
  		 */
  		while (lv && (!lv->lv_niovecs || index < lv->lv_niovecs)) {
  			struct xfs_log_iovec	*reg;
  			struct xlog_op_header	*ophdr;
  			int			copy_len;
  			int			copy_off;
  			bool			ordered = false;
  
  			/* ordered log vectors have no regions to write */
  			if (lv->lv_buf_len == XFS_LOG_VEC_ORDERED) {
  				ASSERT(lv->lv_niovecs == 0);
  				ordered = true;
  				goto next_lv;
  			}
  
  			reg = &vecp[index];
  			ASSERT(reg->i_len % sizeof(int32_t) == 0);
  			ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
  
  			/*
  			 * Before we start formatting log vectors, we need to
  			 * write a start record. Only do this for the first
  			 * iclog we write to.
  			 */
  			if (need_start_rec) {
  				xlog_write_start_rec(ptr, ticket);
  				xlog_write_adv_cnt(&ptr, &len, &log_offset,
  						sizeof(struct xlog_op_header));
  			}
  
  			ophdr = xlog_write_setup_ophdr(log, ptr, ticket, flags);
  			if (!ophdr)
  				return -EIO;
  
  			xlog_write_adv_cnt(&ptr, &len, &log_offset,
  					   sizeof(struct xlog_op_header));
  
  			len += xlog_write_setup_copy(ticket, ophdr,
  						     iclog->ic_size-log_offset,
  						     reg->i_len,
  						     &copy_off, &copy_len,
  						     &partial_copy,
  						     &partial_copy_len);
  			xlog_verify_dest_ptr(log, ptr);
  
  			/*
  			 * Copy region.
  			 *
  			 * Unmount records just log an opheader, so can have
  			 * empty payloads with no data region to copy. Hence we
  			 * only copy the payload if the vector says it has data
  			 * to copy.
  			 */
  			ASSERT(copy_len >= 0);
  			if (copy_len > 0) {
  				memcpy(ptr, reg->i_addr + copy_off, copy_len);
  				xlog_write_adv_cnt(&ptr, &len, &log_offset,
  						   copy_len);
  			}
  			copy_len += sizeof(struct xlog_op_header);
  			record_cnt++;
  			if (need_start_rec) {
  				copy_len += sizeof(struct xlog_op_header);
  				record_cnt++;
  				need_start_rec = false;
  			}
  			data_cnt += contwr ? copy_len : 0;
  
  			error = xlog_write_copy_finish(log, iclog, flags,
  						       &record_cnt, &data_cnt,
  						       &partial_copy,
  						       &partial_copy_len,
  						       log_offset,
  						       commit_iclog);
  			if (error)
  				return error;
  
  			/*
  			 * if we had a partial copy, we need to get more iclog
  			 * space but we don't want to increment the region
  			 * index because there is still more is this region to
  			 * write.
  			 *
  			 * If we completed writing this region, and we flushed
  			 * the iclog (indicated by resetting of the record
  			 * count), then we also need to get more log space. If
  			 * this was the last record, though, we are done and
  			 * can just return.
  			 */
  			if (partial_copy)
  				break;
  
  			if (++index == lv->lv_niovecs) {
  next_lv:
  				lv = lv->lv_next;
  				index = 0;
  				if (lv)
  					vecp = lv->lv_iovecp;
  			}
  			if (record_cnt == 0 && !ordered) {
  				if (!lv)
  					return 0;
  				break;
  			}
  		}
  	}
  
  	ASSERT(len == 0);
  
  	spin_lock(&log->l_icloglock);
  	xlog_state_finish_copy(log, iclog, record_cnt, data_cnt);
  	if (commit_iclog) {
  		ASSERT(flags & XLOG_COMMIT_TRANS);
  		*commit_iclog = iclog;
  	} else {
  		error = xlog_state_release_iclog(log, iclog);
  	}
  	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));
  
  	/*
  	 * 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;
  }
  
  /*
   * 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;
  	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;
  
  	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)
  {
  	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,
  	bool			*ioerror)
  {
  	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_IOERROR:
  		/*
  		 * Between marking a filesystem SHUTDOWN and stopping the log,
  		 * we do flush all iclogs to disk (if there wasn't a log I/O
  		 * error). So, we do want things to go smoothly in case of just
  		 * a SHUTDOWN w/o a LOG_IO_ERROR.
  		 */
  		*ioerror = true;
  		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;
  	}
  }
  
  /*
   * Keep processing entries in the iclog callback list until we come around and
   * it is empty.  We need to atomically see that the list is empty and change the
   * state to DIRTY so that we don't miss any more callbacks being added.
   *
   * This function is called with the icloglock held and returns with it held. We
   * drop it while running callbacks, however, as holding it over thousands of
   * callbacks is unnecessary and causes excessive contention if we do.
   */
  static void
  xlog_state_do_iclog_callbacks(
  	struct xlog		*log,
  	struct xlog_in_core	*iclog)
  		__releases(&log->l_icloglock)
  		__acquires(&log->l_icloglock)
  {
  	spin_unlock(&log->l_icloglock);
  	spin_lock(&iclog->ic_callback_lock);
  	while (!list_empty(&iclog->ic_callbacks)) {
  		LIST_HEAD(tmp);
  
  		list_splice_init(&iclog->ic_callbacks, &tmp);
  
  		spin_unlock(&iclog->ic_callback_lock);
  		xlog_cil_process_committed(&tmp);
  		spin_lock(&iclog->ic_callback_lock);
  	}
  
  	/*
  	 * Pick up the icloglock while still holding the callback lock so we
  	 * serialise against anyone trying to add more callbacks to this iclog
  	 * now we've finished processing.
  	 */
  	spin_lock(&log->l_icloglock);
  	spin_unlock(&iclog->ic_callback_lock);
  }
  
  STATIC void
  xlog_state_do_callback(
  	struct xlog		*log)
  {
  	struct xlog_in_core	*iclog;
  	struct xlog_in_core	*first_iclog;
  	bool			cycled_icloglock;
  	bool			ioerror;
  	int			flushcnt = 0;
  	int			repeats = 0;
  
  	spin_lock(&log->l_icloglock);
  	do {
  		/*
  		 * Scan all iclogs starting with the one pointed to by the
  		 * log.  Reset this starting point each time the log is
  		 * unlocked (during callbacks).
  		 *
  		 * Keep looping through iclogs until one full pass is made
  		 * without running any callbacks.
  		 */
  		first_iclog = log->l_iclog;
  		iclog = log->l_iclog;
  		cycled_icloglock = false;
  		ioerror = false;
  		repeats++;
  
  		do {
  			if (xlog_state_iodone_process_iclog(log, iclog,
  							&ioerror))
  				break;
  
  			if (iclog->ic_state != XLOG_STATE_CALLBACK &&
  			    iclog->ic_state != XLOG_STATE_IOERROR) {
  				iclog = iclog->ic_next;
  				continue;
  			}
  
  			/*
  			 * Running callbacks will drop the icloglock which means
  			 * we'll have to run at least one more complete loop.
  			 */
  			cycled_icloglock = true;
  			xlog_state_do_iclog_callbacks(log, iclog);
  			if (XLOG_FORCED_SHUTDOWN(log))
  				wake_up_all(&iclog->ic_force_wait);
  			else
  				xlog_state_clean_iclog(log, iclog);
  			iclog = iclog->ic_next;
  		} while (first_iclog != iclog);
  
  		if (repeats > 5000) {
  			flushcnt += repeats;
  			repeats = 0;
  			xfs_warn(log->l_mp,
  				"%s: possible infinite loop (%d iterations)",
  				__func__, flushcnt);
  		}
  	} while (!ioerror && cycled_icloglock);
  
  	if (log->l_iclog->ic_state == XLOG_STATE_ACTIVE ||
  	    log->l_iclog->ic_state == XLOG_STATE_IOERROR)
  		wake_up_all(&log->l_flush_wait);
  
  	spin_unlock(&log->l_icloglock);
  }
  
  
  /*
   * Finish transitioning this iclog to the dirty state.
   *
   * Make sure that we completely execute this routine only when this is
   * the last call to the iclog.  There is a good chance that iclog flushes,
   * when we reach the end of the physical log, get turned into 2 separate
   * calls to bwrite.  Hence, one iclog flush could generate two calls to this
   * routine.  By using the reference count bwritecnt, we guarantee that only
   * the second completion goes through.
   *
   * 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);
  
  	/*
  	 * 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_FORCED_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			*continued_write,
  	int			*logoffsetp)
  {
  	int		  log_offset;
  	xlog_rec_header_t *head;
  	xlog_in_core_t	  *iclog;
  
  restart:
  	spin_lock(&log->l_icloglock);
  	if (XLOG_FORCED_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;
  
  	/* 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;
  		xlog_tic_add_region(ticket,
  				    log->l_iclog_hsize,
  				    XLOG_REG_TYPE_LRHEADER);
  		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);
  		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) {
  		*continued_write = 0;
  		iclog->ic_offset += len;
  	} else {
  		*continued_write = 1;
  		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;
  	xlog_tic_reset_res(ticket);
  
  	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;
  		xlog_tic_reset_res(ticket);
  	}
  
  	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.
   */
  STATIC 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);
  
  	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 (xfs_sb_version_haslogv2(&log->l_mp->m_sb) &&
  	    log->l_mp->m_sb.sb_logsunit > 1) {
  		uint32_t sunit_bb = BTOBB(log->l_mp->m_sb.sb_logsunit);
  		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;
  }
  
  /*
   * 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_lsn_t		lsn;
  
  	XFS_STATS_INC(mp, xs_log_force);
  	trace_xfs_log_force(mp, 0, _RET_IP_);
  
  	xlog_cil_force(log);
  
  	spin_lock(&log->l_icloglock);
  	iclog = log->l_iclog;
  	if (iclog->ic_state == XLOG_STATE_IOERROR)
  		goto out_error;
  
  	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 are the only one with access to this iclog.
  			 *
  			 * Flush it out now.  There should be a roundoff of zero
  			 * to show that someone has already taken care of the
  			 * roundoff from the previous sync.
  			 */
  			atomic_inc(&iclog->ic_refcnt);
  			lsn = be64_to_cpu(iclog->ic_header.h_lsn);
  			xlog_state_switch_iclogs(log, iclog, 0);
  			if (xlog_state_release_iclog(log, iclog))
  				goto out_error;
  
  			if (be64_to_cpu(iclog->ic_header.h_lsn) != lsn)
  				goto out_unlock;
  		} else {
  			/*
  			 * Someone else is writing to this iclog.
  			 *
  			 * Use its call to flush out the data.  However, the
  			 * other thread may not force out this LR, so we mark
  			 * it WANT_SYNC.
  			 */
  			xlog_state_switch_iclogs(log, iclog, 0);
  		}
  	} else {
  		/*
  		 * If the head iclog is not active nor dirty, we just attach
  		 * ourselves to the head and go to sleep if necessary.
  		 */
  		;
  	}
  
  	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;
  }
  
  static int
  __xfs_log_force_lsn(
  	struct xfs_mount	*mp,
  	xfs_lsn_t		lsn,
  	uint			flags,
  	int			*log_flushed,
  	bool			already_slept)
  {
  	struct xlog		*log = mp->m_log;
  	struct xlog_in_core	*iclog;
  
  	spin_lock(&log->l_icloglock);
  	iclog = log->l_iclog;
  	if (iclog->ic_state == XLOG_STATE_IOERROR)
  		goto out_error;
  
  	while (be64_to_cpu(iclog->ic_header.h_lsn) != lsn) {
  		iclog = iclog->ic_next;
  		if (iclog == log->l_iclog)
  			goto out_unlock;
  	}
  
  	if (iclog->ic_state == 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)) {
  			XFS_STATS_INC(mp, xs_log_force_sleep);
  
  			xlog_wait(&iclog->ic_prev->ic_write_wait,
  					&log->l_icloglock);
  			return -EAGAIN;
  		}
  		atomic_inc(&iclog->ic_refcnt);
  		xlog_state_switch_iclogs(log, iclog, 0);
  		if (xlog_state_release_iclog(log, iclog))
  			goto out_error;
  		if (log_flushed)
  			*log_flushed = 1;
  	}
  
  	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 in-core log to disk for a specific LSN.
   *
   * Find in-core log with lsn.
   *	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.
   */
  int
  xfs_log_force_lsn(
  	struct xfs_mount	*mp,
  	xfs_lsn_t		lsn,
  	uint			flags,
  	int			*log_flushed)
  {
  	int			ret;
  	ASSERT(lsn != 0);
  
  	XFS_STATS_INC(mp, xs_log_force);
  	trace_xfs_log_force(mp, lsn, _RET_IP_);
  
  	lsn = xlog_cil_force_lsn(mp->m_log, lsn);
  	if (lsn == NULLCOMMITLSN)
  		return 0;
  
  	ret = __xfs_log_force_lsn(mp, lsn, flags, log_flushed, false);
  	if (ret == -EAGAIN)
  		ret = __xfs_log_force_lsn(mp, 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_zone, 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.
   */
  int
  xfs_log_calc_unit_res(
  	struct xfs_mount	*mp,
  	int			unit_bytes)
  {
  	struct xlog		*log = mp->m_log;
  	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;
  
  	/* for roundoff padding for transaction data and one for commit record */
  	if (xfs_sb_version_haslogv2(&mp->m_sb) && mp->m_sb.sb_logsunit > 1) {
  		/* log su roundoff */
  		unit_bytes += 2 * mp->m_sb.sb_logsunit;
  	} else {
  		/* BB roundoff */
  		unit_bytes += 2 * BBSIZE;
          }
  
  	return unit_bytes;
  }
  
  /*
   * Allocate and initialise a new log ticket.
   */
  struct xlog_ticket *
  xlog_ticket_alloc(
  	struct xlog		*log,
  	int			unit_bytes,
  	int			cnt,
  	char			client,
  	bool			permanent)
  {
  	struct xlog_ticket	*tic;
  	int			unit_res;
  
  	tic = kmem_cache_zalloc(xfs_log_ticket_zone, GFP_NOFS | __GFP_NOFAIL);
  
  	unit_res = xfs_log_calc_unit_res(log->l_mp, unit_bytes);
  
  	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		= prandom_u32();
  	tic->t_clientid		= client;
  	if (permanent)
  		tic->t_flags |= XLOG_TIC_PERM_RESERV;
  
  	xlog_tic_reset_res(tic);
  
  	return tic;
  }
  
  #if defined(DEBUG)
  /*
   * Make sure that the destination ptr is within the valid data region of
   * one of the iclogs.  This uses backup pointers stored in a different
   * part of the log in case we trash the log structure.
   */
  STATIC void
  xlog_verify_dest_ptr(
  	struct xlog	*log,
  	void		*ptr)
  {
  	int i;
  	int good_ptr = 0;
  
  	for (i = 0; i < log->l_iclog_bufs; i++) {
  		if (ptr >= log->l_iclog_bak[i] &&
  		    ptr <= log->l_iclog_bak[i] + log->l_iclog_size)
  			good_ptr++;
  	}
  
  	if (!good_ptr)
  		xfs_emerg(log->l_mp, "%s: invalid ptr", __func__);
  }
  
  /*
   * 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 &&
  		    !(log->l_flags & XLOG_TAIL_WARN)) {
  			xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
  				"%s: cycle - 1 != tail_cycle", __func__);
  			log->l_flags |= XLOG_TAIL_WARN;
  		}
  
  		if (space > BBTOB(tail_blocks) &&
  		    !(log->l_flags & XLOG_TAIL_WARN)) {
  			xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
  				"%s: space > BBTOB(tail_blocks)", __func__);
  			log->l_flags |= XLOG_TAIL_WARN;
  		}
  	}
  }
  
  /* check if it will fit */
  STATIC void
  xlog_verify_tail_lsn(
  	struct xlog		*log,
  	struct xlog_in_core	*iclog,
  	xfs_lsn_t		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((char *)&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: invalid clientid %d op "PTR_FMT" offset 0x%lx",
  				__func__, 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((uintptr_t)&ophead->oh_len -
  				    (uintptr_t)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
  
  /*
   * Mark all iclogs IOERROR. l_icloglock is held by the caller.
   */
  STATIC int
  xlog_state_ioerror(
  	struct xlog	*log)
  {
  	xlog_in_core_t	*iclog, *ic;
  
  	iclog = log->l_iclog;
  	if (iclog->ic_state != XLOG_STATE_IOERROR) {
  		/*
  		 * Mark all the incore logs IOERROR.
  		 * From now on, no log flushes will result.
  		 */
  		ic = iclog;
  		do {
  			ic->ic_state = XLOG_STATE_IOERROR;
  			ic = ic->ic_next;
  		} while (ic != iclog);
  		return 0;
  	}
  	/*
  	 * Return non-zero, if state transition has already happened.
  	 */
  	return 1;
  }
  
  /*
   * This is called from xfs_force_shutdown, when we're forcibly
   * shutting down the filesystem, typically because of an IO error.
   * Our main objectives here are to make sure that:
   *	a. if !logerror, flush the logs to disk. Anything modified
   *	   after this is ignored.
   *	b. the filesystem gets marked 'SHUTDOWN' for all interested
   *	   parties to find out, 'atomically'.
   *	c. those who're sleeping on log reservations, pinned objects and
   *	    other resources get woken up, and be told the bad news.
   *	d. nothing new gets queued up after (b) and (c) are done.
   *
   * Note: for the !logerror case we need to flush the regions held in memory out
   * to disk first. This needs to be done before the log is marked as shutdown,
   * otherwise the iclog writes will fail.
   */
  int
  xfs_log_force_umount(
  	struct xfs_mount	*mp,
  	int			logerror)
  {
  	struct xlog	*log;
  	int		retval;
  
  	log = mp->m_log;
  
  	/*
  	 * If this happens during log recovery, don't worry about
  	 * locking; the log isn't open for business yet.
  	 */
  	if (!log ||
  	    log->l_flags & XLOG_ACTIVE_RECOVERY) {
  		mp->m_flags |= XFS_MOUNT_FS_SHUTDOWN;
  		if (mp->m_sb_bp)
  			mp->m_sb_bp->b_flags |= XBF_DONE;
  		return 0;
  	}
  
  	/*
  	 * Somebody could've already done the hard work for us.
  	 * No need to get locks for this.
  	 */
  	if (logerror && log->l_iclog->ic_state == XLOG_STATE_IOERROR) {
  		ASSERT(XLOG_FORCED_SHUTDOWN(log));
  		return 1;
  	}
  
  	/*
  	 * Flush all the completed transactions to disk before marking the log
  	 * being shut down. We need to do it in this order to ensure that
  	 * completed operations are safely on disk before we shut down, and that
  	 * we don't have to issue any buffer IO after the shutdown flags are set
  	 * to guarantee this.
  	 */
  	if (!logerror)
  		xfs_log_force(mp, XFS_LOG_SYNC);
  
  	/*
  	 * mark the filesystem and the as in a shutdown state and wake
  	 * everybody up to tell them the bad news.
  	 */
  	spin_lock(&log->l_icloglock);
  	mp->m_flags |= XFS_MOUNT_FS_SHUTDOWN;
  	if (mp->m_sb_bp)
  		mp->m_sb_bp->b_flags |= XBF_DONE;
  
  	/*
  	 * Mark the log and the iclogs with IO error flags to prevent any
  	 * further log IO from being issued or completed.
  	 */
  	log->l_flags |= XLOG_IO_ERROR;
  	retval = xlog_state_ioerror(log);
  	spin_unlock(&log->l_icloglock);
  
  	/*
  	 * 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_commit_wait);
  	spin_unlock(&log->l_cilp->xc_push_lock);
  	xlog_state_do_callback(log);
  
  	/* return non-zero if log IOERROR transition had already happened */
  	return retval;
  }
  
  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 (mp->m_flags & XFS_MOUNT_NORECOVERY)
  		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;
  }
  
  bool
  xfs_log_in_recovery(
  	struct xfs_mount	*mp)
  {
  	struct xlog		*log = mp->m_log;
  
  	return log->l_flags & XLOG_ACTIVE_RECOVERY;
  }
  