WSL2-Linux-Kernel/fs/xfs/xfs_log.c

/*
 * Copyright (c) 2000-2005 Silicon Graphics, Inc.
 * All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_types.h"
#include "xfs_log.h"
#include "xfs_trans.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_mount.h"
#include "xfs_error.h"
#include "xfs_log_priv.h"
#include "xfs_buf_item.h"
#include "xfs_bmap_btree.h"
#include "xfs_alloc_btree.h"
#include "xfs_ialloc_btree.h"
#include "xfs_log_recover.h"
#include "xfs_trans_priv.h"
#include "xfs_dinode.h"
#include "xfs_inode.h"
#include "xfs_trace.h"

kmem_zone_t	*xfs_log_ticket_zone;

/* Local miscellaneous function prototypes */
STATIC int	 xlog_commit_record(struct log *log, struct xlog_ticket *ticket,
				    xlog_in_core_t **, xfs_lsn_t *);
STATIC xlog_t *  xlog_alloc_log(xfs_mount_t	*mp,
				xfs_buftarg_t	*log_target,
				xfs_daddr_t	blk_offset,
				int		num_bblks);
STATIC int	 xlog_space_left(struct log *log, atomic64_t *head);
STATIC int	 xlog_sync(xlog_t *log, xlog_in_core_t *iclog);
STATIC void	 xlog_dealloc_log(xlog_t *log);

/* local state machine functions */
STATIC void xlog_state_done_syncing(xlog_in_core_t *iclog, int);
STATIC void xlog_state_do_callback(xlog_t *log,int aborted, xlog_in_core_t *iclog);
STATIC int  xlog_state_get_iclog_space(xlog_t		*log,
				       int		len,
				       xlog_in_core_t	**iclog,
				       xlog_ticket_t	*ticket,
				       int		*continued_write,
				       int		*logoffsetp);
STATIC int  xlog_state_release_iclog(xlog_t		*log,
				     xlog_in_core_t	*iclog);
STATIC void xlog_state_switch_iclogs(xlog_t		*log,
				     xlog_in_core_t *iclog,
				     int		eventual_size);
STATIC void xlog_state_want_sync(xlog_t	*log, xlog_in_core_t *iclog);

STATIC void xlog_grant_push_ail(struct log	*log,
				int		need_bytes);
STATIC void xlog_regrant_reserve_log_space(xlog_t	 *log,
					   xlog_ticket_t *ticket);
STATIC void xlog_ungrant_log_space(xlog_t	 *log,
				   xlog_ticket_t *ticket);

#if defined(DEBUG)
STATIC void	xlog_verify_dest_ptr(xlog_t *log, char *ptr);
STATIC void	xlog_verify_grant_tail(struct log *log);
STATIC void	xlog_verify_iclog(xlog_t *log, xlog_in_core_t *iclog,
				  int count, boolean_t syncing);
STATIC void	xlog_verify_tail_lsn(xlog_t *log, xlog_in_core_t *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,d)
#define xlog_verify_tail_lsn(a,b,c)
#endif

STATIC int	xlog_iclogs_empty(xlog_t *log);

static void
xlog_grant_sub_space(
	struct log	*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 log	*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 log		*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 log		*log,
	struct xlog_grant_head	*head,
	int			*free_bytes)
{
	struct xlog_ticket	*tic;
	int			need_bytes;

	list_for_each_entry(tic, &head->waiters, t_queue) {
		need_bytes = xlog_ticket_reservation(log, head, tic);
		if (*free_bytes < need_bytes)
			return false;

		*free_bytes -= need_bytes;
		trace_xfs_log_grant_wake_up(log, tic);
		wake_up_process(tic->t_task);
	}

	return true;
}

STATIC int
xlog_grant_head_wait(
	struct log		*log,
	struct xlog_grant_head	*head,
	struct xlog_ticket	*tic,
	int			need_bytes)
{
	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(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 XFS_ERROR(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 log		*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++;
}

/*
 * Replenish the byte reservation required by moving the grant write head.
 */
int
xfs_log_regrant(
	struct xfs_mount	*mp,
	struct xlog_ticket	*tic)
{
	struct log		*log = mp->m_log;
	int			need_bytes;
	int			error = 0;

	if (XLOG_FORCED_SHUTDOWN(log))
		return XFS_ERROR(EIO);

	XFS_STATS_INC(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 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,
	uint		 	t_type)
{
	struct log		*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 XFS_ERROR(EIO);

	XFS_STATS_INC(xs_try_logspace);

	ASSERT(*ticp == NULL);
	tic = xlog_ticket_alloc(log, unit_bytes, cnt, client, permanent,
				KM_SLEEP | KM_MAYFAIL);
	if (!tic)
		return XFS_ERROR(ENOMEM);

	tic->t_trans_type = t_type;
	*ticp = tic;

	xlog_grant_push_ail(log, tic->t_unit_res * tic->t_cnt);

	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;
}


/*
 * NOTES:
 *
 *	1. currblock field gets updated at startup and after in-core logs
 *		marked as with WANT_SYNC.
 */

/*
 * This routine is called when a user of a log manager ticket is done with
 * the reservation.  If the ticket was ever used, then a commit record for
 * the associated transaction is written out as a log operation header with
 * no data.  The flag XLOG_TIC_INITED is set when the first write occurs with
 * a given ticket.  If the ticket was one with a permanent reservation, then
 * a few operations are done differently.  Permanent reservation tickets by
 * default don't release the reservation.  They just commit the current
 * transaction with the belief that the reservation is still needed.  A flag
 * must be passed in before permanent reservations are actually released.
 * When these type of tickets are not released, they need to be set into
 * the inited state again.  By doing this, a start record will be written
 * out when the next write occurs.
 */
xfs_lsn_t
xfs_log_done(
	struct xfs_mount	*mp,
	struct xlog_ticket	*ticket,
	struct xlog_in_core	**iclog,
	uint			flags)
{
	struct log		*log = mp->m_log;
	xfs_lsn_t		lsn = 0;

	if (XLOG_FORCED_SHUTDOWN(log) ||
	    /*
	     * If nothing was ever written, don't write out commit record.
	     * If we get an error, just continue and give back the log ticket.
	     */
	    (((ticket->t_flags & XLOG_TIC_INITED) == 0) &&
	     (xlog_commit_record(log, ticket, iclog, &lsn)))) {
		lsn = (xfs_lsn_t) -1;
		if (ticket->t_flags & XLOG_TIC_PERM_RESERV) {
			flags |= XFS_LOG_REL_PERM_RESERV;
		}
	}


	if ((ticket->t_flags & XLOG_TIC_PERM_RESERV) == 0 ||
	    (flags & XFS_LOG_REL_PERM_RESERV)) {
		trace_xfs_log_done_nonperm(log, ticket);

		/*
		 * Release ticket if not permanent reservation or a specific
		 * request has been made to release a permanent reservation.
		 */
		xlog_ungrant_log_space(log, ticket);
		xfs_log_ticket_put(ticket);
	} else {
		trace_xfs_log_done_perm(log, ticket);

		xlog_regrant_reserve_log_space(log, ticket);
		/* If this ticket was a permanent reservation and we aren't
		 * trying to release it, reset the inited flags; so next time
		 * we write, a start record will be written out.
		 */
		ticket->t_flags |= XLOG_TIC_INITED;
	}

	return lsn;
}

/*
 * Attaches a new iclog I/O completion callback routine during
 * transaction commit.  If the log is in error state, a non-zero
 * return code is handed back and the caller is responsible for
 * executing the callback at an appropriate time.
 */
int
xfs_log_notify(
	struct xfs_mount	*mp,
	struct xlog_in_core	*iclog,
	xfs_log_callback_t	*cb)
{
	int	abortflg;

	spin_lock(&iclog->ic_callback_lock);
	abortflg = (iclog->ic_state & XLOG_STATE_IOERROR);
	if (!abortflg) {
		ASSERT_ALWAYS((iclog->ic_state == XLOG_STATE_ACTIVE) ||
			      (iclog->ic_state == XLOG_STATE_WANT_SYNC));
		cb->cb_next = NULL;
		*(iclog->ic_callback_tail) = cb;
		iclog->ic_callback_tail = &(cb->cb_next);
	}
	spin_unlock(&iclog->ic_callback_lock);
	return abortflg;
}

int
xfs_log_release_iclog(
	struct xfs_mount	*mp,
	struct xlog_in_core	*iclog)
{
	if (xlog_state_release_iclog(mp->m_log, iclog)) {
		xfs_force_shutdown(mp, SHUTDOWN_LOG_IO_ERROR);
		return EIO;
	}

	return 0;
}

/*
 * Mount a log filesystem
 *
 * mp		- ubiquitous xfs mount point structure
 * log_target	- buftarg of on-disk log device
 * blk_offset	- Start block # where block size is 512 bytes (BBSIZE)
 * num_bblocks	- Number of BBSIZE blocks in on-disk log
 *
 * Return error or zero.
 */
int
xfs_log_mount(
	xfs_mount_t	*mp,
	xfs_buftarg_t	*log_target,
	xfs_daddr_t	blk_offset,
	int		num_bblks)
{
	int		error;

	if (!(mp->m_flags & XFS_MOUNT_NORECOVERY))
		xfs_notice(mp, "Mounting Filesystem");
	else {
		xfs_notice(mp,
"Mounting filesystem in no-recovery mode.  Filesystem will be inconsistent.");
		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;
	}

	/*
	 * 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);
			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.
 *
 * mp		- ubiquitous xfs mount point structure
 */
int
xfs_log_mount_finish(xfs_mount_t *mp)
{
	int	error;

	if (!(mp->m_flags & XFS_MOUNT_NORECOVERY))
		error = xlog_recover_finish(mp->m_log);
	else {
		error = 0;
		ASSERT(mp->m_flags & XFS_MOUNT_RDONLY);
	}

	return error;
}

/*
 * Final log writes as part of unmount.
 *
 * Mark the filesystem clean as unmount happens.  Note that during relocation
 * this routine needs to be executed as part of source-bag while the
 * deallocation must not be done until source-end.
 */

/*
 * 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 "nUmount" is a bit foo.
 * As far as I know, there weren't any dependencies on the old behaviour.
 */

int
xfs_log_unmount_write(xfs_mount_t *mp)
{
	xlog_t		 *log = mp->m_log;
	xlog_in_core_t	 *iclog;
#ifdef DEBUG
	xlog_in_core_t	 *first_iclog;
#endif
	xlog_ticket_t	*tic = NULL;
	xfs_lsn_t	 lsn;
	int		 error;

	/*
	 * Don't write out unmount record on read-only mounts.
	 * Or, if we are doing a forced umount (typically because of IO errors).
	 */
	if (mp->m_flags & XFS_MOUNT_RDONLY)
		return 0;

	error = _xfs_log_force(mp, XFS_LOG_SYNC, NULL);
	ASSERT(error || !(XLOG_FORCED_SHUTDOWN(log)));

#ifdef DEBUG
	first_iclog = iclog = log->l_iclog;
	do {
		if (!(iclog->ic_state & XLOG_STATE_IOERROR)) {
			ASSERT(iclog->ic_state & XLOG_STATE_ACTIVE);
			ASSERT(iclog->ic_offset == 0);
		}
		iclog = iclog->ic_next;
	} while (iclog != first_iclog);
#endif
	if (! (XLOG_FORCED_SHUTDOWN(log))) {
		error = xfs_log_reserve(mp, 600, 1, &tic,
					XFS_LOG, 0, XLOG_UNMOUNT_REC_TYPE);
		if (!error) {
			/* the data section must be 32 bit size aligned */
			struct {
			    __uint16_t magic;
			    __uint16_t pad1;
			    __uint32_t pad2; /* may as well make it 64 bits */
			} magic = {
				.magic = XLOG_UNMOUNT_TYPE,
			};
			struct xfs_log_iovec reg = {
				.i_addr = &magic,
				.i_len = sizeof(magic),
				.i_type = XLOG_REG_TYPE_UNMOUNT,
			};
			struct xfs_log_vec vec = {
				.lv_niovecs = 1,
				.lv_iovecp = &reg,
			};

			/* remove inited flag, and account for space used */
			tic->t_flags = 0;
			tic->t_curr_res -= sizeof(magic);
			error = xlog_write(log, &vec, tic, &lsn,
					   NULL, XLOG_UNMOUNT_TRANS);
			/*
			 * At this point, we're umounting anyway,
			 * so there's no point in transitioning log state
			 * to IOERROR. Just continue...
			 */
		}

		if (error)
			xfs_alert(mp, "%s: unmount record failed", __func__);


		spin_lock(&log->l_icloglock);
		iclog = log->l_iclog;
		atomic_inc(&iclog->ic_refcnt);
		xlog_state_want_sync(log, iclog);
		spin_unlock(&log->l_icloglock);
		error = xlog_state_release_iclog(log, iclog);

		spin_lock(&log->l_icloglock);
		if (!(iclog->ic_state == XLOG_STATE_ACTIVE ||
		      iclog->ic_state == XLOG_STATE_DIRTY)) {
			if (!XLOG_FORCED_SHUTDOWN(log)) {
				xlog_wait(&iclog->ic_force_wait,
							&log->l_icloglock);
			} else {
				spin_unlock(&log->l_icloglock);
			}
		} else {
			spin_unlock(&log->l_icloglock);
		}
		if (tic) {
			trace_xfs_log_umount_write(log, tic);
			xlog_ungrant_log_space(log, tic);
			xfs_log_ticket_put(tic);
		}
	} else {
		/*
		 * We're already in forced_shutdown mode, couldn't
		 * even attempt to write out the unmount transaction.
		 *
		 * Go through the motions of sync'ing and releasing
		 * the iclog, even though no I/O will actually happen,
		 * we need to wait for other log I/Os that may already
		 * be in progress.  Do this as a separate section of
		 * code so we'll know if we ever get stuck here that
		 * we're in this odd situation of trying to unmount
		 * a file system that went into forced_shutdown as
		 * the result of an unmount..
		 */
		spin_lock(&log->l_icloglock);
		iclog = log->l_iclog;
		atomic_inc(&iclog->ic_refcnt);

		xlog_state_want_sync(log, iclog);
		spin_unlock(&log->l_icloglock);
		error =  xlog_state_release_iclog(log, iclog);

		spin_lock(&log->l_icloglock);

		if ( ! (   iclog->ic_state == XLOG_STATE_ACTIVE
			|| iclog->ic_state == XLOG_STATE_DIRTY
			|| iclog->ic_state == XLOG_STATE_IOERROR) ) {

				xlog_wait(&iclog->ic_force_wait,
							&log->l_icloglock);
		} else {
			spin_unlock(&log->l_icloglock);
		}
	}

	return error;
}	/* xfs_log_unmount_write */

/*
 * Deallocate log structures for unmount/relocation.
 *
 * We need to stop the aild from running before we destroy
 * and deallocate the log as the aild references the log.
 */
void
xfs_log_unmount(xfs_mount_t *mp)
{
	xfs_trans_ail_destroy(mp);
	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);
}

/*
 * Wake up processes waiting for log space after we have moved the log tail.
 */
void
xfs_log_space_wake(
	struct xfs_mount	*mp)
{
	struct log		*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 (no AIL and nothing in the iclogs).
 * 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.
 *
 * Because this is called as part of the sync process, we should also indicate
 * that dummy transactions should be issued in anything but the covered or
 * idle states. This ensures that the log tail is accurately reflected in
 * the log at the end of the sync, hence if a crash occurrs avoids replay
 * of transactions where the metadata is already on disk.
 */
int
xfs_log_need_covered(xfs_mount_t *mp)
{
	int		needed = 0;
	xlog_t		*log = mp->m_log;

	if (!xfs_fs_writable(mp))
		return 0;

	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) &&
		    xlog_iclogs_empty(log)) {
			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;
		}
		/* FALLTHRU */
	default:
		needed = 1;
		break;
	}
	spin_unlock(&log->l_icloglock);
	return needed;
}

/*
 * 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 log		*log = mp->m_log;
	struct xfs_log_item	*lip;
	xfs_lsn_t		tail_lsn;

	assert_spin_locked(&mp->m_ail->xa_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);
	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->xa_lock);
	tail_lsn = xlog_assign_tail_lsn_locked(mp);
	spin_unlock(&mp->m_ail->xa_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 log	*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\n"
			"  tail_cycle = %d, tail_bytes = %d\n"
			"  GH   cycle = %d, GH   bytes = %d",
			tail_cycle, tail_bytes, head_cycle, head_bytes);
		ASSERT(0);
		free_bytes = log->l_logsize;
	}
	return free_bytes;
}


/*
 * Log function which is called when an io completes.
 *
 * The log manager needs its own routine, in order to control what
 * happens with the buffer after the write completes.
 */
void
xlog_iodone(xfs_buf_t *bp)
{
	xlog_in_core_t	*iclog = bp->b_fspriv;
	xlog_t		*l = iclog->ic_log;
	int		aborted = 0;

	/*
	 * Race to shutdown the filesystem if we see an error.
	 */
	if (XFS_TEST_ERROR((xfs_buf_geterror(bp)), l->l_mp,
			XFS_ERRTAG_IODONE_IOERR, XFS_RANDOM_IODONE_IOERR)) {
		xfs_buf_ioerror_alert(bp, __func__);
		xfs_buf_stale(bp);
		xfs_force_shutdown(l->l_mp, SHUTDOWN_LOG_IO_ERROR);
		/*
		 * This flag will be propagated to the trans-committed
		 * callback routines to let them know that the log-commit
		 * didn't succeed.
		 */
		aborted = XFS_LI_ABORTED;
	} else if (iclog->ic_state & XLOG_STATE_IOERROR) {
		aborted = XFS_LI_ABORTED;
	}

	/* log I/O is always issued ASYNC */
	ASSERT(XFS_BUF_ISASYNC(bp));
	xlog_state_done_syncing(iclog, aborted);
	/*
	 * do not reference the buffer (bp) here as we could race
	 * with it being freed after writing the unmount record to the
	 * log.
	 */

}	/* xlog_iodone */

/*
 * 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(xfs_mount_t	*mp,
			   xlog_t	*log)
{
	int size;
	int xhdrs;

	if (mp->m_logbufs <= 0)
		log->l_iclog_bufs = XLOG_MAX_ICLOGS;
	else
		log->l_iclog_bufs = mp->m_logbufs;

	/*
	 * Buffer size passed in from mount system call.
	 */
	if (mp->m_logbsize > 0) {
		size = log->l_iclog_size = mp->m_logbsize;
		log->l_iclog_size_log = 0;
		while (size != 1) {
			log->l_iclog_size_log++;
			size >>= 1;
		}

		if (xfs_sb_version_haslogv2(&mp->m_sb)) {
			/* # headers = size / 32k
			 * one header holds cycles from 32k of data
			 */

			xhdrs = mp->m_logbsize / XLOG_HEADER_CYCLE_SIZE;
			if (mp->m_logbsize % XLOG_HEADER_CYCLE_SIZE)
				xhdrs++;
			log->l_iclog_hsize = xhdrs << BBSHIFT;
			log->l_iclog_heads = xhdrs;
		} else {
			ASSERT(mp->m_logbsize <= XLOG_BIG_RECORD_BSIZE);
			log->l_iclog_hsize = BBSIZE;
			log->l_iclog_heads = 1;
		}
		goto done;
	}

	/* All machines use 32kB buffers by default. */
	log->l_iclog_size = XLOG_BIG_RECORD_BSIZE;
	log->l_iclog_size_log = XLOG_BIG_RECORD_BSHIFT;

	/* the default log size is 16k or 32k which is one header sector */
	log->l_iclog_hsize = BBSIZE;
	log->l_iclog_heads = 1;

done:
	/* are we being asked to make the sizes selected above visible? */
	if (mp->m_logbufs == 0)
		mp->m_logbufs = log->l_iclog_bufs;
	if (mp->m_logbsize == 0)
		mp->m_logbsize = log->l_iclog_size;
}	/* xlog_get_iclog_buffer_size */


/*
 * 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 xlog_t *
xlog_alloc_log(xfs_mount_t	*mp,
	       xfs_buftarg_t	*log_target,
	       xfs_daddr_t	blk_offset,
	       int		num_bblks)
{
	xlog_t			*log;
	xlog_rec_header_t	*head;
	xlog_in_core_t		**iclogp;
	xlog_in_core_t		*iclog, *prev_iclog=NULL;
	xfs_buf_t		*bp;
	int			i;
	int			error = ENOMEM;
	uint			log2_size = 0;

	log = kmem_zalloc(sizeof(xlog_t), 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;

	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);

	error = ENOMEM;
	bp = xfs_buf_alloc(mp->m_logdev_targp, 0, BTOBB(log->l_iclog_size), 0);
	if (!bp)
		goto out_free_log;
	bp->b_iodone = xlog_iodone;
	ASSERT(xfs_buf_islocked(bp));
	log->l_xbuf = bp;

	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++) {
		*iclogp = kmem_zalloc(sizeof(xlog_in_core_t), KM_MAYFAIL);
		if (!*iclogp)
			goto out_free_iclog;

		iclog = *iclogp;
		iclog->ic_prev = prev_iclog;
		prev_iclog = iclog;

		bp = xfs_buf_get_uncached(mp->m_logdev_targp,
						BTOBB(log->l_iclog_size), 0);
		if (!bp)
			goto out_free_iclog;

		bp->b_iodone = xlog_iodone;
		iclog->ic_bp = bp;
		iclog->ic_data = bp->b_addr;
#ifdef DEBUG
		log->l_iclog_bak[i] = (xfs_caddr_t)&(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 = BBTOB(bp->b_length) - 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);
		iclog->ic_callback_tail = &(iclog->ic_callback);
		iclog->ic_datap = (char *)iclog->ic_data + log->l_iclog_hsize;

		ASSERT(xfs_buf_islocked(iclog->ic_bp));
		init_waitqueue_head(&iclog->ic_force_wait);
		init_waitqueue_head(&iclog->ic_write_wait);

		iclogp = &iclog->ic_next;
	}
	*iclogp = log->l_iclog;			/* complete ring */
	log->l_iclog->ic_prev = prev_iclog;	/* re-write 1st prev ptr */

	error = xlog_cil_init(log);
	if (error)
		goto out_free_iclog;
	return log;

out_free_iclog:
	for (iclog = log->l_iclog; iclog; iclog = prev_iclog) {
		prev_iclog = iclog->ic_next;
		if (iclog->ic_bp)
			xfs_buf_free(iclog->ic_bp);
		kmem_free(iclog);
	}
	spinlock_destroy(&log->l_icloglock);
	xfs_buf_free(log->l_xbuf);
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.  Return the lsn of the commit record.
 */
STATIC int
xlog_commit_record(
	struct log		*log,
	struct xlog_ticket	*ticket,
	struct xlog_in_core	**iclog,
	xfs_lsn_t		*commitlsnp)
{
	struct xfs_mount *mp = log->l_mp;
	int	error;
	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,
	};

	ASSERT_ALWAYS(iclog);
	error = xlog_write(log, &vec, ticket, commitlsnp, iclog,
					XLOG_COMMIT_TRANS);
	if (error)
		xfs_force_shutdown(mp, SHUTDOWN_LOG_IO_ERROR);
	return error;
}

/*
 * Push on the buffer cache code if we ever use more than 75% of the on-disk
 * log space.  This code pushes on the lsn which would supposedly free up
 * the 25% which we want to leave free.  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 log	*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;

	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;

	/*
	 * 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.
	 */
	if (!XLOG_FORCED_SHUTDOWN(log))
		xfs_ail_push(log->l_ailp, threshold_lsn);
}

/*
 * The bdstrat callback function for log bufs. This gives us a central
 * place to trap bufs in case we get hit by a log I/O error and need to
 * shutdown. Actually, in practice, even when we didn't get a log error,
 * we transition the iclogs to IOERROR state *after* flushing all existing
 * iclogs to disk. This is because we don't want anymore new transactions to be
 * started or completed afterwards.
 */
STATIC int
xlog_bdstrat(
	struct xfs_buf		*bp)
{
	struct xlog_in_core	*iclog = bp->b_fspriv;

	if (iclog->ic_state & XLOG_STATE_IOERROR) {
		xfs_buf_ioerror(bp, EIO);
		xfs_buf_stale(bp);
		xfs_buf_ioend(bp, 0);
		/*
		 * 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.
		 */
		return 0;
	}

	xfs_buf_iorequest(bp);
	return 0;
}

/*
 * 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
 * log_sync (and then only bwrite()) know about the fact that the log may
 * not start with block zero on a given device.  The log block start offset
 * is added immediately before calling bwrite().
 */

STATIC int
xlog_sync(xlog_t		*log,
	  xlog_in_core_t	*iclog)
{
	xfs_caddr_t	dptr;		/* pointer to byte sized element */
	xfs_buf_t	*bp;
	int		i;
	uint		count;		/* byte count of bwrite */
	uint		count_init;	/* initial count before roundup */
	int		roundoff;       /* roundoff to BB or stripe */
	int		split = 0;	/* split write into two regions */
	int		error;
	int		v2 = xfs_sb_version_haslogv2(&log->l_mp->m_sb);

	XFS_STATS_INC(xs_log_writes);
	ASSERT(atomic_read(&iclog->ic_refcnt) == 0);

	/* Add for LR header */
	count_init = log->l_iclog_hsize + iclog->ic_offset;

	/* Round out the log write size */
	if (v2 && log->l_mp->m_sb.sb_logsunit > 1) {
		/* we have a v2 stripe unit to use */
		count = XLOG_LSUNITTOB(log, XLOG_BTOLSUNIT(log, count_init));
	} else {
		count = BBTOB(BTOBB(count_init));
	}
	roundoff = count - count_init;
	ASSERT(roundoff >= 0);
	ASSERT((v2 && log->l_mp->m_sb.sb_logsunit > 1 && 
                roundoff < log->l_mp->m_sb.sb_logsunit)
		|| 
		(log->l_mp->m_sb.sb_logsunit <= 1 && 
		 roundoff < BBTOB(1)));

	/* 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 */
	if (v2) {
		iclog->ic_header.h_len =
			cpu_to_be32(iclog->ic_offset + roundoff);
	} else {
		iclog->ic_header.h_len =
			cpu_to_be32(iclog->ic_offset);
	}

	bp = iclog->ic_bp;
	XFS_BUF_SET_ADDR(bp, BLOCK_LSN(be64_to_cpu(iclog->ic_header.h_lsn)));

	XFS_STATS_ADD(xs_log_blocks, BTOBB(count));

	/* Do we need to split this write into 2 parts? */
	if (XFS_BUF_ADDR(bp) + BTOBB(count) > log->l_logBBsize) {
		split = count - (BBTOB(log->l_logBBsize - XFS_BUF_ADDR(bp)));
		count = BBTOB(log->l_logBBsize - XFS_BUF_ADDR(bp));
		iclog->ic_bwritecnt = 2;	/* split into 2 writes */
	} else {
		iclog->ic_bwritecnt = 1;
	}
	bp->b_io_length = BTOBB(count);
	bp->b_fspriv = iclog;
	XFS_BUF_ZEROFLAGS(bp);
	XFS_BUF_ASYNC(bp);
	bp->b_flags |= XBF_SYNCIO;

	if (log->l_mp->m_flags & XFS_MOUNT_BARRIER) {
		bp->b_flags |= XBF_FUA;

		/*
		 * 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_mp->m_logdev_targp != log->l_mp->m_ddev_targp)
			xfs_blkdev_issue_flush(log->l_mp->m_ddev_targp);
		else
			bp->b_flags |= XBF_FLUSH;
	}

	ASSERT(XFS_BUF_ADDR(bp) <= log->l_logBBsize-1);
	ASSERT(XFS_BUF_ADDR(bp) + BTOBB(count) <= log->l_logBBsize);

	xlog_verify_iclog(log, iclog, count, B_TRUE);

	/* account for log which doesn't start at block #0 */
	XFS_BUF_SET_ADDR(bp, XFS_BUF_ADDR(bp) + log->l_logBBstart);
	/*
	 * Don't call xfs_bwrite here. We do log-syncs even when the filesystem
	 * is shutting down.
	 */
	XFS_BUF_WRITE(bp);

	error = xlog_bdstrat(bp);
	if (error) {
		xfs_buf_ioerror_alert(bp, "xlog_sync");
		return error;
	}
	if (split) {
		bp = iclog->ic_log->l_xbuf;
		XFS_BUF_SET_ADDR(bp, 0);	     /* logical 0 */
		xfs_buf_associate_memory(bp,
				(char *)&iclog->ic_header + count, split);
		bp->b_fspriv = iclog;
		XFS_BUF_ZEROFLAGS(bp);
		XFS_BUF_ASYNC(bp);
		bp->b_flags |= XBF_SYNCIO;
		if (log->l_mp->m_flags & XFS_MOUNT_BARRIER)
			bp->b_flags |= XBF_FUA;
		dptr = bp->b_addr;
		/*
		 * Bump the cycle numbers at the start of each block
		 * since this part of the buffer is at the start of
		 * a new cycle.  Watch out for the header magic number
		 * case, though.
		 */
		for (i = 0; i < split; i += BBSIZE) {
			be32_add_cpu((__be32 *)dptr, 1);
			if (be32_to_cpu(*(__be32 *)dptr) == XLOG_HEADER_MAGIC_NUM)
				be32_add_cpu((__be32 *)dptr, 1);
			dptr += BBSIZE;
		}

		ASSERT(XFS_BUF_ADDR(bp) <= log->l_logBBsize-1);
		ASSERT(XFS_BUF_ADDR(bp) + BTOBB(count) <= log->l_logBBsize);

		/* account for internal log which doesn't start at block #0 */
		XFS_BUF_SET_ADDR(bp, XFS_BUF_ADDR(bp) + log->l_logBBstart);
		XFS_BUF_WRITE(bp);
		error = xlog_bdstrat(bp);
		if (error) {
			xfs_buf_ioerror_alert(bp, "xlog_sync (split)");
			return error;
		}
	}
	return 0;
}	/* xlog_sync */


/*
 * Deallocate a log structure
 */
STATIC void
xlog_dealloc_log(xlog_t *log)
{
	xlog_in_core_t	*iclog, *next_iclog;
	int		i;

	xlog_cil_destroy(log);

	/*
	 * always need to ensure that the extra buffer does not point to memory
	 * owned by another log buffer before we free it.
	 */
	xfs_buf_set_empty(log->l_xbuf, BTOBB(log->l_iclog_size));
	xfs_buf_free(log->l_xbuf);

	iclog = log->l_iclog;
	for (i=0; i<log->l_iclog_bufs; i++) {
		xfs_buf_free(iclog->ic_bp);
		next_iclog = iclog->ic_next;
		kmem_free(iclog);
		iclog = next_iclog;
	}
	spinlock_destroy(&log->l_icloglock);

	log->l_mp->m_log = NULL;
	kmem_free(log);
}	/* xlog_dealloc_log */

/*
 * Update counters atomically now that memcpy is done.
 */
/* ARGSUSED */
static inline void
xlog_state_finish_copy(xlog_t		*log,
		       xlog_in_core_t	*iclog,
		       int		record_cnt,
		       int		copy_bytes)
{
	spin_lock(&log->l_icloglock);

	be32_add_cpu(&iclog->ic_header.h_num_logops, record_cnt);
	iclog->ic_offset += copy_bytes;

	spin_unlock(&log->l_icloglock);
}	/* xlog_state_finish_copy */




/*
 * 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 */
	static char *res_type_str[XLOG_REG_TYPE_MAX] = {
	    "bformat",
	    "bchunk",
	    "efi_format",
	    "efd_format",
	    "iformat",
	    "icore",
	    "iext",
	    "ibroot",
	    "ilocal",
	    "iattr_ext",
	    "iattr_broot",
	    "iattr_local",
	    "qformat",
	    "dquot",
	    "quotaoff",
	    "LR header",
	    "unmount",
	    "commit",
	    "trans header"
	};
	static char *trans_type_str[XFS_TRANS_TYPE_MAX] = {
	    "SETATTR_NOT_SIZE",
	    "SETATTR_SIZE",
	    "INACTIVE",
	    "CREATE",
	    "CREATE_TRUNC",
	    "TRUNCATE_FILE",
	    "REMOVE",
	    "LINK",
	    "RENAME",
	    "MKDIR",
	    "RMDIR",
	    "SYMLINK",
	    "SET_DMATTRS",
	    "GROWFS",
	    "STRAT_WRITE",
	    "DIOSTRAT",
	    "WRITE_SYNC",
	    "WRITEID",
	    "ADDAFORK",
	    "ATTRINVAL",
	    "ATRUNCATE",
	    "ATTR_SET",
	    "ATTR_RM",
	    "ATTR_FLAG",
	    "CLEAR_AGI_BUCKET",
	    "QM_SBCHANGE",
	    "DUMMY1",
	    "DUMMY2",
	    "QM_QUOTAOFF",
	    "QM_DQALLOC",
	    "QM_SETQLIM",
	    "QM_DQCLUSTER",
	    "QM_QINOCREATE",
	    "QM_QUOTAOFF_END",
	    "SB_UNIT",
	    "FSYNC_TS",
	    "GROWFSRT_ALLOC",
	    "GROWFSRT_ZERO",
	    "GROWFSRT_FREE",
	    "SWAPEXT"
	};

	xfs_warn(mp,
		"xlog_write: reservation summary:\n"
		"  trans type  = %s (%u)\n"
		"  unit res    = %d bytes\n"
		"  current res = %d bytes\n"
		"  total reg   = %u bytes (o/flow = %u bytes)\n"
		"  ophdrs      = %u (ophdr space = %u bytes)\n"
		"  ophdr + reg = %u bytes\n"
		"  num regions = %u\n",
		((ticket->t_trans_type <= 0 ||
		  ticket->t_trans_type > XFS_TRANS_TYPE_MAX) ?
		  "bad-trans-type" : trans_type_str[ticket->t_trans_type-1]),
		ticket->t_trans_type,
		ticket->t_unit_res,
		ticket->t_curr_res,
		ticket->t_res_arr_sum, ticket->t_res_o_flow,
		ticket->t_res_num_ophdrs, ophdr_spc,
		ticket->t_res_arr_sum +
		ticket->t_res_o_flow + ophdr_spc,
		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\n", i,
			    ((r_type <= 0 || r_type > XLOG_REG_TYPE_MAX) ?
			    "bad-rtype" : res_type_str[r_type-1]),
			    ticket->t_res_arr[i].r_len);
	}

	xfs_alert_tag(mp, XFS_PTAG_LOGRES,
		"xlog_write: reservation ran out. Need to up reservation");
	xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
}

/*
 * Calculate the potential space needed by the log vector.  Each region gets
 * its own xlog_op_header_t 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)
{
	struct xfs_log_vec	*lv;
	int			headers = 0;
	int			len = 0;
	int			i;

	/* acct for start rec of xact */
	if (ticket->t_flags & XLOG_TIC_INITED)
		headers++;

	for (lv = log_vector; lv; lv = lv->lv_next) {
		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;
}

/*
 * If first write for transaction, insert start record  We can't be trying to
 * commit if we are inited.  We can't have any "partial_copy" if we are inited.
 */
static int
xlog_write_start_rec(
	struct xlog_op_header	*ophdr,
	struct xlog_ticket	*ticket)
{
	if (!(ticket->t_flags & XLOG_TIC_INITED))
		return 0;

	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;

	ticket->t_flags &= ~XLOG_TIC_INITED;

	return sizeof(struct xlog_op_header);
}

static xlog_op_header_t *
xlog_write_setup_ophdr(
	struct log		*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 0x%p",
			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
 * 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 log		*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)
{
	if (*partial_copy) {
		/*
		 * This iclog has already been marked WANT_SYNC by
		 * xlog_state_get_iclog_space.
		 */
		xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
		*record_cnt = 0;
		*data_cnt = 0;
		return xlog_state_release_iclog(log, 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. */
		xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
		*record_cnt = 0;
		*data_cnt = 0;

		spin_lock(&log->l_icloglock);
		xlog_state_want_sync(log, iclog);
		spin_unlock(&log->l_icloglock);

		if (!commit_iclog)
			return xlog_state_release_iclog(log, iclog);
		ASSERT(flags & XLOG_COMMIT_TRANS);
		*commit_iclog = iclog;
	}

	return 0;
}

/*
 * Write some region out to in-core log
 *
 * This will be called when writing externally provided regions or when
 * writing out a commit record for a given transaction.
 *
 * General algorithm:
 *	1. Find total length of this write.  This may include adding to the
 *		lengths passed in.
 *	2. Check whether we violate the tickets reservation.
 *	3. While writing to this iclog
 *	    A. Reserve as much space in this iclog as can get
 *	    B. If this is first write, save away start lsn
 *	    C. While writing this region:
 *		1. If first write of transaction, write start record
 *		2. Write log operation header (header per region)
 *		3. Find out if we can fit entire region into this iclog
 *		4. Potentially, verify destination memcpy ptr
 *		5. Memcpy (partial) region
 *		6. If partial copy, release iclog; otherwise, continue
 *			copying more regions into current iclog
 *	4. Mark want sync bit (in simulation mode)
 *	5. Release iclog for potential flush to on-disk log.
 *
 * ERRORS:
 * 1.	Panic if reservation is overrun.  This should never happen since
 *	reservation amounts are generated internal to the filesystem.
 * NOTES:
 * 1. Tickets are single threaded data structures.
 * 2. The XLOG_END_TRANS & XLOG_CONTINUE_TRANS flags are passed down to the
 *	syncing routine.  When a single log_write region needs to span
 *	multiple in-core logs, the XLOG_CONTINUE_TRANS bit should be set
 *	on all log operation writes which don't contain the end of the
 *	region.  The XLOG_END_TRANS bit is used for the in-core log
 *	operation which contains the end of the continued log_write region.
 * 3. When xlog_state_get_iclog_space() grabs the rest of the current iclog,
 *	we don't really know exactly how much space will be used.  As a result,
 *	we don't update ic_offset until the end when we know exactly how many
 *	bytes have been written out.
 */
int
xlog_write(
	struct log		*log,
	struct xfs_log_vec	*log_vector,
	struct xlog_ticket	*ticket,
	xfs_lsn_t		*start_lsn,
	struct xlog_in_core	**commit_iclog,
	uint			flags)
{
	struct xlog_in_core	*iclog = NULL;
	struct xfs_log_iovec	*vecp;
	struct xfs_log_vec	*lv;
	int			len;
	int			index;
	int			partial_copy = 0;
	int			partial_copy_len = 0;
	int			contwr = 0;
	int			record_cnt = 0;
	int			data_cnt = 0;
	int			error;

	*start_lsn = 0;

	len = xlog_write_calc_vec_length(ticket, log_vector);

	/*
	 * Region headers and bytes are already accounted for.
	 * We only need to take into account start records and
	 * split regions in this function.
	 */
	if (ticket->t_flags & XLOG_TIC_INITED)
		ticket->t_curr_res -= sizeof(xlog_op_header_t);

	/*
	 * Commit record headers need to be accounted for. These
	 * come in as separate writes so are easy to detect.
	 */
	if (flags & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS))
		ticket->t_curr_res -= sizeof(xlog_op_header_t);

	if (ticket->t_curr_res < 0)
		xlog_print_tic_res(log->l_mp, ticket);

	index = 0;
	lv = log_vector;
	vecp = lv->lv_iovecp;
	while (lv && 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 && index < lv->lv_niovecs) {
			struct xfs_log_iovec	*reg = &vecp[index];
			struct xlog_op_header	*ophdr;
			int			start_rec_copy;
			int			copy_len;
			int			copy_off;

			ASSERT(reg->i_len % sizeof(__int32_t) == 0);
			ASSERT((unsigned long)ptr % sizeof(__int32_t) == 0);

			start_rec_copy = xlog_write_start_rec(ptr, ticket);
			if (start_rec_copy) {
				record_cnt++;
				xlog_write_adv_cnt(&ptr, &len, &log_offset,
						   start_rec_copy);
			}

			ophdr = xlog_write_setup_ophdr(log, ptr, ticket, flags);
			if (!ophdr)
				return XFS_ERROR(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 */
			ASSERT(copy_len >= 0);
			memcpy(ptr, reg->i_addr + copy_off, copy_len);
			xlog_write_adv_cnt(&ptr, &len, &log_offset, copy_len);

			copy_len += start_rec_copy + sizeof(xlog_op_header_t);
			record_cnt++;
			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) {
				lv = lv->lv_next;
				index = 0;
				if (lv)
					vecp = lv->lv_iovecp;
			}
			if (record_cnt == 0) {
				if (!lv)
					return 0;
				break;
			}
		}
	}

	ASSERT(len == 0);

	xlog_state_finish_copy(log, iclog, record_cnt, data_cnt);
	if (!commit_iclog)
		return xlog_state_release_iclog(log, iclog);

	ASSERT(flags & XLOG_COMMIT_TRANS);
	*commit_iclog = iclog;
	return 0;
}


/*****************************************************************************
 *
 *		State Machine functions
 *
 *****************************************************************************
 */

/* Clean iclogs starting from the head.  This ordering must be
 * maintained, so an iclog doesn't become ACTIVE beyond one that
 * is SYNCING.  This is also required to maintain the notion that we use
 * a ordered wait queue to hold off would be writers to the log when every
 * iclog is trying to sync to disk.
 *
 * State Change: DIRTY -> ACTIVE
 */
STATIC void
xlog_state_clean_log(xlog_t *log)
{
	xlog_in_core_t	*iclog;
	int changed = 0;

	iclog = log->l_iclog;
	do {
		if (iclog->ic_state == XLOG_STATE_DIRTY) {
			iclog->ic_state	= XLOG_STATE_ACTIVE;
			iclog->ic_offset       = 0;
			ASSERT(iclog->ic_callback == NULL);
			/*
			 * 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 (!changed &&
			   (be32_to_cpu(iclog->ic_header.h_num_logops) ==
			   		XLOG_COVER_OPS)) {
				changed = 1;
			} else {
				/*
				 * We have two dirty iclogs so start over
				 * This could also be num of ops indicates
				 * this is not the dummy going out.
				 */
				changed = 2;
			}
			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;
		} else if (iclog->ic_state == XLOG_STATE_ACTIVE)
			/* do nothing */;
		else
			break;	/* stop cleaning */
		iclog = iclog->ic_next;
	} while (iclog != log->l_iclog);

	/* log is locked when we are called */
	/*
	 * Change state for the dummy log recording.
	 * We usually go to NEED. But we go to NEED2 if the changed indicates
	 * we are done writing the dummy record.
	 * If we are done with the second dummy recored (DONE2), then
	 * we go to IDLE.
	 */
	if (changed) {
		switch (log->l_covered_state) {
		case XLOG_STATE_COVER_IDLE:
		case XLOG_STATE_COVER_NEED:
		case XLOG_STATE_COVER_NEED2:
			log->l_covered_state = XLOG_STATE_COVER_NEED;
			break;

		case XLOG_STATE_COVER_DONE:
			if (changed == 1)
				log->l_covered_state = XLOG_STATE_COVER_NEED2;
			else
				log->l_covered_state = XLOG_STATE_COVER_NEED;
			break;

		case XLOG_STATE_COVER_DONE2:
			if (changed == 1)
				log->l_covered_state = XLOG_STATE_COVER_IDLE;
			else
				log->l_covered_state = XLOG_STATE_COVER_NEED;
			break;

		default:
			ASSERT(0);
		}
	}
}	/* xlog_state_clean_log */

STATIC xfs_lsn_t
xlog_get_lowest_lsn(
	xlog_t		*log)
{
	xlog_in_core_t  *lsn_log;
	xfs_lsn_t	lowest_lsn, lsn;

	lsn_log = log->l_iclog;
	lowest_lsn = 0;
	do {
	    if (!(lsn_log->ic_state & (XLOG_STATE_ACTIVE|XLOG_STATE_DIRTY))) {
		lsn = be64_to_cpu(lsn_log->ic_header.h_lsn);
		if ((lsn && !lowest_lsn) ||
		    (XFS_LSN_CMP(lsn, lowest_lsn) < 0)) {
			lowest_lsn = lsn;
		}
	    }
	    lsn_log = lsn_log->ic_next;
	} while (lsn_log != log->l_iclog);
	return lowest_lsn;
}


STATIC void
xlog_state_do_callback(
	xlog_t		*log,
	int		aborted,
	xlog_in_core_t	*ciclog)
{
	xlog_in_core_t	   *iclog;
	xlog_in_core_t	   *first_iclog;	/* used to know when we've
						 * processed all iclogs once */
	xfs_log_callback_t *cb, *cb_next;
	int		   flushcnt = 0;
	xfs_lsn_t	   lowest_lsn;
	int		   ioerrors;	/* counter: iclogs with errors */
	int		   loopdidcallbacks; /* flag: inner loop did callbacks*/
	int		   funcdidcallbacks; /* flag: function did callbacks */
	int		   repeats;	/* for issuing console warnings if
					 * looping too many times */
	int		   wake = 0;

	spin_lock(&log->l_icloglock);
	first_iclog = iclog = log->l_iclog;
	ioerrors = 0;
	funcdidcallbacks = 0;
	repeats = 0;

	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;
		loopdidcallbacks = 0;
		repeats++;

		do {

			/* skip all iclogs in the ACTIVE & DIRTY states */
			if (iclog->ic_state &
			    (XLOG_STATE_ACTIVE|XLOG_STATE_DIRTY)) {
				iclog = iclog->ic_next;
				continue;
			}

			/*
			 * 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.
			 */
			if (!(iclog->ic_state & XLOG_STATE_IOERROR)) {
				/*
				 * Can only perform callbacks in order.  Since
				 * this iclog is not in the DONE_SYNC/
				 * DO_CALLBACK state, we skip the rest and
				 * just try to clean up.  If we set our iclog
				 * to DO_CALLBACK, we will not process it when
				 * we retry since a previous iclog is in the
				 * CALLBACK and the state cannot change since
				 * we are holding the l_icloglock.
				 */
				if (!(iclog->ic_state &
					(XLOG_STATE_DONE_SYNC |
						 XLOG_STATE_DO_CALLBACK))) {
					if (ciclog && (ciclog->ic_state ==
							XLOG_STATE_DONE_SYNC)) {
						ciclog->ic_state = XLOG_STATE_DO_CALLBACK;
					}
					break;
				}
				/*
				 * We now have an iclog that is in either the
				 * DO_CALLBACK or DONE_SYNC states. The other
				 * states (WANT_SYNC, SYNCING, or CALLBACK were
				 * caught by the above if and are going to
				 * clean (i.e. we aren't doing their callbacks)
				 * see the above if.
				 */

				/*
				 * We will do one more check here to see if we
				 * have chased our tail around.
				 */

				lowest_lsn = xlog_get_lowest_lsn(log);
				if (lowest_lsn &&
				    XFS_LSN_CMP(lowest_lsn,
						be64_to_cpu(iclog->ic_header.h_lsn)) < 0) {
					iclog = iclog->ic_next;
					continue; /* Leave this iclog for
						   * another thread */
				}

				iclog->ic_state = XLOG_STATE_CALLBACK;


				/*
				 * update the last_sync_lsn before we drop the
				 * icloglock to ensure we are the only one that
				 * can update it.
				 */
				ASSERT(XFS_LSN_CMP(atomic64_read(&log->l_last_sync_lsn),
					be64_to_cpu(iclog->ic_header.h_lsn)) <= 0);
				atomic64_set(&log->l_last_sync_lsn,
					be64_to_cpu(iclog->ic_header.h_lsn));

			} else
				ioerrors++;

			spin_unlock(&log->l_icloglock);

			/*
			 * Keep processing entries in the 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.
			 */
			spin_lock(&iclog->ic_callback_lock);
			cb = iclog->ic_callback;
			while (cb) {
				iclog->ic_callback_tail = &(iclog->ic_callback);
				iclog->ic_callback = NULL;
				spin_unlock(&iclog->ic_callback_lock);

				/* perform callbacks in the order given */
				for (; cb; cb = cb_next) {
					cb_next = cb->cb_next;
					cb->cb_func(cb->cb_arg, aborted);
				}
				spin_lock(&iclog->ic_callback_lock);
				cb = iclog->ic_callback;
			}

			loopdidcallbacks++;
			funcdidcallbacks++;

			spin_lock(&log->l_icloglock);
			ASSERT(iclog->ic_callback == NULL);
			spin_unlock(&iclog->ic_callback_lock);
			if (!(iclog->ic_state & XLOG_STATE_IOERROR))
				iclog->ic_state = XLOG_STATE_DIRTY;

			/*
			 * Transition from DIRTY to ACTIVE if applicable.
			 * NOP if STATE_IOERROR.
			 */
			xlog_state_clean_log(log);

			/* wake up threads waiting in xfs_log_force() */
			wake_up_all(&iclog->ic_force_wait);

			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 (!ioerrors && loopdidcallbacks);

	/*
	 * make one last gasp attempt to see if iclogs are being left in
	 * limbo..
	 */
#ifdef DEBUG
	if (funcdidcallbacks) {
		first_iclog = iclog = log->l_iclog;
		do {
			ASSERT(iclog->ic_state != XLOG_STATE_DO_CALLBACK);
			/*
			 * Terminate the loop if iclogs are found in states
			 * which will cause other threads to clean up iclogs.
			 *
			 * SYNCING - i/o completion will go through logs
			 * DONE_SYNC - interrupt thread should be waiting for
			 *              l_icloglock
			 * IOERROR - give up hope all ye who enter here
			 */
			if (iclog->ic_state == XLOG_STATE_WANT_SYNC ||
			    iclog->ic_state == XLOG_STATE_SYNCING ||
			    iclog->ic_state == XLOG_STATE_DONE_SYNC ||
			    iclog->ic_state == XLOG_STATE_IOERROR )
				break;
			iclog = iclog->ic_next;
		} while (first_iclog != iclog);
	}
#endif

	if (log->l_iclog->ic_state & (XLOG_STATE_ACTIVE|XLOG_STATE_IOERROR))
		wake = 1;
	spin_unlock(&log->l_icloglock);

	if (wake)
		wake_up_all(&log->l_flush_wait);
}


/*
 * 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(
	xlog_in_core_t	*iclog,
	int		aborted)
{
	xlog_t		   *log = iclog->ic_log;

	spin_lock(&log->l_icloglock);

	ASSERT(iclog->ic_state == XLOG_STATE_SYNCING ||
	       iclog->ic_state == XLOG_STATE_IOERROR);
	ASSERT(atomic_read(&iclog->ic_refcnt) == 0);
	ASSERT(iclog->ic_bwritecnt == 1 || iclog->ic_bwritecnt == 2);


	/*
	 * If we got an error, either on the first buffer, or in the case of
	 * split log writes, on the second, we mark ALL iclogs STATE_IOERROR,
	 * and none should ever be attempted to be written to disk
	 * again.
	 */
	if (iclog->ic_state != XLOG_STATE_IOERROR) {
		if (--iclog->ic_bwritecnt == 1) {
			spin_unlock(&log->l_icloglock);
			return;
		}
		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, aborted, iclog);	/* also cleans log */
}	/* xlog_state_done_syncing */


/*
 * 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(xlog_t	  *log,
			   int		  len,
			   xlog_in_core_t **iclogp,
			   xlog_ticket_t  *ticket,
			   int		  *continued_write,
			   int		  *logoffsetp)
{
	int		  log_offset;
	xlog_rec_header_t *head;
	xlog_in_core_t	  *iclog;
	int		  error;

restart:
	spin_lock(&log->l_icloglock);
	if (XLOG_FORCED_SHUTDOWN(log)) {
		spin_unlock(&log->l_icloglock);
		return XFS_ERROR(EIO);
	}

	iclog = log->l_iclog;
	if (iclog->ic_state != XLOG_STATE_ACTIVE) {
		XFS_STATS_INC(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)) {
		xlog_state_switch_iclogs(log, iclog, iclog->ic_size);

		/*
		 * If I'm 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)) {
			/* we are the only one */
			spin_unlock(&log->l_icloglock);
			error = xlog_state_release_iclog(log, iclog);
			if (error)
				return error;
		} else {
			spin_unlock(&log->l_icloglock);
		}
		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;
}	/* xlog_state_get_iclog_space */

/* The first cnt-1 times 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.
 */
STATIC void
xlog_regrant_reserve_log_space(xlog_t	     *log,
			       xlog_ticket_t *ticket)
{
	trace_xfs_log_regrant_reserve_enter(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_regrant_reserve_sub(log, ticket);

	/* just return if we still have some of the pre-reserved space */
	if (ticket->t_cnt > 0)
		return;

	xlog_grant_add_space(log, &log->l_reserve_head.grant,
					ticket->t_unit_res);

	trace_xfs_log_regrant_reserve_exit(log, ticket);

	ticket->t_curr_res = ticket->t_unit_res;
	xlog_tic_reset_res(ticket);
}	/* xlog_regrant_reserve_log_space */


/*
 * 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.
 */
STATIC void
xlog_ungrant_log_space(xlog_t	     *log,
		       xlog_ticket_t *ticket)
{
	int	bytes;

	if (ticket->t_cnt > 0)
		ticket->t_cnt--;

	trace_xfs_log_ungrant_enter(log, ticket);
	trace_xfs_log_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_ungrant_exit(log, ticket);

	xfs_log_space_wake(log->l_mp);
}

/*
 * Flush iclog to disk if this is the last reference to the given iclog and
 * the WANT_SYNC bit is set.
 *
 * When this function is entered, the iclog is not necessarily in the
 * WANT_SYNC state.  It may be sitting around waiting to get filled.
 *
 *
 */
STATIC int
xlog_state_release_iclog(
	xlog_t		*log,
	xlog_in_core_t	*iclog)
{
	int		sync = 0;	/* do we sync? */

	if (iclog->ic_state & XLOG_STATE_IOERROR)
		return XFS_ERROR(EIO);

	ASSERT(atomic_read(&iclog->ic_refcnt) > 0);
	if (!atomic_dec_and_lock(&iclog->ic_refcnt, &log->l_icloglock))
		return 0;

	if (iclog->ic_state & XLOG_STATE_IOERROR) {
		spin_unlock(&log->l_icloglock);
		return XFS_ERROR(EIO);
	}
	ASSERT(iclog->ic_state == XLOG_STATE_ACTIVE ||
	       iclog->ic_state == XLOG_STATE_WANT_SYNC);

	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);
		sync++;
		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 */
	}
	spin_unlock(&log->l_icloglock);

	/*
	 * We let the log lock go, so it's possible that we hit a log I/O
	 * error or some other SHUTDOWN condition that marks the iclog
	 * as XLOG_STATE_IOERROR before the bwrite. However, we know that
	 * this iclog has consistent data, so we ignore IOERROR
	 * flags after this point.
	 */
	if (sync)
		return xlog_sync(log, iclog);
	return 0;
}	/* xlog_state_release_iclog */


/*
 * 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.
 * When this routine is called from xlog_state_get_iclog_space(), the
 * exact size of the iclog has not yet been determined.  All we know is
 * that every data block.  We have run out of space in this log record.
 */
STATIC void
xlog_state_switch_iclogs(xlog_t		*log,
			 xlog_in_core_t *iclog,
			 int		eventual_size)
{
	ASSERT(iclog->ic_state == XLOG_STATE_ACTIVE);
	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) {
		log->l_curr_cycle++;
		if (log->l_curr_cycle == XLOG_HEADER_MAGIC_NUM)
			log->l_curr_cycle++;
		log->l_curr_block -= log->l_logBBsize;
		ASSERT(log->l_curr_block >= 0);
	}
	ASSERT(iclog == log->l_iclog);
	log->l_iclog = iclog->ic_next;
}	/* xlog_state_switch_iclogs */

/*
 * 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,
	int			*log_flushed)
{
	struct log		*log = mp->m_log;
	struct xlog_in_core	*iclog;
	xfs_lsn_t		lsn;

	XFS_STATS_INC(xs_log_force);

	xlog_cil_force(log);

	spin_lock(&log->l_icloglock);

	iclog = log->l_iclog;
	if (iclog->ic_state & XLOG_STATE_IOERROR) {
		spin_unlock(&log->l_icloglock);
		return XFS_ERROR(EIO);
	}

	/* If the head iclog is not active nor dirty, we just attach
	 * ourselves to the head and go to sleep.
	 */
	if (iclog->ic_state == XLOG_STATE_ACTIVE ||
	    iclog->ic_state == XLOG_STATE_DIRTY) {
		/*
		 * 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.
		 */
		if (iclog->ic_state == XLOG_STATE_DIRTY ||
		    (atomic_read(&iclog->ic_refcnt) == 0
		     && iclog->ic_offset == 0)) {
			iclog = iclog->ic_prev;
			if (iclog->ic_state == XLOG_STATE_ACTIVE ||
			    iclog->ic_state == XLOG_STATE_DIRTY)
				goto no_sleep;
			else
				goto maybe_sleep;
		} else {
			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);
				spin_unlock(&log->l_icloglock);

				if (xlog_state_release_iclog(log, iclog))
					return XFS_ERROR(EIO);

				if (log_flushed)
					*log_flushed = 1;
				spin_lock(&log->l_icloglock);
				if (be64_to_cpu(iclog->ic_header.h_lsn) == lsn &&
				    iclog->ic_state != XLOG_STATE_DIRTY)
					goto maybe_sleep;
				else
					goto no_sleep;
			} 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);
				goto maybe_sleep;
			}
		}
	}

	/* By the time we come around again, the iclog could've been filled
	 * which would give it another lsn.  If we have a new lsn, just
	 * return because the relevant data has been flushed.
	 */
maybe_sleep:
	if (flags & XFS_LOG_SYNC) {
		/*
		 * We must check if we're shutting down here, before
		 * we wait, while we're holding the l_icloglock.
		 * Then we check again after waking up, in case our
		 * sleep was disturbed by a bad news.
		 */
		if (iclog->ic_state & XLOG_STATE_IOERROR) {
			spin_unlock(&log->l_icloglock);
			return XFS_ERROR(EIO);
		}
		XFS_STATS_INC(xs_log_force_sleep);
		xlog_wait(&iclog->ic_force_wait, &log->l_icloglock);
		/*
		 * No need to grab the log lock here since we're
		 * only deciding whether or not to return EIO
		 * and the memory read should be atomic.
		 */
		if (iclog->ic_state & XLOG_STATE_IOERROR)
			return XFS_ERROR(EIO);
		if (log_flushed)
			*log_flushed = 1;
	} else {

no_sleep:
		spin_unlock(&log->l_icloglock);
	}
	return 0;
}

/*
 * Wrapper for _xfs_log_force(), to be used when caller doesn't care
 * about errors or whether the log was flushed or not. This is the normal
 * interface to use when trying to unpin items or move the log forward.
 */
void
xfs_log_force(
	xfs_mount_t	*mp,
	uint		flags)
{
	int	error;

	trace_xfs_log_force(mp, 0);
	error = _xfs_log_force(mp, flags, NULL);
	if (error)
		xfs_warn(mp, "%s: error %d returned.", __func__, error);
}

/*
 * 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 signal variable. All callers
 * to force a given lsn to disk will wait on a the sv 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
 * sv.
 */
int
_xfs_log_force_lsn(
	struct xfs_mount	*mp,
	xfs_lsn_t		lsn,
	uint			flags,
	int			*log_flushed)
{
	struct log		*log = mp->m_log;
	struct xlog_in_core	*iclog;
	int			already_slept = 0;

	ASSERT(lsn != 0);

	XFS_STATS_INC(xs_log_force);

	lsn = xlog_cil_force_lsn(log, lsn);
	if (lsn == NULLCOMMITLSN)
		return 0;

try_again:
	spin_lock(&log->l_icloglock);
	iclog = log->l_iclog;
	if (iclog->ic_state & XLOG_STATE_IOERROR) {
		spin_unlock(&log->l_icloglock);
		return XFS_ERROR(EIO);
	}

	do {
		if (be64_to_cpu(iclog->ic_header.h_lsn) != lsn) {
			iclog = iclog->ic_next;
			continue;
		}

		if (iclog->ic_state == XLOG_STATE_DIRTY) {
			spin_unlock(&log->l_icloglock);
			return 0;
		}

		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 | XLOG_STATE_SYNCING))) {
				ASSERT(!(iclog->ic_state & XLOG_STATE_IOERROR));

				XFS_STATS_INC(xs_log_force_sleep);

				xlog_wait(&iclog->ic_prev->ic_write_wait,
							&log->l_icloglock);
				if (log_flushed)
					*log_flushed = 1;
				already_slept = 1;
				goto try_again;
			}
			atomic_inc(&iclog->ic_refcnt);
			xlog_state_switch_iclogs(log, iclog, 0);
			spin_unlock(&log->l_icloglock);
			if (xlog_state_release_iclog(log, iclog))
				return XFS_ERROR(EIO);
			if (log_flushed)
				*log_flushed = 1;
			spin_lock(&log->l_icloglock);
		}

		if ((flags & XFS_LOG_SYNC) && /* sleep */
		    !(iclog->ic_state &
		      (XLOG_STATE_ACTIVE | XLOG_STATE_DIRTY))) {
			/*
			 * Don't wait on completion if we know that we've
			 * gotten a log write error.
			 */
			if (iclog->ic_state & XLOG_STATE_IOERROR) {
				spin_unlock(&log->l_icloglock);
				return XFS_ERROR(EIO);
			}
			XFS_STATS_INC(xs_log_force_sleep);
			xlog_wait(&iclog->ic_force_wait, &log->l_icloglock);
			/*
			 * No need to grab the log lock here since we're
			 * only deciding whether or not to return EIO
			 * and the memory read should be atomic.
			 */
			if (iclog->ic_state & XLOG_STATE_IOERROR)
				return XFS_ERROR(EIO);

			if (log_flushed)
				*log_flushed = 1;
		} else {		/* just return */
			spin_unlock(&log->l_icloglock);
		}

		return 0;
	} while (iclog != log->l_iclog);

	spin_unlock(&log->l_icloglock);
	return 0;
}

/*
 * Wrapper for _xfs_log_force_lsn(), to be used when caller doesn't care
 * about errors or whether the log was flushed or not. This is the normal
 * interface to use when trying to unpin items or move the log forward.
 */
void
xfs_log_force_lsn(
	xfs_mount_t	*mp,
	xfs_lsn_t	lsn,
	uint		flags)
{
	int	error;

	trace_xfs_log_force(mp, lsn);
	error = _xfs_log_force_lsn(mp, lsn, flags, NULL);
	if (error)
		xfs_warn(mp, "%s: error %d returned.", __func__, error);
}

/*
 * Called when we want to mark the current iclog as being ready to sync to
 * disk.
 */
STATIC void
xlog_state_want_sync(xlog_t *log, xlog_in_core_t *iclog)
{
	assert_spin_locked(&log->l_icloglock);

	if (iclog->ic_state == XLOG_STATE_ACTIVE) {
		xlog_state_switch_iclogs(log, iclog, 0);
	} else {
		ASSERT(iclog->ic_state &
			(XLOG_STATE_WANT_SYNC|XLOG_STATE_IOERROR));
	}
}


/*****************************************************************************
 *
 *		TICKET functions
 *
 *****************************************************************************
 */

/*
 * 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_zone_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;
}

/*
 * Allocate and initialise a new log ticket.
 */
xlog_ticket_t *
xlog_ticket_alloc(
	struct log	*log,
	int		unit_bytes,
	int		cnt,
	char		client,
	bool		permanent,
	xfs_km_flags_t	alloc_flags)
{
	struct xlog_ticket *tic;
	uint		num_headers;
	int		iclog_space;

	tic = kmem_zone_zalloc(xfs_log_ticket_zone, alloc_flags);
	if (!tic)
		return NULL;

	/*
	 * 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(&log->l_mp->m_sb) &&
	    log->l_mp->m_sb.sb_logsunit > 1) {
		/* log su roundoff */
		unit_bytes += 2*log->l_mp->m_sb.sb_logsunit;
	} else {
		/* BB roundoff */
		unit_bytes += 2*BBSIZE;
        }

	atomic_set(&tic->t_ref, 1);
	tic->t_task		= current;
	INIT_LIST_HEAD(&tic->t_queue);
	tic->t_unit_res		= unit_bytes;
	tic->t_curr_res		= unit_bytes;
	tic->t_cnt		= cnt;
	tic->t_ocnt		= cnt;
	tic->t_tid		= random32();
	tic->t_clientid		= client;
	tic->t_flags		= XLOG_TIC_INITED;
	tic->t_trans_type	= 0;
	if (permanent)
		tic->t_flags |= XLOG_TIC_PERM_RESERV;

	xlog_tic_reset_res(tic);

	return tic;
}


/******************************************************************************
 *
 *		Log debug routines
 *
 ******************************************************************************
 */
#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.
 */
void
xlog_verify_dest_ptr(
	struct log	*log,
	char		*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 log	*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(xlog_t	    *log,
		     xlog_in_core_t *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__);
    }
}	/* xlog_verify_tail_lsn */

/*
 * 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(xlog_t	 *log,
		  xlog_in_core_t *iclog,
		  int		 count,
		  boolean_t	 syncing)
{
	xlog_op_header_t	*ophead;
	xlog_in_core_t		*icptr;
	xlog_in_core_2_t	*xhdr;
	xfs_caddr_t		ptr;
	xfs_caddr_t		base_ptr;
	__psint_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++) {
		if (icptr == NULL)
			xfs_emerg(log->l_mp, "%s: invalid ptr", __func__);
		icptr = icptr->ic_next;
	}
	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__);

	ptr = (xfs_caddr_t) &iclog->ic_header;
	for (ptr += BBSIZE; ptr < ((xfs_caddr_t)&iclog->ic_header) + 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);
	ptr = iclog->ic_datap;
	base_ptr = ptr;
	ophead = (xlog_op_header_t *)ptr;
	xhdr = iclog->ic_data;
	for (i = 0; i < len; i++) {
		ophead = (xlog_op_header_t *)ptr;

		/* clientid is only 1 byte */
		field_offset = (__psint_t)
			       ((xfs_caddr_t)&(ophead->oh_clientid) - base_ptr);
		if (syncing == B_FALSE || (field_offset & 0x1ff)) {
			clientid = ophead->oh_clientid;
		} else {
			idx = BTOBBT((xfs_caddr_t)&(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 0x%p offset 0x%lx",
				__func__, clientid, ophead,
				(unsigned long)field_offset);

		/* check length */
		field_offset = (__psint_t)
			       ((xfs_caddr_t)&(ophead->oh_len) - base_ptr);
		if (syncing == B_FALSE || (field_offset & 0x1ff)) {
			op_len = be32_to_cpu(ophead->oh_len);
		} else {
			idx = BTOBBT((__psint_t)&ophead->oh_len -
				    (__psint_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;
	}
}	/* xlog_verify_iclog */
#endif

/*
 * Mark all iclogs IOERROR. l_icloglock is held by the caller.
 */
STATIC int
xlog_state_ioerror(
	xlog_t	*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. the filesystem gets marked 'SHUTDOWN' for all interested
 *	   parties to find out, 'atomically'.
 *	b. those who're sleeping on log reservations, pinned objects and
 *	    other resources get woken up, and be told the bad news.
 *	c. nothing new gets queued up after (a) and (b) are done.
 *	d. if !logerror, flush the iclogs to disk, then seal them off
 *	   for business.
 *
 * Note: for delayed logging the !logerror case needs to flush the regions
 * held in memory out to the iclogs before flushing them to disk. This needs
 * to be done before the log is marked as shutdown, otherwise the flush to the
 * iclogs will fail.
 */
int
xfs_log_force_umount(
	struct xfs_mount	*mp,
	int			logerror)
{
	xlog_t		*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)
			XFS_BUF_DONE(mp->m_sb_bp);
		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;
	}
	retval = 0;

	/*
	 * Flush the in memory commit item list before marking the log as
	 * being shut down. We need to do it in this order to ensure all the
	 * completed transactions are flushed to disk with the xfs_log_force()
	 * call below.
	 */
	if (!logerror)
		xlog_cil_force(log);

	/*
	 * 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)
		XFS_BUF_DONE(mp->m_sb_bp);

	/*
	 * This flag is sort of redundant because of the mount flag, but
	 * it's good to maintain the separation between the log and the rest
	 * of XFS.
	 */
	log->l_flags |= XLOG_IO_ERROR;

	/*
	 * If we hit a log error, we want to mark all the iclogs IOERROR
	 * while we're still holding the loglock.
	 */
	if (logerror)
		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);

	if (!(log->l_iclog->ic_state & XLOG_STATE_IOERROR)) {
		ASSERT(!logerror);
		/*
		 * Force the incore logs to disk before shutting the
		 * log down completely.
		 */
		_xfs_log_force(mp, XFS_LOG_SYNC, NULL);

		spin_lock(&log->l_icloglock);
		retval = xlog_state_ioerror(log);
		spin_unlock(&log->l_icloglock);
	}
	/*
	 * Wake up everybody waiting on xfs_log_force.
	 * Callback all log item committed functions as if the
	 * log writes were completed.
	 */
	xlog_state_do_callback(log, XFS_LI_ABORTED, NULL);

#ifdef XFSERRORDEBUG
	{
		xlog_in_core_t	*iclog;

		spin_lock(&log->l_icloglock);
		iclog = log->l_iclog;
		do {
			ASSERT(iclog->ic_callback == 0);
			iclog = iclog->ic_next;
		} while (iclog != log->l_iclog);
		spin_unlock(&log->l_icloglock);
	}
#endif
	/* return non-zero if log IOERROR transition had already happened */
	return retval;
}

STATIC int
xlog_iclogs_empty(xlog_t *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;
}