xfs_log.c

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

kmem_zone_t *xfs_log_ticket_zone;

/* Local miscellaneous function prototypes */
STATIC int
xlog_commit_record(
    struct 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,
    boolean_t       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)
{
    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_unit_res * tic->t_cnt);

    trace_xfs_log_reserve(log, tic);

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

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

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


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

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

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

    mp->m_log = xlog_alloc_log(mp, log_target, blk_offset, num_bblks);
    if (IS_ERR(mp->m_log)) {
        error = -PTR_ERR(mp->m_log);
        goto out;
    }

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

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

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

        error = xlog_recover(mp->m_log);

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

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

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

    return 0;

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

/*
 * Finish the recovery of the file system.  This is separate from
 * the xfs_log_mount() call, because it depends on the code in
 * xfs_mountfs() to read in the root and real-time bitmap inodes
 * between calling xfs_log_mount() and here.
 *
 * mp       - ubiquitous xfs mount point structure
 */
int
xfs_log_mount_finish(xfs_mount_t *mp)
{
    int error;

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

    return error;
}

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

/*
 * Unmount record used to have a string "Unmount filesystem--" in the
 * data section where the "Un" was really a magic number (XLOG_UNMOUNT_TYPE).
 * We just write the magic number now since that particular field isn't
 * currently architecture converted and "nUmount" is a bit foo.
 * As far as I know, there weren't any dependencies on the old behaviour.
 */

int
xfs_log_unmount_write(xfs_mount_t *mp)
{
    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 */

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

}   /* xlog_iodone */

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

STATIC void
xlog_get_iclog_buffer_size(
    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 */


/*
 * 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;

    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);
}

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

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

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

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

    /* move grant heads by roundoff in sync */
    xlog_grant_add_space(log, &log->l_reserve_head.grant, roundoff);
    xlog_grant_add_space(log, &log->l_write_head.grant, roundoff);

    /* put cycle number in every block */
    xlog_pack_data(log, iclog, roundoff); 

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

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

    XFS_STATS_ADD(xs_log_blocks, BTOBB(count));

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

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

        /*
         * Flush the data device before flushing the log to make
         * sure all meta data written back from the AIL actually made
         * it to disk before stamping the new log tail LSN into the
         * log buffer.  For an external log we need to issue the
         * flush explicitly, and unfortunately synchronously here;
         * for an internal log we can simply use the block layer
         * state machine for preflushes.
         */
        if (log->l_mp->m_logdev_targp != log->l_mp->m_ddev_targp)
            xfs_blkdev_issue_flush(log->l_mp->m_ddev_targp);
        else
            bp->b_flags |= XBF_FLUSH;
    }

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

    xlog_verify_iclog(log, iclog, count, B_TRUE);

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

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

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

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


/*
 * Deallocate a log structure
 */
STATIC void
xlog_dealloc_log(
    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_CORRUPT_INCORE);
}

/*
 * Calculate the potential space needed by the log vector.  Each region gets
 * its own xlog_op_header_t and may need to be double word aligned.
 */
static int
xlog_write_calc_vec_length(
    struct xlog_ticket  *ticket,
    struct xfs_log_vec  *log_vector)
{
    struct xfs_log_vec  *lv;
    int         headers = 0;
    int         len = 0;
    int         i;

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

    for (lv = log_vector; lv; lv = lv->lv_next) {
        headers += lv->lv_niovecs;

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

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

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

    return len;
}

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

    ophdr->oh_tid   = cpu_to_be32(ticket->t_tid);
    ophdr->oh_clientid = ticket->t_clientid;
    ophdr->oh_len = 0;
    ophdr->oh_flags = XLOG_START_TRANS;
    ophdr->oh_res2 = 0;

    ticket->t_flags &= ~XLOG_TIC_INITED;

    return sizeof(struct xlog_op_header);
}

static xlog_op_header_t *
xlog_write_setup_ophdr(
    struct 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
 * 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 && index < lv->lv_niovecs) {
        void        *ptr;
        int     log_offset;

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

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

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

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

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

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

            ophdr = xlog_write_setup_ophdr(log, ptr, ticket, flags);
            if (!ophdr)
                return XFS_ERROR(EIO);

            xlog_write_adv_cnt(&ptr, &len, &log_offset,
                       sizeof(struct xlog_op_header));

            len += xlog_write_setup_copy(ticket, ophdr,
                             iclog->ic_size-log_offset,
                             reg->i_len,
                             &copy_off, &copy_len,
                             &partial_copy,
                             &partial_copy_len);
            xlog_verify_dest_ptr(log, ptr);

            /* copy region */
            ASSERT(copy_len >= 0);
            memcpy(ptr, reg->i_addr + copy_off, copy_len);
            xlog_write_adv_cnt(&ptr, &len, &log_offset, copy_len);

            copy_len += start_rec_copy + sizeof(xlog_op_header_t);
            record_cnt++;
            data_cnt += contwr ? copy_len : 0;

            error = xlog_write_copy_finish(log, iclog, flags,
                               &record_cnt, &data_cnt,
                               &partial_copy,
                               &partial_copy_len,
                               log_offset,
                               commit_iclog);
            if (error)
                return error;

            /*
             * if we had a partial copy, we need to get more iclog
             * space but we don't want to increment the region
             * index because there is still more is this region to
             * write.
             *
             * If we completed writing this region, and we flushed
             * the iclog (indicated by resetting of the record
             * count), then we also need to get more log space. If
             * this was the last record, though, we are done and
             * can just return.
             */
            if (partial_copy)
                break;

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

    ASSERT(len == 0);

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

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


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

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

/*
 * 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;
    uint        num_headers;
    int     iclog_space;

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

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

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

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

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

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

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

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

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

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

    xlog_tic_reset_res(tic);

    return tic;
}


/******************************************************************************
 *
 *      Log debug routines
 *
 ******************************************************************************
 */
#if defined(DEBUG)
/*
 * Make sure that the destination ptr is within the valid data region of
 * one of the iclogs.  This uses backup pointers stored in a different
 * part of the log in case we trash the log structure.
 */
void
xlog_verify_dest_ptr(
    struct 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,
    boolean_t       syncing)
{
    xlog_op_header_t    *ophead;
    xlog_in_core_t      *icptr;
    xlog_in_core_2_t    *xhdr;
    xfs_caddr_t     ptr;
    xfs_caddr_t     base_ptr;
    __psint_t       field_offset;
    __uint8_t       clientid;
    int         len, i, j, k, op_len;
    int         idx;

    /* check validity of iclog pointers */
    spin_lock(&log->l_icloglock);
    icptr = log->l_iclog;
    for (i=0; i < log->l_iclog_bufs; i++) {
        if (icptr == NULL)
            xfs_emerg(log->l_mp, "%s: invalid ptr", __func__);
        icptr = icptr->ic_next;
    }
    if (icptr != log->l_iclog)
        xfs_emerg(log->l_mp, "%s: corrupt iclog ring", __func__);
    spin_unlock(&log->l_icloglock);

    /* check log magic numbers */
    if (iclog->ic_header.h_magicno != cpu_to_be32(XLOG_HEADER_MAGIC_NUM))
        xfs_emerg(log->l_mp, "%s: invalid magic num", __func__);

    ptr = (xfs_caddr_t) &iclog->ic_header;
    for (ptr += BBSIZE; ptr < ((xfs_caddr_t)&iclog->ic_header) + count;
         ptr += BBSIZE) {
        if (*(__be32 *)ptr == cpu_to_be32(XLOG_HEADER_MAGIC_NUM))
            xfs_emerg(log->l_mp, "%s: unexpected magic num",
                __func__);
    }

    /* check fields */
    len = be32_to_cpu(iclog->ic_header.h_num_logops);
    ptr = iclog->ic_datap;
    base_ptr = ptr;
    ophead = (xlog_op_header_t *)ptr;
    xhdr = iclog->ic_data;
    for (i = 0; i < len; i++) {
        ophead = (xlog_op_header_t *)ptr;

        /* clientid is only 1 byte */
        field_offset = (__psint_t)
                   ((xfs_caddr_t)&(ophead->oh_clientid) - base_ptr);
        if (syncing == B_FALSE || (field_offset & 0x1ff)) {
            clientid = ophead->oh_clientid;
        } else {
            idx = BTOBBT((xfs_caddr_t)&(ophead->oh_clientid) - iclog->ic_datap);
            if (idx >= (XLOG_HEADER_CYCLE_SIZE / BBSIZE)) {
                j = idx / (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
                k = idx % (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
                clientid = xlog_get_client_id(
                    xhdr[j].hic_xheader.xh_cycle_data[k]);
            } else {
                clientid = xlog_get_client_id(
                    iclog->ic_header.h_cycle_data[idx]);
            }
        }
        if (clientid != XFS_TRANSACTION && clientid != XFS_LOG)
            xfs_warn(log->l_mp,
                "%s: invalid clientid %d op 0x%p offset 0x%lx",
                __func__, clientid, ophead,
                (unsigned long)field_offset);

        /* check length */
        field_offset = (__psint_t)
                   ((xfs_caddr_t)&(ophead->oh_len) - base_ptr);
        if (syncing == B_FALSE || (field_offset & 0x1ff)) {
            op_len = be32_to_cpu(ophead->oh_len);
        } else {
            idx = BTOBBT((__psint_t)&ophead->oh_len -
                    (__psint_t)iclog->ic_datap);
            if (idx >= (XLOG_HEADER_CYCLE_SIZE / BBSIZE)) {
                j = idx / (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
                k = idx % (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
                op_len = be32_to_cpu(xhdr[j].hic_xheader.xh_cycle_data[k]);
            } else {
                op_len = be32_to_cpu(iclog->ic_header.h_cycle_data[idx]);
            }
        }
        ptr += sizeof(xlog_op_header_t) + op_len;
    }
}   /* xlog_verify_iclog */
#endif

/*
 * Mark all iclogs IOERROR. l_icloglock is held by the caller.
 */
STATIC int
xlog_state_ioerror(
    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;
}