/*
   * Copyright (c) 2010 Red Hat, Inc. All Rights Reserved.
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License as
   * published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it would be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write the Free Software Foundation,
   * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
   */
  
  #include "xfs.h"
  #include "xfs_fs.h"
  #include "xfs_types.h"
  #include "xfs_bit.h"
  #include "xfs_log.h"
  #include "xfs_inum.h"
  #include "xfs_trans.h"
  #include "xfs_trans_priv.h"
  #include "xfs_log_priv.h"
  #include "xfs_sb.h"
  #include "xfs_ag.h"

  #include "xfs_mount.h"
  #include "xfs_error.h"
  #include "xfs_alloc.h"

  #include "xfs_discard.h"

  
  /*

   * Perform initial CIL structure initialisation.

   */
  int
  xlog_cil_init(
  	struct log	*log)
  {
  	struct xfs_cil	*cil;
  	struct xfs_cil_ctx *ctx;

  	cil = kmem_zalloc(sizeof(*cil), KM_SLEEP|KM_MAYFAIL);
  	if (!cil)
  		return ENOMEM;
  
  	ctx = kmem_zalloc(sizeof(*ctx), KM_SLEEP|KM_MAYFAIL);
  	if (!ctx) {
  		kmem_free(cil);
  		return ENOMEM;
  	}
  
  	INIT_LIST_HEAD(&cil->xc_cil);
  	INIT_LIST_HEAD(&cil->xc_committing);
  	spin_lock_init(&cil->xc_cil_lock);
  	init_rwsem(&cil->xc_ctx_lock);

  	init_waitqueue_head(&cil->xc_commit_wait);

  
  	INIT_LIST_HEAD(&ctx->committing);
  	INIT_LIST_HEAD(&ctx->busy_extents);
  	ctx->sequence = 1;
  	ctx->cil = cil;
  	cil->xc_ctx = ctx;

  	cil->xc_current_sequence = ctx->sequence;

  
  	cil->xc_log = log;
  	log->l_cilp = cil;
  	return 0;
  }
  
  void
  xlog_cil_destroy(
  	struct log	*log)
  {

  	if (log->l_cilp->xc_ctx) {
  		if (log->l_cilp->xc_ctx->ticket)
  			xfs_log_ticket_put(log->l_cilp->xc_ctx->ticket);
  		kmem_free(log->l_cilp->xc_ctx);
  	}
  
  	ASSERT(list_empty(&log->l_cilp->xc_cil));
  	kmem_free(log->l_cilp);
  }
  
  /*
   * Allocate a new ticket. Failing to get a new ticket makes it really hard to
   * recover, so we don't allow failure here. Also, we allocate in a context that
   * we don't want to be issuing transactions from, so we need to tell the
   * allocation code this as well.
   *
   * We don't reserve any space for the ticket - we are going to steal whatever
   * space we require from transactions as they commit. To ensure we reserve all
   * the space required, we need to set the current reservation of the ticket to
   * zero so that we know to steal the initial transaction overhead from the
   * first transaction commit.
   */
  static struct xlog_ticket *
  xlog_cil_ticket_alloc(
  	struct log	*log)
  {
  	struct xlog_ticket *tic;
  
  	tic = xlog_ticket_alloc(log, 0, 1, XFS_TRANSACTION, 0,
  				KM_SLEEP|KM_NOFS);
  	tic->t_trans_type = XFS_TRANS_CHECKPOINT;
  
  	/*
  	 * set the current reservation to zero so we know to steal the basic
  	 * transaction overhead reservation from the first transaction commit.
  	 */
  	tic->t_curr_res = 0;
  	return tic;
  }
  
  /*
   * After the first stage of log recovery is done, we know where the head and
   * tail of the log are. We need this log initialisation done before we can
   * initialise the first CIL checkpoint context.
   *
   * Here we allocate a log ticket to track space usage during a CIL push.  This
   * ticket is passed to xlog_write() directly so that we don't slowly leak log
   * space by failing to account for space used by log headers and additional
   * region headers for split regions.
   */
  void
  xlog_cil_init_post_recovery(
  	struct log	*log)
  {

  	log->l_cilp->xc_ctx->ticket = xlog_cil_ticket_alloc(log);
  	log->l_cilp->xc_ctx->sequence = 1;
  	log->l_cilp->xc_ctx->commit_lsn = xlog_assign_lsn(log->l_curr_cycle,
  								log->l_curr_block);
  }
  
  /*

   * Format log item into a flat buffers
   *
   * For delayed logging, we need to hold a formatted buffer containing all the
   * changes on the log item. This enables us to relog the item in memory and
   * write it out asynchronously without needing to relock the object that was
   * modified at the time it gets written into the iclog.
   *
   * This function builds a vector for the changes in each log item in the
   * transaction. It then works out the length of the buffer needed for each log
   * item, allocates them and formats the vector for the item into the buffer.
   * The buffer is then attached to the log item are then inserted into the
   * Committed Item List for tracking until the next checkpoint is written out.
   *
   * We don't set up region headers during this process; we simply copy the
   * regions into the flat buffer. We can do this because we still have to do a
   * formatting step to write the regions into the iclog buffer.  Writing the
   * ophdrs during the iclog write means that we can support splitting large
   * regions across iclog boundares without needing a change in the format of the
   * item/region encapsulation.
   *
   * Hence what we need to do now is change the rewrite the vector array to point
   * to the copied region inside the buffer we just allocated. This allows us to
   * format the regions into the iclog as though they are being formatted
   * directly out of the objects themselves.
   */

  static struct xfs_log_vec *
  xlog_cil_prepare_log_vecs(
  	struct xfs_trans	*tp)

  {

  	struct xfs_log_item_desc *lidp;
  	struct xfs_log_vec	*lv = NULL;
  	struct xfs_log_vec	*ret_lv = NULL;

  
  	/* Bail out if we didn't find a log item.  */
  	if (list_empty(&tp->t_items)) {
  		ASSERT(0);
  		return NULL;
  	}
  
  	list_for_each_entry(lidp, &tp->t_items, lid_trans) {
  		struct xfs_log_vec *new_lv;

  		void	*ptr;
  		int	index;
  		int	len = 0;

  		uint	niovecs;

  		/* Skip items which aren't dirty in this transaction. */
  		if (!(lidp->lid_flags & XFS_LID_DIRTY))
  			continue;
  
  		/* Skip items that do not have any vectors for writing */

  		niovecs = IOP_SIZE(lidp->lid_item);
  		if (!niovecs)

  			continue;
  
  		new_lv = kmem_zalloc(sizeof(*new_lv) +

  				niovecs * sizeof(struct xfs_log_iovec),

  				KM_SLEEP);
  
  		/* The allocated iovec region lies beyond the log vector. */
  		new_lv->lv_iovecp = (struct xfs_log_iovec *)&new_lv[1];

  		new_lv->lv_niovecs = niovecs;

  		new_lv->lv_item = lidp->lid_item;

  		/* build the vector array and calculate it's length */

  		IOP_FORMAT(new_lv->lv_item, new_lv->lv_iovecp);
  		for (index = 0; index < new_lv->lv_niovecs; index++)
  			len += new_lv->lv_iovecp[index].i_len;

  		new_lv->lv_buf_len = len;
  		new_lv->lv_buf = kmem_alloc(new_lv->lv_buf_len,
  				KM_SLEEP|KM_NOFS);
  		ptr = new_lv->lv_buf;

  		for (index = 0; index < new_lv->lv_niovecs; index++) {
  			struct xfs_log_iovec *vec = &new_lv->lv_iovecp[index];

  
  			memcpy(ptr, vec->i_addr, vec->i_len);
  			vec->i_addr = ptr;
  			ptr += vec->i_len;
  		}

  		ASSERT(ptr == new_lv->lv_buf + new_lv->lv_buf_len);
  
  		if (!ret_lv)
  			ret_lv = new_lv;
  		else
  			lv->lv_next = new_lv;
  		lv = new_lv;

  	}

  
  	return ret_lv;

  }

  /*
   * Prepare the log item for insertion into the CIL. Calculate the difference in
   * log space and vectors it will consume, and if it is a new item pin it as
   * well.
   */
  STATIC void
  xfs_cil_prepare_item(
  	struct log		*log,
  	struct xfs_log_vec	*lv,
  	int			*len,
  	int			*diff_iovecs)
  {
  	struct xfs_log_vec	*old = lv->lv_item->li_lv;
  
  	if (old) {
  		/* existing lv on log item, space used is a delta */
  		ASSERT(!list_empty(&lv->lv_item->li_cil));
  		ASSERT(old->lv_buf && old->lv_buf_len && old->lv_niovecs);
  
  		*len += lv->lv_buf_len - old->lv_buf_len;
  		*diff_iovecs += lv->lv_niovecs - old->lv_niovecs;
  		kmem_free(old->lv_buf);
  		kmem_free(old);
  	} else {
  		/* new lv, must pin the log item */
  		ASSERT(!lv->lv_item->li_lv);
  		ASSERT(list_empty(&lv->lv_item->li_cil));
  
  		*len += lv->lv_buf_len;
  		*diff_iovecs += lv->lv_niovecs;
  		IOP_PIN(lv->lv_item);
  
  	}
  
  	/* attach new log vector to log item */
  	lv->lv_item->li_lv = lv;
  
  	/*
  	 * If this is the first time the item is being committed to the
  	 * CIL, store the sequence number on the log item so we can
  	 * tell in future commits whether this is the first checkpoint
  	 * the item is being committed into.
  	 */
  	if (!lv->lv_item->li_seq)
  		lv->lv_item->li_seq = log->l_cilp->xc_ctx->sequence;
  }
  
  /*
   * Insert the log items into the CIL and calculate the difference in space
   * consumed by the item. Add the space to the checkpoint ticket and calculate
   * if the change requires additional log metadata. If it does, take that space

   * as well. Remove the amount of space we added to the checkpoint ticket from

   * the current transaction ticket so that the accounting works out correctly.
   */

  static void
  xlog_cil_insert_items(
  	struct log		*log,
  	struct xfs_log_vec	*log_vector,

  	struct xlog_ticket	*ticket)

  {

  	struct xfs_cil		*cil = log->l_cilp;
  	struct xfs_cil_ctx	*ctx = cil->xc_ctx;
  	struct xfs_log_vec	*lv;
  	int			len = 0;
  	int			diff_iovecs = 0;
  	int			iclog_space;

  
  	ASSERT(log_vector);

  
  	/*
  	 * Do all the accounting aggregation and switching of log vectors
  	 * around in a separate loop to the insertion of items into the CIL.
  	 * Then we can do a separate loop to update the CIL within a single
  	 * lock/unlock pair. This reduces the number of round trips on the CIL
  	 * lock from O(nr_logvectors) to O(1) and greatly reduces the overall
  	 * hold time for the transaction commit.
  	 *
  	 * If this is the first time the item is being placed into the CIL in
  	 * this context, pin it so it can't be written to disk until the CIL is
  	 * flushed to the iclog and the iclog written to disk.
  	 *
  	 * We can do this safely because the context can't checkpoint until we
  	 * are done so it doesn't matter exactly how we update the CIL.
  	 */
  	for (lv = log_vector; lv; lv = lv->lv_next)
  		xfs_cil_prepare_item(log, lv, &len, &diff_iovecs);
  
  	/* account for space used by new iovec headers  */
  	len += diff_iovecs * sizeof(xlog_op_header_t);
  
  	spin_lock(&cil->xc_cil_lock);
  
  	/* move the items to the tail of the CIL */

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

  		list_move_tail(&lv->lv_item->li_cil, &cil->xc_cil);
  
  	ctx->nvecs += diff_iovecs;
  
  	/*
  	 * Now transfer enough transaction reservation to the context ticket
  	 * for the checkpoint. The context ticket is special - the unit
  	 * reservation has to grow as well as the current reservation as we
  	 * steal from tickets so we can correctly determine the space used
  	 * during the transaction commit.
  	 */
  	if (ctx->ticket->t_curr_res == 0) {
  		/* first commit in checkpoint, steal the header reservation */
  		ASSERT(ticket->t_curr_res >= ctx->ticket->t_unit_res + len);
  		ctx->ticket->t_curr_res = ctx->ticket->t_unit_res;
  		ticket->t_curr_res -= ctx->ticket->t_unit_res;
  	}
  
  	/* do we need space for more log record headers? */
  	iclog_space = log->l_iclog_size - log->l_iclog_hsize;
  	if (len > 0 && (ctx->space_used / iclog_space !=
  				(ctx->space_used + len) / iclog_space)) {
  		int hdrs;
  
  		hdrs = (len + iclog_space - 1) / iclog_space;
  		/* need to take into account split region headers, too */
  		hdrs *= log->l_iclog_hsize + sizeof(struct xlog_op_header);
  		ctx->ticket->t_unit_res += hdrs;
  		ctx->ticket->t_curr_res += hdrs;
  		ticket->t_curr_res -= hdrs;
  		ASSERT(ticket->t_curr_res >= len);
  	}
  	ticket->t_curr_res -= len;
  	ctx->space_used += len;
  
  	spin_unlock(&cil->xc_cil_lock);

  }
  
  static void
  xlog_cil_free_logvec(
  	struct xfs_log_vec	*log_vector)
  {
  	struct xfs_log_vec	*lv;
  
  	for (lv = log_vector; lv; ) {
  		struct xfs_log_vec *next = lv->lv_next;
  		kmem_free(lv->lv_buf);
  		kmem_free(lv);
  		lv = next;
  	}
  }
  
  /*

   * Mark all items committed and clear busy extents. We free the log vector
   * chains in a separate pass so that we unpin the log items as quickly as
   * possible.
   */
  static void
  xlog_cil_committed(
  	void	*args,
  	int	abort)
  {
  	struct xfs_cil_ctx	*ctx = args;

  	struct xfs_mount	*mp = ctx->cil->xc_log->l_mp;

  	xfs_trans_committed_bulk(ctx->cil->xc_log->l_ailp, ctx->lv_chain,
  					ctx->start_lsn, abort);

  	xfs_alloc_busy_sort(&ctx->busy_extents);

  	xfs_alloc_busy_clear(mp, &ctx->busy_extents,
  			     (mp->m_flags & XFS_MOUNT_DISCARD) && !abort);

  
  	spin_lock(&ctx->cil->xc_cil_lock);
  	list_del(&ctx->committing);
  	spin_unlock(&ctx->cil->xc_cil_lock);
  
  	xlog_cil_free_logvec(ctx->lv_chain);

  
  	if (!list_empty(&ctx->busy_extents)) {
  		ASSERT(mp->m_flags & XFS_MOUNT_DISCARD);
  
  		xfs_discard_extents(mp, &ctx->busy_extents);
  		xfs_alloc_busy_clear(mp, &ctx->busy_extents, false);
  	}

  	kmem_free(ctx);
  }
  
  /*

   * Push the Committed Item List to the log. If @push_seq flag is zero, then it
   * is a background flush and so we can chose to ignore it. Otherwise, if the
   * current sequence is the same as @push_seq we need to do a flush. If
   * @push_seq is less than the current sequence, then it has already been
   * flushed and we don't need to do anything - the caller will wait for it to
   * complete if necessary.
   *
   * @push_seq is a value rather than a flag because that allows us to do an
   * unlocked check of the sequence number for a match. Hence we can allows log
   * forces to run racily and not issue pushes for the same sequence twice. If we
   * get a race between multiple pushes for the same sequence they will block on
   * the first one and then abort, hence avoiding needless pushes.

   */

  STATIC int

  xlog_cil_push(
  	struct log		*log,

  	xfs_lsn_t		push_seq)

  {
  	struct xfs_cil		*cil = log->l_cilp;
  	struct xfs_log_vec	*lv;
  	struct xfs_cil_ctx	*ctx;
  	struct xfs_cil_ctx	*new_ctx;
  	struct xlog_in_core	*commit_iclog;
  	struct xlog_ticket	*tic;
  	int			num_lv;
  	int			num_iovecs;
  	int			len;
  	int			error = 0;
  	struct xfs_trans_header thdr;
  	struct xfs_log_iovec	lhdr;
  	struct xfs_log_vec	lvhdr = { NULL };
  	xfs_lsn_t		commit_lsn;
  
  	if (!cil)
  		return 0;

  	ASSERT(!push_seq || push_seq <= cil->xc_ctx->sequence);

  	new_ctx = kmem_zalloc(sizeof(*new_ctx), KM_SLEEP|KM_NOFS);
  	new_ctx->ticket = xlog_cil_ticket_alloc(log);

  	/*
  	 * Lock out transaction commit, but don't block for background pushes
  	 * unless we are well over the CIL space limit. See the definition of
  	 * XLOG_CIL_HARD_SPACE_LIMIT() for the full explanation of the logic
  	 * used here.
  	 */

  	if (!down_write_trylock(&cil->xc_ctx_lock)) {

  		if (!push_seq &&
  		    cil->xc_ctx->space_used < XLOG_CIL_HARD_SPACE_LIMIT(log))

  			goto out_free_ticket;
  		down_write(&cil->xc_ctx_lock);
  	}

  	ctx = cil->xc_ctx;
  
  	/* check if we've anything to push */
  	if (list_empty(&cil->xc_cil))
  		goto out_skip;

  	/* check for spurious background flush */

  	if (!push_seq && cil->xc_ctx->space_used < XLOG_CIL_SPACE_LIMIT(log))
  		goto out_skip;
  
  	/* check for a previously pushed seqeunce */

  	if (push_seq && push_seq < cil->xc_ctx->sequence)

  		goto out_skip;

  	/*
  	 * pull all the log vectors off the items in the CIL, and
  	 * remove the items from the CIL. We don't need the CIL lock
  	 * here because it's only needed on the transaction commit
  	 * side which is currently locked out by the flush lock.
  	 */
  	lv = NULL;
  	num_lv = 0;
  	num_iovecs = 0;
  	len = 0;
  	while (!list_empty(&cil->xc_cil)) {
  		struct xfs_log_item	*item;
  		int			i;
  
  		item = list_first_entry(&cil->xc_cil,
  					struct xfs_log_item, li_cil);
  		list_del_init(&item->li_cil);
  		if (!ctx->lv_chain)
  			ctx->lv_chain = item->li_lv;
  		else
  			lv->lv_next = item->li_lv;
  		lv = item->li_lv;
  		item->li_lv = NULL;
  
  		num_lv++;
  		num_iovecs += lv->lv_niovecs;
  		for (i = 0; i < lv->lv_niovecs; i++)
  			len += lv->lv_iovecp[i].i_len;
  	}
  
  	/*
  	 * initialise the new context and attach it to the CIL. Then attach
  	 * the current context to the CIL committing lsit so it can be found
  	 * during log forces to extract the commit lsn of the sequence that
  	 * needs to be forced.
  	 */
  	INIT_LIST_HEAD(&new_ctx->committing);
  	INIT_LIST_HEAD(&new_ctx->busy_extents);
  	new_ctx->sequence = ctx->sequence + 1;
  	new_ctx->cil = cil;
  	cil->xc_ctx = new_ctx;
  
  	/*

  	 * mirror the new sequence into the cil structure so that we can do
  	 * unlocked checks against the current sequence in log forces without
  	 * risking deferencing a freed context pointer.
  	 */
  	cil->xc_current_sequence = new_ctx->sequence;
  
  	/*

  	 * The switch is now done, so we can drop the context lock and move out
  	 * of a shared context. We can't just go straight to the commit record,
  	 * though - we need to synchronise with previous and future commits so
  	 * that the commit records are correctly ordered in the log to ensure
  	 * that we process items during log IO completion in the correct order.
  	 *
  	 * For example, if we get an EFI in one checkpoint and the EFD in the
  	 * next (e.g. due to log forces), we do not want the checkpoint with
  	 * the EFD to be committed before the checkpoint with the EFI.  Hence
  	 * we must strictly order the commit records of the checkpoints so
  	 * that: a) the checkpoint callbacks are attached to the iclogs in the
  	 * correct order; and b) the checkpoints are replayed in correct order
  	 * in log recovery.
  	 *
  	 * Hence we need to add this context to the committing context list so
  	 * that higher sequences will wait for us to write out a commit record
  	 * before they do.
  	 */
  	spin_lock(&cil->xc_cil_lock);
  	list_add(&ctx->committing, &cil->xc_committing);
  	spin_unlock(&cil->xc_cil_lock);
  	up_write(&cil->xc_ctx_lock);
  
  	/*
  	 * Build a checkpoint transaction header and write it to the log to
  	 * begin the transaction. We need to account for the space used by the
  	 * transaction header here as it is not accounted for in xlog_write().
  	 *
  	 * The LSN we need to pass to the log items on transaction commit is
  	 * the LSN reported by the first log vector write. If we use the commit
  	 * record lsn then we can move the tail beyond the grant write head.
  	 */
  	tic = ctx->ticket;
  	thdr.th_magic = XFS_TRANS_HEADER_MAGIC;
  	thdr.th_type = XFS_TRANS_CHECKPOINT;
  	thdr.th_tid = tic->t_tid;
  	thdr.th_num_items = num_iovecs;

  	lhdr.i_addr = &thdr;

  	lhdr.i_len = sizeof(xfs_trans_header_t);
  	lhdr.i_type = XLOG_REG_TYPE_TRANSHDR;
  	tic->t_curr_res -= lhdr.i_len + sizeof(xlog_op_header_t);
  
  	lvhdr.lv_niovecs = 1;
  	lvhdr.lv_iovecp = &lhdr;
  	lvhdr.lv_next = ctx->lv_chain;
  
  	error = xlog_write(log, &lvhdr, tic, &ctx->start_lsn, NULL, 0);
  	if (error)

  		goto out_abort_free_ticket;

  
  	/*
  	 * now that we've written the checkpoint into the log, strictly
  	 * order the commit records so replay will get them in the right order.
  	 */
  restart:
  	spin_lock(&cil->xc_cil_lock);
  	list_for_each_entry(new_ctx, &cil->xc_committing, committing) {
  		/*
  		 * Higher sequences will wait for this one so skip them.
  		 * Don't wait for own own sequence, either.
  		 */
  		if (new_ctx->sequence >= ctx->sequence)
  			continue;
  		if (!new_ctx->commit_lsn) {
  			/*
  			 * It is still being pushed! Wait for the push to
  			 * complete, then start again from the beginning.
  			 */

  			xlog_wait(&cil->xc_commit_wait, &cil->xc_cil_lock);

  			goto restart;
  		}
  	}
  	spin_unlock(&cil->xc_cil_lock);

  	/* xfs_log_done always frees the ticket on error. */

  	commit_lsn = xfs_log_done(log->l_mp, tic, &commit_iclog, 0);

  	if (commit_lsn == -1)

  		goto out_abort;
  
  	/* attach all the transactions w/ busy extents to iclog */
  	ctx->log_cb.cb_func = xlog_cil_committed;
  	ctx->log_cb.cb_arg = ctx;
  	error = xfs_log_notify(log->l_mp, commit_iclog, &ctx->log_cb);
  	if (error)
  		goto out_abort;
  
  	/*
  	 * now the checkpoint commit is complete and we've attached the
  	 * callbacks to the iclog we can assign the commit LSN to the context
  	 * and wake up anyone who is waiting for the commit to complete.
  	 */
  	spin_lock(&cil->xc_cil_lock);
  	ctx->commit_lsn = commit_lsn;

  	wake_up_all(&cil->xc_commit_wait);

  	spin_unlock(&cil->xc_cil_lock);
  
  	/* release the hounds! */
  	return xfs_log_release_iclog(log->l_mp, commit_iclog);
  
  out_skip:
  	up_write(&cil->xc_ctx_lock);

  out_free_ticket:

  	xfs_log_ticket_put(new_ctx->ticket);
  	kmem_free(new_ctx);
  	return 0;

  out_abort_free_ticket:
  	xfs_log_ticket_put(tic);

  out_abort:
  	xlog_cil_committed(ctx, XFS_LI_ABORTED);
  	return XFS_ERROR(EIO);
  }
  
  /*

   * Commit a transaction with the given vector to the Committed Item List.
   *
   * To do this, we need to format the item, pin it in memory if required and
   * account for the space used by the transaction. Once we have done that we
   * need to release the unused reservation for the transaction, attach the
   * transaction to the checkpoint context so we carry the busy extents through
   * to checkpoint completion, and then unlock all the items in the transaction.
   *
   * For more specific information about the order of operations in
   * xfs_log_commit_cil() please refer to the comments in
   * xfs_trans_commit_iclog().
   *
   * Called with the context lock already held in read mode to lock out
   * background commit, returns without it held once background commits are
   * allowed again.
   */

  int

  xfs_log_commit_cil(
  	struct xfs_mount	*mp,
  	struct xfs_trans	*tp,

  	xfs_lsn_t		*commit_lsn,
  	int			flags)
  {
  	struct log		*log = mp->m_log;
  	int			log_flags = 0;
  	int			push = 0;

  	struct xfs_log_vec	*log_vector;

  
  	if (flags & XFS_TRANS_RELEASE_LOG_RES)
  		log_flags = XFS_LOG_REL_PERM_RESERV;

  	/*

  	 * Do all the hard work of formatting items (including memory

  	 * allocation) outside the CIL context lock. This prevents stalling CIL
  	 * pushes when we are low on memory and a transaction commit spends a
  	 * lot of time in memory reclaim.
  	 */

  	log_vector = xlog_cil_prepare_log_vecs(tp);
  	if (!log_vector)
  		return ENOMEM;

  	/* lock out background commit */
  	down_read(&log->l_cilp->xc_ctx_lock);

  	if (commit_lsn)
  		*commit_lsn = log->l_cilp->xc_ctx->sequence;
  
  	xlog_cil_insert_items(log, log_vector, tp->t_ticket);

  
  	/* check we didn't blow the reservation */
  	if (tp->t_ticket->t_curr_res < 0)
  		xlog_print_tic_res(log->l_mp, tp->t_ticket);
  
  	/* attach the transaction to the CIL if it has any busy extents */
  	if (!list_empty(&tp->t_busy)) {
  		spin_lock(&log->l_cilp->xc_cil_lock);
  		list_splice_init(&tp->t_busy,
  					&log->l_cilp->xc_ctx->busy_extents);
  		spin_unlock(&log->l_cilp->xc_cil_lock);
  	}
  
  	tp->t_commit_lsn = *commit_lsn;
  	xfs_log_done(mp, tp->t_ticket, NULL, log_flags);
  	xfs_trans_unreserve_and_mod_sb(tp);
  
  	/*
  	 * Once all the items of the transaction have been copied to the CIL,
  	 * the items can be unlocked and freed.
  	 *
  	 * This needs to be done before we drop the CIL context lock because we
  	 * have to update state in the log items and unlock them before they go
  	 * to disk. If we don't, then the CIL checkpoint can race with us and
  	 * we can run checkpoint completion before we've updated and unlocked
  	 * the log items. This affects (at least) processing of stale buffers,
  	 * inodes and EFIs.
  	 */
  	xfs_trans_free_items(tp, *commit_lsn, 0);
  
  	/* check for background commit before unlock */
  	if (log->l_cilp->xc_ctx->space_used > XLOG_CIL_SPACE_LIMIT(log))
  		push = 1;
  
  	up_read(&log->l_cilp->xc_ctx_lock);
  
  	/*
  	 * We need to push CIL every so often so we don't cache more than we
  	 * can fit in the log. The limit really is that a checkpoint can't be
  	 * more than half the log (the current checkpoint is not allowed to
  	 * overwrite the previous checkpoint), but commit latency and memory
  	 * usage limit this to a smaller size in most cases.
  	 */
  	if (push)
  		xlog_cil_push(log, 0);

  	return 0;

  }
  
  /*

   * Conditionally push the CIL based on the sequence passed in.
   *
   * We only need to push if we haven't already pushed the sequence
   * number given. Hence the only time we will trigger a push here is
   * if the push sequence is the same as the current context.
   *
   * We return the current commit lsn to allow the callers to determine if a
   * iclog flush is necessary following this call.
   *
   * XXX: Initially, just push the CIL unconditionally and return whatever
   * commit lsn is there. It'll be empty, so this is broken for now.
   */
  xfs_lsn_t

  xlog_cil_force_lsn(

  	struct log	*log,

  	xfs_lsn_t	sequence)

  {
  	struct xfs_cil		*cil = log->l_cilp;
  	struct xfs_cil_ctx	*ctx;
  	xfs_lsn_t		commit_lsn = NULLCOMMITLSN;

  	ASSERT(sequence <= cil->xc_current_sequence);
  
  	/*
  	 * check to see if we need to force out the current context.
  	 * xlog_cil_push() handles racing pushes for the same sequence,
  	 * so no need to deal with it here.
  	 */
  	if (sequence == cil->xc_current_sequence)
  		xlog_cil_push(log, sequence);

  
  	/*
  	 * See if we can find a previous sequence still committing.

  	 * We need to wait for all previous sequence commits to complete
  	 * before allowing the force of push_seq to go ahead. Hence block
  	 * on commits for those as well.
  	 */

  restart:

  	spin_lock(&cil->xc_cil_lock);

  	list_for_each_entry(ctx, &cil->xc_committing, committing) {

  		if (ctx->sequence > sequence)

  			continue;
  		if (!ctx->commit_lsn) {
  			/*
  			 * It is still being pushed! Wait for the push to
  			 * complete, then start again from the beginning.
  			 */

  			xlog_wait(&cil->xc_commit_wait, &cil->xc_cil_lock);

  			goto restart;
  		}

  		if (ctx->sequence != sequence)

  			continue;
  		/* found it! */
  		commit_lsn = ctx->commit_lsn;
  	}
  	spin_unlock(&cil->xc_cil_lock);
  	return commit_lsn;
  }

  
  /*
   * Check if the current log item was first committed in this sequence.
   * We can't rely on just the log item being in the CIL, we have to check
   * the recorded commit sequence number.
   *
   * Note: for this to be used in a non-racy manner, it has to be called with
   * CIL flushing locked out. As a result, it should only be used during the
   * transaction commit process when deciding what to format into the item.
   */
  bool
  xfs_log_item_in_current_chkpt(
  	struct xfs_log_item *lip)
  {
  	struct xfs_cil_ctx *ctx;

  	if (list_empty(&lip->li_cil))
  		return false;
  
  	ctx = lip->li_mountp->m_log->l_cilp->xc_ctx;
  
  	/*
  	 * li_seq is written on the first commit of a log item to record the
  	 * first checkpoint it is written to. Hence if it is different to the
  	 * current sequence, we're in a new checkpoint.
  	 */
  	if (XFS_LSN_CMP(lip->li_seq, ctx->sequence) != 0)
  		return false;
  	return true;
  }