Linux 3.12.5

[linux/fpc-iii.git] / 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"
#include "xfs_fsops.h"
#include "xfs_cksum.h"

kmem_zone_t     *xfs_log_ticket_zone;

/* Local miscellaneous function prototypes */
STATIC int
xlog_commit_record(
        struct xlog             *log,
        struct xlog_ticket      *ticket,
        struct xlog_in_core     **iclog,
        xfs_lsn_t               *commitlsnp);

STATIC struct xlog *
xlog_alloc_log(
        struct xfs_mount        *mp,
        struct xfs_buftarg      *log_target,
        xfs_daddr_t             blk_offset,
        int                     num_bblks);
STATIC int
xlog_space_left(
        struct xlog             *log,
        atomic64_t              *head);
STATIC int
xlog_sync(
        struct xlog             *log,
        struct xlog_in_core     *iclog);
STATIC void
xlog_dealloc_log(
        struct xlog             *log);

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

STATIC void
xlog_grant_push_ail(
        struct xlog             *log,
        int                     need_bytes);
STATIC void
xlog_regrant_reserve_log_space(
        struct xlog             *log,
        struct xlog_ticket      *ticket);
STATIC void
xlog_ungrant_log_space(
        struct xlog             *log,
        struct xlog_ticket      *ticket);

#if defined(DEBUG)
STATIC void
xlog_verify_dest_ptr(
        struct xlog             *log,
        char                    *ptr);
STATIC void
xlog_verify_grant_tail(
        struct xlog *log);
STATIC void
xlog_verify_iclog(
        struct xlog             *log,
        struct xlog_in_core     *iclog,
        int                     count,
        bool                    syncing);
STATIC void
xlog_verify_tail_lsn(
        struct xlog             *log,
        struct xlog_in_core     *iclog,
        xfs_lsn_t               tail_lsn);
#else
#define xlog_verify_dest_ptr(a,b)
#define xlog_verify_grant_tail(a)
#define xlog_verify_iclog(a,b,c,d)
#define xlog_verify_tail_lsn(a,b,c)
#endif

STATIC int
xlog_iclogs_empty(
        struct xlog             *log);

static void
xlog_grant_sub_space(
        struct xlog             *log,
        atomic64_t              *head,
        int                     bytes)
{
        int64_t head_val = atomic64_read(head);
        int64_t new, old;

        do {
                int     cycle, space;

                xlog_crack_grant_head_val(head_val, &cycle, &space);

                space -= bytes;
                if (space < 0) {
                        space += log->l_logsize;
                        cycle--;
                }

                old = head_val;
                new = xlog_assign_grant_head_val(cycle, space);
                head_val = atomic64_cmpxchg(head, old, new);
        } while (head_val != old);
}

static void
xlog_grant_add_space(
        struct xlog             *log,
        atomic64_t              *head,
        int                     bytes)
{
        int64_t head_val = atomic64_read(head);
        int64_t new, old;

        do {
                int             tmp;
                int             cycle, space;

                xlog_crack_grant_head_val(head_val, &cycle, &space);

                tmp = log->l_logsize - space;
                if (tmp > bytes)
                        space += bytes;
                else {
                        space = bytes - tmp;
                        cycle++;
                }

                old = head_val;
                new = xlog_assign_grant_head_val(cycle, space);
                head_val = atomic64_cmpxchg(head, old, new);
        } while (head_val != old);
}

STATIC void
xlog_grant_head_init(
        struct xlog_grant_head  *head)
{
        xlog_assign_grant_head(&head->grant, 1, 0);
        INIT_LIST_HEAD(&head->waiters);
        spin_lock_init(&head->lock);
}

STATIC void
xlog_grant_head_wake_all(
        struct xlog_grant_head  *head)
{
        struct xlog_ticket      *tic;

        spin_lock(&head->lock);
        list_for_each_entry(tic, &head->waiters, t_queue)
                wake_up_process(tic->t_task);
        spin_unlock(&head->lock);
}

static inline int
xlog_ticket_reservation(
        struct xlog             *log,
        struct xlog_grant_head  *head,
        struct xlog_ticket      *tic)
{
        if (head == &log->l_write_head) {
                ASSERT(tic->t_flags & XLOG_TIC_PERM_RESERV);
                return tic->t_unit_res;
        } else {
                if (tic->t_flags & XLOG_TIC_PERM_RESERV)
                        return tic->t_unit_res * tic->t_cnt;
                else
                        return tic->t_unit_res;
        }
}

STATIC bool
xlog_grant_head_wake(
        struct xlog             *log,
        struct xlog_grant_head  *head,
        int                     *free_bytes)
{
        struct xlog_ticket      *tic;
        int                     need_bytes;

        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 xlog             *log,
        struct xlog_grant_head  *head,
        struct xlog_ticket      *tic,
        int                     need_bytes) __releases(&head->lock)
                                            __acquires(&head->lock)
{
        list_add_tail(&tic->t_queue, &head->waiters);

        do {
                if (XLOG_FORCED_SHUTDOWN(log))
                        goto shutdown;
                xlog_grant_push_ail(log, need_bytes);

                __set_current_state(TASK_UNINTERRUPTIBLE);
                spin_unlock(&head->lock);

                XFS_STATS_INC(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 xlog             *log,
        struct xlog_grant_head  *head,
        struct xlog_ticket      *tic,
        int                     *need_bytes)
{
        int                     free_bytes;
        int                     error = 0;

        ASSERT(!(log->l_flags & XLOG_ACTIVE_RECOVERY));

        /*
         * If there are other waiters on the queue then give them a chance at
         * logspace before us.  Wake up the first waiters, if we do not wake
         * up all the waiters then go to sleep waiting for more free space,
         * otherwise try to get some space for this transaction.
         */
        *need_bytes = xlog_ticket_reservation(log, head, tic);
        free_bytes = xlog_space_left(log, &head->grant);
        if (!list_empty_careful(&head->waiters)) {
                spin_lock(&head->lock);
                if (!xlog_grant_head_wake(log, head, &free_bytes) ||
                    free_bytes < *need_bytes) {
                        error = xlog_grant_head_wait(log, head, tic,
                                                     *need_bytes);
                }
                spin_unlock(&head->lock);
        } else if (free_bytes < *need_bytes) {
                spin_lock(&head->lock);
                error = xlog_grant_head_wait(log, head, tic, *need_bytes);
                spin_unlock(&head->lock);
        }

        return error;
}

static void
xlog_tic_reset_res(xlog_ticket_t *tic)
{
        tic->t_res_num = 0;
        tic->t_res_arr_sum = 0;
        tic->t_res_num_ophdrs = 0;
}

static void
xlog_tic_add_region(xlog_ticket_t *tic, uint len, uint type)
{
        if (tic->t_res_num == XLOG_TIC_LEN_MAX) {
                /* add to overflow and start again */
                tic->t_res_o_flow += tic->t_res_arr_sum;
                tic->t_res_num = 0;
                tic->t_res_arr_sum = 0;
        }

        tic->t_res_arr[tic->t_res_num].r_len = len;
        tic->t_res_arr[tic->t_res_num].r_type = type;
        tic->t_res_arr_sum += len;
        tic->t_res_num++;
}

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

        if (XLOG_FORCED_SHUTDOWN(log))
                return 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 xlog             *log = mp->m_log;
        struct xlog_ticket      *tic;
        int                     need_bytes;
        int                     error = 0;

        ASSERT(client == XFS_TRANSACTION || client == XFS_LOG);

        if (XLOG_FORCED_SHUTDOWN(log))
                return 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_cnt ? tic->t_unit_res * tic->t_cnt
                                            : tic->t_unit_res);

        trace_xfs_log_reserve(log, tic);

        error = xlog_grant_head_check(log, &log->l_reserve_head, tic,
                                      &need_bytes);
        if (error)
                goto out_error;

        xlog_grant_add_space(log, &log->l_reserve_head.grant, need_bytes);
        xlog_grant_add_space(log, &log->l_write_head.grant, need_bytes);
        trace_xfs_log_reserve_exit(log, tic);
        xlog_verify_grant_tail(log);
        return 0;

out_error:
        /*
         * If we are failing, make sure the ticket doesn't have any current
         * reservations.  We don't want to add this back when the ticket/
         * transaction gets cancelled.
         */
        tic->t_curr_res = 0;
        tic->t_cnt = 0; /* ungrant will give back unit_res * t_cnt. */
        return error;
}


/*
 * 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 xlog             *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 = 0;
        int             min_logfsbs;

        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;
        }

        /*
         * Validate the given log space and drop a critical message via syslog
         * if the log size is too small that would lead to some unexpected
         * situations in transaction log space reservation stage.
         *
         * Note: we can't just reject the mount if the validation fails.  This
         * would mean that people would have to downgrade their kernel just to
         * remedy the situation as there is no way to grow the log (short of
         * black magic surgery with xfs_db).
         *
         * We can, however, reject mounts for CRC format filesystems, as the
         * mkfs binary being used to make the filesystem should never create a
         * filesystem with a log that is too small.
         */
        min_logfsbs = xfs_log_calc_minimum_size(mp);

        if (mp->m_sb.sb_logblocks < min_logfsbs) {
                xfs_warn(mp,
                "Log size %d blocks too small, minimum size is %d blocks",
                         mp->m_sb.sb_logblocks, min_logfsbs);
                error = EINVAL;
        } else if (mp->m_sb.sb_logblocks > XFS_MAX_LOG_BLOCKS) {
                xfs_warn(mp,
                "Log size %d blocks too large, maximum size is %lld blocks",
                         mp->m_sb.sb_logblocks, XFS_MAX_LOG_BLOCKS);
                error = EINVAL;
        } else if (XFS_FSB_TO_B(mp, mp->m_sb.sb_logblocks) > XFS_MAX_LOG_BYTES) {
                xfs_warn(mp,
                "log size %lld bytes too large, maximum size is %lld bytes",
                         XFS_FSB_TO_B(mp, mp->m_sb.sb_logblocks),
                         XFS_MAX_LOG_BYTES);
                error = EINVAL;
        }
        if (error) {
                if (xfs_sb_version_hascrc(&mp->m_sb)) {
                        xfs_crit(mp, "AAIEEE! Log failed size checks. Abort!");
                        ASSERT(0);
                        goto out_free_log;
                }
                xfs_crit(mp,
"Log size out of supported range. Continuing onwards, but if log hangs are\n"
"experienced then please report this message in the bug report.");
        }

        /*
         * Initialize the AIL now we have a log.
         */
        error = xfs_trans_ail_init(mp);
        if (error) {
                xfs_warn(mp, "AIL initialisation failed: error %d", error);
                goto out_free_log;
        }
        mp->m_log->l_ailp = mp->m_ail;

        /*
         * skip log recovery on a norecovery mount.  pretend it all
         * just worked.
         */
        if (!(mp->m_flags & XFS_MOUNT_NORECOVERY)) {
                int     readonly = (mp->m_flags & XFS_MOUNT_RDONLY);

                if (readonly)
                        mp->m_flags &= ~XFS_MOUNT_RDONLY;

                error = xlog_recover(mp->m_log);

                if (readonly)
                        mp->m_flags |= XFS_MOUNT_RDONLY;
                if (error) {
                        xfs_warn(mp, "log mount/recovery failed: error %d",
                                error);
                        goto out_destroy_ail;
                }
        }

        /* Normal transactions can now occur */
        mp->m_log->l_flags &= ~XLOG_ACTIVE_RECOVERY;

        /*
         * Now the log has been fully initialised and we know were our
         * space grant counters are, we can initialise the permanent ticket
         * needed for delayed logging to work.
         */
        xlog_cil_init_post_recovery(mp->m_log);

        return 0;

out_destroy_ail:
        xfs_trans_ail_destroy(mp);
out_free_log:
        xlog_dealloc_log(mp->m_log);
out:
        return error;
}

/*
 * Finish the recovery of the file system.  This is separate from the
 * xfs_log_mount() call, because it depends on the code in xfs_mountfs() to read
 * in the root and real-time bitmap inodes between calling xfs_log_mount() and
 * here.
 *
 * If we finish recovery successfully, start the background log work. If we are
 * not doing recovery, then we have a RO filesystem and we don't need to start
 * it.
 */
int
xfs_log_mount_finish(xfs_mount_t *mp)
{
        int     error = 0;

        if (!(mp->m_flags & XFS_MOUNT_NORECOVERY)) {
                error = xlog_recover_finish(mp->m_log);
                if (!error)
                        xfs_log_work_queue(mp);
        } else {
                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 "Unmount" 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)
{
        struct xlog      *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 */

/*
 * Empty the log for unmount/freeze.
 *
 * To do this, we first need to shut down the background log work so it is not
 * trying to cover the log as we clean up. We then need to unpin all objects in
 * the log so we can then flush them out. Once they have completed their IO and
 * run the callbacks removing themselves from the AIL, we can write the unmount
 * record.
 */
void
xfs_log_quiesce(
        struct xfs_mount        *mp)
{
        cancel_delayed_work_sync(&mp->m_log->l_work);
        xfs_log_force(mp, XFS_LOG_SYNC);

        /*
         * The superblock buffer is uncached and while xfs_ail_push_all_sync()
         * will push it, xfs_wait_buftarg() will not wait for it. Further,
         * xfs_buf_iowait() cannot be used because it was pushed with the
         * XBF_ASYNC flag set, so we need to use a lock/unlock pair to wait for
         * the IO to complete.
         */
        xfs_ail_push_all_sync(mp->m_ail);
        xfs_wait_buftarg(mp->m_ddev_targp);
        xfs_buf_lock(mp->m_sb_bp);
        xfs_buf_unlock(mp->m_sb_bp);

        xfs_log_unmount_write(mp);
}

/*
 * Shut down and release the AIL and Log.
 *
 * During unmount, we need to ensure we flush all the dirty metadata objects
 * from the AIL so that the log is empty before we write the unmount record to
 * the log. Once this is done, we can tear down the AIL and the log.
 */
void
xfs_log_unmount(
        struct xfs_mount        *mp)
{
        xfs_log_quiesce(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 xlog             *log = mp->m_log;
        int                     free_bytes;

        if (XLOG_FORCED_SHUTDOWN(log))
                return;

        if (!list_empty_careful(&log->l_write_head.waiters)) {
                ASSERT(!(log->l_flags & XLOG_ACTIVE_RECOVERY));

                spin_lock(&log->l_write_head.lock);
                free_bytes = xlog_space_left(log, &log->l_write_head.grant);
                xlog_grant_head_wake(log, &log->l_write_head, &free_bytes);
                spin_unlock(&log->l_write_head.lock);
        }

        if (!list_empty_careful(&log->l_reserve_head.waiters)) {
                ASSERT(!(log->l_flags & XLOG_ACTIVE_RECOVERY));

                spin_lock(&log->l_reserve_head.lock);
                free_bytes = xlog_space_left(log, &log->l_reserve_head.grant);
                xlog_grant_head_wake(log, &log->l_reserve_head, &free_bytes);
                spin_unlock(&log->l_reserve_head.lock);
        }
}

/*
 * Determine if we have a transaction that has gone to disk
 * that needs to be covered. To begin the transition to the idle state
 * firstly the log needs to be idle (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;
        struct xlog     *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 xlog             *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 xlog     *log,
        atomic64_t      *head)
{
        int             free_bytes;
        int             tail_bytes;
        int             tail_cycle;
        int             head_cycle;
        int             head_bytes;

        xlog_crack_grant_head(head, &head_cycle, &head_bytes);
        xlog_crack_atomic_lsn(&log->l_tail_lsn, &tail_cycle, &tail_bytes);
        tail_bytes = BBTOB(tail_bytes);
        if (tail_cycle == head_cycle && head_bytes >= tail_bytes)
                free_bytes = log->l_logsize - (head_bytes - tail_bytes);
        else if (tail_cycle + 1 < head_cycle)
                return 0;
        else if (tail_cycle < head_cycle) {
                ASSERT(tail_cycle == (head_cycle - 1));
                free_bytes = tail_bytes - head_bytes;
        } else {
                /*
                 * The reservation head is behind the tail.
                 * In this case we just want to return the size of the
                 * log as the amount of space left.
                 */
                xfs_alert(log->l_mp,
                        "xlog_space_left: head behind tail\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)
{
        struct xlog_in_core     *iclog = bp->b_fspriv;
        struct xlog             *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.
         */
}

/*
 * Return size of each in-core log record buffer.
 *
 * All machines get 8 x 32kB buffers by default, unless tuned otherwise.
 *
 * If the filesystem blocksize is too large, we may need to choose a
 * larger size since the directory code currently logs entire blocks.
 */

STATIC void
xlog_get_iclog_buffer_size(
        struct xfs_mount        *mp,
        struct xlog             *log)
{
        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 */


void
xfs_log_work_queue(
        struct xfs_mount        *mp)
{
        queue_delayed_work(mp->m_log_workqueue, &mp->m_log->l_work,
                                msecs_to_jiffies(xfs_syncd_centisecs * 10));
}

/*
 * Every sync period we need to unpin all items in the AIL and push them to
 * disk. If there is nothing dirty, then we might need to cover the log to
 * indicate that the filesystem is idle.
 */
void
xfs_log_worker(
        struct work_struct      *work)
{
        struct xlog             *log = container_of(to_delayed_work(work),
                                                struct xlog, l_work);
        struct xfs_mount        *mp = log->l_mp;

        /* dgc: errors ignored - not fatal and nowhere to report them */
        if (xfs_log_need_covered(mp))
                xfs_fs_log_dummy(mp);
        else
                xfs_log_force(mp, 0);

        /* start pushing all the metadata that is currently dirty */
        xfs_ail_push_all(mp->m_ail);

        /* queue us up again */
        xfs_log_work_queue(mp);
}

/*
 * This routine initializes some of the log structure for a given mount point.
 * Its primary purpose is to fill in enough, so recovery can occur.  However,
 * some other stuff may be filled in too.
 */
STATIC struct xlog *
xlog_alloc_log(
        struct xfs_mount        *mp,
        struct xfs_buftarg      *log_target,
        xfs_daddr_t             blk_offset,
        int                     num_bblks)
{
        struct xlog             *log;
        xlog_rec_header_t       *head;
        xlog_in_core_t          **iclogp;
        xlog_in_core_t          *iclog, *prev_iclog=NULL;
        xfs_buf_t               *bp;
        int                     i;
        int                     error = ENOMEM;
        uint                    log2_size = 0;

        log = kmem_zalloc(sizeof(struct xlog), KM_MAYFAIL);
        if (!log) {
                xfs_warn(mp, "Log allocation failed: No memory!");
                goto out;
        }

        log->l_mp          = mp;
        log->l_targ        = log_target;
        log->l_logsize     = BBTOB(num_bblks);
        log->l_logBBstart  = blk_offset;
        log->l_logBBsize   = num_bblks;
        log->l_covered_state = XLOG_STATE_COVER_IDLE;
        log->l_flags       |= XLOG_ACTIVE_RECOVERY;
        INIT_DELAYED_WORK(&log->l_work, xfs_log_worker);

        log->l_prev_block  = -1;
        /* log->l_tail_lsn = 0x100000000LL; cycle = 1; current block = 0 */
        xlog_assign_atomic_lsn(&log->l_tail_lsn, 1, 0);
        xlog_assign_atomic_lsn(&log->l_last_sync_lsn, 1, 0);
        log->l_curr_cycle  = 1;     /* 0 is bad since this is initial value */

        xlog_grant_head_init(&log->l_reserve_head);
        xlog_grant_head_init(&log->l_write_head);

        error = EFSCORRUPTED;
        if (xfs_sb_version_hassector(&mp->m_sb)) {
                log2_size = mp->m_sb.sb_logsectlog;
                if (log2_size < BBSHIFT) {
                        xfs_warn(mp, "Log sector size too small (0x%x < 0x%x)",
                                log2_size, BBSHIFT);
                        goto out_free_log;
                }

                log2_size -= BBSHIFT;
                if (log2_size > mp->m_sectbb_log) {
                        xfs_warn(mp, "Log sector size too large (0x%x > 0x%x)",
                                log2_size, mp->m_sectbb_log);
                        goto out_free_log;
                }

                /* for larger sector sizes, must have v2 or external log */
                if (log2_size && log->l_logBBstart > 0 &&
                            !xfs_sb_version_haslogv2(&mp->m_sb)) {
                        xfs_warn(mp,
                "log sector size (0x%x) invalid for configuration.",
                                log2_size);
                        goto out_free_log;
                }
        }
        log->l_sectBBsize = 1 << log2_size;

        xlog_get_iclog_buffer_size(mp, log);

        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 xlog             *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 xlog     *log,
        int             need_bytes)
{
        xfs_lsn_t       threshold_lsn = 0;
        xfs_lsn_t       last_sync_lsn;
        int             free_blocks;
        int             free_bytes;
        int             threshold_block;
        int             threshold_cycle;
        int             free_threshold;

        ASSERT(BTOBB(need_bytes) < log->l_logBBsize);

        free_bytes = xlog_space_left(log, &log->l_reserve_head.grant);
        free_blocks = BTOBBT(free_bytes);

        /*
         * Set the threshold for the minimum number of free blocks in the
         * log to the maximum of what the caller needs, one quarter of the
         * log, and 256 blocks.
         */
        free_threshold = BTOBB(need_bytes);
        free_threshold = MAX(free_threshold, (log->l_logBBsize >> 2));
        free_threshold = MAX(free_threshold, 256);
        if (free_blocks >= free_threshold)
                return;

        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);
}

/*
 * Stamp cycle number in every block
 */
STATIC void
xlog_pack_data(
        struct xlog             *log,
        struct xlog_in_core     *iclog,
        int                     roundoff)
{
        int                     i, j, k;
        int                     size = iclog->ic_offset + roundoff;
        __be32                  cycle_lsn;
        xfs_caddr_t             dp;

        cycle_lsn = CYCLE_LSN_DISK(iclog->ic_header.h_lsn);

        dp = iclog->ic_datap;
        for (i = 0; i < BTOBB(size); i++) {
                if (i >= (XLOG_HEADER_CYCLE_SIZE / BBSIZE))
                        break;
                iclog->ic_header.h_cycle_data[i] = *(__be32 *)dp;
                *(__be32 *)dp = cycle_lsn;
                dp += BBSIZE;
        }

        if (xfs_sb_version_haslogv2(&log->l_mp->m_sb)) {
                xlog_in_core_2_t *xhdr = iclog->ic_data;

                for ( ; i < BTOBB(size); i++) {
                        j = i / (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
                        k = i % (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
                        xhdr[j].hic_xheader.xh_cycle_data[k] = *(__be32 *)dp;
                        *(__be32 *)dp = cycle_lsn;
                        dp += BBSIZE;
                }

                for (i = 1; i < log->l_iclog_heads; i++)
                        xhdr[i].hic_xheader.xh_cycle = cycle_lsn;
        }
}

/*
 * Calculate the checksum for a log buffer.
 *
 * This is a little more complicated than it should be because the various
 * headers and the actual data are non-contiguous.
 */
__le32
xlog_cksum(
        struct xlog             *log,
        struct xlog_rec_header  *rhead,
        char                    *dp,
        int                     size)
{
        __uint32_t              crc;

        /* first generate the crc for the record header ... */
        crc = xfs_start_cksum((char *)rhead,
                              sizeof(struct xlog_rec_header),
                              offsetof(struct xlog_rec_header, h_crc));

        /* ... then for additional cycle data for v2 logs ... */
        if (xfs_sb_version_haslogv2(&log->l_mp->m_sb)) {
                union xlog_in_core2 *xhdr = (union xlog_in_core2 *)rhead;
                int             i;

                for (i = 1; i < log->l_iclog_heads; i++) {
                        crc = crc32c(crc, &xhdr[i].hic_xheader,
                                     sizeof(struct xlog_rec_ext_header));
                }
        }

        /* ... and finally for the payload */
        crc = crc32c(crc, dp, size);

        return xfs_end_cksum(crc);
}

/*
 * 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(
        struct xlog             *log,
        struct xlog_in_core     *iclog)
{
        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);
        int             size;

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

        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) {
                char            *dptr;

                split = count - (BBTOB(log->l_logBBsize - XFS_BUF_ADDR(bp)));
                count = BBTOB(log->l_logBBsize - XFS_BUF_ADDR(bp));
                iclog->ic_bwritecnt = 2;

                /*
                 * Bump the cycle numbers at the start of each block in the
                 * part of the iclog that ends up in the buffer that gets
                 * written to the start of the log.
                 *
                 * Watch out for the header magic number case, though.
                 */
                dptr = (char *)&iclog->ic_header + count;
                for (i = 0; i < split; i += BBSIZE) {
                        __uint32_t cycle = be32_to_cpu(*(__be32 *)dptr);
                        if (++cycle == XLOG_HEADER_MAGIC_NUM)
                                cycle++;
                        *(__be32 *)dptr = cpu_to_be32(cycle);

                        dptr += BBSIZE;
                }
        } else {
                iclog->ic_bwritecnt = 1;
        }

        /* calculcate the checksum */
        iclog->ic_header.h_crc = xlog_cksum(log, &iclog->ic_header,
                                            iclog->ic_datap, size);

        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, 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;

                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(
        struct xlog     *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(
        struct xlog             *log,
        struct xlog_in_core     *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_LOG_IO_ERROR);
}

/*
 * 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) {
                /* we don't write ordered log vectors */
                if (lv->lv_buf_len == XFS_LOG_VEC_ORDERED)
                        continue;

                headers += lv->lv_niovecs;

                for (i = 0; i < lv->lv_niovecs; i++) {
                        struct xfs_log_iovec    *vecp = &lv->lv_iovecp[i];

                        len += vecp->i_len;
                        xlog_tic_add_region(ticket, vecp->i_len, vecp->i_type);
                }
        }

        ticket->t_res_num_ophdrs += headers;
        len += headers * sizeof(struct xlog_op_header);

        return len;
}

/*
 * 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 xlog             *log,
        struct xlog_op_header   *ophdr,
        struct xlog_ticket      *ticket,
        uint                    flags)
{
        ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
        ophdr->oh_clientid = ticket->t_clientid;
        ophdr->oh_res2 = 0;

        /* are we copying a commit or unmount record? */
        ophdr->oh_flags = flags;

        /*
         * We've seen logs corrupted with bad transaction client ids.  This
         * makes sure that XFS doesn't generate them on.  Turn this into an EIO
         * and shut down the filesystem.
         */
        switch (ophdr->oh_clientid)  {
        case XFS_TRANSACTION:
        case XFS_VOLUME:
        case XFS_LOG:
                break;
        default:
                xfs_warn(log->l_mp,
                        "Bad XFS transaction clientid 0x%x in ticket 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
 * be written in an obvious, self documenting manner.
 */
static int
xlog_write_setup_copy(
        struct xlog_ticket      *ticket,
        struct xlog_op_header   *ophdr,
        int                     space_available,
        int                     space_required,
        int                     *copy_off,
        int                     *copy_len,
        int                     *last_was_partial_copy,
        int                     *bytes_consumed)
{
        int                     still_to_copy;

        still_to_copy = space_required - *bytes_consumed;
        *copy_off = *bytes_consumed;

        if (still_to_copy <= space_available) {
                /* write of region completes here */
                *copy_len = still_to_copy;
                ophdr->oh_len = cpu_to_be32(*copy_len);
                if (*last_was_partial_copy)
                        ophdr->oh_flags |= (XLOG_END_TRANS|XLOG_WAS_CONT_TRANS);
                *last_was_partial_copy = 0;
                *bytes_consumed = 0;
                return 0;
        }

        /* partial write of region, needs extra log op header reservation */
        *copy_len = space_available;
        ophdr->oh_len = cpu_to_be32(*copy_len);
        ophdr->oh_flags |= XLOG_CONTINUE_TRANS;
        if (*last_was_partial_copy)
                ophdr->oh_flags |= XLOG_WAS_CONT_TRANS;
        *bytes_consumed += *copy_len;
        (*last_was_partial_copy)++;

        /* account for new log op header */
        ticket->t_curr_res -= sizeof(struct xlog_op_header);
        ticket->t_res_num_ophdrs++;

        return sizeof(struct xlog_op_header);
}

static int
xlog_write_copy_finish(
        struct xlog             *log,
        struct xlog_in_core     *iclog,
        uint                    flags,
        int                     *record_cnt,
        int                     *data_cnt,
        int                     *partial_copy,
        int                     *partial_copy_len,
        int                     log_offset,
        struct xlog_in_core     **commit_iclog)
{
        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 xlog             *log,
        struct xfs_log_vec      *log_vector,
        struct xlog_ticket      *ticket,
        xfs_lsn_t               *start_lsn,
        struct xlog_in_core     **commit_iclog,
        uint                    flags)
{
        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 && (!lv->lv_niovecs || index < lv->lv_niovecs)) {
                void            *ptr;
                int             log_offset;

                error = xlog_state_get_iclog_space(log, len, &iclog, ticket,
                                                   &contwr, &log_offset);
                if (error)
                        return error;

                ASSERT(log_offset <= iclog->ic_size - 1);
                ptr = iclog->ic_datap + log_offset;

                /* start_lsn is the first lsn written to. That's all we need. */
                if (!*start_lsn)
                        *start_lsn = be64_to_cpu(iclog->ic_header.h_lsn);

                /*
                 * This loop writes out as many regions as can fit in the amount
                 * of space which was allocated by xlog_state_get_iclog_space().
                 */
                while (lv && (!lv->lv_niovecs || index < lv->lv_niovecs)) {
                        struct xfs_log_iovec    *reg;
                        struct xlog_op_header   *ophdr;
                        int                     start_rec_copy;
                        int                     copy_len;
                        int                     copy_off;
                        bool                    ordered = false;

                        /* ordered log vectors have no regions to write */
                        if (lv->lv_buf_len == XFS_LOG_VEC_ORDERED) {
                                ASSERT(lv->lv_niovecs == 0);
                                ordered = true;
                                goto next_lv;
                        }

                        reg = &vecp[index];
                        ASSERT(reg->i_len % sizeof(__int32_t) == 0);
                        ASSERT((unsigned long)ptr % sizeof(__int32_t) == 0);

                        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) {
next_lv:
                                lv = lv->lv_next;
                                index = 0;
                                if (lv)
                                        vecp = lv->lv_iovecp;
                        }
                        if (record_cnt == 0 && ordered == false) {
                                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(
        struct xlog *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(
        struct xlog     *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(
        struct xlog             *log,
        int                     aborted,
        struct xlog_in_core     *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;


                                /*
                                 * Completion of a iclog IO does not imply that
                                 * a transaction has completed, as transactions
                                 * can be large enough to span many iclogs. We
                                 * cannot change the tail of the log half way
                                 * through a transaction as this may be the only
                                 * transaction in the log and moving th etail to
                                 * point to the middle of it will prevent
                                 * recovery from finding the start of the
                                 * transaction. Hence we should only update the
                                 * last_sync_lsn if this iclog contains
                                 * transaction completion callbacks on it.
                                 *
                                 * We have to do this before we drop the
                                 * icloglock to ensure we are the only one that
                                 * can update it.
                                 */
                                ASSERT(XFS_LSN_CMP(atomic64_read(&log->l_last_sync_lsn),
                                        be64_to_cpu(iclog->ic_header.h_lsn)) <= 0);
                                if (iclog->ic_callback)
                                        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)
{
        struct xlog        *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(
        struct xlog             *log,
        int                     len,
        struct xlog_in_core     **iclogp,
        struct xlog_ticket      *ticket,
        int                     *continued_write,
        int                     *logoffsetp)
{
        int               log_offset;
        xlog_rec_header_t *head;
        xlog_in_core_t    *iclog;
        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(
        struct xlog             *log,
        struct xlog_ticket      *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(
        struct xlog             *log,
        struct xlog_ticket      *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(
        struct xlog             *log,
        struct xlog_in_core     *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(
        struct xlog             *log,
        struct xlog_in_core     *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 xlog             *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 xlog             *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(
        struct xlog             *log,
        struct xlog_in_core     *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;
}

/*
 * Figure out the total log space unit (in bytes) that would be
 * required for a log ticket.
 */
int
xfs_log_calc_unit_res(
        struct xfs_mount        *mp,
        int                     unit_bytes)
{
        struct xlog             *log = mp->m_log;
        int                     iclog_space;
        uint                    num_headers;

        /*
         * Permanent reservations have up to 'cnt'-1 active log operations
         * in the log.  A unit in this case is the amount of space for one
         * of these log operations.  Normal reservations have a cnt of 1
         * and their unit amount is the total amount of space required.
         *
         * The following lines of code account for non-transaction data
         * which occupy space in the on-disk log.
         *
         * Normal form of a transaction is:
         * <oph><trans-hdr><start-oph><reg1-oph><reg1><reg2-oph>...<commit-oph>
         * and then there are LR hdrs, split-recs and roundoff at end of syncs.
         *
         * We need to account for all the leadup data and trailer data
         * around the transaction data.
         * And then we need to account for the worst case in terms of using
         * more space.
         * The worst case will happen if:
         * - the placement of the transaction happens to be such that the
         *   roundoff is at its maximum
         * - the transaction data is synced before the commit record is synced
         *   i.e. <transaction-data><roundoff> | <commit-rec><roundoff>
         *   Therefore the commit record is in its own Log Record.
         *   This can happen as the commit record is called with its
         *   own region to xlog_write().
         *   This then means that in the worst case, roundoff can happen for
         *   the commit-rec as well.
         *   The commit-rec is smaller than padding in this scenario and so it is
         *   not added separately.
         */

        /* for trans header */
        unit_bytes += sizeof(xlog_op_header_t);
        unit_bytes += sizeof(xfs_trans_header_t);

        /* for start-rec */
        unit_bytes += sizeof(xlog_op_header_t);

        /*
         * for LR headers - the space for data in an iclog is the size minus
         * the space used for the headers. If we use the iclog size, then we
         * undercalculate the number of headers required.
         *
         * Furthermore - the addition of op headers for split-recs might
         * increase the space required enough to require more log and op
         * headers, so take that into account too.
         *
         * IMPORTANT: This reservation makes the assumption that if this
         * transaction is the first in an iclog and hence has the LR headers
         * accounted to it, then the remaining space in the iclog is
         * exclusively for this transaction.  i.e. if the transaction is larger
         * than the iclog, it will be the only thing in that iclog.
         * Fundamentally, this means we must pass the entire log vector to
         * xlog_write to guarantee this.
         */
        iclog_space = log->l_iclog_size - log->l_iclog_hsize;
        num_headers = howmany(unit_bytes, iclog_space);

        /* for split-recs - ophdrs added when data split over LRs */
        unit_bytes += sizeof(xlog_op_header_t) * num_headers;

        /* add extra header reservations if we overrun */
        while (!num_headers ||
               howmany(unit_bytes, iclog_space) > num_headers) {
                unit_bytes += sizeof(xlog_op_header_t);
                num_headers++;
        }
        unit_bytes += log->l_iclog_hsize * num_headers;

        /* for commit-rec LR header - note: padding will subsume the ophdr */
        unit_bytes += log->l_iclog_hsize;

        /* for roundoff padding for transaction data and one for commit record */
        if (xfs_sb_version_haslogv2(&mp->m_sb) && mp->m_sb.sb_logsunit > 1) {
                /* log su roundoff */
                unit_bytes += 2 * mp->m_sb.sb_logsunit;
        } else {
                /* BB roundoff */
                unit_bytes += 2 * BBSIZE;
        }

        return unit_bytes;
}

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

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

        unit_res = xfs_log_calc_unit_res(log->l_mp, unit_bytes);

        atomic_set(&tic->t_ref, 1);
        tic->t_task             = current;
        INIT_LIST_HEAD(&tic->t_queue);
        tic->t_unit_res         = unit_res;
        tic->t_curr_res         = unit_res;
        tic->t_cnt              = cnt;
        tic->t_ocnt             = cnt;
        tic->t_tid              = prandom_u32();
        tic->t_clientid         = client;
        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 xlog     *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 xlog     *log)
{
        int             tail_cycle, tail_blocks;
        int             cycle, space;

        xlog_crack_grant_head(&log->l_write_head.grant, &cycle, &space);
        xlog_crack_atomic_lsn(&log->l_tail_lsn, &tail_cycle, &tail_blocks);
        if (tail_cycle != cycle) {
                if (cycle - 1 != tail_cycle &&
                    !(log->l_flags & XLOG_TAIL_WARN)) {
                        xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
                                "%s: cycle - 1 != tail_cycle", __func__);
                        log->l_flags |= XLOG_TAIL_WARN;
                }

                if (space > BBTOB(tail_blocks) &&
                    !(log->l_flags & XLOG_TAIL_WARN)) {
                        xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
                                "%s: space > BBTOB(tail_blocks)", __func__);
                        log->l_flags |= XLOG_TAIL_WARN;
                }
        }
}

/* check if it will fit */
STATIC void
xlog_verify_tail_lsn(
        struct xlog             *log,
        struct xlog_in_core     *iclog,
        xfs_lsn_t               tail_lsn)
{
    int blocks;

    if (CYCLE_LSN(tail_lsn) == log->l_prev_cycle) {
        blocks =
            log->l_logBBsize - (log->l_prev_block - BLOCK_LSN(tail_lsn));
        if (blocks < BTOBB(iclog->ic_offset)+BTOBB(log->l_iclog_hsize))
                xfs_emerg(log->l_mp, "%s: ran out of log space", __func__);
    } else {
        ASSERT(CYCLE_LSN(tail_lsn)+1 == log->l_prev_cycle);

        if (BLOCK_LSN(tail_lsn) == log->l_prev_block)
                xfs_emerg(log->l_mp, "%s: tail wrapped", __func__);

        blocks = BLOCK_LSN(tail_lsn) - log->l_prev_block;
        if (blocks < BTOBB(iclog->ic_offset) + 1)
                xfs_emerg(log->l_mp, "%s: ran out of log space", __func__);
    }
}       /* 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(
        struct xlog             *log,
        struct xlog_in_core     *iclog,
        int                     count,
        bool                    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 || (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 || (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(
        struct xlog     *log)
{
        xlog_in_core_t  *iclog, *ic;

        iclog = log->l_iclog;
        if (! (iclog->ic_state & XLOG_STATE_IOERROR)) {
                /*
                 * Mark all the incore logs IOERROR.
                 * From now on, no log flushes will result.
                 */
                ic = iclog;
                do {
                        ic->ic_state = XLOG_STATE_IOERROR;
                        ic = ic->ic_next;
                } while (ic != iclog);
                return 0;
        }
        /*
         * Return non-zero, if state transition has already happened.
         */
        return 1;
}

/*
 * This is called from xfs_force_shutdown, when we're forcibly
 * shutting down the filesystem, typically because of an IO error.
 * Our main objectives here are to make sure that:
 *      a. 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)
{
        struct xlog     *log;
        int             retval;

        log = mp->m_log;

        /*
         * If this happens during log recovery, don't worry about
         * locking; the log isn't open for business yet.
         */
        if (!log ||
            log->l_flags & XLOG_ACTIVE_RECOVERY) {
                mp->m_flags |= XFS_MOUNT_FS_SHUTDOWN;
                if (mp->m_sb_bp)
                        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(
        struct xlog     *log)
{
        xlog_in_core_t  *iclog;

        iclog = log->l_iclog;
        do {
                /* endianness does not matter here, zero is zero in
                 * any language.
                 */
                if (iclog->ic_header.h_num_logops)
                        return 0;
                iclog = iclog->ic_next;
        } while (iclog != log->l_iclog);
        return 1;
}