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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (c) 2000-2005 Silicon Graphics, Inc.
  * All Rights Reserved.
  */
 #include "xfs.h"
 #include "xfs_fs.h"
 #include "xfs_shared.h"
 #include "xfs_format.h"
 #include "xfs_log_format.h"
 #include "xfs_trans_resv.h"
 #include "xfs_mount.h"
 #include "xfs_errortag.h"
 #include "xfs_error.h"
 #include "xfs_trans.h"
 #include "xfs_trans_priv.h"
 #include "xfs_log.h"
 #include "xfs_log_priv.h"
 #include "xfs_trace.h"
 #include "xfs_sysfs.h"
 #include "xfs_sb.h"
 #include "xfs_health.h"
 
 struct kmem_cache   *xfs_log_ticket_cache;
 
 /* Local miscellaneous function prototypes */
 STATIC struct xlog *
 xlog_alloc_log(
     struct xfs_mount    *mp,
     struct xfs_buftarg  *log_target,
     xfs_daddr_t     blk_offset,
     int         num_bblks);
 STATIC int
 xlog_space_left(
     struct xlog     *log,
     atomic64_t      *head);
 STATIC void
 xlog_dealloc_log(
     struct xlog     *log);
 
 /* local state machine functions */
 STATIC void xlog_state_done_syncing(
     struct xlog_in_core *iclog);
 STATIC void xlog_state_do_callback(
     struct xlog     *log);
 STATIC int
 xlog_state_get_iclog_space(
     struct xlog     *log,
     int         len,
     struct xlog_in_core **iclog,
     struct xlog_ticket  *ticket,
     int         *logoffsetp);
 STATIC void
 xlog_grant_push_ail(
     struct xlog     *log,
     int         need_bytes);
 STATIC void
 xlog_sync(
     struct xlog     *log,
     struct xlog_in_core *iclog,
     struct xlog_ticket  *ticket);
 #if defined(DEBUG)
 STATIC void
 xlog_verify_grant_tail(
     struct xlog *log);
 STATIC void
 xlog_verify_iclog(
     struct xlog     *log,
     struct xlog_in_core *iclog,
     int         count);
 STATIC void
 xlog_verify_tail_lsn(
     struct xlog     *log,
     struct xlog_in_core *iclog);
 #else
 #define xlog_verify_grant_tail(a)
 #define xlog_verify_iclog(a,b,c)
 #define xlog_verify_tail_lsn(a,b)
 #endif
 
 STATIC int
 xlog_iclogs_empty(
     struct xlog     *log);
 
 static int
 xfs_log_cover(struct xfs_mount *);
 
 /*
  * We need to make sure the buffer pointer returned is naturally aligned for the
  * biggest basic data type we put into it. We have already accounted for this
  * padding when sizing the buffer.
  *
  * However, this padding does not get written into the log, and hence we have to
  * track the space used by the log vectors separately to prevent log space hangs
  * due to inaccurate accounting (i.e. a leak) of the used log space through the
  * CIL context ticket.
  *
  * We also add space for the xlog_op_header that describes this region in the
  * log. This prepends the data region we return to the caller to copy their data
  * into, so do all the static initialisation of the ophdr now. Because the ophdr
  * is not 8 byte aligned, we have to be careful to ensure that we align the
  * start of the buffer such that the region we return to the call is 8 byte
  * aligned and packed against the tail of the ophdr.
  */
 void *
 xlog_prepare_iovec(
     struct xfs_log_vec  *lv,
     struct xfs_log_iovec    **vecp,
     uint            type)
 {
     struct xfs_log_iovec    *vec = *vecp;
     struct xlog_op_header   *oph;
     uint32_t        len;
     void            *buf;
 
     if (vec) {
         ASSERT(vec - lv->lv_iovecp < lv->lv_niovecs);
         vec++;
     } else {
         vec = &lv->lv_iovecp[0];
     }
 
     len = lv->lv_buf_len + sizeof(struct xlog_op_header);
     if (!IS_ALIGNED(len, sizeof(uint64_t))) {
         lv->lv_buf_len = round_up(len, sizeof(uint64_t)) -
                     sizeof(struct xlog_op_header);
     }
 
     vec->i_type = type;
     vec->i_addr = lv->lv_buf + lv->lv_buf_len;
 
     oph = vec->i_addr;
     oph->oh_clientid = XFS_TRANSACTION;
     oph->oh_res2 = 0;
     oph->oh_flags = 0;
 
     buf = vec->i_addr + sizeof(struct xlog_op_header);
     ASSERT(IS_ALIGNED((unsigned long)buf, sizeof(uint64_t)));
 
     *vecp = vec;
     return buf;
 }
 
 static void
 xlog_grant_sub_space(
     struct xlog     *log,
     atomic64_t      *head,
     int         bytes)
 {
     int64_t head_val = atomic64_read(head);
     int64_t new, old;
 
     do {
         int cycle, space;
 
         xlog_crack_grant_head_val(head_val, &cycle, &space);
 
         space -= bytes;
         if (space < 0) {
             space += log->l_logsize;
             cycle--;
         }
 
         old = head_val;
         new = xlog_assign_grant_head_val(cycle, space);
         head_val = atomic64_cmpxchg(head, old, new);
     } while (head_val != old);
 }
 
 static void
 xlog_grant_add_space(
     struct xlog     *log,
     atomic64_t      *head,
     int         bytes)
 {
     int64_t head_val = atomic64_read(head);
     int64_t new, old;
 
     do {
         int     tmp;
         int     cycle, space;
 
         xlog_crack_grant_head_val(head_val, &cycle, &space);
 
         tmp = log->l_logsize - space;
         if (tmp > bytes)
             space += bytes;
         else {
             space = bytes - tmp;
             cycle++;
         }
 
         old = head_val;
         new = xlog_assign_grant_head_val(cycle, space);
         head_val = atomic64_cmpxchg(head, old, new);
     } while (head_val != old);
 }
 
 STATIC void
 xlog_grant_head_init(
     struct xlog_grant_head  *head)
 {
     xlog_assign_grant_head(&head->grant, 1, 0);
     INIT_LIST_HEAD(&head->waiters);
     spin_lock_init(&head->lock);
 }
 
 STATIC void
 xlog_grant_head_wake_all(
     struct xlog_grant_head  *head)
 {
     struct xlog_ticket  *tic;
 
     spin_lock(&head->lock);
     list_for_each_entry(tic, &head->waiters, t_queue)
         wake_up_process(tic->t_task);
     spin_unlock(&head->lock);
 }
 
 static inline int
 xlog_ticket_reservation(
     struct xlog     *log,
     struct xlog_grant_head  *head,
     struct xlog_ticket  *tic)
 {
     if (head == &log->l_write_head) {
         ASSERT(tic->t_flags & XLOG_TIC_PERM_RESERV);
         return tic->t_unit_res;
     } else {
         if (tic->t_flags & XLOG_TIC_PERM_RESERV)
             return tic->t_unit_res * tic->t_cnt;
         else
             return tic->t_unit_res;
     }
 }
 
 STATIC bool
 xlog_grant_head_wake(
     struct xlog     *log,
     struct xlog_grant_head  *head,
     int         *free_bytes)
 {
     struct xlog_ticket  *tic;
     int         need_bytes;
     bool            woken_task = false;
 
     list_for_each_entry(tic, &head->waiters, t_queue) {
 
         /*
          * There is a chance that the size of the CIL checkpoints in
          * progress at the last AIL push target calculation resulted in
          * limiting the target to the log head (l_last_sync_lsn) at the
          * time. This may not reflect where the log head is now as the
          * CIL checkpoints may have completed.
          *
          * Hence when we are woken here, it may be that the head of the
          * log that has moved rather than the tail. As the tail didn't
          * move, there still won't be space available for the
          * reservation we require.  However, if the AIL has already
          * pushed to the target defined by the old log head location, we
          * will hang here waiting for something else to update the AIL
          * push target.
          *
          * Therefore, if there isn't space to wake the first waiter on
          * the grant head, we need to push the AIL again to ensure the
          * target reflects both the current log tail and log head
          * position before we wait for the tail to move again.
          */
 
         need_bytes = xlog_ticket_reservation(log, head, tic);
         if (*free_bytes < need_bytes) {
             if (!woken_task)
                 xlog_grant_push_ail(log, need_bytes);
             return false;
         }
 
         *free_bytes -= need_bytes;
         trace_xfs_log_grant_wake_up(log, tic);
         wake_up_process(tic->t_task);
         woken_task = true;
     }
 
     return true;
 }
 
 STATIC int
 xlog_grant_head_wait(
     struct xlog     *log,
     struct xlog_grant_head  *head,
     struct xlog_ticket  *tic,
     int         need_bytes) __releases(&head->lock)
                         __acquires(&head->lock)
 {
     list_add_tail(&tic->t_queue, &head->waiters);
 
     do {
         if (xlog_is_shutdown(log))
             goto shutdown;
         xlog_grant_push_ail(log, need_bytes);
 
         __set_current_state(TASK_UNINTERRUPTIBLE);
         spin_unlock(&head->lock);
 
         XFS_STATS_INC(log->l_mp, xs_sleep_logspace);
 
         trace_xfs_log_grant_sleep(log, tic);
         schedule();
         trace_xfs_log_grant_wake(log, tic);
 
         spin_lock(&head->lock);
         if (xlog_is_shutdown(log))
             goto shutdown;
     } while (xlog_space_left(log, &head->grant) < need_bytes);
 
     list_del_init(&tic->t_queue);
     return 0;
 shutdown:
     list_del_init(&tic->t_queue);
     return -EIO;
 }
 
 /*
  * Atomically get the log space required for a log ticket.
  *
  * Once a ticket gets put onto head->waiters, it will only return after the
  * needed reservation is satisfied.
  *
  * This function is structured so that it has a lock free fast path. This is
  * necessary because every new transaction reservation will come through this
  * path. Hence any lock will be globally hot if we take it unconditionally on
  * every pass.
  *
  * As tickets are only ever moved on and off head->waiters under head->lock, we
  * only need to take that lock if we are going to add the ticket to the queue
  * and sleep. We can avoid taking the lock if the ticket was never added to
  * head->waiters because the t_queue list head will be empty and we hold the
  * only reference to it so it can safely be checked unlocked.
  */
 STATIC int
 xlog_grant_head_check(
     struct xlog     *log,
     struct xlog_grant_head  *head,
     struct xlog_ticket  *tic,
     int         *need_bytes)
 {
     int         free_bytes;
     int         error = 0;
 
     ASSERT(!xlog_in_recovery(log));
 
     /*
      * If there are other waiters on the queue then give them a chance at
      * logspace before us.  Wake up the first waiters, if we do not wake
      * up all the waiters then go to sleep waiting for more free space,
      * otherwise try to get some space for this transaction.
      */
     *need_bytes = xlog_ticket_reservation(log, head, tic);
     free_bytes = xlog_space_left(log, &head->grant);
     if (!list_empty_careful(&head->waiters)) {
         spin_lock(&head->lock);
         if (!xlog_grant_head_wake(log, head, &free_bytes) ||
             free_bytes < *need_bytes) {
             error = xlog_grant_head_wait(log, head, tic,
                              *need_bytes);
         }
         spin_unlock(&head->lock);
     } else if (free_bytes < *need_bytes) {
         spin_lock(&head->lock);
         error = xlog_grant_head_wait(log, head, tic, *need_bytes);
         spin_unlock(&head->lock);
     }
 
     return error;
 }
 
 bool
 xfs_log_writable(
     struct xfs_mount    *mp)
 {
     /*
      * Do not write to the log on norecovery mounts, if the data or log
      * devices are read-only, or if the filesystem is shutdown. Read-only
      * mounts allow internal writes for log recovery and unmount purposes,
      * so don't restrict that case.
      */
     if (xfs_has_norecovery(mp))
         return false;
     if (xfs_readonly_buftarg(mp->m_ddev_targp))
         return false;
     if (xfs_readonly_buftarg(mp->m_log->l_targ))
         return false;
     if (xlog_is_shutdown(mp->m_log))
         return false;
     return true;
 }
 
 /*
  * Replenish the byte reservation required by moving the grant write head.
  */
 int
 xfs_log_regrant(
     struct xfs_mount    *mp,
     struct xlog_ticket  *tic)
 {
     struct xlog     *log = mp->m_log;
     int         need_bytes;
     int         error = 0;
 
     if (xlog_is_shutdown(log))
         return -EIO;
 
     XFS_STATS_INC(mp, xs_try_logspace);
 
     /*
      * This is a new transaction on the ticket, so we need to change the
      * transaction ID so that the next transaction has a different TID in
      * the log. Just add one to the existing tid so that we can see chains
      * of rolling transactions in the log easily.
      */
     tic->t_tid++;
 
     xlog_grant_push_ail(log, tic->t_unit_res);
 
     tic->t_curr_res = tic->t_unit_res;
     if (tic->t_cnt > 0)
         return 0;
 
     trace_xfs_log_regrant(log, tic);
 
     error = xlog_grant_head_check(log, &log->l_write_head, tic,
                       &need_bytes);
     if (error)
         goto out_error;
 
     xlog_grant_add_space(log, &log->l_write_head.grant, need_bytes);
     trace_xfs_log_regrant_exit(log, tic);
     xlog_verify_grant_tail(log);
     return 0;
 
 out_error:
     /*
      * If we are failing, make sure the ticket doesn't have any current
      * reservations.  We don't want to add this back when the ticket/
      * transaction gets cancelled.
      */
     tic->t_curr_res = 0;
     tic->t_cnt = 0; /* ungrant will give back unit_res * t_cnt. */
     return error;
 }
 
 /*
  * Reserve log space and return a ticket corresponding to the reservation.
  *
  * Each reservation is going to reserve extra space for a log record header.
  * When writes happen to the on-disk log, we don't subtract the length of the
  * log record header from any reservation.  By wasting space in each
  * reservation, we prevent over allocation problems.
  */
 int
 xfs_log_reserve(
     struct xfs_mount    *mp,
     int         unit_bytes,
     int         cnt,
     struct xlog_ticket  **ticp,
     bool            permanent)
 {
     struct xlog     *log = mp->m_log;
     struct xlog_ticket  *tic;
     int         need_bytes;
     int         error = 0;
 
     if (xlog_is_shutdown(log))
         return -EIO;
 
     XFS_STATS_INC(mp, xs_try_logspace);
 
     ASSERT(*ticp == NULL);
     tic = xlog_ticket_alloc(log, unit_bytes, cnt, permanent);
     *ticp = tic;
 
     xlog_grant_push_ail(log, tic->t_cnt ? tic->t_unit_res * tic->t_cnt
                         : tic->t_unit_res);
 
     trace_xfs_log_reserve(log, tic);
 
     error = xlog_grant_head_check(log, &log->l_reserve_head, tic,
                       &need_bytes);
     if (error)
         goto out_error;
 
     xlog_grant_add_space(log, &log->l_reserve_head.grant, need_bytes);
     xlog_grant_add_space(log, &log->l_write_head.grant, need_bytes);
     trace_xfs_log_reserve_exit(log, tic);
     xlog_verify_grant_tail(log);
     return 0;
 
 out_error:
     /*
      * If we are failing, make sure the ticket doesn't have any current
      * reservations.  We don't want to add this back when the ticket/
      * transaction gets cancelled.
      */
     tic->t_curr_res = 0;
     tic->t_cnt = 0; /* ungrant will give back unit_res * t_cnt. */
     return error;
 }
 
 /*
  * Run all the pending iclog callbacks and wake log force waiters and iclog
  * space waiters so they can process the newly set shutdown state. We really
  * don't care what order we process callbacks here because the log is shut down
  * and so state cannot change on disk anymore. However, we cannot wake waiters
  * until the callbacks have been processed because we may be in unmount and
  * we must ensure that all AIL operations the callbacks perform have completed
  * before we tear down the AIL.
  *
  * We avoid processing actively referenced iclogs so that we don't run callbacks
  * while the iclog owner might still be preparing the iclog for IO submssion.
  * These will be caught by xlog_state_iclog_release() and call this function
  * again to process any callbacks that may have been added to that iclog.
  */
 static void
 xlog_state_shutdown_callbacks(
     struct xlog     *log)
 {
     struct xlog_in_core *iclog;
     LIST_HEAD(cb_list);
 
     iclog = log->l_iclog;
     do {
         if (atomic_read(&iclog->ic_refcnt)) {
             /* Reference holder will re-run iclog callbacks. */
             continue;
         }
         list_splice_init(&iclog->ic_callbacks, &cb_list);
         spin_unlock(&log->l_icloglock);
 
         xlog_cil_process_committed(&cb_list);
 
         spin_lock(&log->l_icloglock);
         wake_up_all(&iclog->ic_write_wait);
         wake_up_all(&iclog->ic_force_wait);
     } while ((iclog = iclog->ic_next) != log->l_iclog);
 
     wake_up_all(&log->l_flush_wait);
 }
 
 /*
  * Flush iclog to disk if this is the last reference to the given iclog and the
  * it is in the WANT_SYNC state.
  *
  * If XLOG_ICL_NEED_FUA is already set on the iclog, we need to ensure that the
  * log tail is updated correctly. NEED_FUA indicates that the iclog will be
  * written to stable storage, and implies that a commit record is contained
  * within the iclog. We need to ensure that the log tail does not move beyond
  * the tail that the first commit record in the iclog ordered against, otherwise
  * correct recovery of that checkpoint becomes dependent on future operations
  * performed on this iclog.
  *
  * Hence if NEED_FUA is set and the current iclog tail lsn is empty, write the
  * current tail into iclog. Once the iclog tail is set, future operations must
  * not modify it, otherwise they potentially violate ordering constraints for
  * the checkpoint commit that wrote the initial tail lsn value. The tail lsn in
  * the iclog will get zeroed on activation of the iclog after sync, so we
  * always capture the tail lsn on the iclog on the first NEED_FUA release
  * regardless of the number of active reference counts on this iclog.
  */
 int
 xlog_state_release_iclog(
     struct xlog     *log,
     struct xlog_in_core *iclog,
     struct xlog_ticket  *ticket)
 {
     xfs_lsn_t       tail_lsn;
     bool            last_ref;
 
     lockdep_assert_held(&log->l_icloglock);
 
     trace_xlog_iclog_release(iclog, _RET_IP_);
     /*
      * Grabbing the current log tail needs to be atomic w.r.t. the writing
      * of the tail LSN into the iclog so we guarantee that the log tail does
      * not move between the first time we know that the iclog needs to be
      * made stable and when we eventually submit it.
      */
     if ((iclog->ic_state == XLOG_STATE_WANT_SYNC ||
          (iclog->ic_flags & XLOG_ICL_NEED_FUA)) &&
         !iclog->ic_header.h_tail_lsn) {
         tail_lsn = xlog_assign_tail_lsn(log->l_mp);
         iclog->ic_header.h_tail_lsn = cpu_to_be64(tail_lsn);
     }
 
     last_ref = atomic_dec_and_test(&iclog->ic_refcnt);
 
     if (xlog_is_shutdown(log)) {
         /*
          * If there are no more references to this iclog, process the
          * pending iclog callbacks that were waiting on the release of
          * this iclog.
          */
         if (last_ref)
             xlog_state_shutdown_callbacks(log);
         return -EIO;
     }
 
     if (!last_ref)
         return 0;
 
     if (iclog->ic_state != XLOG_STATE_WANT_SYNC) {
         ASSERT(iclog->ic_state == XLOG_STATE_ACTIVE);
         return 0;
     }
 
     iclog->ic_state = XLOG_STATE_SYNCING;
     xlog_verify_tail_lsn(log, iclog);
     trace_xlog_iclog_syncing(iclog, _RET_IP_);
 
     spin_unlock(&log->l_icloglock);
     xlog_sync(log, iclog, ticket);
     spin_lock(&log->l_icloglock);
     return 0;
 }
 
 /*
  * Mount a log filesystem
  *
  * mp       - ubiquitous xfs mount point structure
  * log_target   - buftarg of on-disk log device
  * blk_offset   - Start block # where block size is 512 bytes (BBSIZE)
  * num_bblocks  - Number of BBSIZE blocks in on-disk log
  *
  * Return error or zero.
  */
 int
 xfs_log_mount(
     xfs_mount_t *mp,
     xfs_buftarg_t   *log_target,
     xfs_daddr_t blk_offset,
     int     num_bblks)
 {
     struct xlog *log;
     bool        fatal = xfs_has_crc(mp);
     int     error = 0;
     int     min_logfsbs;
 
     if (!xfs_has_norecovery(mp)) {
         xfs_notice(mp, "Mounting V%d Filesystem",
                XFS_SB_VERSION_NUM(&mp->m_sb));
     } else {
         xfs_notice(mp,
 "Mounting V%d filesystem in no-recovery mode. Filesystem will be inconsistent.",
                XFS_SB_VERSION_NUM(&mp->m_sb));
         ASSERT(xfs_is_readonly(mp));
     }
 
     log = xlog_alloc_log(mp, log_target, blk_offset, num_bblks);
     if (IS_ERR(log)) {
         error = PTR_ERR(log);
         goto out;
     }
     mp->m_log = log;
 
     /*
      * Validate the given log space and drop a critical message via syslog
      * if the log size is too small that would lead to some unexpected
      * situations in transaction log space reservation stage.
      *
      * Note: we can't just reject the mount if the validation fails.  This
      * would mean that people would have to downgrade their kernel just to
      * remedy the situation as there is no way to grow the log (short of
      * black magic surgery with xfs_db).
      *
      * We can, however, reject mounts for CRC format filesystems, as the
      * mkfs binary being used to make the filesystem should never create a
      * filesystem with a log that is too small.
      */
     min_logfsbs = xfs_log_calc_minimum_size(mp);
 
     if (mp->m_sb.sb_logblocks < min_logfsbs) {
         xfs_warn(mp,
         "Log size %d blocks too small, minimum size is %d blocks",
              mp->m_sb.sb_logblocks, min_logfsbs);
         error = -EINVAL;
     } else if (mp->m_sb.sb_logblocks > XFS_MAX_LOG_BLOCKS) {
         xfs_warn(mp,
         "Log size %d blocks too large, maximum size is %lld blocks",
              mp->m_sb.sb_logblocks, XFS_MAX_LOG_BLOCKS);
         error = -EINVAL;
     } else if (XFS_FSB_TO_B(mp, mp->m_sb.sb_logblocks) > XFS_MAX_LOG_BYTES) {
         xfs_warn(mp,
         "log size %lld bytes too large, maximum size is %lld bytes",
              XFS_FSB_TO_B(mp, mp->m_sb.sb_logblocks),
              XFS_MAX_LOG_BYTES);
         error = -EINVAL;
     } else if (mp->m_sb.sb_logsunit > 1 &&
            mp->m_sb.sb_logsunit % mp->m_sb.sb_blocksize) {
         xfs_warn(mp,
         "log stripe unit %u bytes must be a multiple of block size",
              mp->m_sb.sb_logsunit);
         error = -EINVAL;
         fatal = true;
     }
     if (error) {
         /*
          * Log check errors are always fatal on v5; or whenever bad
          * metadata leads to a crash.
          */
         if (fatal) {
             xfs_crit(mp, "AAIEEE! Log failed size checks. Abort!");
             ASSERT(0);
             goto out_free_log;
         }
         xfs_crit(mp, "Log size out of supported range.");
         xfs_crit(mp,
 "Continuing onwards, but if log hangs are experienced then please report this message in the bug report.");
     }
 
     /*
      * Initialize the AIL now we have a log.
      */
     error = xfs_trans_ail_init(mp);
     if (error) {
         xfs_warn(mp, "AIL initialisation failed: error %d", error);
         goto out_free_log;
     }
     log->l_ailp = mp->m_ail;
 
     /*
      * skip log recovery on a norecovery mount.  pretend it all
      * just worked.
      */
     if (!xfs_has_norecovery(mp)) {
         /*
          * log recovery ignores readonly state and so we need to clear
          * mount-based read only state so it can write to disk.
          */
         bool    readonly = test_and_clear_bit(XFS_OPSTATE_READONLY,
                         &mp->m_opstate);
         error = xlog_recover(log);
         if (readonly)
             set_bit(XFS_OPSTATE_READONLY, &mp->m_opstate);
         if (error) {
             xfs_warn(mp, "log mount/recovery failed: error %d",
                 error);
             xlog_recover_cancel(log);
             goto out_destroy_ail;
         }
     }
 
     error = xfs_sysfs_init(&log->l_kobj, &xfs_log_ktype, &mp->m_kobj,
                    "log");
     if (error)
         goto out_destroy_ail;
 
     /* Normal transactions can now occur */
     clear_bit(XLOG_ACTIVE_RECOVERY, &log->l_opstate);
 
     /*
      * Now the log has been fully initialised and we know were our
      * space grant counters are, we can initialise the permanent ticket
      * needed for delayed logging to work.
      */
     xlog_cil_init_post_recovery(log);
 
     return 0;
 
 out_destroy_ail:
     xfs_trans_ail_destroy(mp);
 out_free_log:
     xlog_dealloc_log(log);
 out:
     return error;
 }
 
 /*
  * Finish the recovery of the file system.  This is separate from the
  * xfs_log_mount() call, because it depends on the code in xfs_mountfs() to read
  * in the root and real-time bitmap inodes between calling xfs_log_mount() and
  * here.
  *
  * If we finish recovery successfully, start the background log work. If we are
  * not doing recovery, then we have a RO filesystem and we don't need to start
  * it.
  */
 int
 xfs_log_mount_finish(
     struct xfs_mount    *mp)
 {
     struct xlog     *log = mp->m_log;
     bool            readonly;
     int         error = 0;
 
     if (xfs_has_norecovery(mp)) {
         ASSERT(xfs_is_readonly(mp));
         return 0;
     }
 
     /*
      * log recovery ignores readonly state and so we need to clear
      * mount-based read only state so it can write to disk.
      */
     readonly = test_and_clear_bit(XFS_OPSTATE_READONLY, &mp->m_opstate);
 
     /*
      * During the second phase of log recovery, we need iget and
      * iput to behave like they do for an active filesystem.
      * xfs_fs_drop_inode needs to be able to prevent the deletion
      * of inodes before we're done replaying log items on those
      * inodes.  Turn it off immediately after recovery finishes
      * so that we don't leak the quota inodes if subsequent mount
      * activities fail.
      *
      * We let all inodes involved in redo item processing end up on
      * the LRU instead of being evicted immediately so that if we do
      * something to an unlinked inode, the irele won't cause
      * premature truncation and freeing of the inode, which results
      * in log recovery failure.  We have to evict the unreferenced
      * lru inodes after clearing SB_ACTIVE because we don't
      * otherwise clean up the lru if there's a subsequent failure in
      * xfs_mountfs, which leads to us leaking the inodes if nothing
      * else (e.g. quotacheck) references the inodes before the
      * mount failure occurs.
      */
     mp->m_super->s_flags |= SB_ACTIVE;
     xfs_log_work_queue(mp);
     if (xlog_recovery_needed(log))
         error = xlog_recover_finish(log);
     mp->m_super->s_flags &= ~SB_ACTIVE;
     evict_inodes(mp->m_super);
 
     /*
      * Drain the buffer LRU after log recovery. This is required for v4
      * filesystems to avoid leaving around buffers with NULL verifier ops,
      * but we do it unconditionally to make sure we're always in a clean
      * cache state after mount.
      *
      * Don't push in the error case because the AIL may have pending intents
      * that aren't removed until recovery is cancelled.
      */
     if (xlog_recovery_needed(log)) {
         if (!error) {
             xfs_log_force(mp, XFS_LOG_SYNC);
             xfs_ail_push_all_sync(mp->m_ail);
         }
         xfs_notice(mp, "Ending recovery (logdev: %s)",
                 mp->m_logname ? mp->m_logname : "internal");
     } else {
         xfs_info(mp, "Ending clean mount");
     }
     xfs_buftarg_drain(mp->m_ddev_targp);
 
     clear_bit(XLOG_RECOVERY_NEEDED, &log->l_opstate);
     if (readonly)
         set_bit(XFS_OPSTATE_READONLY, &mp->m_opstate);
 
     /* Make sure the log is dead if we're returning failure. */
     ASSERT(!error || xlog_is_shutdown(log));
 
     return error;
 }
 
 /*
  * The mount has failed. Cancel the recovery if it hasn't completed and destroy
  * the log.
  */
 void
 xfs_log_mount_cancel(
     struct xfs_mount    *mp)
 {
     xlog_recover_cancel(mp->m_log);
     xfs_log_unmount(mp);
 }
 
 /*
  * Flush out the iclog to disk ensuring that device caches are flushed and
  * the iclog hits stable storage before any completion waiters are woken.
  */
 static inline int
 xlog_force_iclog(
     struct xlog_in_core *iclog)
 {
     atomic_inc(&iclog->ic_refcnt);
     iclog->ic_flags |= XLOG_ICL_NEED_FLUSH | XLOG_ICL_NEED_FUA;
     if (iclog->ic_state == XLOG_STATE_ACTIVE)
         xlog_state_switch_iclogs(iclog->ic_log, iclog, 0);
     return xlog_state_release_iclog(iclog->ic_log, iclog, NULL);
 }
 
 /*
  * Wait for the iclog and all prior iclogs to be written disk as required by the
  * log force state machine. Waiting on ic_force_wait ensures iclog completions
  * have been ordered and callbacks run before we are woken here, hence
  * guaranteeing that all the iclogs up to this one are on stable storage.
  */
 int
 xlog_wait_on_iclog(
     struct xlog_in_core *iclog)
         __releases(iclog->ic_log->l_icloglock)
 {
     struct xlog     *log = iclog->ic_log;
 
     trace_xlog_iclog_wait_on(iclog, _RET_IP_);
     if (!xlog_is_shutdown(log) &&
         iclog->ic_state != XLOG_STATE_ACTIVE &&
         iclog->ic_state != XLOG_STATE_DIRTY) {
         XFS_STATS_INC(log->l_mp, xs_log_force_sleep);
         xlog_wait(&iclog->ic_force_wait, &log->l_icloglock);
     } else {
         spin_unlock(&log->l_icloglock);
     }
 
     if (xlog_is_shutdown(log))
         return -EIO;
     return 0;
 }
 
 /*
  * Write out an unmount record using the ticket provided. We have to account for
  * the data space used in the unmount ticket as this write is not done from a
  * transaction context that has already done the accounting for us.
  */
 static int
 xlog_write_unmount_record(
     struct xlog     *log,
     struct xlog_ticket  *ticket)
 {
     struct  {
         struct xlog_op_header ophdr;
         struct xfs_unmount_log_format ulf;
     } unmount_rec = {
         .ophdr = {
             .oh_clientid = XFS_LOG,
             .oh_tid = cpu_to_be32(ticket->t_tid),
             .oh_flags = XLOG_UNMOUNT_TRANS,
         },
         .ulf = {
             .magic = XLOG_UNMOUNT_TYPE,
         },
     };
     struct xfs_log_iovec reg = {
         .i_addr = &unmount_rec,
         .i_len = sizeof(unmount_rec),
         .i_type = XLOG_REG_TYPE_UNMOUNT,
     };
     struct xfs_log_vec vec = {
         .lv_niovecs = 1,
         .lv_iovecp = &reg,
     };
     LIST_HEAD(lv_chain);
     list_add(&vec.lv_list, &lv_chain);
 
     BUILD_BUG_ON((sizeof(struct xlog_op_header) +
               sizeof(struct xfs_unmount_log_format)) !=
                             sizeof(unmount_rec));
 
     /* account for space used by record data */
     ticket->t_curr_res -= sizeof(unmount_rec);
 
     return xlog_write(log, NULL, &lv_chain, ticket, reg.i_len);
 }
 
 /*
  * Mark the filesystem clean by writing an unmount record to the head of the
  * log.
  */
 static void
 xlog_unmount_write(
     struct xlog     *log)
 {
     struct xfs_mount    *mp = log->l_mp;
     struct xlog_in_core *iclog;
     struct xlog_ticket  *tic = NULL;
     int         error;
 
     error = xfs_log_reserve(mp, 600, 1, &tic, 0);
     if (error)
         goto out_err;
 
     error = xlog_write_unmount_record(log, tic);
     /*
      * At this point, we're umounting anyway, so there's no point in
      * transitioning log state to shutdown. Just continue...
      */
 out_err:
     if (error)
         xfs_alert(mp, "%s: unmount record failed", __func__);
 
     spin_lock(&log->l_icloglock);
     iclog = log->l_iclog;
     error = xlog_force_iclog(iclog);
     xlog_wait_on_iclog(iclog);
 
     if (tic) {
         trace_xfs_log_umount_write(log, tic);
         xfs_log_ticket_ungrant(log, tic);
     }
 }
 
 static void
 xfs_log_unmount_verify_iclog(
     struct xlog     *log)
 {
     struct xlog_in_core *iclog = log->l_iclog;
 
     do {
         ASSERT(iclog->ic_state == XLOG_STATE_ACTIVE);
         ASSERT(iclog->ic_offset == 0);
     } while ((iclog = iclog->ic_next) != log->l_iclog);
 }
 
 /*
  * Unmount record used to have a string "Unmount filesystem--" in the
  * data section where the "Un" was really a magic number (XLOG_UNMOUNT_TYPE).
  * We just write the magic number now since that particular field isn't
  * currently architecture converted and "Unmount" is a bit foo.
  * As far as I know, there weren't any dependencies on the old behaviour.
  */
 static void
 xfs_log_unmount_write(
     struct xfs_mount    *mp)
 {
     struct xlog     *log = mp->m_log;
 
     if (!xfs_log_writable(mp))
         return;
 
     xfs_log_force(mp, XFS_LOG_SYNC);
 
     if (xlog_is_shutdown(log))
         return;
 
     /*
      * If we think the summary counters are bad, avoid writing the unmount
      * record to force log recovery at next mount, after which the summary
      * counters will be recalculated.  Refer to xlog_check_unmount_rec for
      * more details.
      */
     if (XFS_TEST_ERROR(xfs_fs_has_sickness(mp, XFS_SICK_FS_COUNTERS), mp,
             XFS_ERRTAG_FORCE_SUMMARY_RECALC)) {
         xfs_alert(mp, "%s: will fix summary counters at next mount",
                 __func__);
         return;
     }
 
     xfs_log_unmount_verify_iclog(log);
     xlog_unmount_write(log);
 }
 
 /*
  * Empty the log for unmount/freeze.
  *
  * To do this, we first need to shut down the background log work so it is not
  * trying to cover the log as we clean up. We then need to unpin all objects in
  * the log so we can then flush them out. Once they have completed their IO and
  * run the callbacks removing themselves from the AIL, we can cover the log.
  */
 int
 xfs_log_quiesce(
     struct xfs_mount    *mp)
 {
     /*
      * Clear log incompat features since we're quiescing the log.  Report
      * failures, though it's not fatal to have a higher log feature
      * protection level than the log contents actually require.
      */
     if (xfs_clear_incompat_log_features(mp)) {
         int error;
 
         error = xfs_sync_sb(mp, false);
         if (error)
             xfs_warn(mp,
     "Failed to clear log incompat features on quiesce");
     }
 
     cancel_delayed_work_sync(&mp->m_log->l_work);
     xfs_log_force(mp, XFS_LOG_SYNC);
 
     /*
      * The superblock buffer is uncached and while xfs_ail_push_all_sync()
      * will push it, xfs_buftarg_wait() will not wait for it. Further,
      * xfs_buf_iowait() cannot be used because it was pushed with the
      * XBF_ASYNC flag set, so we need to use a lock/unlock pair to wait for
      * the IO to complete.
      */
     xfs_ail_push_all_sync(mp->m_ail);
     xfs_buftarg_wait(mp->m_ddev_targp);
     xfs_buf_lock(mp->m_sb_bp);
     xfs_buf_unlock(mp->m_sb_bp);
 
     return xfs_log_cover(mp);
 }
 
 void
 xfs_log_clean(
     struct xfs_mount    *mp)
 {
     xfs_log_quiesce(mp);
     xfs_log_unmount_write(mp);
 }
 
 /*
  * Shut down and release the AIL and Log.
  *
  * During unmount, we need to ensure we flush all the dirty metadata objects
  * from the AIL so that the log is empty before we write the unmount record to
  * the log. Once this is done, we can tear down the AIL and the log.
  */
 void
 xfs_log_unmount(
     struct xfs_mount    *mp)
 {
     xfs_log_clean(mp);
 
     xfs_buftarg_drain(mp->m_ddev_targp);
 
     xfs_trans_ail_destroy(mp);
 
     xfs_sysfs_del(&mp->m_log->l_kobj);
 
     xlog_dealloc_log(mp->m_log);
 }
 
 void
 xfs_log_item_init(
     struct xfs_mount    *mp,
     struct xfs_log_item *item,
     int         type,
     const struct xfs_item_ops *ops)
 {
     item->li_log = mp->m_log;
     item->li_ailp = mp->m_ail;
     item->li_type = type;
     item->li_ops = ops;
     item->li_lv = NULL;
 
     INIT_LIST_HEAD(&item->li_ail);
     INIT_LIST_HEAD(&item->li_cil);
     INIT_LIST_HEAD(&item->li_bio_list);
     INIT_LIST_HEAD(&item->li_trans);
 }
 
 /*
  * Wake up processes waiting for log space after we have moved the log tail.
  */
 void
 xfs_log_space_wake(
     struct xfs_mount    *mp)
 {
     struct xlog     *log = mp->m_log;
     int         free_bytes;
 
     if (xlog_is_shutdown(log))
         return;
 
     if (!list_empty_careful(&log->l_write_head.waiters)) {
         ASSERT(!xlog_in_recovery(log));
 
         spin_lock(&log->l_write_head.lock);
         free_bytes = xlog_space_left(log, &log->l_write_head.grant);
         xlog_grant_head_wake(log, &log->l_write_head, &free_bytes);
         spin_unlock(&log->l_write_head.lock);
     }
 
     if (!list_empty_careful(&log->l_reserve_head.waiters)) {
         ASSERT(!xlog_in_recovery(log));
 
         spin_lock(&log->l_reserve_head.lock);
         free_bytes = xlog_space_left(log, &log->l_reserve_head.grant);
         xlog_grant_head_wake(log, &log->l_reserve_head, &free_bytes);
         spin_unlock(&log->l_reserve_head.lock);
     }
 }
 
 /*
  * Determine if we have a transaction that has gone to disk that needs to be
  * covered. To begin the transition to the idle state firstly the log needs to
  * be idle. That means the CIL, the AIL and the iclogs needs to be empty before
  * we start attempting to cover the log.
  *
  * Only if we are then in a state where covering is needed, the caller is
  * informed that dummy transactions are required to move the log into the idle
  * state.
  *
  * If there are any items in the AIl or CIL, then we do not want to attempt to
  * cover the log as we may be in a situation where there isn't log space
  * available to run a dummy transaction and this can lead to deadlocks when the
  * tail of the log is pinned by an item that is modified in the CIL.  Hence
  * there's no point in running a dummy transaction at this point because we
  * can't start trying to idle the log until both the CIL and AIL are empty.
  */
 static bool
 xfs_log_need_covered(
     struct xfs_mount    *mp)
 {
     struct xlog     *log = mp->m_log;
     bool            needed = false;
 
     if (!xlog_cil_empty(log))
         return false;
 
     spin_lock(&log->l_icloglock);
     switch (log->l_covered_state) {
     case XLOG_STATE_COVER_DONE:
     case XLOG_STATE_COVER_DONE2:
     case XLOG_STATE_COVER_IDLE:
         break;
     case XLOG_STATE_COVER_NEED:
     case XLOG_STATE_COVER_NEED2:
         if (xfs_ail_min_lsn(log->l_ailp))
             break;
         if (!xlog_iclogs_empty(log))
             break;
 
         needed = true;
         if (log->l_covered_state == XLOG_STATE_COVER_NEED)
             log->l_covered_state = XLOG_STATE_COVER_DONE;
         else
             log->l_covered_state = XLOG_STATE_COVER_DONE2;
         break;
     default:
         needed = true;
         break;
     }
     spin_unlock(&log->l_icloglock);
     return needed;
 }
 
 /*
  * Explicitly cover the log. This is similar to background log covering but
  * intended for usage in quiesce codepaths. The caller is responsible to ensure
  * the log is idle and suitable for covering. The CIL, iclog buffers and AIL
  * must all be empty.
  */
 static int
 xfs_log_cover(
     struct xfs_mount    *mp)
 {
     int         error = 0;
     bool            need_covered;
 
     ASSERT((xlog_cil_empty(mp->m_log) && xlog_iclogs_empty(mp->m_log) &&
             !xfs_ail_min_lsn(mp->m_log->l_ailp)) ||
         xlog_is_shutdown(mp->m_log));
 
     if (!xfs_log_writable(mp))
         return 0;
 
     /*
      * xfs_log_need_covered() is not idempotent because it progresses the
      * state machine if the log requires covering. Therefore, we must call
      * this function once and use the result until we've issued an sb sync.
      * Do so first to make that abundantly clear.
      *
      * Fall into the covering sequence if the log needs covering or the
      * mount has lazy superblock accounting to sync to disk. The sb sync
      * used for covering accumulates the in-core counters, so covering
      * handles this for us.
      */
     need_covered = xfs_log_need_covered(mp);
     if (!need_covered && !xfs_has_lazysbcount(mp))
         return 0;
 
     /*
      * To cover the log, commit the superblock twice (at most) in
      * independent checkpoints. The first serves as a reference for the
      * tail pointer. The sync transaction and AIL push empties the AIL and
      * updates the in-core tail to the LSN of the first checkpoint. The
      * second commit updates the on-disk tail with the in-core LSN,
      * covering the log. Push the AIL one more time to leave it empty, as
      * we found it.
      */
     do {
         error = xfs_sync_sb(mp, true);
         if (error)
             break;
         xfs_ail_push_all_sync(mp->m_ail);
     } while (xfs_log_need_covered(mp));
 
     return error;
 }
 
 /*
  * We may be holding the log iclog lock upon entering this routine.
  */
 xfs_lsn_t
 xlog_assign_tail_lsn_locked(
     struct xfs_mount    *mp)
 {
     struct xlog     *log = mp->m_log;
     struct xfs_log_item *lip;
     xfs_lsn_t       tail_lsn;
 
     assert_spin_locked(&mp->m_ail->ail_lock);
 
     /*
      * To make sure we always have a valid LSN for the log tail we keep
      * track of the last LSN which was committed in log->l_last_sync_lsn,
      * and use that when the AIL was empty.
      */
     lip = xfs_ail_min(mp->m_ail);
     if (lip)
         tail_lsn = lip->li_lsn;
     else
         tail_lsn = atomic64_read(&log->l_last_sync_lsn);
     trace_xfs_log_assign_tail_lsn(log, tail_lsn);
     atomic64_set(&log->l_tail_lsn, tail_lsn);
     return tail_lsn;
 }
 
 xfs_lsn_t
 xlog_assign_tail_lsn(
     struct xfs_mount    *mp)
 {
     xfs_lsn_t       tail_lsn;
 
     spin_lock(&mp->m_ail->ail_lock);
     tail_lsn = xlog_assign_tail_lsn_locked(mp);
     spin_unlock(&mp->m_ail->ail_lock);
 
     return tail_lsn;
 }
 
 /*
  * Return the space in the log between the tail and the head.  The head
  * is passed in the cycle/bytes formal parms.  In the special case where
  * the reserve head has wrapped passed the tail, this calculation is no
  * longer valid.  In this case, just return 0 which means there is no space
  * in the log.  This works for all places where this function is called
  * with the reserve head.  Of course, if the write head were to ever
  * wrap the tail, we should blow up.  Rather than catch this case here,
  * we depend on other ASSERTions in other parts of the code.   XXXmiken
  *
  * If reservation head is behind the tail, we have a problem. Warn about it,
  * but then treat it as if the log is empty.
  *
  * If the log is shut down, the head and tail may be invalid or out of whack, so
  * shortcut invalidity asserts in this case so that we don't trigger them
  * falsely.
  */
 STATIC int
 xlog_space_left(
     struct xlog *log,
     atomic64_t  *head)
 {
     int     tail_bytes;
     int     tail_cycle;
     int     head_cycle;
     int     head_bytes;
 
     xlog_crack_grant_head(head, &head_cycle, &head_bytes);
     xlog_crack_atomic_lsn(&log->l_tail_lsn, &tail_cycle, &tail_bytes);
     tail_bytes = BBTOB(tail_bytes);
     if (tail_cycle == head_cycle && head_bytes >= tail_bytes)
         return log->l_logsize - (head_bytes - tail_bytes);
     if (tail_cycle + 1 < head_cycle)
         return 0;
 
     /* Ignore potential inconsistency when shutdown. */
     if (xlog_is_shutdown(log))
         return log->l_logsize;
 
     if (tail_cycle < head_cycle) {
         ASSERT(tail_cycle == (head_cycle - 1));
         return tail_bytes - head_bytes;
     }
 
     /*
      * The reservation head is behind the tail. In this case we just want to
      * return the size of the log as the amount of space left.
      */
     xfs_alert(log->l_mp, "xlog_space_left: head behind tail");
     xfs_alert(log->l_mp, "  tail_cycle = %d, tail_bytes = %d",
           tail_cycle, tail_bytes);
     xfs_alert(log->l_mp, "  GH   cycle = %d, GH   bytes = %d",
           head_cycle, head_bytes);
     ASSERT(0);
     return log->l_logsize;
 }
 
 
 static void
 xlog_ioend_work(
     struct work_struct  *work)
 {
     struct xlog_in_core     *iclog =
         container_of(work, struct xlog_in_core, ic_end_io_work);
     struct xlog     *log = iclog->ic_log;
     int         error;
 
     error = blk_status_to_errno(iclog->ic_bio.bi_status);
 #ifdef DEBUG
     /* treat writes with injected CRC errors as failed */
     if (iclog->ic_fail_crc)
         error = -EIO;
 #endif
 
     /*
      * Race to shutdown the filesystem if we see an error.
      */
     if (XFS_TEST_ERROR(error, log->l_mp, XFS_ERRTAG_IODONE_IOERR)) {
         xfs_alert(log->l_mp, "log I/O error %d", error);
         xlog_force_shutdown(log, SHUTDOWN_LOG_IO_ERROR);
     }
 
     xlog_state_done_syncing(iclog);
     bio_uninit(&iclog->ic_bio);
 
     /*
      * Drop the lock to signal that we are done. Nothing references the
      * iclog after this, so an unmount waiting on this lock can now tear it
      * down safely. As such, it is unsafe to reference the iclog after the
      * unlock as we could race with it being freed.
      */
     up(&iclog->ic_sema);
 }
 
 /*
  * Return size of each in-core log record buffer.
  *
  * All machines get 8 x 32kB buffers by default, unless tuned otherwise.
  *
  * If the filesystem blocksize is too large, we may need to choose a
  * larger size since the directory code currently logs entire blocks.
  */
 STATIC void
 xlog_get_iclog_buffer_size(
     struct xfs_mount    *mp,
     struct xlog     *log)
 {
     if (mp->m_logbufs <= 0)
         mp->m_logbufs = XLOG_MAX_ICLOGS;
     if (mp->m_logbsize <= 0)
         mp->m_logbsize = XLOG_BIG_RECORD_BSIZE;
 
     log->l_iclog_bufs = mp->m_logbufs;
     log->l_iclog_size = mp->m_logbsize;
 
     /*
      * # headers = size / 32k - one header holds cycles from 32k of data.
      */
     log->l_iclog_heads =
         DIV_ROUND_UP(mp->m_logbsize, XLOG_HEADER_CYCLE_SIZE);
     log->l_iclog_hsize = log->l_iclog_heads << BBSHIFT;
 }
 
 void
 xfs_log_work_queue(
     struct xfs_mount        *mp)
 {
     queue_delayed_work(mp->m_sync_workqueue, &mp->m_log->l_work,
                 msecs_to_jiffies(xfs_syncd_centisecs * 10));
 }
 
 /*
  * Clear the log incompat flags if we have the opportunity.
  *
  * This only happens if we're about to log the second dummy transaction as part
  * of covering the log and we can get the log incompat feature usage lock.
  */
 static inline void
 xlog_clear_incompat(
     struct xlog     *log)
 {
     struct xfs_mount    *mp = log->l_mp;
 
     if (!xfs_sb_has_incompat_log_feature(&mp->m_sb,
                 XFS_SB_FEAT_INCOMPAT_LOG_ALL))
         return;
 
     if (log->l_covered_state != XLOG_STATE_COVER_DONE2)
         return;
 
     if (!down_write_trylock(&log->l_incompat_users))
         return;
 
     xfs_clear_incompat_log_features(mp);
     up_write(&log->l_incompat_users);
 }
 
 /*
  * Every sync period we need to unpin all items in the AIL and push them to
  * disk. If there is nothing dirty, then we might need to cover the log to
  * indicate that the filesystem is idle.
  */
 static void
 xfs_log_worker(
     struct work_struct  *work)
 {
     struct xlog     *log = container_of(to_delayed_work(work),
                         struct xlog, l_work);
     struct xfs_mount    *mp = log->l_mp;
 
     /* dgc: errors ignored - not fatal and nowhere to report them */
     if (xfs_fs_writable(mp, SB_FREEZE_WRITE) && xfs_log_need_covered(mp)) {
         /*
          * Dump a transaction into the log that contains no real change.
          * This is needed to stamp the current tail LSN into the log
          * during the covering operation.
          *
          * We cannot use an inode here for this - that will push dirty
          * state back up into the VFS and then periodic inode flushing
          * will prevent log covering from making progress. Hence we
          * synchronously log the superblock instead to ensure the
          * superblock is immediately unpinned and can be written back.
          */
         xlog_clear_incompat(log);
         xfs_sync_sb(mp, true);
     } else
         xfs_log_force(mp, 0);
 
     /* start pushing all the metadata that is currently dirty */
     xfs_ail_push_all(mp->m_ail);
 
     /* queue us up again */
     xfs_log_work_queue(mp);
 }
 
 /*
  * This routine initializes some of the log structure for a given mount point.
  * Its primary purpose is to fill in enough, so recovery can occur.  However,
  * some other stuff may be filled in too.
  */
 STATIC struct xlog *
 xlog_alloc_log(
     struct xfs_mount    *mp,
     struct xfs_buftarg  *log_target,
     xfs_daddr_t     blk_offset,
     int         num_bblks)
 {
     struct xlog     *log;
     xlog_rec_header_t   *head;
     xlog_in_core_t      **iclogp;
     xlog_in_core_t      *iclog, *prev_iclog=NULL;
     int         i;
     int         error = -ENOMEM;
     uint            log2_size = 0;
 
     log = kmem_zalloc(sizeof(struct xlog), KM_MAYFAIL);
     if (!log) {
         xfs_warn(mp, "Log allocation failed: No memory!");
         goto out;
     }
 
     log->l_mp      = mp;
     log->l_targ    = log_target;
     log->l_logsize     = BBTOB(num_bblks);
     log->l_logBBstart  = blk_offset;
     log->l_logBBsize   = num_bblks;
     log->l_covered_state = XLOG_STATE_COVER_IDLE;
     set_bit(XLOG_ACTIVE_RECOVERY, &log->l_opstate);
     INIT_DELAYED_WORK(&log->l_work, xfs_log_worker);
 
     log->l_prev_block  = -1;
     /* log->l_tail_lsn = 0x100000000LL; cycle = 1; current block = 0 */
     xlog_assign_atomic_lsn(&log->l_tail_lsn, 1, 0);
     xlog_assign_atomic_lsn(&log->l_last_sync_lsn, 1, 0);
     log->l_curr_cycle  = 1;     /* 0 is bad since this is initial value */
 
     if (xfs_has_logv2(mp) && mp->m_sb.sb_logsunit > 1)
         log->l_iclog_roundoff = mp->m_sb.sb_logsunit;
     else
         log->l_iclog_roundoff = BBSIZE;
 
     xlog_grant_head_init(&log->l_reserve_head);
     xlog_grant_head_init(&log->l_write_head);
 
     error = -EFSCORRUPTED;
     if (xfs_has_sector(mp)) {
             log2_size = mp->m_sb.sb_logsectlog;
         if (log2_size < BBSHIFT) {
             xfs_warn(mp, "Log sector size too small (0x%x < 0x%x)",
                 log2_size, BBSHIFT);
             goto out_free_log;
         }
 
             log2_size -= BBSHIFT;
         if (log2_size > mp->m_sectbb_log) {
             xfs_warn(mp, "Log sector size too large (0x%x > 0x%x)",
                 log2_size, mp->m_sectbb_log);
             goto out_free_log;
         }
 
         /* for larger sector sizes, must have v2 or external log */
         if (log2_size && log->l_logBBstart > 0 &&
                 !xfs_has_logv2(mp)) {
             xfs_warn(mp,
         "log sector size (0x%x) invalid for configuration.",
                 log2_size);
             goto out_free_log;
         }
     }
     log->l_sectBBsize = 1 << log2_size;
 
     init_rwsem(&log->l_incompat_users);
 
     xlog_get_iclog_buffer_size(mp, log);
 
     spin_lock_init(&log->l_icloglock);
     init_waitqueue_head(&log->l_flush_wait);
 
     iclogp = &log->l_iclog;
     /*
      * The amount of memory to allocate for the iclog structure is
      * rather funky due to the way the structure is defined.  It is
      * done this way so that we can use different sizes for machines
      * with different amounts of memory.  See the definition of
      * xlog_in_core_t in xfs_log_priv.h for details.
      */
     ASSERT(log->l_iclog_size >= 4096);
     for (i = 0; i < log->l_iclog_bufs; i++) {
         size_t bvec_size = howmany(log->l_iclog_size, PAGE_SIZE) *
                 sizeof(struct bio_vec);
 
         iclog = kmem_zalloc(sizeof(*iclog) + bvec_size, KM_MAYFAIL);
         if (!iclog)
             goto out_free_iclog;
 
         *iclogp = iclog;
         iclog->ic_prev = prev_iclog;
         prev_iclog = iclog;
 
         iclog->ic_data = kvzalloc(log->l_iclog_size,
                 GFP_KERNEL | __GFP_RETRY_MAYFAIL);
         if (!iclog->ic_data)
             goto out_free_iclog;
         head = &iclog->ic_header;
         memset(head, 0, sizeof(xlog_rec_header_t));
         head->h_magicno = cpu_to_be32(XLOG_HEADER_MAGIC_NUM);
         head->h_version = cpu_to_be32(
             xfs_has_logv2(log->l_mp) ? 2 : 1);
         head->h_size = cpu_to_be32(log->l_iclog_size);
         /* new fields */
         head->h_fmt = cpu_to_be32(XLOG_FMT);
         memcpy(&head->h_fs_uuid, &mp->m_sb.sb_uuid, sizeof(uuid_t));
 
         iclog->ic_size = log->l_iclog_size - log->l_iclog_hsize;
         iclog->ic_state = XLOG_STATE_ACTIVE;
         iclog->ic_log = log;
         atomic_set(&iclog->ic_refcnt, 0);
         INIT_LIST_HEAD(&iclog->ic_callbacks);
         iclog->ic_datap = (void *)iclog->ic_data + log->l_iclog_hsize;
 
         init_waitqueue_head(&iclog->ic_force_wait);
         init_waitqueue_head(&iclog->ic_write_wait);
         INIT_WORK(&iclog->ic_end_io_work, xlog_ioend_work);
         sema_init(&iclog->ic_sema, 1);
 
         iclogp = &iclog->ic_next;
     }
     *iclogp = log->l_iclog;         /* complete ring */
     log->l_iclog->ic_prev = prev_iclog; /* re-write 1st prev ptr */
 
     log->l_ioend_workqueue = alloc_workqueue("xfs-log/%s",
             XFS_WQFLAGS(WQ_FREEZABLE | WQ_MEM_RECLAIM |
                     WQ_HIGHPRI),
             0, mp->m_super->s_id);
     if (!log->l_ioend_workqueue)
         goto out_free_iclog;
 
     error = xlog_cil_init(log);
     if (error)
         goto out_destroy_workqueue;
     return log;
 
 out_destroy_workqueue:
     destroy_workqueue(log->l_ioend_workqueue);
 out_free_iclog:
     for (iclog = log->l_iclog; iclog; iclog = prev_iclog) {
         prev_iclog = iclog->ic_next;
         kmem_free(iclog->ic_data);
         kmem_free(iclog);
         if (prev_iclog == log->l_iclog)
             break;
     }
 out_free_log:
     kmem_free(log);
 out:
     return ERR_PTR(error);
 }   /* xlog_alloc_log */
 
 /*
  * Compute the LSN that we'd need to push the log tail towards in order to have
  * (a) enough on-disk log space to log the number of bytes specified, (b) at
  * least 25% of the log space free, and (c) at least 256 blocks free.  If the
  * log free space already meets all three thresholds, this function returns
  * NULLCOMMITLSN.
  */
 xfs_lsn_t
 xlog_grant_push_threshold(
     struct xlog *log,
     int     need_bytes)
 {
     xfs_lsn_t   threshold_lsn = 0;
     xfs_lsn_t   last_sync_lsn;
     int     free_blocks;
     int     free_bytes;
     int     threshold_block;
     int     threshold_cycle;
     int     free_threshold;
 
     ASSERT(BTOBB(need_bytes) < log->l_logBBsize);
 
     free_bytes = xlog_space_left(log, &log->l_reserve_head.grant);
     free_blocks = BTOBBT(free_bytes);
 
     /*
      * Set the threshold for the minimum number of free blocks in the
      * log to the maximum of what the caller needs, one quarter of the
      * log, and 256 blocks.
      */
     free_threshold = BTOBB(need_bytes);
     free_threshold = max(free_threshold, (log->l_logBBsize >> 2));
     free_threshold = max(free_threshold, 256);
     if (free_blocks >= free_threshold)
         return NULLCOMMITLSN;
 
     xlog_crack_atomic_lsn(&log->l_tail_lsn, &threshold_cycle,
                         &threshold_block);
     threshold_block += free_threshold;
     if (threshold_block >= log->l_logBBsize) {
         threshold_block -= log->l_logBBsize;
         threshold_cycle += 1;
     }
     threshold_lsn = xlog_assign_lsn(threshold_cycle,
                     threshold_block);
     /*
      * Don't pass in an lsn greater than the lsn of the last
      * log record known to be on disk. Use a snapshot of the last sync lsn
      * so that it doesn't change between the compare and the set.
      */
     last_sync_lsn = atomic64_read(&log->l_last_sync_lsn);
     if (XFS_LSN_CMP(threshold_lsn, last_sync_lsn) > 0)
         threshold_lsn = last_sync_lsn;
 
     return threshold_lsn;
 }
 
 /*
  * Push the tail of the log if we need to do so to maintain the free log space
  * thresholds set out by xlog_grant_push_threshold.  We may need to adopt a
  * policy which pushes on an lsn which is further along in the log once we
  * reach the high water mark.  In this manner, we would be creating a low water
  * mark.
  */
 STATIC void
 xlog_grant_push_ail(
     struct xlog *log,
     int     need_bytes)
 {
     xfs_lsn_t   threshold_lsn;
 
     threshold_lsn = xlog_grant_push_threshold(log, need_bytes);
     if (threshold_lsn == NULLCOMMITLSN || xlog_is_shutdown(log))
         return;
 
     /*
      * Get the transaction layer to kick the dirty buffers out to
      * disk asynchronously. No point in trying to do this if
      * the filesystem is shutting down.
      */
     xfs_ail_push(log->l_ailp, threshold_lsn);
 }
 
 /*
  * Stamp cycle number in every block
  */
 STATIC void
 xlog_pack_data(
     struct xlog     *log,
     struct xlog_in_core *iclog,
     int         roundoff)
 {
     int         i, j, k;
     int         size = iclog->ic_offset + roundoff;
     __be32          cycle_lsn;
     char            *dp;
 
     cycle_lsn = CYCLE_LSN_DISK(iclog->ic_header.h_lsn);
 
     dp = iclog->ic_datap;
     for (i = 0; i < BTOBB(size); i++) {
         if (i >= (XLOG_HEADER_CYCLE_SIZE / BBSIZE))
             break;
         iclog->ic_header.h_cycle_data[i] = *(__be32 *)dp;
         *(__be32 *)dp = cycle_lsn;
         dp += BBSIZE;
     }
 
     if (xfs_has_logv2(log->l_mp)) {
         xlog_in_core_2_t *xhdr = iclog->ic_data;
 
         for ( ; i < BTOBB(size); i++) {
             j = i / (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
             k = i % (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
             xhdr[j].hic_xheader.xh_cycle_data[k] = *(__be32 *)dp;
             *(__be32 *)dp = cycle_lsn;
             dp += BBSIZE;
         }
 
         for (i = 1; i < log->l_iclog_heads; i++)
             xhdr[i].hic_xheader.xh_cycle = cycle_lsn;
     }
 }
 
 /*
  * Calculate the checksum for a log buffer.
  *
  * This is a little more complicated than it should be because the various
  * headers and the actual data are non-contiguous.
  */
 __le32
 xlog_cksum(
     struct xlog     *log,
     struct xlog_rec_header  *rhead,
     char            *dp,
     int         size)
 {
     uint32_t        crc;
 
     /* first generate the crc for the record header ... */
     crc = xfs_start_cksum_update((char *)rhead,
                   sizeof(struct xlog_rec_header),
                   offsetof(struct xlog_rec_header, h_crc));
 
     /* ... then for additional cycle data for v2 logs ... */
     if (xfs_has_logv2(log->l_mp)) {
         union xlog_in_core2 *xhdr = (union xlog_in_core2 *)rhead;
         int     i;
         int     xheads;
 
         xheads = DIV_ROUND_UP(size, XLOG_HEADER_CYCLE_SIZE);
 
         for (i = 1; i < xheads; i++) {
             crc = crc32c(crc, &xhdr[i].hic_xheader,
                      sizeof(struct xlog_rec_ext_header));
         }
     }
 
     /* ... and finally for the payload */
     crc = crc32c(crc, dp, size);
 
     return xfs_end_cksum(crc);
 }
 
 static void
 xlog_bio_end_io(
     struct bio      *bio)
 {
     struct xlog_in_core *iclog = bio->bi_private;
 
     queue_work(iclog->ic_log->l_ioend_workqueue,
            &iclog->ic_end_io_work);
 }
 
 static int
 xlog_map_iclog_data(
     struct bio      *bio,
     void            *data,
     size_t          count)
 {
     do {
         struct page *page = kmem_to_page(data);
         unsigned int    off = offset_in_page(data);
         size_t      len = min_t(size_t, count, PAGE_SIZE - off);
 
         if (bio_add_page(bio, page, len, off) != len)
             return -EIO;
 
         data += len;
         count -= len;
     } while (count);
 
     return 0;
 }
 
 STATIC void
 xlog_write_iclog(
     struct xlog     *log,
     struct xlog_in_core *iclog,
     uint64_t        bno,
     unsigned int        count)
 {
     ASSERT(bno < log->l_logBBsize);
     trace_xlog_iclog_write(iclog, _RET_IP_);
 
     /*
      * We lock the iclogbufs here so that we can serialise against I/O
      * completion during unmount.  We might be processing a shutdown
      * triggered during unmount, and that can occur asynchronously to the
      * unmount thread, and hence we need to ensure that completes before
      * tearing down the iclogbufs.  Hence we need to hold the buffer lock
      * across the log IO to archieve that.
      */
     down(&iclog->ic_sema);
     if (xlog_is_shutdown(log)) {
         /*
          * It would seem logical to return EIO here, but we rely on
          * the log state machine to propagate I/O errors instead of
          * doing it here.  We kick of the state machine and unlock
          * the buffer manually, the code needs to be kept in sync
          * with the I/O completion path.
          */
         xlog_state_done_syncing(iclog);
         up(&iclog->ic_sema);
         return;
     }
 
     /*
      * We use REQ_SYNC | REQ_IDLE here to tell the block layer the are more
      * IOs coming immediately after this one. This prevents the block layer
      * writeback throttle from throttling log writes behind background
      * metadata writeback and causing priority inversions.
      */
     bio_init(&iclog->ic_bio, log->l_targ->bt_bdev, iclog->ic_bvec,
          howmany(count, PAGE_SIZE),
          REQ_OP_WRITE | REQ_META | REQ_SYNC | REQ_IDLE);
     iclog->ic_bio.bi_iter.bi_sector = log->l_logBBstart + bno;
     iclog->ic_bio.bi_end_io = xlog_bio_end_io;
     iclog->ic_bio.bi_private = iclog;
 
     if (iclog->ic_flags & XLOG_ICL_NEED_FLUSH) {
         iclog->ic_bio.bi_opf |= REQ_PREFLUSH;
         /*
          * For external log devices, we also need to flush the data
          * device cache first to ensure all metadata writeback covered
          * by the LSN in this iclog is on stable storage. This is slow,
          * but it *must* complete before we issue the external log IO.
          *
          * If the flush fails, we cannot conclude that past metadata
          * writeback from the log succeeded.  Repeating the flush is
          * not possible, hence we must shut down with log IO error to
          * avoid shutdown re-entering this path and erroring out again.
          */
         if (log->l_targ != log->l_mp->m_ddev_targp &&
             blkdev_issue_flush(log->l_mp->m_ddev_targp->bt_bdev)) {
             xlog_force_shutdown(log, SHUTDOWN_LOG_IO_ERROR);
             return;
         }
     }
     if (iclog->ic_flags & XLOG_ICL_NEED_FUA)
         iclog->ic_bio.bi_opf |= REQ_FUA;
 
     iclog->ic_flags &= ~(XLOG_ICL_NEED_FLUSH | XLOG_ICL_NEED_FUA);
 
     if (xlog_map_iclog_data(&iclog->ic_bio, iclog->ic_data, count)) {
         xlog_force_shutdown(log, SHUTDOWN_LOG_IO_ERROR);
         return;
     }
     if (is_vmalloc_addr(iclog->ic_data))
         flush_kernel_vmap_range(iclog->ic_data, count);
 
     /*
      * If this log buffer would straddle the end of the log we will have
      * to split it up into two bios, so that we can continue at the start.
      */
     if (bno + BTOBB(count) > log->l_logBBsize) {
         struct bio *split;
 
         split = bio_split(&iclog->ic_bio, log->l_logBBsize - bno,
                   GFP_NOIO, &fs_bio_set);
         bio_chain(split, &iclog->ic_bio);
         submit_bio(split);
 
         /* restart at logical offset zero for the remainder */
         iclog->ic_bio.bi_iter.bi_sector = log->l_logBBstart;
     }
 
     submit_bio(&iclog->ic_bio);
 }
 
 /*
  * We need to bump cycle number for the part of the iclog that is
  * written to the start of the log. Watch out for the header magic
  * number case, though.
  */
 static void
 xlog_split_iclog(
     struct xlog     *log,
     void            *data,
     uint64_t        bno,
     unsigned int        count)
 {
     unsigned int        split_offset = BBTOB(log->l_logBBsize - bno);
     unsigned int        i;
 
     for (i = split_offset; i < count; i += BBSIZE) {
         uint32_t cycle = get_unaligned_be32(data + i);
 
         if (++cycle == XLOG_HEADER_MAGIC_NUM)
             cycle++;
         put_unaligned_be32(cycle, data + i);
     }
 }
 
 static int
 xlog_calc_iclog_size(
     struct xlog     *log,
     struct xlog_in_core *iclog,
     uint32_t        *roundoff)
 {
     uint32_t        count_init, count;
 
     /* Add for LR header */
     count_init = log->l_iclog_hsize + iclog->ic_offset;
     count = roundup(count_init, log->l_iclog_roundoff);
 
     *roundoff = count - count_init;
 
     ASSERT(count >= count_init);
     ASSERT(*roundoff < log->l_iclog_roundoff);
     return count;
 }
 
 /*
  * Flush out the in-core log (iclog) to the on-disk log in an asynchronous
  * fashion.  Previously, we should have moved the current iclog
  * ptr in the log to point to the next available iclog.  This allows further
  * write to continue while this code syncs out an iclog ready to go.
  * Before an in-core log can be written out, the data section must be scanned
  * to save away the 1st word of each BBSIZE block into the header.  We replace
  * it with the current cycle count.  Each BBSIZE block is tagged with the
  * cycle count because there in an implicit assumption that drives will
  * guarantee that entire 512 byte blocks get written at once.  In other words,
  * we can't have part of a 512 byte block written and part not written.  By
  * tagging each block, we will know which blocks are valid when recovering
  * after an unclean shutdown.
  *
  * This routine is single threaded on the iclog.  No other thread can be in
  * this routine with the same iclog.  Changing contents of iclog can there-
  * fore be done without grabbing the state machine lock.  Updating the global
  * log will require grabbing the lock though.
  *
  * The entire log manager uses a logical block numbering scheme.  Only
  * xlog_write_iclog knows about the fact that the log may not start with
  * block zero on a given device.
  */
 STATIC void
 xlog_sync(
     struct xlog     *log,
     struct xlog_in_core *iclog,
     struct xlog_ticket  *ticket)
 {
     unsigned int        count;      /* byte count of bwrite */
     unsigned int        roundoff;       /* roundoff to BB or stripe */
     uint64_t        bno;
     unsigned int        size;
 
     ASSERT(atomic_read(&iclog->ic_refcnt) == 0);
     trace_xlog_iclog_sync(iclog, _RET_IP_);
 
     count = xlog_calc_iclog_size(log, iclog, &roundoff);
 
     /*
      * If we have a ticket, account for the roundoff via the ticket
      * reservation to avoid touching the hot grant heads needlessly.
      * Otherwise, we have to move grant heads directly.
      */
     if (ticket) {
         ticket->t_curr_res -= roundoff;
     } else {
         xlog_grant_add_space(log, &log->l_reserve_head.grant, roundoff);
         xlog_grant_add_space(log, &log->l_write_head.grant, roundoff);
     }
 
     /* put cycle number in every block */
     xlog_pack_data(log, iclog, roundoff);
 
     /* real byte length */
     size = iclog->ic_offset;
     if (xfs_has_logv2(log->l_mp))
         size += roundoff;
     iclog->ic_header.h_len = cpu_to_be32(size);
 
     XFS_STATS_INC(log->l_mp, xs_log_writes);
     XFS_STATS_ADD(log->l_mp, xs_log_blocks, BTOBB(count));
 
     bno = BLOCK_LSN(be64_to_cpu(iclog->ic_header.h_lsn));
 
     /* Do we need to split this write into 2 parts? */
     if (bno + BTOBB(count) > log->l_logBBsize)
         xlog_split_iclog(log, &iclog->ic_header, bno, count);
 
     /* calculcate the checksum */
     iclog->ic_header.h_crc = xlog_cksum(log, &iclog->ic_header,
                         iclog->ic_datap, size);
     /*
      * Intentionally corrupt the log record CRC based on the error injection
      * frequency, if defined. This facilitates testing log recovery in the
      * event of torn writes. Hence, set the IOABORT state to abort the log
      * write on I/O completion and shutdown the fs. The subsequent mount
      * detects the bad CRC and attempts to recover.
      */
 #ifdef DEBUG
     if (XFS_TEST_ERROR(false, log->l_mp, XFS_ERRTAG_LOG_BAD_CRC)) {
         iclog->ic_header.h_crc &= cpu_to_le32(0xAAAAAAAA);
         iclog->ic_fail_crc = true;
         xfs_warn(log->l_mp,
     "Intentionally corrupted log record at LSN 0x%llx. Shutdown imminent.",
              be64_to_cpu(iclog->ic_header.h_lsn));
     }
 #endif
     xlog_verify_iclog(log, iclog, count);
     xlog_write_iclog(log, iclog, bno, count);
 }
 
 /*
  * Deallocate a log structure
  */
 STATIC void
 xlog_dealloc_log(
     struct xlog *log)
 {
     xlog_in_core_t  *iclog, *next_iclog;
     int     i;
 
     /*
      * Cycle all the iclogbuf locks to make sure all log IO completion
      * is done before we tear down these buffers.
      */
     iclog = log->l_iclog;
     for (i = 0; i < log->l_iclog_bufs; i++) {
         down(&iclog->ic_sema);
         up(&iclog->ic_sema);
         iclog = iclog->ic_next;
     }
 
     /*
      * Destroy the CIL after waiting for iclog IO completion because an
      * iclog EIO error will try to shut down the log, which accesses the
      * CIL to wake up the waiters.
      */
     xlog_cil_destroy(log);
 
     iclog = log->l_iclog;
     for (i = 0; i < log->l_iclog_bufs; i++) {
         next_iclog = iclog->ic_next;
         kmem_free(iclog->ic_data);
         kmem_free(iclog);
         iclog = next_iclog;
     }
 
     log->l_mp->m_log = NULL;
     destroy_workqueue(log->l_ioend_workqueue);
     kmem_free(log);
 }
 
 /*
  * Update counters atomically now that memcpy is done.
  */
 static inline void
 xlog_state_finish_copy(
     struct xlog     *log,
     struct xlog_in_core *iclog,
     int         record_cnt,
     int         copy_bytes)
 {
     lockdep_assert_held(&log->l_icloglock);
 
     be32_add_cpu(&iclog->ic_header.h_num_logops, record_cnt);
     iclog->ic_offset += copy_bytes;
 }
 
 /*
  * print out info relating to regions written which consume
  * the reservation
  */
 void
 xlog_print_tic_res(
     struct xfs_mount    *mp,
     struct xlog_ticket  *ticket)
 {
     xfs_warn(mp, "ticket reservation summary:");
     xfs_warn(mp, "  unit res    = %d bytes", ticket->t_unit_res);
     xfs_warn(mp, "  current res = %d bytes", ticket->t_curr_res);
     xfs_warn(mp, "  original count  = %d", ticket->t_ocnt);
     xfs_warn(mp, "  remaining count = %d", ticket->t_cnt);
 }
 
 /*
  * Print a summary of the transaction.
  */
 void
 xlog_print_trans(
     struct xfs_trans    *tp)
 {
     struct xfs_mount    *mp = tp->t_mountp;
     struct xfs_log_item *lip;
 
     /* dump core transaction and ticket info */
     xfs_warn(mp, "transaction summary:");
     xfs_warn(mp, "  log res   = %d", tp->t_log_res);
     xfs_warn(mp, "  log count = %d", tp->t_log_count);
     xfs_warn(mp, "  flags     = 0x%x", tp->t_flags);
 
     xlog_print_tic_res(mp, tp->t_ticket);
 
     /* dump each log item */
     list_for_each_entry(lip, &tp->t_items, li_trans) {
         struct xfs_log_vec  *lv = lip->li_lv;
         struct xfs_log_iovec    *vec;
         int         i;
 
         xfs_warn(mp, "log item: ");
         xfs_warn(mp, "  type    = 0x%x", lip->li_type);
         xfs_warn(mp, "  flags   = 0x%lx", lip->li_flags);
         if (!lv)
             continue;
         xfs_warn(mp, "  niovecs = %d", lv->lv_niovecs);
         xfs_warn(mp, "  size    = %d", lv->lv_size);
         xfs_warn(mp, "  bytes   = %d", lv->lv_bytes);
         xfs_warn(mp, "  buf len = %d", lv->lv_buf_len);
 
         /* dump each iovec for the log item */
         vec = lv->lv_iovecp;
         for (i = 0; i < lv->lv_niovecs; i++) {
             int dumplen = min(vec->i_len, 32);
 
             xfs_warn(mp, "  iovec[%d]", i);
             xfs_warn(mp, "    type  = 0x%x", vec->i_type);
             xfs_warn(mp, "    len   = %d", vec->i_len);
             xfs_warn(mp, "    first %d bytes of iovec[%d]:", dumplen, i);
             xfs_hex_dump(vec->i_addr, dumplen);
 
             vec++;
         }
     }
 }
 
 static inline void
 xlog_write_iovec(
     struct xlog_in_core *iclog,
     uint32_t        *log_offset,
     void            *data,
     uint32_t        write_len,
     int         *bytes_left,
     uint32_t        *record_cnt,
     uint32_t        *data_cnt)
 {
     ASSERT(*log_offset < iclog->ic_log->l_iclog_size);
     ASSERT(*log_offset % sizeof(int32_t) == 0);
     ASSERT(write_len % sizeof(int32_t) == 0);
 
     memcpy(iclog->ic_datap + *log_offset, data, write_len);
     *log_offset += write_len;
     *bytes_left -= write_len;
     (*record_cnt)++;
     *data_cnt += write_len;
 }
 
 /*
  * Write log vectors into a single iclog which is guaranteed by the caller
  * to have enough space to write the entire log vector into.
  */
 static void
 xlog_write_full(
     struct xfs_log_vec  *lv,
     struct xlog_ticket  *ticket,
     struct xlog_in_core *iclog,
     uint32_t        *log_offset,
     uint32_t        *len,
     uint32_t        *record_cnt,
     uint32_t        *data_cnt)
 {
     int         index;
 
     ASSERT(*log_offset + *len <= iclog->ic_size ||
         iclog->ic_state == XLOG_STATE_WANT_SYNC);
 
     /*
      * Ordered log vectors have no regions to write so this
      * loop will naturally skip them.
      */
     for (index = 0; index < lv->lv_niovecs; index++) {
         struct xfs_log_iovec    *reg = &lv->lv_iovecp[index];
         struct xlog_op_header   *ophdr = reg->i_addr;
 
         ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
         xlog_write_iovec(iclog, log_offset, reg->i_addr,
                 reg->i_len, len, record_cnt, data_cnt);
     }
 }
 
 static int
 xlog_write_get_more_iclog_space(
     struct xlog_ticket  *ticket,
     struct xlog_in_core **iclogp,
     uint32_t        *log_offset,
     uint32_t        len,
     uint32_t        *record_cnt,
     uint32_t        *data_cnt)
 {
     struct xlog_in_core *iclog = *iclogp;
     struct xlog     *log = iclog->ic_log;
     int         error;
 
     spin_lock(&log->l_icloglock);
     ASSERT(iclog->ic_state == XLOG_STATE_WANT_SYNC);
     xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
     error = xlog_state_release_iclog(log, iclog, ticket);
     spin_unlock(&log->l_icloglock);
     if (error)
         return error;
 
     error = xlog_state_get_iclog_space(log, len, &iclog, ticket,
                     log_offset);
     if (error)
         return error;
     *record_cnt = 0;
     *data_cnt = 0;
     *iclogp = iclog;
     return 0;
 }
 
 /*
  * Write log vectors into a single iclog which is smaller than the current chain
  * length. We write until we cannot fit a full record into the remaining space
  * and then stop. We return the log vector that is to be written that cannot
  * wholly fit in the iclog.
  */
 static int
 xlog_write_partial(
     struct xfs_log_vec  *lv,
     struct xlog_ticket  *ticket,
     struct xlog_in_core **iclogp,
     uint32_t        *log_offset,
     uint32_t        *len,
     uint32_t        *record_cnt,
     uint32_t        *data_cnt)
 {
     struct xlog_in_core *iclog = *iclogp;
     struct xlog_op_header   *ophdr;
     int         index = 0;
     uint32_t        rlen;
     int         error;
 
     /* walk the logvec, copying until we run out of space in the iclog */
     for (index = 0; index < lv->lv_niovecs; index++) {
         struct xfs_log_iovec    *reg = &lv->lv_iovecp[index];
         uint32_t        reg_offset = 0;
 
         /*
          * The first region of a continuation must have a non-zero
          * length otherwise log recovery will just skip over it and
          * start recovering from the next opheader it finds. Because we
          * mark the next opheader as a continuation, recovery will then
          * incorrectly add the continuation to the previous region and
          * that breaks stuff.
          *
          * Hence if there isn't space for region data after the
          * opheader, then we need to start afresh with a new iclog.
          */
         if (iclog->ic_size - *log_offset <=
                     sizeof(struct xlog_op_header)) {
             error = xlog_write_get_more_iclog_space(ticket,
                     &iclog, log_offset, *len, record_cnt,
                     data_cnt);
             if (error)
                 return error;
         }
 
         ophdr = reg->i_addr;
         rlen = min_t(uint32_t, reg->i_len, iclog->ic_size - *log_offset);
 
         ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
         ophdr->oh_len = cpu_to_be32(rlen - sizeof(struct xlog_op_header));
         if (rlen != reg->i_len)
             ophdr->oh_flags |= XLOG_CONTINUE_TRANS;
 
         xlog_write_iovec(iclog, log_offset, reg->i_addr,
                 rlen, len, record_cnt, data_cnt);
 
         /* If we wrote the whole region, move to the next. */
         if (rlen == reg->i_len)
             continue;
 
         /*
          * We now have a partially written iovec, but it can span
          * multiple iclogs so we loop here. First we release the iclog
          * we currently have, then we get a new iclog and add a new
          * opheader. Then we continue copying from where we were until
          * we either complete the iovec or fill the iclog. If we
          * complete the iovec, then we increment the index and go right
          * back to the top of the outer loop. if we fill the iclog, we
          * run the inner loop again.
          *
          * This is complicated by the tail of a region using all the
          * space in an iclog and hence requiring us to release the iclog
          * and get a new one before returning to the outer loop. We must
          * always guarantee that we exit this inner loop with at least
          * space for log transaction opheaders left in the current
          * iclog, hence we cannot just terminate the loop at the end
          * of the of the continuation. So we loop while there is no
          * space left in the current iclog, and check for the end of the
          * continuation after getting a new iclog.
          */
         do {
             /*
              * Ensure we include the continuation opheader in the
              * space we need in the new iclog by adding that size
              * to the length we require. This continuation opheader
              * needs to be accounted to the ticket as the space it
              * consumes hasn't been accounted to the lv we are
              * writing.
              */
             error = xlog_write_get_more_iclog_space(ticket,
                     &iclog, log_offset,
                     *len + sizeof(struct xlog_op_header),
                     record_cnt, data_cnt);
             if (error)
                 return error;
 
             ophdr = iclog->ic_datap + *log_offset;
             ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
             ophdr->oh_clientid = XFS_TRANSACTION;
             ophdr->oh_res2 = 0;
             ophdr->oh_flags = XLOG_WAS_CONT_TRANS;
 
             ticket->t_curr_res -= sizeof(struct xlog_op_header);
             *log_offset += sizeof(struct xlog_op_header);
             *data_cnt += sizeof(struct xlog_op_header);
 
             /*
              * If rlen fits in the iclog, then end the region
              * continuation. Otherwise we're going around again.
              */
             reg_offset += rlen;
             rlen = reg->i_len - reg_offset;
             if (rlen <= iclog->ic_size - *log_offset)
                 ophdr->oh_flags |= XLOG_END_TRANS;
             else
                 ophdr->oh_flags |= XLOG_CONTINUE_TRANS;
 
             rlen = min_t(uint32_t, rlen, iclog->ic_size - *log_offset);
             ophdr->oh_len = cpu_to_be32(rlen);
 
             xlog_write_iovec(iclog, log_offset,
                     reg->i_addr + reg_offset,
                     rlen, len, record_cnt, data_cnt);
 
         } while (ophdr->oh_flags & XLOG_CONTINUE_TRANS);
     }
 
     /*
      * No more iovecs remain in this logvec so return the next log vec to
      * the caller so it can go back to fast path copying.
      */
     *iclogp = iclog;
     return 0;
 }
 
 /*
  * Write some region out to in-core log
  *
  * This will be called when writing externally provided regions or when
  * writing out a commit record for a given transaction.
  *
  * General algorithm:
  *  1. Find total length of this write.  This may include adding to the
  *      lengths passed in.
  *  2. Check whether we violate the tickets reservation.
  *  3. While writing to this iclog
  *      A. Reserve as much space in this iclog as can get
  *      B. If this is first write, save away start lsn
  *      C. While writing this region:
  *      1. If first write of transaction, write start record
  *      2. Write log operation header (header per region)
  *      3. Find out if we can fit entire region into this iclog
  *      4. Potentially, verify destination memcpy ptr
  *      5. Memcpy (partial) region
  *      6. If partial copy, release iclog; otherwise, continue
  *          copying more regions into current iclog
  *  4. Mark want sync bit (in simulation mode)
  *  5. Release iclog for potential flush to on-disk log.
  *
  * ERRORS:
  * 1.   Panic if reservation is overrun.  This should never happen since
  *  reservation amounts are generated internal to the filesystem.
  * NOTES:
  * 1. Tickets are single threaded data structures.
  * 2. The XLOG_END_TRANS & XLOG_CONTINUE_TRANS flags are passed down to the
  *  syncing routine.  When a single log_write region needs to span
  *  multiple in-core logs, the XLOG_CONTINUE_TRANS bit should be set
  *  on all log operation writes which don't contain the end of the
  *  region.  The XLOG_END_TRANS bit is used for the in-core log
  *  operation which contains the end of the continued log_write region.
  * 3. When xlog_state_get_iclog_space() grabs the rest of the current iclog,
  *  we don't really know exactly how much space will be used.  As a result,
  *  we don't update ic_offset until the end when we know exactly how many
  *  bytes have been written out.
  */
 int
 xlog_write(
     struct xlog     *log,
     struct xfs_cil_ctx  *ctx,
     struct list_head    *lv_chain,
     struct xlog_ticket  *ticket,
     uint32_t        len)
 
 {
     struct xlog_in_core *iclog = NULL;
     struct xfs_log_vec  *lv;
     uint32_t        record_cnt = 0;
     uint32_t        data_cnt = 0;
     int         error = 0;
     int         log_offset;
 
     if (ticket->t_curr_res < 0) {
         xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
              "ctx ticket reservation ran out. Need to up reservation");
         xlog_print_tic_res(log->l_mp, ticket);
         xlog_force_shutdown(log, SHUTDOWN_LOG_IO_ERROR);
     }
 
     error = xlog_state_get_iclog_space(log, len, &iclog, ticket,
                        &log_offset);
     if (error)
         return error;
 
     ASSERT(log_offset <= iclog->ic_size - 1);
 
     /*
      * If we have a context pointer, pass it the first iclog we are
      * writing to so it can record state needed for iclog write
      * ordering.
      */
     if (ctx)
         xlog_cil_set_ctx_write_state(ctx, iclog);
 
     list_for_each_entry(lv, lv_chain, lv_list) {
         /*
          * If the entire log vec does not fit in the iclog, punt it to
          * the partial copy loop which can handle this case.
          */
         if (lv->lv_niovecs &&
             lv->lv_bytes > iclog->ic_size - log_offset) {
             error = xlog_write_partial(lv, ticket, &iclog,
                     &log_offset, &len, &record_cnt,
                     &data_cnt);
             if (error) {
                 /*
                  * We have no iclog to release, so just return
                  * the error immediately.
                  */
                 return error;
             }
         } else {
             xlog_write_full(lv, ticket, iclog, &log_offset,
                      &len, &record_cnt, &data_cnt);
         }
     }
     ASSERT(len == 0);
 
     /*
      * We've already been guaranteed that the last writes will fit inside
      * the current iclog, and hence it will already have the space used by
      * those writes accounted to it. Hence we do not need to update the
      * iclog with the number of bytes written here.
      */
     spin_lock(&log->l_icloglock);
     xlog_state_finish_copy(log, iclog, record_cnt, 0);
     error = xlog_state_release_iclog(log, iclog, ticket);
     spin_unlock(&log->l_icloglock);
 
     return error;
 }
 
 static void
 xlog_state_activate_iclog(
     struct xlog_in_core *iclog,
     int         *iclogs_changed)
 {
     ASSERT(list_empty_careful(&iclog->ic_callbacks));
     trace_xlog_iclog_activate(iclog, _RET_IP_);
 
     /*
      * If the number of ops in this iclog indicate it just contains the
      * dummy transaction, we can change state into IDLE (the second time
      * around). Otherwise we should change the state into NEED a dummy.
      * We don't need to cover the dummy.
      */
     if (*iclogs_changed == 0 &&
         iclog->ic_header.h_num_logops == cpu_to_be32(XLOG_COVER_OPS)) {
         *iclogs_changed = 1;
     } else {
         /*
          * We have two dirty iclogs so start over.  This could also be
          * num of ops indicating this is not the dummy going out.
          */
         *iclogs_changed = 2;
     }
 
     iclog->ic_state = XLOG_STATE_ACTIVE;
     iclog->ic_offset = 0;
     iclog->ic_header.h_num_logops = 0;
     memset(iclog->ic_header.h_cycle_data, 0,
         sizeof(iclog->ic_header.h_cycle_data));
     iclog->ic_header.h_lsn = 0;
     iclog->ic_header.h_tail_lsn = 0;
 }
 
 /*
  * Loop through all iclogs and mark all iclogs currently marked DIRTY as
  * ACTIVE after iclog I/O has completed.
  */
 static void
 xlog_state_activate_iclogs(
     struct xlog     *log,
     int         *iclogs_changed)
 {
     struct xlog_in_core *iclog = log->l_iclog;
 
     do {
         if (iclog->ic_state == XLOG_STATE_DIRTY)
             xlog_state_activate_iclog(iclog, iclogs_changed);
         /*
          * The ordering of marking iclogs ACTIVE must be maintained, so
          * an iclog doesn't become ACTIVE beyond one that is SYNCING.
          */
         else if (iclog->ic_state != XLOG_STATE_ACTIVE)
             break;
     } while ((iclog = iclog->ic_next) != log->l_iclog);
 }
 
 static int
 xlog_covered_state(
     int         prev_state,
     int         iclogs_changed)
 {
     /*
      * We go to NEED for any non-covering writes. We go to NEED2 if we just
      * wrote the first covering record (DONE). We go to IDLE if we just
      * wrote the second covering record (DONE2) and remain in IDLE until a
      * non-covering write occurs.
      */
     switch (prev_state) {
     case XLOG_STATE_COVER_IDLE:
         if (iclogs_changed == 1)
             return XLOG_STATE_COVER_IDLE;
         fallthrough;
     case XLOG_STATE_COVER_NEED:
     case XLOG_STATE_COVER_NEED2:
         break;
     case XLOG_STATE_COVER_DONE:
         if (iclogs_changed == 1)
             return XLOG_STATE_COVER_NEED2;
         break;
     case XLOG_STATE_COVER_DONE2:
         if (iclogs_changed == 1)
             return XLOG_STATE_COVER_IDLE;
         break;
     default:
         ASSERT(0);
     }
 
     return XLOG_STATE_COVER_NEED;
 }
 
 STATIC void
 xlog_state_clean_iclog(
     struct xlog     *log,
     struct xlog_in_core *dirty_iclog)
 {
     int         iclogs_changed = 0;
 
     trace_xlog_iclog_clean(dirty_iclog, _RET_IP_);
 
     dirty_iclog->ic_state = XLOG_STATE_DIRTY;
 
     xlog_state_activate_iclogs(log, &iclogs_changed);
     wake_up_all(&dirty_iclog->ic_force_wait);
 
     if (iclogs_changed) {
         log->l_covered_state = xlog_covered_state(log->l_covered_state,
                 iclogs_changed);
     }
 }
 
 STATIC xfs_lsn_t
 xlog_get_lowest_lsn(
     struct xlog     *log)
 {
     struct xlog_in_core *iclog = log->l_iclog;
     xfs_lsn_t       lowest_lsn = 0, lsn;
 
     do {
         if (iclog->ic_state == XLOG_STATE_ACTIVE ||
             iclog->ic_state == XLOG_STATE_DIRTY)
             continue;
 
         lsn = be64_to_cpu(iclog->ic_header.h_lsn);
         if ((lsn && !lowest_lsn) || XFS_LSN_CMP(lsn, lowest_lsn) < 0)
             lowest_lsn = lsn;
     } while ((iclog = iclog->ic_next) != log->l_iclog);
 
     return lowest_lsn;
 }
 
 /*
  * Completion of a iclog IO does not imply that a transaction has completed, as
  * transactions can be large enough to span many iclogs. We cannot change the
  * tail of the log half way through a transaction as this may be the only
  * transaction in the log and moving the tail to point to the middle of it
  * will prevent recovery from finding the start of the transaction. Hence we
  * should only update the last_sync_lsn if this iclog contains transaction
  * completion callbacks on it.
  *
  * We have to do this before we drop the icloglock to ensure we are the only one
  * that can update it.
  *
  * If we are moving the last_sync_lsn forwards, we also need to ensure we kick
  * the reservation grant head pushing. This is due to the fact that the push
  * target is bound by the current last_sync_lsn value. Hence if we have a large
  * amount of log space bound up in this committing transaction then the
  * last_sync_lsn value may be the limiting factor preventing tail pushing from
  * freeing space in the log. Hence once we've updated the last_sync_lsn we
  * should push the AIL to ensure the push target (and hence the grant head) is
  * no longer bound by the old log head location and can move forwards and make
  * progress again.
  */
 static void
 xlog_state_set_callback(
     struct xlog     *log,
     struct xlog_in_core *iclog,
     xfs_lsn_t       header_lsn)
 {
     trace_xlog_iclog_callback(iclog, _RET_IP_);
     iclog->ic_state = XLOG_STATE_CALLBACK;
 
     ASSERT(XFS_LSN_CMP(atomic64_read(&log->l_last_sync_lsn),
                header_lsn) <= 0);
 
     if (list_empty_careful(&iclog->ic_callbacks))
         return;
 
     atomic64_set(&log->l_last_sync_lsn, header_lsn);
     xlog_grant_push_ail(log, 0);
 }
 
 /*
  * Return true if we need to stop processing, false to continue to the next
  * iclog. The caller will need to run callbacks if the iclog is returned in the
  * XLOG_STATE_CALLBACK state.
  */
 static bool
 xlog_state_iodone_process_iclog(
     struct xlog     *log,
     struct xlog_in_core *iclog)
 {
     xfs_lsn_t       lowest_lsn;
     xfs_lsn_t       header_lsn;
 
     switch (iclog->ic_state) {
     case XLOG_STATE_ACTIVE:
     case XLOG_STATE_DIRTY:
         /*
          * Skip all iclogs in the ACTIVE & DIRTY states:
          */
         return false;
     case XLOG_STATE_DONE_SYNC:
         /*
          * Now that we have an iclog that is in the DONE_SYNC state, do
          * one more check here to see if we have chased our tail around.
          * If this is not the lowest lsn iclog, then we will leave it
          * for another completion to process.
          */
         header_lsn = be64_to_cpu(iclog->ic_header.h_lsn);
         lowest_lsn = xlog_get_lowest_lsn(log);
         if (lowest_lsn && XFS_LSN_CMP(lowest_lsn, header_lsn) < 0)
             return false;
         xlog_state_set_callback(log, iclog, header_lsn);
         return false;
     default:
         /*
          * Can only perform callbacks in order.  Since this iclog is not
          * in the DONE_SYNC state, we skip the rest and just try to
          * clean up.
          */
         return true;
     }
 }
 
 /*
  * Loop over all the iclogs, running attached callbacks on them. Return true if
  * we ran any callbacks, indicating that we dropped the icloglock. We don't need
  * to handle transient shutdown state here at all because
  * xlog_state_shutdown_callbacks() will be run to do the necessary shutdown
  * cleanup of the callbacks.
  */
 static bool
 xlog_state_do_iclog_callbacks(
     struct xlog     *log)
         __releases(&log->l_icloglock)
         __acquires(&log->l_icloglock)
 {
     struct xlog_in_core *first_iclog = log->l_iclog;
     struct xlog_in_core *iclog = first_iclog;
     bool            ran_callback = false;
 
     do {
         LIST_HEAD(cb_list);
 
         if (xlog_state_iodone_process_iclog(log, iclog))
             break;
         if (iclog->ic_state != XLOG_STATE_CALLBACK) {
             iclog = iclog->ic_next;
             continue;
         }
         list_splice_init(&iclog->ic_callbacks, &cb_list);
         spin_unlock(&log->l_icloglock);
 
         trace_xlog_iclog_callbacks_start(iclog, _RET_IP_);
         xlog_cil_process_committed(&cb_list);
         trace_xlog_iclog_callbacks_done(iclog, _RET_IP_);
         ran_callback = true;
 
         spin_lock(&log->l_icloglock);
         xlog_state_clean_iclog(log, iclog);
         iclog = iclog->ic_next;
     } while (iclog != first_iclog);
 
     return ran_callback;
 }
 
 
 /*
  * Loop running iclog completion callbacks until there are no more iclogs in a
  * state that can run callbacks.
  */
 STATIC void
 xlog_state_do_callback(
     struct xlog     *log)
 {
     int         flushcnt = 0;
     int         repeats = 0;
 
     spin_lock(&log->l_icloglock);
     while (xlog_state_do_iclog_callbacks(log)) {
         if (xlog_is_shutdown(log))
             break;
 
         if (++repeats > 5000) {
             flushcnt += repeats;
             repeats = 0;
             xfs_warn(log->l_mp,
                 "%s: possible infinite loop (%d iterations)",
                 __func__, flushcnt);
         }
     }
 
     if (log->l_iclog->ic_state == XLOG_STATE_ACTIVE)
         wake_up_all(&log->l_flush_wait);
 
     spin_unlock(&log->l_icloglock);
 }
 
 
 /*
  * Finish transitioning this iclog to the dirty state.
  *
  * Callbacks could take time, so they are done outside the scope of the
  * global state machine log lock.
  */
 STATIC void
 xlog_state_done_syncing(
     struct xlog_in_core *iclog)
 {
     struct xlog     *log = iclog->ic_log;
 
     spin_lock(&log->l_icloglock);
     ASSERT(atomic_read(&iclog->ic_refcnt) == 0);
     trace_xlog_iclog_sync_done(iclog, _RET_IP_);
 
     /*
      * If we got an error, either on the first buffer, or in the case of
      * split log writes, on the second, we shut down the file system and
      * no iclogs should ever be attempted to be written to disk again.
      */
     if (!xlog_is_shutdown(log)) {
         ASSERT(iclog->ic_state == XLOG_STATE_SYNCING);
         iclog->ic_state = XLOG_STATE_DONE_SYNC;
     }
 
     /*
      * Someone could be sleeping prior to writing out the next
      * iclog buffer, we wake them all, one will get to do the
      * I/O, the others get to wait for the result.
      */
     wake_up_all(&iclog->ic_write_wait);
     spin_unlock(&log->l_icloglock);
     xlog_state_do_callback(log);
 }
 
 /*
  * If the head of the in-core log ring is not (ACTIVE or DIRTY), then we must
  * sleep.  We wait on the flush queue on the head iclog as that should be
  * the first iclog to complete flushing. Hence if all iclogs are syncing,
  * we will wait here and all new writes will sleep until a sync completes.
  *
  * The in-core logs are used in a circular fashion. They are not used
  * out-of-order even when an iclog past the head is free.
  *
  * return:
  *  * log_offset where xlog_write() can start writing into the in-core
  *      log's data space.
  *  * in-core log pointer to which xlog_write() should write.
  *  * boolean indicating this is a continued write to an in-core log.
  *      If this is the last write, then the in-core log's offset field
  *      needs to be incremented, depending on the amount of data which
  *      is copied.
  */
 STATIC int
 xlog_state_get_iclog_space(
     struct xlog     *log,
     int         len,
     struct xlog_in_core **iclogp,
     struct xlog_ticket  *ticket,
     int         *logoffsetp)
 {
     int       log_offset;
     xlog_rec_header_t *head;
     xlog_in_core_t    *iclog;
 
 restart:
     spin_lock(&log->l_icloglock);
     if (xlog_is_shutdown(log)) {
         spin_unlock(&log->l_icloglock);
         return -EIO;
     }
 
     iclog = log->l_iclog;
     if (iclog->ic_state != XLOG_STATE_ACTIVE) {
         XFS_STATS_INC(log->l_mp, xs_log_noiclogs);
 
         /* Wait for log writes to have flushed */
         xlog_wait(&log->l_flush_wait, &log->l_icloglock);
         goto restart;
     }
 
     head = &iclog->ic_header;
 
     atomic_inc(&iclog->ic_refcnt);  /* prevents sync */
     log_offset = iclog->ic_offset;
 
     trace_xlog_iclog_get_space(iclog, _RET_IP_);
 
     /* On the 1st write to an iclog, figure out lsn.  This works
      * if iclogs marked XLOG_STATE_WANT_SYNC always write out what they are
      * committing to.  If the offset is set, that's how many blocks
      * must be written.
      */
     if (log_offset == 0) {
         ticket->t_curr_res -= log->l_iclog_hsize;
         head->h_cycle = cpu_to_be32(log->l_curr_cycle);
         head->h_lsn = cpu_to_be64(
             xlog_assign_lsn(log->l_curr_cycle, log->l_curr_block));
         ASSERT(log->l_curr_block >= 0);
     }
 
     /* If there is enough room to write everything, then do it.  Otherwise,
      * claim the rest of the region and make sure the XLOG_STATE_WANT_SYNC
      * bit is on, so this will get flushed out.  Don't update ic_offset
      * until you know exactly how many bytes get copied.  Therefore, wait
      * until later to update ic_offset.
      *
      * xlog_write() algorithm assumes that at least 2 xlog_op_header_t's
      * can fit into remaining data section.
      */
     if (iclog->ic_size - iclog->ic_offset < 2*sizeof(xlog_op_header_t)) {
         int     error = 0;
 
         xlog_state_switch_iclogs(log, iclog, iclog->ic_size);
 
         /*
          * If we are the only one writing to this iclog, sync it to
          * disk.  We need to do an atomic compare and decrement here to
          * avoid racing with concurrent atomic_dec_and_lock() calls in
          * xlog_state_release_iclog() when there is more than one
          * reference to the iclog.
          */
         if (!atomic_add_unless(&iclog->ic_refcnt, -1, 1))
             error = xlog_state_release_iclog(log, iclog, ticket);
         spin_unlock(&log->l_icloglock);
         if (error)
             return error;
         goto restart;
     }
 
     /* Do we have enough room to write the full amount in the remainder
      * of this iclog?  Or must we continue a write on the next iclog and
      * mark this iclog as completely taken?  In the case where we switch
      * iclogs (to mark it taken), this particular iclog will release/sync
      * to disk in xlog_write().
      */
     if (len <= iclog->ic_size - iclog->ic_offset)
         iclog->ic_offset += len;
     else
         xlog_state_switch_iclogs(log, iclog, iclog->ic_size);
     *iclogp = iclog;
 
     ASSERT(iclog->ic_offset <= iclog->ic_size);
     spin_unlock(&log->l_icloglock);
 
     *logoffsetp = log_offset;
     return 0;
 }
 
 /*
  * The first cnt-1 times a ticket goes through here we don't need to move the
  * grant write head because the permanent reservation has reserved cnt times the
  * unit amount.  Release part of current permanent unit reservation and reset
  * current reservation to be one units worth.  Also move grant reservation head
  * forward.
  */
 void
 xfs_log_ticket_regrant(
     struct xlog     *log,
     struct xlog_ticket  *ticket)
 {
     trace_xfs_log_ticket_regrant(log, ticket);
 
     if (ticket->t_cnt > 0)
         ticket->t_cnt--;
 
     xlog_grant_sub_space(log, &log->l_reserve_head.grant,
                     ticket->t_curr_res);
     xlog_grant_sub_space(log, &log->l_write_head.grant,
                     ticket->t_curr_res);
     ticket->t_curr_res = ticket->t_unit_res;
 
     trace_xfs_log_ticket_regrant_sub(log, ticket);
 
     /* just return if we still have some of the pre-reserved space */
     if (!ticket->t_cnt) {
         xlog_grant_add_space(log, &log->l_reserve_head.grant,
                      ticket->t_unit_res);
         trace_xfs_log_ticket_regrant_exit(log, ticket);
 
         ticket->t_curr_res = ticket->t_unit_res;
     }
 
     xfs_log_ticket_put(ticket);
 }
 
 /*
  * Give back the space left from a reservation.
  *
  * All the information we need to make a correct determination of space left
  * is present.  For non-permanent reservations, things are quite easy.  The
  * count should have been decremented to zero.  We only need to deal with the
  * space remaining in the current reservation part of the ticket.  If the
  * ticket contains a permanent reservation, there may be left over space which
  * needs to be released.  A count of N means that N-1 refills of the current
  * reservation can be done before we need to ask for more space.  The first
  * one goes to fill up the first current reservation.  Once we run out of
  * space, the count will stay at zero and the only space remaining will be
  * in the current reservation field.
  */
 void
 xfs_log_ticket_ungrant(
     struct xlog     *log,
     struct xlog_ticket  *ticket)
 {
     int         bytes;
 
     trace_xfs_log_ticket_ungrant(log, ticket);
 
     if (ticket->t_cnt > 0)
         ticket->t_cnt--;
 
     trace_xfs_log_ticket_ungrant_sub(log, ticket);
 
     /*
      * If this is a permanent reservation ticket, we may be able to free
      * up more space based on the remaining count.
      */
     bytes = ticket->t_curr_res;
     if (ticket->t_cnt > 0) {
         ASSERT(ticket->t_flags & XLOG_TIC_PERM_RESERV);
         bytes += ticket->t_unit_res*ticket->t_cnt;
     }
 
     xlog_grant_sub_space(log, &log->l_reserve_head.grant, bytes);
     xlog_grant_sub_space(log, &log->l_write_head.grant, bytes);
 
     trace_xfs_log_ticket_ungrant_exit(log, ticket);
 
     xfs_log_space_wake(log->l_mp);
     xfs_log_ticket_put(ticket);
 }
 
 /*
  * This routine will mark the current iclog in the ring as WANT_SYNC and move
  * the current iclog pointer to the next iclog in the ring.
  */
 void
 xlog_state_switch_iclogs(
     struct xlog     *log,
     struct xlog_in_core *iclog,
     int         eventual_size)
 {
     ASSERT(iclog->ic_state == XLOG_STATE_ACTIVE);
     assert_spin_locked(&log->l_icloglock);
     trace_xlog_iclog_switch(iclog, _RET_IP_);
 
     if (!eventual_size)
         eventual_size = iclog->ic_offset;
     iclog->ic_state = XLOG_STATE_WANT_SYNC;
     iclog->ic_header.h_prev_block = cpu_to_be32(log->l_prev_block);
     log->l_prev_block = log->l_curr_block;
     log->l_prev_cycle = log->l_curr_cycle;
 
     /* roll log?: ic_offset changed later */
     log->l_curr_block += BTOBB(eventual_size)+BTOBB(log->l_iclog_hsize);
 
     /* Round up to next log-sunit */
     if (log->l_iclog_roundoff > BBSIZE) {
         uint32_t sunit_bb = BTOBB(log->l_iclog_roundoff);
         log->l_curr_block = roundup(log->l_curr_block, sunit_bb);
     }
 
     if (log->l_curr_block >= log->l_logBBsize) {
         /*
          * Rewind the current block before the cycle is bumped to make
          * sure that the combined LSN never transiently moves forward
          * when the log wraps to the next cycle. This is to support the
          * unlocked sample of these fields from xlog_valid_lsn(). Most
          * other cases should acquire l_icloglock.
          */
         log->l_curr_block -= log->l_logBBsize;
         ASSERT(log->l_curr_block >= 0);
         smp_wmb();
         log->l_curr_cycle++;
         if (log->l_curr_cycle == XLOG_HEADER_MAGIC_NUM)
             log->l_curr_cycle++;
     }
     ASSERT(iclog == log->l_iclog);
     log->l_iclog = iclog->ic_next;
 }
 
 /*
  * Force the iclog to disk and check if the iclog has been completed before
  * xlog_force_iclog() returns. This can happen on synchronous (e.g.
  * pmem) or fast async storage because we drop the icloglock to issue the IO.
  * If completion has already occurred, tell the caller so that it can avoid an
  * unnecessary wait on the iclog.
  */
 static int
 xlog_force_and_check_iclog(
     struct xlog_in_core *iclog,
     bool            *completed)
 {
     xfs_lsn_t       lsn = be64_to_cpu(iclog->ic_header.h_lsn);
     int         error;
 
     *completed = false;
     error = xlog_force_iclog(iclog);
     if (error)
         return error;
 
     /*
      * If the iclog has already been completed and reused the header LSN
      * will have been rewritten by completion
      */
     if (be64_to_cpu(iclog->ic_header.h_lsn) != lsn)
         *completed = true;
     return 0;
 }
 
 /*
  * Write out all data in the in-core log as of this exact moment in time.
  *
  * Data may be written to the in-core log during this call.  However,
  * we don't guarantee this data will be written out.  A change from past
  * implementation means this routine will *not* write out zero length LRs.
  *
  * Basically, we try and perform an intelligent scan of the in-core logs.
  * If we determine there is no flushable data, we just return.  There is no
  * flushable data if:
  *
  *  1. the current iclog is active and has no data; the previous iclog
  *      is in the active or dirty state.
  *  2. the current iclog is drity, and the previous iclog is in the
  *      active or dirty state.
  *
  * We may sleep if:
  *
  *  1. the current iclog is not in the active nor dirty state.
  *  2. the current iclog dirty, and the previous iclog is not in the
  *      active nor dirty state.
  *  3. the current iclog is active, and there is another thread writing
  *      to this particular iclog.
  *  4. a) the current iclog is active and has no other writers
  *     b) when we return from flushing out this iclog, it is still
  *      not in the active nor dirty state.
  */
 int
 xfs_log_force(
     struct xfs_mount    *mp,
     uint            flags)
 {
     struct xlog     *log = mp->m_log;
     struct xlog_in_core *iclog;
 
     XFS_STATS_INC(mp, xs_log_force);
     trace_xfs_log_force(mp, 0, _RET_IP_);
 
     xlog_cil_force(log);
 
     spin_lock(&log->l_icloglock);
     if (xlog_is_shutdown(log))
         goto out_error;
 
     iclog = log->l_iclog;
     trace_xlog_iclog_force(iclog, _RET_IP_);
 
     if (iclog->ic_state == XLOG_STATE_DIRTY ||
         (iclog->ic_state == XLOG_STATE_ACTIVE &&
          atomic_read(&iclog->ic_refcnt) == 0 && iclog->ic_offset == 0)) {
         /*
          * If the head is dirty or (active and empty), then we need to
          * look at the previous iclog.
          *
          * If the previous iclog is active or dirty we are done.  There
          * is nothing to sync out. Otherwise, we attach ourselves to the
          * previous iclog and go to sleep.
          */
         iclog = iclog->ic_prev;
     } else if (iclog->ic_state == XLOG_STATE_ACTIVE) {
         if (atomic_read(&iclog->ic_refcnt) == 0) {
             /* We have exclusive access to this iclog. */
             bool    completed;
 
             if (xlog_force_and_check_iclog(iclog, &completed))
                 goto out_error;
 
             if (completed)
                 goto out_unlock;
         } else {
             /*
              * Someone else is still writing to this iclog, so we
              * need to ensure that when they release the iclog it
              * gets synced immediately as we may be waiting on it.
              */
             xlog_state_switch_iclogs(log, iclog, 0);
         }
     }
 
     /*
      * The iclog we are about to wait on may contain the checkpoint pushed
      * by the above xlog_cil_force() call, but it may not have been pushed
      * to disk yet. Like the ACTIVE case above, we need to make sure caches
      * are flushed when this iclog is written.
      */
     if (iclog->ic_state == XLOG_STATE_WANT_SYNC)
         iclog->ic_flags |= XLOG_ICL_NEED_FLUSH | XLOG_ICL_NEED_FUA;
 
     if (flags & XFS_LOG_SYNC)
         return xlog_wait_on_iclog(iclog);
 out_unlock:
     spin_unlock(&log->l_icloglock);
     return 0;
 out_error:
     spin_unlock(&log->l_icloglock);
     return -EIO;
 }
 
 /*
  * Force the log to a specific LSN.
  *
  * If an iclog with that lsn can be found:
  *  If it is in the DIRTY state, just return.
  *  If it is in the ACTIVE state, move the in-core log into the WANT_SYNC
  *      state and go to sleep or return.
  *  If it is in any other state, go to sleep or return.
  *
  * Synchronous forces are implemented with a wait queue.  All callers trying
  * to force a given lsn to disk must wait on the queue attached to the
  * specific in-core log.  When given in-core log finally completes its write
  * to disk, that thread will wake up all threads waiting on the queue.
  */
 static int
 xlog_force_lsn(
     struct xlog     *log,
     xfs_lsn_t       lsn,
     uint            flags,
     int         *log_flushed,
     bool            already_slept)
 {
     struct xlog_in_core *iclog;
     bool            completed;
 
     spin_lock(&log->l_icloglock);
     if (xlog_is_shutdown(log))
         goto out_error;
 
     iclog = log->l_iclog;
     while (be64_to_cpu(iclog->ic_header.h_lsn) != lsn) {
         trace_xlog_iclog_force_lsn(iclog, _RET_IP_);
         iclog = iclog->ic_next;
         if (iclog == log->l_iclog)
             goto out_unlock;
     }
 
     switch (iclog->ic_state) {
     case XLOG_STATE_ACTIVE:
         /*
          * We sleep here if we haven't already slept (e.g. this is the
          * first time we've looked at the correct iclog buf) and the
          * buffer before us is going to be sync'ed.  The reason for this
          * is that if we are doing sync transactions here, by waiting
          * for the previous I/O to complete, we can allow a few more
          * transactions into this iclog before we close it down.
          *
          * Otherwise, we mark the buffer WANT_SYNC, and bump up the
          * refcnt so we can release the log (which drops the ref count).
          * The state switch keeps new transaction commits from using
          * this buffer.  When the current commits finish writing into
          * the buffer, the refcount will drop to zero and the buffer
          * will go out then.
          */
         if (!already_slept &&
             (iclog->ic_prev->ic_state == XLOG_STATE_WANT_SYNC ||
              iclog->ic_prev->ic_state == XLOG_STATE_SYNCING)) {
             xlog_wait(&iclog->ic_prev->ic_write_wait,
                     &log->l_icloglock);
             return -EAGAIN;
         }
         if (xlog_force_and_check_iclog(iclog, &completed))
             goto out_error;
         if (log_flushed)
             *log_flushed = 1;
         if (completed)
             goto out_unlock;
         break;
     case XLOG_STATE_WANT_SYNC:
         /*
          * This iclog may contain the checkpoint pushed by the
          * xlog_cil_force_seq() call, but there are other writers still
          * accessing it so it hasn't been pushed to disk yet. Like the
          * ACTIVE case above, we need to make sure caches are flushed
          * when this iclog is written.
          */
         iclog->ic_flags |= XLOG_ICL_NEED_FLUSH | XLOG_ICL_NEED_FUA;
         break;
     default:
         /*
          * The entire checkpoint was written by the CIL force and is on
          * its way to disk already. It will be stable when it
          * completes, so we don't need to manipulate caches here at all.
          * We just need to wait for completion if necessary.
          */
         break;
     }
 
     if (flags & XFS_LOG_SYNC)
         return xlog_wait_on_iclog(iclog);
 out_unlock:
     spin_unlock(&log->l_icloglock);
     return 0;
 out_error:
     spin_unlock(&log->l_icloglock);
     return -EIO;
 }
 
 /*
  * Force the log to a specific checkpoint sequence.
  *
  * First force the CIL so that all the required changes have been flushed to the
  * iclogs. If the CIL force completed it will return a commit LSN that indicates
  * the iclog that needs to be flushed to stable storage. If the caller needs
  * a synchronous log force, we will wait on the iclog with the LSN returned by
  * xlog_cil_force_seq() to be completed.
  */
 int
 xfs_log_force_seq(
     struct xfs_mount    *mp,
     xfs_csn_t       seq,
     uint            flags,
     int         *log_flushed)
 {
     struct xlog     *log = mp->m_log;
     xfs_lsn_t       lsn;
     int         ret;
     ASSERT(seq != 0);
 
     XFS_STATS_INC(mp, xs_log_force);
     trace_xfs_log_force(mp, seq, _RET_IP_);
 
     lsn = xlog_cil_force_seq(log, seq);
     if (lsn == NULLCOMMITLSN)
         return 0;
 
     ret = xlog_force_lsn(log, lsn, flags, log_flushed, false);
     if (ret == -EAGAIN) {
         XFS_STATS_INC(mp, xs_log_force_sleep);
         ret = xlog_force_lsn(log, lsn, flags, log_flushed, true);
     }
     return ret;
 }
 
 /*
  * Free a used ticket when its refcount falls to zero.
  */
 void
 xfs_log_ticket_put(
     xlog_ticket_t   *ticket)
 {
     ASSERT(atomic_read(&ticket->t_ref) > 0);
     if (atomic_dec_and_test(&ticket->t_ref))
         kmem_cache_free(xfs_log_ticket_cache, ticket);
 }
 
 xlog_ticket_t *
 xfs_log_ticket_get(
     xlog_ticket_t   *ticket)
 {
     ASSERT(atomic_read(&ticket->t_ref) > 0);
     atomic_inc(&ticket->t_ref);
     return ticket;
 }
 
 /*
  * Figure out the total log space unit (in bytes) that would be
  * required for a log ticket.
  */
 static int
 xlog_calc_unit_res(
     struct xlog     *log,
     int         unit_bytes,
     int         *niclogs)
 {
     int         iclog_space;
     uint            num_headers;
 
     /*
      * Permanent reservations have up to 'cnt'-1 active log operations
      * in the log.  A unit in this case is the amount of space for one
      * of these log operations.  Normal reservations have a cnt of 1
      * and their unit amount is the total amount of space required.
      *
      * The following lines of code account for non-transaction data
      * which occupy space in the on-disk log.
      *
      * Normal form of a transaction is:
      * <oph><trans-hdr><start-oph><reg1-oph><reg1><reg2-oph>...<commit-oph>
      * and then there are LR hdrs, split-recs and roundoff at end of syncs.
      *
      * We need to account for all the leadup data and trailer data
      * around the transaction data.
      * And then we need to account for the worst case in terms of using
      * more space.
      * The worst case will happen if:
      * - the placement of the transaction happens to be such that the
      *   roundoff is at its maximum
      * - the transaction data is synced before the commit record is synced
      *   i.e. <transaction-data><roundoff> | <commit-rec><roundoff>
      *   Therefore the commit record is in its own Log Record.
      *   This can happen as the commit record is called with its
      *   own region to xlog_write().
      *   This then means that in the worst case, roundoff can happen for
      *   the commit-rec as well.
      *   The commit-rec is smaller than padding in this scenario and so it is
      *   not added separately.
      */
 
     /* for trans header */
     unit_bytes += sizeof(xlog_op_header_t);
     unit_bytes += sizeof(xfs_trans_header_t);
 
     /* for start-rec */
     unit_bytes += sizeof(xlog_op_header_t);
 
     /*
      * for LR headers - the space for data in an iclog is the size minus
      * the space used for the headers. If we use the iclog size, then we
      * undercalculate the number of headers required.
      *
      * Furthermore - the addition of op headers for split-recs might
      * increase the space required enough to require more log and op
      * headers, so take that into account too.
      *
      * IMPORTANT: This reservation makes the assumption that if this
      * transaction is the first in an iclog and hence has the LR headers
      * accounted to it, then the remaining space in the iclog is
      * exclusively for this transaction.  i.e. if the transaction is larger
      * than the iclog, it will be the only thing in that iclog.
      * Fundamentally, this means we must pass the entire log vector to
      * xlog_write to guarantee this.
      */
     iclog_space = log->l_iclog_size - log->l_iclog_hsize;
     num_headers = howmany(unit_bytes, iclog_space);
 
     /* for split-recs - ophdrs added when data split over LRs */
     unit_bytes += sizeof(xlog_op_header_t) * num_headers;
 
     /* add extra header reservations if we overrun */
     while (!num_headers ||
            howmany(unit_bytes, iclog_space) > num_headers) {
         unit_bytes += sizeof(xlog_op_header_t);
         num_headers++;
     }
     unit_bytes += log->l_iclog_hsize * num_headers;
 
     /* for commit-rec LR header - note: padding will subsume the ophdr */
     unit_bytes += log->l_iclog_hsize;
 
     /* roundoff padding for transaction data and one for commit record */
     unit_bytes += 2 * log->l_iclog_roundoff;
 
     if (niclogs)
         *niclogs = num_headers;
     return unit_bytes;
 }
 
 int
 xfs_log_calc_unit_res(
     struct xfs_mount    *mp,
     int         unit_bytes)
 {
     return xlog_calc_unit_res(mp->m_log, unit_bytes, NULL);
 }
 
 /*
  * Allocate and initialise a new log ticket.
  */
 struct xlog_ticket *
 xlog_ticket_alloc(
     struct xlog     *log,
     int         unit_bytes,
     int         cnt,
     bool            permanent)
 {
     struct xlog_ticket  *tic;
     int         unit_res;
 
     tic = kmem_cache_zalloc(xfs_log_ticket_cache, GFP_NOFS | __GFP_NOFAIL);
 
     unit_res = xlog_calc_unit_res(log, unit_bytes, &tic->t_iclog_hdrs);
 
     atomic_set(&tic->t_ref, 1);
     tic->t_task     = current;
     INIT_LIST_HEAD(&tic->t_queue);
     tic->t_unit_res     = unit_res;
     tic->t_curr_res     = unit_res;
     tic->t_cnt      = cnt;
     tic->t_ocnt     = cnt;
     tic->t_tid      = prandom_u32();
     if (permanent)
         tic->t_flags |= XLOG_TIC_PERM_RESERV;
 
     return tic;
 }
 
 #if defined(DEBUG)
 /*
  * Check to make sure the grant write head didn't just over lap the tail.  If
  * the cycles are the same, we can't be overlapping.  Otherwise, make sure that
  * the cycles differ by exactly one and check the byte count.
  *
  * This check is run unlocked, so can give false positives. Rather than assert
  * on failures, use a warn-once flag and a panic tag to allow the admin to
  * determine if they want to panic the machine when such an error occurs. For
  * debug kernels this will have the same effect as using an assert but, unlinke
  * an assert, it can be turned off at runtime.
  */
 STATIC void
 xlog_verify_grant_tail(
     struct xlog *log)
 {
     int     tail_cycle, tail_blocks;
     int     cycle, space;
 
     xlog_crack_grant_head(&log->l_write_head.grant, &cycle, &space);
     xlog_crack_atomic_lsn(&log->l_tail_lsn, &tail_cycle, &tail_blocks);
     if (tail_cycle != cycle) {
         if (cycle - 1 != tail_cycle &&
             !test_and_set_bit(XLOG_TAIL_WARN, &log->l_opstate)) {
             xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
                 "%s: cycle - 1 != tail_cycle", __func__);
         }
 
         if (space > BBTOB(tail_blocks) &&
             !test_and_set_bit(XLOG_TAIL_WARN, &log->l_opstate)) {
             xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
                 "%s: space > BBTOB(tail_blocks)", __func__);
         }
     }
 }
 
 /* check if it will fit */
 STATIC void
 xlog_verify_tail_lsn(
     struct xlog     *log,
     struct xlog_in_core *iclog)
 {
     xfs_lsn_t   tail_lsn = be64_to_cpu(iclog->ic_header.h_tail_lsn);
     int     blocks;
 
     if (CYCLE_LSN(tail_lsn) == log->l_prev_cycle) {
     blocks =
         log->l_logBBsize - (log->l_prev_block - BLOCK_LSN(tail_lsn));
     if (blocks < BTOBB(iclog->ic_offset)+BTOBB(log->l_iclog_hsize))
         xfs_emerg(log->l_mp, "%s: ran out of log space", __func__);
     } else {
     ASSERT(CYCLE_LSN(tail_lsn)+1 == log->l_prev_cycle);
 
     if (BLOCK_LSN(tail_lsn) == log->l_prev_block)
         xfs_emerg(log->l_mp, "%s: tail wrapped", __func__);
 
     blocks = BLOCK_LSN(tail_lsn) - log->l_prev_block;
     if (blocks < BTOBB(iclog->ic_offset) + 1)
         xfs_emerg(log->l_mp, "%s: ran out of log space", __func__);
     }
 }
 
 /*
  * Perform a number of checks on the iclog before writing to disk.
  *
  * 1. Make sure the iclogs are still circular
  * 2. Make sure we have a good magic number
  * 3. Make sure we don't have magic numbers in the data
  * 4. Check fields of each log operation header for:
  *  A. Valid client identifier
  *  B. tid ptr value falls in valid ptr space (user space code)
  *  C. Length in log record header is correct according to the
  *      individual operation headers within record.
  * 5. When a bwrite will occur within 5 blocks of the front of the physical
  *  log, check the preceding blocks of the physical log to make sure all
  *  the cycle numbers agree with the current cycle number.
  */
 STATIC void
 xlog_verify_iclog(
     struct xlog     *log,
     struct xlog_in_core *iclog,
     int         count)
 {
     xlog_op_header_t    *ophead;
     xlog_in_core_t      *icptr;
     xlog_in_core_2_t    *xhdr;
     void            *base_ptr, *ptr, *p;
     ptrdiff_t       field_offset;
     uint8_t         clientid;
     int         len, i, j, k, op_len;
     int         idx;
 
     /* check validity of iclog pointers */
     spin_lock(&log->l_icloglock);
     icptr = log->l_iclog;
     for (i = 0; i < log->l_iclog_bufs; i++, icptr = icptr->ic_next)
         ASSERT(icptr);
 
     if (icptr != log->l_iclog)
         xfs_emerg(log->l_mp, "%s: corrupt iclog ring", __func__);
     spin_unlock(&log->l_icloglock);
 
     /* check log magic numbers */
     if (iclog->ic_header.h_magicno != cpu_to_be32(XLOG_HEADER_MAGIC_NUM))
         xfs_emerg(log->l_mp, "%s: invalid magic num", __func__);
 
     base_ptr = ptr = &iclog->ic_header;
     p = &iclog->ic_header;
     for (ptr += BBSIZE; ptr < base_ptr + count; ptr += BBSIZE) {
         if (*(__be32 *)ptr == cpu_to_be32(XLOG_HEADER_MAGIC_NUM))
             xfs_emerg(log->l_mp, "%s: unexpected magic num",
                 __func__);
     }
 
     /* check fields */
     len = be32_to_cpu(iclog->ic_header.h_num_logops);
     base_ptr = ptr = iclog->ic_datap;
     ophead = ptr;
     xhdr = iclog->ic_data;
     for (i = 0; i < len; i++) {
         ophead = ptr;
 
         /* clientid is only 1 byte */
         p = &ophead->oh_clientid;
         field_offset = p - base_ptr;
         if (field_offset & 0x1ff) {
             clientid = ophead->oh_clientid;
         } else {
             idx = BTOBBT((void *)&ophead->oh_clientid - iclog->ic_datap);
             if (idx >= (XLOG_HEADER_CYCLE_SIZE / BBSIZE)) {
                 j = idx / (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
                 k = idx % (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
                 clientid = xlog_get_client_id(
                     xhdr[j].hic_xheader.xh_cycle_data[k]);
             } else {
                 clientid = xlog_get_client_id(
                     iclog->ic_header.h_cycle_data[idx]);
             }
         }
         if (clientid != XFS_TRANSACTION && clientid != XFS_LOG) {
             xfs_warn(log->l_mp,
                 "%s: op %d invalid clientid %d op "PTR_FMT" offset 0x%lx",
                 __func__, i, clientid, ophead,
                 (unsigned long)field_offset);
         }
 
         /* check length */
         p = &ophead->oh_len;
         field_offset = p - base_ptr;
         if (field_offset & 0x1ff) {
             op_len = be32_to_cpu(ophead->oh_len);
         } else {
             idx = BTOBBT((void *)&ophead->oh_len - iclog->ic_datap);
             if (idx >= (XLOG_HEADER_CYCLE_SIZE / BBSIZE)) {
                 j = idx / (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
                 k = idx % (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
                 op_len = be32_to_cpu(xhdr[j].hic_xheader.xh_cycle_data[k]);
             } else {
                 op_len = be32_to_cpu(iclog->ic_header.h_cycle_data[idx]);
             }
         }
         ptr += sizeof(xlog_op_header_t) + op_len;
     }
 }
 #endif
 
 /*
  * Perform a forced shutdown on the log.
  *
  * This can be called from low level log code to trigger a shutdown, or from the
  * high level mount shutdown code when the mount shuts down.
  *
  * Our main objectives here are to make sure that:
  *  a. if the shutdown was not due to a log IO error, flush the logs to
  *     disk. Anything modified after this is ignored.
  *  b. the log gets atomically marked 'XLOG_IO_ERROR' for all interested
  *     parties to find out. Nothing new gets queued after this is done.
  *  c. Tasks sleeping on log reservations, pinned objects and
  *     other resources get woken up.
  *  d. The mount is also marked as shut down so that log triggered shutdowns
  *     still behave the same as if they called xfs_forced_shutdown().
  *
  * Return true if the shutdown cause was a log IO error and we actually shut the
  * log down.
  */
 bool
 xlog_force_shutdown(
     struct xlog *log,
     uint32_t    shutdown_flags)
 {
     bool        log_error = (shutdown_flags & SHUTDOWN_LOG_IO_ERROR);
 
     if (!log)
         return false;
 
     /*
      * Flush all the completed transactions to disk before marking the log
      * being shut down. We need to do this first as shutting down the log
      * before the force will prevent the log force from flushing the iclogs
      * to disk.
      *
      * When we are in recovery, there are no transactions to flush, and
      * we don't want to touch the log because we don't want to perturb the
      * current head/tail for future recovery attempts. Hence we need to
      * avoid a log force in this case.
      *
      * If we are shutting down due to a log IO error, then we must avoid
      * trying to write the log as that may just result in more IO errors and
      * an endless shutdown/force loop.
      */
     if (!log_error && !xlog_in_recovery(log))
         xfs_log_force(log->l_mp, XFS_LOG_SYNC);
 
     /*
      * Atomically set the shutdown state. If the shutdown state is already
      * set, there someone else is performing the shutdown and so we are done
      * here. This should never happen because we should only ever get called
      * once by the first shutdown caller.
      *
      * Much of the log state machine transitions assume that shutdown state
      * cannot change once they hold the log->l_icloglock. Hence we need to
      * hold that lock here, even though we use the atomic test_and_set_bit()
      * operation to set the shutdown state.
      */
     spin_lock(&log->l_icloglock);
     if (test_and_set_bit(XLOG_IO_ERROR, &log->l_opstate)) {
         spin_unlock(&log->l_icloglock);
         return false;
     }
     spin_unlock(&log->l_icloglock);
 
     /*
      * If this log shutdown also sets the mount shutdown state, issue a
      * shutdown warning message.
      */
     if (!test_and_set_bit(XFS_OPSTATE_SHUTDOWN, &log->l_mp->m_opstate)) {
         xfs_alert_tag(log->l_mp, XFS_PTAG_SHUTDOWN_LOGERROR,
 "Filesystem has been shut down due to log error (0x%x).",
                 shutdown_flags);
         xfs_alert(log->l_mp,
 "Please unmount the filesystem and rectify the problem(s).");
         if (xfs_error_level >= XFS_ERRLEVEL_HIGH)
             xfs_stack_trace();
     }
 
     /*
      * We don't want anybody waiting for log reservations after this. That
      * means we have to wake up everybody queued up on reserveq as well as
      * writeq.  In addition, we make sure in xlog_{re}grant_log_space that
      * we don't enqueue anything once the SHUTDOWN flag is set, and this
      * action is protected by the grant locks.
      */
     xlog_grant_head_wake_all(&log->l_reserve_head);
     xlog_grant_head_wake_all(&log->l_write_head);
 
     /*
      * Wake up everybody waiting on xfs_log_force. Wake the CIL push first
      * as if the log writes were completed. The abort handling in the log
      * item committed callback functions will do this again under lock to
      * avoid races.
      */
     spin_lock(&log->l_cilp->xc_push_lock);
     wake_up_all(&log->l_cilp->xc_start_wait);
     wake_up_all(&log->l_cilp->xc_commit_wait);
     spin_unlock(&log->l_cilp->xc_push_lock);
 
     spin_lock(&log->l_icloglock);
     xlog_state_shutdown_callbacks(log);
     spin_unlock(&log->l_icloglock);
 
     wake_up_var(&log->l_opstate);
     return log_error;
 }
 
 STATIC int
 xlog_iclogs_empty(
     struct xlog *log)
 {
     xlog_in_core_t  *iclog;
 
     iclog = log->l_iclog;
     do {
         /* endianness does not matter here, zero is zero in
          * any language.
          */
         if (iclog->ic_header.h_num_logops)
             return 0;
         iclog = iclog->ic_next;
     } while (iclog != log->l_iclog);
     return 1;
 }
 
 /*
  * Verify that an LSN stamped into a piece of metadata is valid. This is
  * intended for use in read verifiers on v5 superblocks.
  */
 bool
 xfs_log_check_lsn(
     struct xfs_mount    *mp,
     xfs_lsn_t       lsn)
 {
     struct xlog     *log = mp->m_log;
     bool            valid;
 
     /*
      * norecovery mode skips mount-time log processing and unconditionally
      * resets the in-core LSN. We can't validate in this mode, but
      * modifications are not allowed anyways so just return true.
      */
     if (xfs_has_norecovery(mp))
         return true;
 
     /*
      * Some metadata LSNs are initialized to NULL (e.g., the agfl). This is
      * handled by recovery and thus safe to ignore here.
      */
     if (lsn == NULLCOMMITLSN)
         return true;
 
     valid = xlog_valid_lsn(mp->m_log, lsn);
 
     /* warn the user about what's gone wrong before verifier failure */
     if (!valid) {
         spin_lock(&log->l_icloglock);
         xfs_warn(mp,
 "Corruption warning: Metadata has LSN (%d:%d) ahead of current LSN (%d:%d). "
 "Please unmount and run xfs_repair (>= v4.3) to resolve.",
              CYCLE_LSN(lsn), BLOCK_LSN(lsn),
              log->l_curr_cycle, log->l_curr_block);
         spin_unlock(&log->l_icloglock);
     }
 
     return valid;
 }
 
 /*
  * Notify the log that we're about to start using a feature that is protected
  * by a log incompat feature flag.  This will prevent log covering from
  * clearing those flags.
  */
 void
 xlog_use_incompat_feat(
     struct xlog     *log)
 {
     down_read(&log->l_incompat_users);
 }
 
 /* Notify the log that we've finished using log incompat features. */
 void
 xlog_drop_incompat_feat(
     struct xlog     *log)
 {
     up_read(&log->l_incompat_users);
 }