text: /*
   * Copyright (c) 2000-2002,2005 Silicon Graphics, Inc.
   * All Rights Reserved.
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License as
   * published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it would be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write the Free Software Foundation,
   * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
   */
  #include "xfs.h"
  #include "xfs_fs.h"
  #include "xfs_shared.h"
  #include "xfs_format.h"
  #include "xfs_log_format.h"
  #include "xfs_trans_resv.h"
  #include "xfs_bit.h"
  #include "xfs_sb.h"
  #include "xfs_mount.h"
  #include "xfs_inode.h"
  #include "xfs_btree.h"
  #include "xfs_ialloc.h"
  #include "xfs_ialloc_btree.h"
  #include "xfs_alloc.h"
  #include "xfs_rtalloc.h"
  #include "xfs_error.h"
  #include "xfs_bmap.h"
  #include "xfs_cksum.h"
  #include "xfs_trans.h"
  #include "xfs_buf_item.h"
  #include "xfs_icreate_item.h"
  #include "xfs_icache.h"
  #include "xfs_trace.h"
  #include "xfs_log.h"
  
  
  /*
   * Allocation group level functions.
   */
  static inline int
  xfs_ialloc_cluster_alignment(
  	struct xfs_mount	*mp)
  {
  	if (xfs_sb_version_hasalign(&mp->m_sb) &&
  	    mp->m_sb.sb_inoalignmt >=
  			XFS_B_TO_FSBT(mp, mp->m_inode_cluster_size))
  		return mp->m_sb.sb_inoalignmt;
  	return 1;
  }
  
  /*
   * Lookup a record by ino in the btree given by cur.
   */
  int					/* error */
  xfs_inobt_lookup(
  	struct xfs_btree_cur	*cur,	/* btree cursor */
  	xfs_agino_t		ino,	/* starting inode of chunk */
  	xfs_lookup_t		dir,	/* <=, >=, == */
  	int			*stat)	/* success/failure */
  {
  	cur->bc_rec.i.ir_startino = ino;
  	cur->bc_rec.i.ir_holemask = 0;
  	cur->bc_rec.i.ir_count = 0;
  	cur->bc_rec.i.ir_freecount = 0;
  	cur->bc_rec.i.ir_free = 0;
  	return xfs_btree_lookup(cur, dir, stat);
  }
  
  /*
   * Update the record referred to by cur to the value given.
   * This either works (return 0) or gets an EFSCORRUPTED error.
   */
  STATIC int				/* error */
  xfs_inobt_update(
  	struct xfs_btree_cur	*cur,	/* btree cursor */
  	xfs_inobt_rec_incore_t	*irec)	/* btree record */
  {
  	union xfs_btree_rec	rec;
  
  	rec.inobt.ir_startino = cpu_to_be32(irec->ir_startino);
  	if (xfs_sb_version_hassparseinodes(&cur->bc_mp->m_sb)) {
  		rec.inobt.ir_u.sp.ir_holemask = cpu_to_be16(irec->ir_holemask);
  		rec.inobt.ir_u.sp.ir_count = irec->ir_count;
  		rec.inobt.ir_u.sp.ir_freecount = irec->ir_freecount;
  	} else {
  		/* ir_holemask/ir_count not supported on-disk */
  		rec.inobt.ir_u.f.ir_freecount = cpu_to_be32(irec->ir_freecount);
  	}
  	rec.inobt.ir_free = cpu_to_be64(irec->ir_free);
  	return xfs_btree_update(cur, &rec);
  }
  
  /*
   * Get the data from the pointed-to record.
   */
  int					/* error */
  xfs_inobt_get_rec(
  	struct xfs_btree_cur	*cur,	/* btree cursor */
  	xfs_inobt_rec_incore_t	*irec,	/* btree record */
  	int			*stat)	/* output: success/failure */
  {
  	union xfs_btree_rec	*rec;
  	int			error;
  
  	error = xfs_btree_get_rec(cur, &rec, stat);
  	if (error || *stat == 0)
  		return error;
  
  	irec->ir_startino = be32_to_cpu(rec->inobt.ir_startino);
  	if (xfs_sb_version_hassparseinodes(&cur->bc_mp->m_sb)) {
  		irec->ir_holemask = be16_to_cpu(rec->inobt.ir_u.sp.ir_holemask);
  		irec->ir_count = rec->inobt.ir_u.sp.ir_count;
  		irec->ir_freecount = rec->inobt.ir_u.sp.ir_freecount;
  	} else {
  		/*
  		 * ir_holemask/ir_count not supported on-disk. Fill in hardcoded
  		 * values for full inode chunks.
  		 */
  		irec->ir_holemask = XFS_INOBT_HOLEMASK_FULL;
  		irec->ir_count = XFS_INODES_PER_CHUNK;
  		irec->ir_freecount =
  				be32_to_cpu(rec->inobt.ir_u.f.ir_freecount);
  	}
  	irec->ir_free = be64_to_cpu(rec->inobt.ir_free);
  
  	return 0;
  }
  
  /*
   * Insert a single inobt record. Cursor must already point to desired location.
   */
  STATIC int
  xfs_inobt_insert_rec(
  	struct xfs_btree_cur	*cur,
  	__uint16_t		holemask,
  	__uint8_t		count,
  	__int32_t		freecount,
  	xfs_inofree_t		free,
  	int			*stat)
  {
  	cur->bc_rec.i.ir_holemask = holemask;
  	cur->bc_rec.i.ir_count = count;
  	cur->bc_rec.i.ir_freecount = freecount;
  	cur->bc_rec.i.ir_free = free;
  	return xfs_btree_insert(cur, stat);
  }
  
  /*
   * Insert records describing a newly allocated inode chunk into the inobt.
   */
  STATIC int
  xfs_inobt_insert(
  	struct xfs_mount	*mp,
  	struct xfs_trans	*tp,
  	struct xfs_buf		*agbp,
  	xfs_agino_t		newino,
  	xfs_agino_t		newlen,
  	xfs_btnum_t		btnum)
  {
  	struct xfs_btree_cur	*cur;
  	struct xfs_agi		*agi = XFS_BUF_TO_AGI(agbp);
  	xfs_agnumber_t		agno = be32_to_cpu(agi->agi_seqno);
  	xfs_agino_t		thisino;
  	int			i;
  	int			error;
  
  	cur = xfs_inobt_init_cursor(mp, tp, agbp, agno, btnum);
  
  	for (thisino = newino;
  	     thisino < newino + newlen;
  	     thisino += XFS_INODES_PER_CHUNK) {
  		error = xfs_inobt_lookup(cur, thisino, XFS_LOOKUP_EQ, &i);
  		if (error) {
  			xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
  			return error;
  		}
  		ASSERT(i == 0);
  
  		error = xfs_inobt_insert_rec(cur, XFS_INOBT_HOLEMASK_FULL,
  					     XFS_INODES_PER_CHUNK,
  					     XFS_INODES_PER_CHUNK,
  					     XFS_INOBT_ALL_FREE, &i);
  		if (error) {
  			xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
  			return error;
  		}
  		ASSERT(i == 1);
  	}
  
  	xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
  
  	return 0;
  }
  
  /*
   * Verify that the number of free inodes in the AGI is correct.
   */
  #ifdef DEBUG
  STATIC int
  xfs_check_agi_freecount(
  	struct xfs_btree_cur	*cur,
  	struct xfs_agi		*agi)
  {
  	if (cur->bc_nlevels == 1) {
  		xfs_inobt_rec_incore_t rec;
  		int		freecount = 0;
  		int		error;
  		int		i;
  
  		error = xfs_inobt_lookup(cur, 0, XFS_LOOKUP_GE, &i);
  		if (error)
  			return error;
  
  		do {
  			error = xfs_inobt_get_rec(cur, &rec, &i);
  			if (error)
  				return error;
  
  			if (i) {
  				freecount += rec.ir_freecount;
  				error = xfs_btree_increment(cur, 0, &i);
  				if (error)
  					return error;
  			}
  		} while (i == 1);
  
  		if (!XFS_FORCED_SHUTDOWN(cur->bc_mp))
  			ASSERT(freecount == be32_to_cpu(agi->agi_freecount));
  	}
  	return 0;
  }
  #else
  #define xfs_check_agi_freecount(cur, agi)	0
  #endif
  
  /*
   * Initialise a new set of inodes. When called without a transaction context
   * (e.g. from recovery) we initiate a delayed write of the inode buffers rather
   * than logging them (which in a transaction context puts them into the AIL
   * for writeback rather than the xfsbufd queue).
   */
  int
  xfs_ialloc_inode_init(
  	struct xfs_mount	*mp,
  	struct xfs_trans	*tp,
  	struct list_head	*buffer_list,
  	int			icount,
  	xfs_agnumber_t		agno,
  	xfs_agblock_t		agbno,
  	xfs_agblock_t		length,
  	unsigned int		gen)
  {
  	struct xfs_buf		*fbuf;
  	struct xfs_dinode	*free;
  	int			nbufs, blks_per_cluster, inodes_per_cluster;
  	int			version;
  	int			i, j;
  	xfs_daddr_t		d;
  	xfs_ino_t		ino = 0;
  
  	/*
  	 * Loop over the new block(s), filling in the inodes.  For small block
  	 * sizes, manipulate the inodes in buffers  which are multiples of the
  	 * blocks size.
  	 */
  	blks_per_cluster = xfs_icluster_size_fsb(mp);
  	inodes_per_cluster = blks_per_cluster << mp->m_sb.sb_inopblog;
  	nbufs = length / blks_per_cluster;
  
  	/*
  	 * Figure out what version number to use in the inodes we create.  If
  	 * the superblock version has caught up to the one that supports the new
  	 * inode format, then use the new inode version.  Otherwise use the old
  	 * version so that old kernels will continue to be able to use the file
  	 * system.
  	 *
  	 * For v3 inodes, we also need to write the inode number into the inode,
  	 * so calculate the first inode number of the chunk here as
  	 * XFS_OFFBNO_TO_AGINO() only works within a filesystem block, not
  	 * across multiple filesystem blocks (such as a cluster) and so cannot
  	 * be used in the cluster buffer loop below.
  	 *
  	 * Further, because we are writing the inode directly into the buffer
  	 * and calculating a CRC on the entire inode, we have ot log the entire
  	 * inode so that the entire range the CRC covers is present in the log.
  	 * That means for v3 inode we log the entire buffer rather than just the
  	 * inode cores.
  	 */
  	if (xfs_sb_version_hascrc(&mp->m_sb)) {
  		version = 3;
  		ino = XFS_AGINO_TO_INO(mp, agno,
  				       XFS_OFFBNO_TO_AGINO(mp, agbno, 0));
  
  		/*
  		 * log the initialisation that is about to take place as an
  		 * logical operation. This means the transaction does not
  		 * need to log the physical changes to the inode buffers as log
  		 * recovery will know what initialisation is actually needed.
  		 * Hence we only need to log the buffers as "ordered" buffers so
  		 * they track in the AIL as if they were physically logged.
  		 */
  		if (tp)
  			xfs_icreate_log(tp, agno, agbno, icount,
  					mp->m_sb.sb_inodesize, length, gen);
  	} else
  		version = 2;
  
  	for (j = 0; j < nbufs; j++) {
  		/*
  		 * Get the block.
  		 */
  		d = XFS_AGB_TO_DADDR(mp, agno, agbno + (j * blks_per_cluster));
  		fbuf = xfs_trans_get_buf(tp, mp->m_ddev_targp, d,
  					 mp->m_bsize * blks_per_cluster,
  					 XBF_UNMAPPED);
  		if (!fbuf)
  			return -ENOMEM;
  
  		/* Initialize the inode buffers and log them appropriately. */
  		fbuf->b_ops = &xfs_inode_buf_ops;
  		xfs_buf_zero(fbuf, 0, BBTOB(fbuf->b_length));
  		for (i = 0; i < inodes_per_cluster; i++) {
  			int	ioffset = i << mp->m_sb.sb_inodelog;
  			uint	isize = xfs_dinode_size(version);
  
  			free = xfs_make_iptr(mp, fbuf, i);
  			free->di_magic = cpu_to_be16(XFS_DINODE_MAGIC);
  			free->di_version = version;
  			free->di_gen = cpu_to_be32(gen);
  			free->di_next_unlinked = cpu_to_be32(NULLAGINO);
  
  			if (version == 3) {
  				free->di_ino = cpu_to_be64(ino);
  				ino++;
  				uuid_copy(&free->di_uuid,
  					  &mp->m_sb.sb_meta_uuid);
  				xfs_dinode_calc_crc(mp, free);
  			} else if (tp) {
  				/* just log the inode core */
  				xfs_trans_log_buf(tp, fbuf, ioffset,
  						  ioffset + isize - 1);
  			}
  		}
  
  		if (tp) {
  			/*
  			 * Mark the buffer as an inode allocation buffer so it
  			 * sticks in AIL at the point of this allocation
  			 * transaction. This ensures the they are on disk before
  			 * the tail of the log can be moved past this
  			 * transaction (i.e. by preventing relogging from moving
  			 * it forward in the log).
  			 */
  			xfs_trans_inode_alloc_buf(tp, fbuf);
  			if (version == 3) {
  				/*
  				 * Mark the buffer as ordered so that they are
  				 * not physically logged in the transaction but
  				 * still tracked in the AIL as part of the
  				 * transaction and pin the log appropriately.
  				 */
  				xfs_trans_ordered_buf(tp, fbuf);
  				xfs_trans_log_buf(tp, fbuf, 0,
  						  BBTOB(fbuf->b_length) - 1);
  			}
  		} else {
  			fbuf->b_flags |= XBF_DONE;
  			xfs_buf_delwri_queue(fbuf, buffer_list);
  			xfs_buf_relse(fbuf);
  		}
  	}
  	return 0;
  }
  
  /*
   * Align startino and allocmask for a recently allocated sparse chunk such that
   * they are fit for insertion (or merge) into the on-disk inode btrees.
   *
   * Background:
   *
   * When enabled, sparse inode support increases the inode alignment from cluster
   * size to inode chunk size. This means that the minimum range between two
   * non-adjacent inode records in the inobt is large enough for a full inode
   * record. This allows for cluster sized, cluster aligned block allocation
   * without need to worry about whether the resulting inode record overlaps with
   * another record in the tree. Without this basic rule, we would have to deal
   * with the consequences of overlap by potentially undoing recent allocations in
   * the inode allocation codepath.
   *
   * Because of this alignment rule (which is enforced on mount), there are two
   * inobt possibilities for newly allocated sparse chunks. One is that the
   * aligned inode record for the chunk covers a range of inodes not already
   * covered in the inobt (i.e., it is safe to insert a new sparse record). The
   * other is that a record already exists at the aligned startino that considers
   * the newly allocated range as sparse. In the latter case, record content is
   * merged in hope that sparse inode chunks fill to full chunks over time.
   */
  STATIC void
  xfs_align_sparse_ino(
  	struct xfs_mount		*mp,
  	xfs_agino_t			*startino,
  	uint16_t			*allocmask)
  {
  	xfs_agblock_t			agbno;
  	xfs_agblock_t			mod;
  	int				offset;
  
  	agbno = XFS_AGINO_TO_AGBNO(mp, *startino);
  	mod = agbno % mp->m_sb.sb_inoalignmt;
  	if (!mod)
  		return;
  
  	/* calculate the inode offset and align startino */
  	offset = mod << mp->m_sb.sb_inopblog;
  	*startino -= offset;
  
  	/*
  	 * Since startino has been aligned down, left shift allocmask such that
  	 * it continues to represent the same physical inodes relative to the
  	 * new startino.
  	 */
  	*allocmask <<= offset / XFS_INODES_PER_HOLEMASK_BIT;
  }
  
  /*
   * Determine whether the source inode record can merge into the target. Both
   * records must be sparse, the inode ranges must match and there must be no
   * allocation overlap between the records.
   */
  STATIC bool
  __xfs_inobt_can_merge(
  	struct xfs_inobt_rec_incore	*trec,	/* tgt record */
  	struct xfs_inobt_rec_incore	*srec)	/* src record */
  {
  	uint64_t			talloc;
  	uint64_t			salloc;
  
  	/* records must cover the same inode range */
  	if (trec->ir_startino != srec->ir_startino)
  		return false;
  
  	/* both records must be sparse */
  	if (!xfs_inobt_issparse(trec->ir_holemask) ||
  	    !xfs_inobt_issparse(srec->ir_holemask))
  		return false;
  
  	/* both records must track some inodes */
  	if (!trec->ir_count || !srec->ir_count)
  		return false;
  
  	/* can't exceed capacity of a full record */
  	if (trec->ir_count + srec->ir_count > XFS_INODES_PER_CHUNK)
  		return false;
  
  	/* verify there is no allocation overlap */
  	talloc = xfs_inobt_irec_to_allocmask(trec);
  	salloc = xfs_inobt_irec_to_allocmask(srec);
  	if (talloc & salloc)
  		return false;
  
  	return true;
  }
  
  /*
   * Merge the source inode record into the target. The caller must call
   * __xfs_inobt_can_merge() to ensure the merge is valid.
   */
  STATIC void
  __xfs_inobt_rec_merge(
  	struct xfs_inobt_rec_incore	*trec,	/* target */
  	struct xfs_inobt_rec_incore	*srec)	/* src */
  {
  	ASSERT(trec->ir_startino == srec->ir_startino);
  
  	/* combine the counts */
  	trec->ir_count += srec->ir_count;
  	trec->ir_freecount += srec->ir_freecount;
  
  	/*
  	 * Merge the holemask and free mask. For both fields, 0 bits refer to
  	 * allocated inodes. We combine the allocated ranges with bitwise AND.
  	 */
  	trec->ir_holemask &= srec->ir_holemask;
  	trec->ir_free &= srec->ir_free;
  }
  
  /*
   * Insert a new sparse inode chunk into the associated inode btree. The inode
   * record for the sparse chunk is pre-aligned to a startino that should match
   * any pre-existing sparse inode record in the tree. This allows sparse chunks
   * to fill over time.
   *
   * This function supports two modes of handling preexisting records depending on
   * the merge flag. If merge is true, the provided record is merged with the
   * existing record and updated in place. The merged record is returned in nrec.
   * If merge is false, an existing record is replaced with the provided record.
   * If no preexisting record exists, the provided record is always inserted.
   *
   * It is considered corruption if a merge is requested and not possible. Given
   * the sparse inode alignment constraints, this should never happen.
   */
  STATIC int
  xfs_inobt_insert_sprec(
  	struct xfs_mount		*mp,
  	struct xfs_trans		*tp,
  	struct xfs_buf			*agbp,
  	int				btnum,
  	struct xfs_inobt_rec_incore	*nrec,	/* in/out: new/merged rec. */
  	bool				merge)	/* merge or replace */
  {
  	struct xfs_btree_cur		*cur;
  	struct xfs_agi			*agi = XFS_BUF_TO_AGI(agbp);
  	xfs_agnumber_t			agno = be32_to_cpu(agi->agi_seqno);
  	int				error;
  	int				i;
  	struct xfs_inobt_rec_incore	rec;
  
  	cur = xfs_inobt_init_cursor(mp, tp, agbp, agno, btnum);
  
  	/* the new record is pre-aligned so we know where to look */
  	error = xfs_inobt_lookup(cur, nrec->ir_startino, XFS_LOOKUP_EQ, &i);
  	if (error)
  		goto error;
  	/* if nothing there, insert a new record and return */
  	if (i == 0) {
  		error = xfs_inobt_insert_rec(cur, nrec->ir_holemask,
  					     nrec->ir_count, nrec->ir_freecount,
  					     nrec->ir_free, &i);
  		if (error)
  			goto error;
  		XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error);
  
  		goto out;
  	}
  
  	/*
  	 * A record exists at this startino. Merge or replace the record
  	 * depending on what we've been asked to do.
  	 */
  	if (merge) {
  		error = xfs_inobt_get_rec(cur, &rec, &i);
  		if (error)
  			goto error;
  		XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error);
  		XFS_WANT_CORRUPTED_GOTO(mp,
  					rec.ir_startino == nrec->ir_startino,
  					error);
  
  		/*
  		 * This should never fail. If we have coexisting records that
  		 * cannot merge, something is seriously wrong.
  		 */
  		XFS_WANT_CORRUPTED_GOTO(mp, __xfs_inobt_can_merge(nrec, &rec),
  					error);
  
  		trace_xfs_irec_merge_pre(mp, agno, rec.ir_startino,
  					 rec.ir_holemask, nrec->ir_startino,
  					 nrec->ir_holemask);
  
  		/* merge to nrec to output the updated record */
  		__xfs_inobt_rec_merge(nrec, &rec);
  
  		trace_xfs_irec_merge_post(mp, agno, nrec->ir_startino,
  					  nrec->ir_holemask);
  
  		error = xfs_inobt_rec_check_count(mp, nrec);
  		if (error)
  			goto error;
  	}
  
  	error = xfs_inobt_update(cur, nrec);
  	if (error)
  		goto error;
  
  out:
  	xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
  	return 0;
  error:
  	xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
  	return error;
  }
  
  /*
   * Allocate new inodes in the allocation group specified by agbp.
   * Return 0 for success, else error code.
   */
  STATIC int				/* error code or 0 */
  xfs_ialloc_ag_alloc(
  	xfs_trans_t	*tp,		/* transaction pointer */
  	xfs_buf_t	*agbp,		/* alloc group buffer */
  	int		*alloc)
  {
  	xfs_agi_t	*agi;		/* allocation group header */
  	xfs_alloc_arg_t	args;		/* allocation argument structure */
  	xfs_agnumber_t	agno;
  	int		error;
  	xfs_agino_t	newino;		/* new first inode's number */
  	xfs_agino_t	newlen;		/* new number of inodes */
  	int		isaligned = 0;	/* inode allocation at stripe unit */
  					/* boundary */
  	uint16_t	allocmask = (uint16_t) -1; /* init. to full chunk */
  	struct xfs_inobt_rec_incore rec;
  	struct xfs_perag *pag;
  	int		do_sparse = 0;
  
  	memset(&args, 0, sizeof(args));
  	args.tp = tp;
  	args.mp = tp->t_mountp;
  	args.fsbno = NULLFSBLOCK;
  
  #ifdef DEBUG
  	/* randomly do sparse inode allocations */
  	if (xfs_sb_version_hassparseinodes(&tp->t_mountp->m_sb) &&
  	    args.mp->m_ialloc_min_blks < args.mp->m_ialloc_blks)
  		do_sparse = prandom_u32() & 1;
  #endif
  
  	/*
  	 * Locking will ensure that we don't have two callers in here
  	 * at one time.
  	 */
  	newlen = args.mp->m_ialloc_inos;
  	if (args.mp->m_maxicount &&
  	    percpu_counter_read_positive(&args.mp->m_icount) + newlen >
  							args.mp->m_maxicount)
  		return -ENOSPC;
  	args.minlen = args.maxlen = args.mp->m_ialloc_blks;
  	/*
  	 * First try to allocate inodes contiguous with the last-allocated
  	 * chunk of inodes.  If the filesystem is striped, this will fill
  	 * an entire stripe unit with inodes.
  	 */
  	agi = XFS_BUF_TO_AGI(agbp);
  	newino = be32_to_cpu(agi->agi_newino);
  	agno = be32_to_cpu(agi->agi_seqno);
  	args.agbno = XFS_AGINO_TO_AGBNO(args.mp, newino) +
  		     args.mp->m_ialloc_blks;
  	if (do_sparse)
  		goto sparse_alloc;
  	if (likely(newino != NULLAGINO &&
  		  (args.agbno < be32_to_cpu(agi->agi_length)))) {
  		args.fsbno = XFS_AGB_TO_FSB(args.mp, agno, args.agbno);
  		args.type = XFS_ALLOCTYPE_THIS_BNO;
  		args.prod = 1;
  
  		/*
  		 * We need to take into account alignment here to ensure that
  		 * we don't modify the free list if we fail to have an exact
  		 * block. If we don't have an exact match, and every oher
  		 * attempt allocation attempt fails, we'll end up cancelling
  		 * a dirty transaction and shutting down.
  		 *
  		 * For an exact allocation, alignment must be 1,
  		 * however we need to take cluster alignment into account when
  		 * fixing up the freelist. Use the minalignslop field to
  		 * indicate that extra blocks might be required for alignment,
  		 * but not to use them in the actual exact allocation.
  		 */
  		args.alignment = 1;
  		args.minalignslop = xfs_ialloc_cluster_alignment(args.mp) - 1;
  
  		/* Allow space for the inode btree to split. */
  		args.minleft = args.mp->m_in_maxlevels - 1;
  		if ((error = xfs_alloc_vextent(&args)))
  			return error;
  
  		/*
  		 * This request might have dirtied the transaction if the AG can
  		 * satisfy the request, but the exact block was not available.
  		 * If the allocation did fail, subsequent requests will relax
  		 * the exact agbno requirement and increase the alignment
  		 * instead. It is critical that the total size of the request
  		 * (len + alignment + slop) does not increase from this point
  		 * on, so reset minalignslop to ensure it is not included in
  		 * subsequent requests.
  		 */
  		args.minalignslop = 0;
  	}
  
  	if (unlikely(args.fsbno == NULLFSBLOCK)) {
  		/*
  		 * Set the alignment for the allocation.
  		 * If stripe alignment is turned on then align at stripe unit
  		 * boundary.
  		 * If the cluster size is smaller than a filesystem block
  		 * then we're doing I/O for inodes in filesystem block size
  		 * pieces, so don't need alignment anyway.
  		 */
  		isaligned = 0;
  		if (args.mp->m_sinoalign) {
  			ASSERT(!(args.mp->m_flags & XFS_MOUNT_NOALIGN));
  			args.alignment = args.mp->m_dalign;
  			isaligned = 1;
  		} else
  			args.alignment = xfs_ialloc_cluster_alignment(args.mp);
  		/*
  		 * Need to figure out where to allocate the inode blocks.
  		 * Ideally they should be spaced out through the a.g.
  		 * For now, just allocate blocks up front.
  		 */
  		args.agbno = be32_to_cpu(agi->agi_root);
  		args.fsbno = XFS_AGB_TO_FSB(args.mp, agno, args.agbno);
  		/*
  		 * Allocate a fixed-size extent of inodes.
  		 */
  		args.type = XFS_ALLOCTYPE_NEAR_BNO;
  		args.prod = 1;
  		/*
  		 * Allow space for the inode btree to split.
  		 */
  		args.minleft = args.mp->m_in_maxlevels - 1;
  		if ((error = xfs_alloc_vextent(&args)))
  			return error;
  	}
  
  	/*
  	 * If stripe alignment is turned on, then try again with cluster
  	 * alignment.
  	 */
  	if (isaligned && args.fsbno == NULLFSBLOCK) {
  		args.type = XFS_ALLOCTYPE_NEAR_BNO;
  		args.agbno = be32_to_cpu(agi->agi_root);
  		args.fsbno = XFS_AGB_TO_FSB(args.mp, agno, args.agbno);
  		args.alignment = xfs_ialloc_cluster_alignment(args.mp);
  		if ((error = xfs_alloc_vextent(&args)))
  			return error;
  	}
  
  	/*
  	 * Finally, try a sparse allocation if the filesystem supports it and
  	 * the sparse allocation length is smaller than a full chunk.
  	 */
  	if (xfs_sb_version_hassparseinodes(&args.mp->m_sb) &&
  	    args.mp->m_ialloc_min_blks < args.mp->m_ialloc_blks &&
  	    args.fsbno == NULLFSBLOCK) {
  sparse_alloc:
  		args.type = XFS_ALLOCTYPE_NEAR_BNO;
  		args.agbno = be32_to_cpu(agi->agi_root);
  		args.fsbno = XFS_AGB_TO_FSB(args.mp, agno, args.agbno);
  		args.alignment = args.mp->m_sb.sb_spino_align;
  		args.prod = 1;
  
  		args.minlen = args.mp->m_ialloc_min_blks;
  		args.maxlen = args.minlen;
  
  		/*
  		 * The inode record will be aligned to full chunk size. We must
  		 * prevent sparse allocation from AG boundaries that result in
  		 * invalid inode records, such as records that start at agbno 0
  		 * or extend beyond the AG.
  		 *
  		 * Set min agbno to the first aligned, non-zero agbno and max to
  		 * the last aligned agbno that is at least one full chunk from
  		 * the end of the AG.
  		 */
  		args.min_agbno = args.mp->m_sb.sb_inoalignmt;
  		args.max_agbno = round_down(args.mp->m_sb.sb_agblocks,
  					    args.mp->m_sb.sb_inoalignmt) -
  				 args.mp->m_ialloc_blks;
  
  		error = xfs_alloc_vextent(&args);
  		if (error)
  			return error;
  
  		newlen = args.len << args.mp->m_sb.sb_inopblog;
  		ASSERT(newlen <= XFS_INODES_PER_CHUNK);
  		allocmask = (1 << (newlen / XFS_INODES_PER_HOLEMASK_BIT)) - 1;
  	}
  
  	if (args.fsbno == NULLFSBLOCK) {
  		*alloc = 0;
  		return 0;
  	}
  	ASSERT(args.len == args.minlen);
  
  	/*
  	 * Stamp and write the inode buffers.
  	 *
  	 * Seed the new inode cluster with a random generation number. This
  	 * prevents short-term reuse of generation numbers if a chunk is
  	 * freed and then immediately reallocated. We use random numbers
  	 * rather than a linear progression to prevent the next generation
  	 * number from being easily guessable.
  	 */
  	error = xfs_ialloc_inode_init(args.mp, tp, NULL, newlen, agno,
  			args.agbno, args.len, prandom_u32());
  
  	if (error)
  		return error;
  	/*
  	 * Convert the results.
  	 */
  	newino = XFS_OFFBNO_TO_AGINO(args.mp, args.agbno, 0);
  
  	if (xfs_inobt_issparse(~allocmask)) {
  		/*
  		 * We've allocated a sparse chunk. Align the startino and mask.
  		 */
  		xfs_align_sparse_ino(args.mp, &newino, &allocmask);
  
  		rec.ir_startino = newino;
  		rec.ir_holemask = ~allocmask;
  		rec.ir_count = newlen;
  		rec.ir_freecount = newlen;
  		rec.ir_free = XFS_INOBT_ALL_FREE;
  
  		/*
  		 * Insert the sparse record into the inobt and allow for a merge
  		 * if necessary. If a merge does occur, rec is updated to the
  		 * merged record.
  		 */
  		error = xfs_inobt_insert_sprec(args.mp, tp, agbp, XFS_BTNUM_INO,
  					       &rec, true);
  		if (error == -EFSCORRUPTED) {
  			xfs_alert(args.mp,
  	"invalid sparse inode record: ino 0x%llx holemask 0x%x count %u",
  				  XFS_AGINO_TO_INO(args.mp, agno,
  						   rec.ir_startino),
  				  rec.ir_holemask, rec.ir_count);
  			xfs_force_shutdown(args.mp, SHUTDOWN_CORRUPT_INCORE);
  		}
  		if (error)
  			return error;
  
  		/*
  		 * We can't merge the part we've just allocated as for the inobt
  		 * due to finobt semantics. The original record may or may not
  		 * exist independent of whether physical inodes exist in this
  		 * sparse chunk.
  		 *
  		 * We must update the finobt record based on the inobt record.
  		 * rec contains the fully merged and up to date inobt record
  		 * from the previous call. Set merge false to replace any
  		 * existing record with this one.
  		 */
  		if (xfs_sb_version_hasfinobt(&args.mp->m_sb)) {
  			error = xfs_inobt_insert_sprec(args.mp, tp, agbp,
  						       XFS_BTNUM_FINO, &rec,
  						       false);
  			if (error)
  				return error;
  		}
  	} else {
  		/* full chunk - insert new records to both btrees */
  		error = xfs_inobt_insert(args.mp, tp, agbp, newino, newlen,
  					 XFS_BTNUM_INO);
  		if (error)
  			return error;
  
  		if (xfs_sb_version_hasfinobt(&args.mp->m_sb)) {
  			error = xfs_inobt_insert(args.mp, tp, agbp, newino,
  						 newlen, XFS_BTNUM_FINO);
  			if (error)
  				return error;
  		}
  	}
  
  	/*
  	 * Update AGI counts and newino.
  	 */
  	be32_add_cpu(&agi->agi_count, newlen);
  	be32_add_cpu(&agi->agi_freecount, newlen);
  	pag = xfs_perag_get(args.mp, agno);
  	pag->pagi_freecount += newlen;
  	xfs_perag_put(pag);
  	agi->agi_newino = cpu_to_be32(newino);
  
  	/*
  	 * Log allocation group header fields
  	 */
  	xfs_ialloc_log_agi(tp, agbp,
  		XFS_AGI_COUNT | XFS_AGI_FREECOUNT | XFS_AGI_NEWINO);
  	/*
  	 * Modify/log superblock values for inode count and inode free count.
  	 */
  	xfs_trans_mod_sb(tp, XFS_TRANS_SB_ICOUNT, (long)newlen);
  	xfs_trans_mod_sb(tp, XFS_TRANS_SB_IFREE, (long)newlen);
  	*alloc = 1;
  	return 0;
  }
  
  STATIC xfs_agnumber_t
  xfs_ialloc_next_ag(
  	xfs_mount_t	*mp)
  {
  	xfs_agnumber_t	agno;
  
  	spin_lock(&mp->m_agirotor_lock);
  	agno = mp->m_agirotor;
  	if (++mp->m_agirotor >= mp->m_maxagi)
  		mp->m_agirotor = 0;
  	spin_unlock(&mp->m_agirotor_lock);
  
  	return agno;
  }
  
  /*
   * Select an allocation group to look for a free inode in, based on the parent
   * inode and the mode.  Return the allocation group buffer.
   */
  STATIC xfs_agnumber_t
  xfs_ialloc_ag_select(
  	xfs_trans_t	*tp,		/* transaction pointer */
  	xfs_ino_t	parent,		/* parent directory inode number */
  	umode_t		mode,		/* bits set to indicate file type */
  	int		okalloc)	/* ok to allocate more space */
  {
  	xfs_agnumber_t	agcount;	/* number of ag's in the filesystem */
  	xfs_agnumber_t	agno;		/* current ag number */
  	int		flags;		/* alloc buffer locking flags */
  	xfs_extlen_t	ineed;		/* blocks needed for inode allocation */
  	xfs_extlen_t	longest = 0;	/* longest extent available */
  	xfs_mount_t	*mp;		/* mount point structure */
  	int		needspace;	/* file mode implies space allocated */
  	xfs_perag_t	*pag;		/* per allocation group data */
  	xfs_agnumber_t	pagno;		/* parent (starting) ag number */
  	int		error;
  
  	/*
  	 * Files of these types need at least one block if length > 0
  	 * (and they won't fit in the inode, but that's hard to figure out).
  	 */
  	needspace = S_ISDIR(mode) || S_ISREG(mode) || S_ISLNK(mode);
  	mp = tp->t_mountp;
  	agcount = mp->m_maxagi;
  	if (S_ISDIR(mode))
  		pagno = xfs_ialloc_next_ag(mp);
  	else {
  		pagno = XFS_INO_TO_AGNO(mp, parent);
  		if (pagno >= agcount)
  			pagno = 0;
  	}
  
  	ASSERT(pagno < agcount);
  
  	/*
  	 * Loop through allocation groups, looking for one with a little
  	 * free space in it.  Note we don't look for free inodes, exactly.
  	 * Instead, we include whether there is a need to allocate inodes
  	 * to mean that blocks must be allocated for them,
  	 * if none are currently free.
  	 */
  	agno = pagno;
  	flags = XFS_ALLOC_FLAG_TRYLOCK;
  	for (;;) {
  		pag = xfs_perag_get(mp, agno);
  		if (!pag->pagi_inodeok) {
  			xfs_ialloc_next_ag(mp);
  			goto nextag;
  		}
  
  		if (!pag->pagi_init) {
  			error = xfs_ialloc_pagi_init(mp, tp, agno);
  			if (error)
  				goto nextag;
  		}
  
  		if (pag->pagi_freecount) {
  			xfs_perag_put(pag);
  			return agno;
  		}
  
  		if (!okalloc)
  			goto nextag;
  
  		if (!pag->pagf_init) {
  			error = xfs_alloc_pagf_init(mp, tp, agno, flags);
  			if (error)
  				goto nextag;
  		}
  
  		/*
  		 * Check that there is enough free space for the file plus a
  		 * chunk of inodes if we need to allocate some. If this is the
  		 * first pass across the AGs, take into account the potential
  		 * space needed for alignment of inode chunks when checking the
  		 * longest contiguous free space in the AG - this prevents us
  		 * from getting ENOSPC because we have free space larger than
  		 * m_ialloc_blks but alignment constraints prevent us from using
  		 * it.
  		 *
  		 * If we can't find an AG with space for full alignment slack to
  		 * be taken into account, we must be near ENOSPC in all AGs.
  		 * Hence we don't include alignment for the second pass and so
  		 * if we fail allocation due to alignment issues then it is most
  		 * likely a real ENOSPC condition.
  		 */
  		ineed = mp->m_ialloc_min_blks;
  		if (flags && ineed > 1)
  			ineed += xfs_ialloc_cluster_alignment(mp);
  		longest = pag->pagf_longest;
  		if (!longest)
  			longest = pag->pagf_flcount > 0;
  
  		if (pag->pagf_freeblks >= needspace + ineed &&
  		    longest >= ineed) {
  			xfs_perag_put(pag);
  			return agno;
  		}
  nextag:
  		xfs_perag_put(pag);
  		/*
  		 * No point in iterating over the rest, if we're shutting
  		 * down.
  		 */
  		if (XFS_FORCED_SHUTDOWN(mp))
  			return NULLAGNUMBER;
  		agno++;
  		if (agno >= agcount)
  			agno = 0;
  		if (agno == pagno) {
  			if (flags == 0)
  				return NULLAGNUMBER;
  			flags = 0;
  		}
  	}
  }
  
  /*
   * Try to retrieve the next record to the left/right from the current one.
   */
  STATIC int
  xfs_ialloc_next_rec(
  	struct xfs_btree_cur	*cur,
  	xfs_inobt_rec_incore_t	*rec,
  	int			*done,
  	int			left)
  {
  	int                     error;
  	int			i;
  
  	if (left)
  		error = xfs_btree_decrement(cur, 0, &i);
  	else
  		error = xfs_btree_increment(cur, 0, &i);
  
  	if (error)
  		return error;
  	*done = !i;
  	if (i) {
  		error = xfs_inobt_get_rec(cur, rec, &i);
  		if (error)
  			return error;
  		XFS_WANT_CORRUPTED_RETURN(cur->bc_mp, i == 1);
  	}
  
  	return 0;
  }
  
  STATIC int
  xfs_ialloc_get_rec(
  	struct xfs_btree_cur	*cur,
  	xfs_agino_t		agino,
  	xfs_inobt_rec_incore_t	*rec,
  	int			*done)
  {
  	int                     error;
  	int			i;
  
  	error = xfs_inobt_lookup(cur, agino, XFS_LOOKUP_EQ, &i);
  	if (error)
  		return error;
  	*done = !i;
  	if (i) {
  		error = xfs_inobt_get_rec(cur, rec, &i);
  		if (error)
  			return error;
  		XFS_WANT_CORRUPTED_RETURN(cur->bc_mp, i == 1);
  	}
  
  	return 0;
  }
  
  /*
   * Return the offset of the first free inode in the record. If the inode chunk
   * is sparsely allocated, we convert the record holemask to inode granularity
   * and mask off the unallocated regions from the inode free mask.
   */
  STATIC int
  xfs_inobt_first_free_inode(
  	struct xfs_inobt_rec_incore	*rec)
  {
  	xfs_inofree_t			realfree;
  
  	/* if there are no holes, return the first available offset */
  	if (!xfs_inobt_issparse(rec->ir_holemask))
  		return xfs_lowbit64(rec->ir_free);
  
  	realfree = xfs_inobt_irec_to_allocmask(rec);
  	realfree &= rec->ir_free;
  
  	return xfs_lowbit64(realfree);
  }
  
  /*
   * Allocate an inode using the inobt-only algorithm.
   */
  STATIC int
  xfs_dialloc_ag_inobt(
  	struct xfs_trans	*tp,
  	struct xfs_buf		*agbp,
  	xfs_ino_t		parent,
  	xfs_ino_t		*inop)
  {
  	struct xfs_mount	*mp = tp->t_mountp;
  	struct xfs_agi		*agi = XFS_BUF_TO_AGI(agbp);
  	xfs_agnumber_t		agno = be32_to_cpu(agi->agi_seqno);
  	xfs_agnumber_t		pagno = XFS_INO_TO_AGNO(mp, parent);
  	xfs_agino_t		pagino = XFS_INO_TO_AGINO(mp, parent);
  	struct xfs_perag	*pag;
  	struct xfs_btree_cur	*cur, *tcur;
  	struct xfs_inobt_rec_incore rec, trec;
  	xfs_ino_t		ino;
  	int			error;
  	int			offset;
  	int			i, j;
  
  	pag = xfs_perag_get(mp, agno);
  
  	ASSERT(pag->pagi_init);
  	ASSERT(pag->pagi_inodeok);
  	ASSERT(pag->pagi_freecount > 0);
  
   restart_pagno:
  	cur = xfs_inobt_init_cursor(mp, tp, agbp, agno, XFS_BTNUM_INO);
  	/*
  	 * If pagino is 0 (this is the root inode allocation) use newino.
  	 * This must work because we've just allocated some.
  	 */
  	if (!pagino)
  		pagino = be32_to_cpu(agi->agi_newino);
  
  	error = xfs_check_agi_freecount(cur, agi);
  	if (error)
  		goto error0;
  
  	/*
  	 * If in the same AG as the parent, try to get near the parent.
  	 */
  	if (pagno == agno) {
  		int		doneleft;	/* done, to the left */
  		int		doneright;	/* done, to the right */
  		int		searchdistance = 10;
  
  		error = xfs_inobt_lookup(cur, pagino, XFS_LOOKUP_LE, &i);
  		if (error)
  			goto error0;
  		XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
  
  		error = xfs_inobt_get_rec(cur, &rec, &j);
  		if (error)
  			goto error0;
  		XFS_WANT_CORRUPTED_GOTO(mp, j == 1, error0);
  
  		if (rec.ir_freecount > 0) {
  			/*
  			 * Found a free inode in the same chunk
  			 * as the parent, done.
  			 */
  			goto alloc_inode;
  		}
  
  
  		/*
  		 * In the same AG as parent, but parent's chunk is full.
  		 */
  
  		/* duplicate the cursor, search left & right simultaneously */
  		error = xfs_btree_dup_cursor(cur, &tcur);
  		if (error)
  			goto error0;
  
  		/*
  		 * Skip to last blocks looked up if same parent inode.
  		 */
  		if (pagino != NULLAGINO &&
  		    pag->pagl_pagino == pagino &&
  		    pag->pagl_leftrec != NULLAGINO &&
  		    pag->pagl_rightrec != NULLAGINO) {
  			error = xfs_ialloc_get_rec(tcur, pag->pagl_leftrec,
  						   &trec, &doneleft);
  			if (error)
  				goto error1;
  
  			error = xfs_ialloc_get_rec(cur, pag->pagl_rightrec,
  						   &rec, &doneright);
  			if (error)
  				goto error1;
  		} else {
  			/* search left with tcur, back up 1 record */
  			error = xfs_ialloc_next_rec(tcur, &trec, &doneleft, 1);
  			if (error)
  				goto error1;
  
  			/* search right with cur, go forward 1 record. */
  			error = xfs_ialloc_next_rec(cur, &rec, &doneright, 0);
  			if (error)
  				goto error1;
  		}
  
  		/*
  		 * Loop until we find an inode chunk with a free inode.
  		 */
  		while (!doneleft || !doneright) {
  			int	useleft;  /* using left inode chunk this time */
  
  			if (!--searchdistance) {
  				/*
  				 * Not in range - save last search
  				 * location and allocate a new inode
  				 */
  				xfs_btree_del_cursor(tcur, XFS_BTREE_NOERROR);
  				pag->pagl_leftrec = trec.ir_startino;
  				pag->pagl_rightrec = rec.ir_startino;
  				pag->pagl_pagino = pagino;
  				goto newino;
  			}
  
  			/* figure out the closer block if both are valid. */
  			if (!doneleft && !doneright) {
  				useleft = pagino -
  				 (trec.ir_startino + XFS_INODES_PER_CHUNK - 1) <
  				  rec.ir_startino - pagino;
  			} else {
  				useleft = !doneleft;
  			}
  
  			/* free inodes to the left? */
  			if (useleft && trec.ir_freecount) {
  				rec = trec;
  				xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
  				cur = tcur;
  
  				pag->pagl_leftrec = trec.ir_startino;
  				pag->pagl_rightrec = rec.ir_startino;
  				pag->pagl_pagino = pagino;
  				goto alloc_inode;
  			}
  
  			/* free inodes to the right? */
  			if (!useleft && rec.ir_freecount) {
  				xfs_btree_del_cursor(tcur, XFS_BTREE_NOERROR);
  
  				pag->pagl_leftrec = trec.ir_startino;
  				pag->pagl_rightrec = rec.ir_startino;
  				pag->pagl_pagino = pagino;
  				goto alloc_inode;
  			}
  
  			/* get next record to check */
  			if (useleft) {
  				error = xfs_ialloc_next_rec(tcur, &trec,
  								 &doneleft, 1);
  			} else {
  				error = xfs_ialloc_next_rec(cur, &rec,
  								 &doneright, 0);
  			}
  			if (error)
  				goto error1;
  		}
  
  		/*
  		 * We've reached the end of the btree. because
  		 * we are only searching a small chunk of the
  		 * btree each search, there is obviously free
  		 * inodes closer to the parent inode than we
  		 * are now. restart the search again.
  		 */
  		pag->pagl_pagino = NULLAGINO;
  		pag->pagl_leftrec = NULLAGINO;
  		pag->pagl_rightrec = NULLAGINO;
  		xfs_btree_del_cursor(tcur, XFS_BTREE_NOERROR);
  		xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
  		goto restart_pagno;
  	}
  
  	/*
  	 * In a different AG from the parent.
  	 * See if the most recently allocated block has any free.
  	 */
  newino:
  	if (agi->agi_newino != cpu_to_be32(NULLAGINO)) {
  		error = xfs_inobt_lookup(cur, be32_to_cpu(agi->agi_newino),
  					 XFS_LOOKUP_EQ, &i);
  		if (error)
  			goto error0;
  
  		if (i == 1) {
  			error = xfs_inobt_get_rec(cur, &rec, &j);
  			if (error)
  				goto error0;
  
  			if (j == 1 && rec.ir_freecount > 0) {
  				/*
  				 * The last chunk allocated in the group
  				 * still has a free inode.
  				 */
  				goto alloc_inode;
  			}
  		}
  	}
  
  	/*
  	 * None left in the last group, search the whole AG
  	 */
  	error = xfs_inobt_lookup(cur, 0, XFS_LOOKUP_GE, &i);
  	if (error)
  		goto error0;
  	XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
  
  	for (;;) {
  		error = xfs_inobt_get_rec(cur, &rec, &i);
  		if (error)
  			goto error0;
  		XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
  		if (rec.ir_freecount > 0)
  			break;
  		error = xfs_btree_increment(cur, 0, &i);
  		if (error)
  			goto error0;
  		XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
  	}
  
  alloc_inode:
  	offset = xfs_inobt_first_free_inode(&rec);
  	ASSERT(offset >= 0);
  	ASSERT(offset < XFS_INODES_PER_CHUNK);
  	ASSERT((XFS_AGINO_TO_OFFSET(mp, rec.ir_startino) %
  				   XFS_INODES_PER_CHUNK) == 0);
  	ino = XFS_AGINO_TO_INO(mp, agno, rec.ir_startino + offset);
  	rec.ir_free &= ~XFS_INOBT_MASK(offset);
  	rec.ir_freecount--;
  	error = xfs_inobt_update(cur, &rec);
  	if (error)
  		goto error0;
  	be32_add_cpu(&agi->agi_freecount, -1);
  	xfs_ialloc_log_agi(tp, agbp, XFS_AGI_FREECOUNT);
  	pag->pagi_freecount--;
  
  	error = xfs_check_agi_freecount(cur, agi);
  	if (error)
  		goto error0;
  
  	xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
  	xfs_trans_mod_sb(tp, XFS_TRANS_SB_IFREE, -1);
  	xfs_perag_put(pag);
  	*inop = ino;
  	return 0;
  error1:
  	xfs_btree_del_cursor(tcur, XFS_BTREE_ERROR);
  error0:
  	xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
  	xfs_perag_put(pag);
  	return error;
  }
  
  /*
   * Use the free inode btree to allocate an inode based on distance from the
   * parent. Note that the provided cursor may be deleted and replaced.
   */
  STATIC int
  xfs_dialloc_ag_finobt_near(
  	xfs_agino_t			pagino,
  	struct xfs_btree_cur		**ocur,
  	struct xfs_inobt_rec_incore	*rec)
  {
  	struct xfs_btree_cur		*lcur = *ocur;	/* left search cursor */
  	struct xfs_btree_cur		*rcur;	/* right search cursor */
  	struct xfs_inobt_rec_incore	rrec;
  	int				error;
  	int				i, j;
  
  	error = xfs_inobt_lookup(lcur, pagino, XFS_LOOKUP_LE, &i);
  	if (error)
  		return error;
  
  	if (i == 1) {
  		error = xfs_inobt_get_rec(lcur, rec, &i);
  		if (error)
  			return error;
  		XFS_WANT_CORRUPTED_RETURN(lcur->bc_mp, i == 1);
  
  		/*
  		 * See if we've landed in the parent inode record. The finobt
  		 * only tracks chunks with at least one free inode, so record
  		 * existence is enough.
  		 */
  		if (pagino >= rec->ir_startino &&
  		    pagino < (rec->ir_startino + XFS_INODES_PER_CHUNK))
  			return 0;
  	}
  
  	error = xfs_btree_dup_cursor(lcur, &rcur);
  	if (error)
  		return error;
  
  	error = xfs_inobt_lookup(rcur, pagino, XFS_LOOKUP_GE, &j);
  	if (error)
  		goto error_rcur;
  	if (j == 1) {
  		error = xfs_inobt_get_rec(rcur, &rrec, &j);
  		if (error)
  			goto error_rcur;
  		XFS_WANT_CORRUPTED_GOTO(lcur->bc_mp, j == 1, error_rcur);
  	}
  
  	XFS_WANT_CORRUPTED_GOTO(lcur->bc_mp, i == 1 || j == 1, error_rcur);
  	if (i == 1 && j == 1) {
  		/*
  		 * Both the left and right records are valid. Choose the closer
  		 * inode chunk to the target.
  		 */
  		if ((pagino - rec->ir_startino + XFS_INODES_PER_CHUNK - 1) >
  		    (rrec.ir_startino - pagino)) {
  			*rec = rrec;
  			xfs_btree_del_cursor(lcur, XFS_BTREE_NOERROR);
  			*ocur = rcur;
  		} else {
  			xfs_btree_del_cursor(rcur, XFS_BTREE_NOERROR);
  		}
  	} else if (j == 1) {
  		/* only the right record is valid */
  		*rec = rrec;
  		xfs_btree_del_cursor(lcur, XFS_BTREE_NOERROR);
  		*ocur = rcur;
  	} else if (i == 1) {
  		/* only the left record is valid */
  		xfs_btree_del_cursor(rcur, XFS_BTREE_NOERROR);
  	}
  
  	return 0;
  
  error_rcur:
  	xfs_btree_del_cursor(rcur, XFS_BTREE_ERROR);
  	return error;
  }
  
  /*
   * Use the free inode btree to find a free inode based on a newino hint. If
   * the hint is NULL, find the first free inode in the AG.
   */
  STATIC int
  xfs_dialloc_ag_finobt_newino(
  	struct xfs_agi			*agi,
  	struct xfs_btree_cur		*cur,
  	struct xfs_inobt_rec_incore	*rec)
  {
  	int error;
  	int i;
  
  	if (agi->agi_newino != cpu_to_be32(NULLAGINO)) {
  		error = xfs_inobt_lookup(cur, be32_to_cpu(agi->agi_newino),
  					 XFS_LOOKUP_EQ, &i);
  		if (error)
  			return error;
  		if (i == 1) {
  			error = xfs_inobt_get_rec(cur, rec, &i);
  			if (error)
  				return error;
  			XFS_WANT_CORRUPTED_RETURN(cur->bc_mp, i == 1);
  			return 0;
  		}
  	}
  
  	/*
  	 * Find the first inode available in the AG.
  	 */
  	error = xfs_inobt_lookup(cur, 0, XFS_LOOKUP_GE, &i);
  	if (error)
  		return error;
  	XFS_WANT_CORRUPTED_RETURN(cur->bc_mp, i == 1);
  
  	error = xfs_inobt_get_rec(cur, rec, &i);
  	if (error)
  		return error;
  	XFS_WANT_CORRUPTED_RETURN(cur->bc_mp, i == 1);
  
  	return 0;
  }
  
  /*
   * Update the inobt based on a modification made to the finobt. Also ensure that
   * the records from both trees are equivalent post-modification.
   */
  STATIC int
  xfs_dialloc_ag_update_inobt(
  	struct xfs_btree_cur		*cur,	/* inobt cursor */
  	struct xfs_inobt_rec_incore	*frec,	/* finobt record */
  	int				offset) /* inode offset */
  {
  	struct xfs_inobt_rec_incore	rec;
  	int				error;
  	int				i;
  
  	error = xfs_inobt_lookup(cur, frec->ir_startino, XFS_LOOKUP_EQ, &i);
  	if (error)
  		return error;
  	XFS_WANT_CORRUPTED_RETURN(cur->bc_mp, i == 1);
  
  	error = xfs_inobt_get_rec(cur, &rec, &i);
  	if (error)
  		return error;
  	XFS_WANT_CORRUPTED_RETURN(cur->bc_mp, i == 1);
  	ASSERT((XFS_AGINO_TO_OFFSET(cur->bc_mp, rec.ir_startino) %
  				   XFS_INODES_PER_CHUNK) == 0);
  
  	rec.ir_free &= ~XFS_INOBT_MASK(offset);
  	rec.ir_freecount--;
  
  	XFS_WANT_CORRUPTED_RETURN(cur->bc_mp, (rec.ir_free == frec->ir_free) &&
  				  (rec.ir_freecount == frec->ir_freecount));
  
  	return xfs_inobt_update(cur, &rec);
  }
  
  /*
   * Allocate an inode using the free inode btree, if available. Otherwise, fall
   * back to the inobt search algorithm.
   *
   * The caller selected an AG for us, and made sure that free inodes are
   * available.
   */
  STATIC int
  xfs_dialloc_ag(
  	struct xfs_trans	*tp,
  	struct xfs_buf		*agbp,
  	xfs_ino_t		parent,
  	xfs_ino_t		*inop)
  {
  	struct xfs_mount		*mp = tp->t_mountp;
  	struct xfs_agi			*agi = XFS_BUF_TO_AGI(agbp);
  	xfs_agnumber_t			agno = be32_to_cpu(agi->agi_seqno);
  	xfs_agnumber_t			pagno = XFS_INO_TO_AGNO(mp, parent);
  	xfs_agino_t			pagino = XFS_INO_TO_AGINO(mp, parent);
  	struct xfs_perag		*pag;
  	struct xfs_btree_cur		*cur;	/* finobt cursor */
  	struct xfs_btree_cur		*icur;	/* inobt cursor */
  	struct xfs_inobt_rec_incore	rec;
  	xfs_ino_t			ino;
  	int				error;
  	int				offset;
  	int				i;
  
  	if (!xfs_sb_version_hasfinobt(&mp->m_sb))
  		return xfs_dialloc_ag_inobt(tp, agbp, parent, inop);
  
  	pag = xfs_perag_get(mp, agno);
  
  	/*
  	 * If pagino is 0 (this is the root inode allocation) use newino.
  	 * This must work because we've just allocated some.
  	 */
  	if (!pagino)
  		pagino = be32_to_cpu(agi->agi_newino);
  
  	cur = xfs_inobt_init_cursor(mp, tp, agbp, agno, XFS_BTNUM_FINO);
  
  	error = xfs_check_agi_freecount(cur, agi);
  	if (error)
  		goto error_cur;
  
  	/*
  	 * The search algorithm depends on whether we're in the same AG as the
  	 * parent. If so, find the closest available inode to the parent. If
  	 * not, consider the agi hint or find the first free inode in the AG.
  	 */
  	if (agno == pagno)
  		error = xfs_dialloc_ag_finobt_near(pagino, &cur, &rec);
  	else
  		error = xfs_dialloc_ag_finobt_newino(agi, cur, &rec);
  	if (error)
  		goto error_cur;
  
  	offset = xfs_inobt_first_free_inode(&rec);
  	ASSERT(offset >= 0);
  	ASSERT(offset < XFS_INODES_PER_CHUNK);
  	ASSERT((XFS_AGINO_TO_OFFSET(mp, rec.ir_startino) %
  				   XFS_INODES_PER_CHUNK) == 0);
  	ino = XFS_AGINO_TO_INO(mp, agno, rec.ir_startino + offset);
  
  	/*
  	 * Modify or remove the finobt record.
  	 */
  	rec.ir_free &= ~XFS_INOBT_MASK(offset);
  	rec.ir_freecount--;
  	if (rec.ir_freecount)
  		error = xfs_inobt_update(cur, &rec);
  	else
  		error = xfs_btree_delete(cur, &i);
  	if (error)
  		goto error_cur;
  
  	/*
  	 * The finobt has now been updated appropriately. We haven't updated the
  	 * agi and superblock yet, so we can create an inobt cursor and validate
  	 * the original freecount. If all is well, make the equivalent update to
  	 * the inobt using the finobt record and offset information.
  	 */
  	icur = xfs_inobt_init_cursor(mp, tp, agbp, agno, XFS_BTNUM_INO);
  
  	error = xfs_check_agi_freecount(icur, agi);
  	if (error)
  		goto error_icur;
  
  	error = xfs_dialloc_ag_update_inobt(icur, &rec, offset);
  	if (error)
  		goto error_icur;
  
  	/*
  	 * Both trees have now been updated. We must update the perag and
  	 * superblock before we can check the freecount for each btree.
  	 */
  	be32_add_cpu(&agi->agi_freecount, -1);
  	xfs_ialloc_log_agi(tp, agbp, XFS_AGI_FREECOUNT);
  	pag->pagi_freecount--;
  
  	xfs_trans_mod_sb(tp, XFS_TRANS_SB_IFREE, -1);
  
  	error = xfs_check_agi_freecount(icur, agi);
  	if (error)
  		goto error_icur;
  	error = xfs_check_agi_freecount(cur, agi);
  	if (error)
  		goto error_icur;
  
  	xfs_btree_del_cursor(icur, XFS_BTREE_NOERROR);
  	xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
  	xfs_perag_put(pag);
  	*inop = ino;
  	return 0;
  
  error_icur:
  	xfs_btree_del_cursor(icur, XFS_BTREE_ERROR);
  error_cur:
  	xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
  	xfs_perag_put(pag);
  	return error;
  }
  
  /*
   * Allocate an inode on disk.
   *
   * Mode is used to tell whether the new inode will need space, and whether it
   * is a directory.
   *
   * This function is designed to be called twice if it has to do an allocation
   * to make more free inodes.  On the first call, *IO_agbp should be set to NULL.
   * If an inode is available without having to performn an allocation, an inode
   * number is returned.  In this case, *IO_agbp is set to NULL.  If an allocation
   * needs to be done, xfs_dialloc returns the current AGI buffer in *IO_agbp.
   * The caller should then commit the current transaction, allocate a
   * new transaction, and call xfs_dialloc() again, passing in the previous value
   * of *IO_agbp.  IO_agbp should be held across the transactions. Since the AGI
   * buffer is locked across the two calls, the second call is guaranteed to have
   * a free inode available.
   *
   * Once we successfully pick an inode its number is returned and the on-disk
   * data structures are updated.  The inode itself is not read in, since doing so
   * would break ordering constraints with xfs_reclaim.
   */
  int
  xfs_dialloc(
  	struct xfs_trans	*tp,
  	xfs_ino_t		parent,
  	umode_t			mode,
  	int			okalloc,
  	struct xfs_buf		**IO_agbp,
  	xfs_ino_t		*inop)
  {
  	struct xfs_mount	*mp = tp->t_mountp;
  	struct xfs_buf		*agbp;
  	xfs_agnumber_t		agno;
  	int			error;
  	int			ialloced;
  	int			noroom = 0;
  	xfs_agnumber_t		start_agno;
  	struct xfs_perag	*pag;
  
  	if (*IO_agbp) {
  		/*
  		 * If the caller passes in a pointer to the AGI buffer,
  		 * continue where we left off before.  In this case, we
  		 * know that the allocation group has free inodes.
  		 */
  		agbp = *IO_agbp;
  		goto out_alloc;
  	}
  
  	/*
  	 * We do not have an agbp, so select an initial allocation
  	 * group for inode allocation.
  	 */
  	start_agno = xfs_ialloc_ag_select(tp, parent, mode, okalloc);
  	if (start_agno == NULLAGNUMBER) {
  		*inop = NULLFSINO;
  		return 0;
  	}
  
  	/*
  	 * If we have already hit the ceiling of inode blocks then clear
  	 * okalloc so we scan all available agi structures for a free
  	 * inode.
  	 *
  	 * Read rough value of mp->m_icount by percpu_counter_read_positive,
  	 * which will sacrifice the preciseness but improve the performance.
  	 */
  	if (mp->m_maxicount &&
  	    percpu_counter_read_positive(&mp->m_icount) + mp->m_ialloc_inos
  							> mp->m_maxicount) {
  		noroom = 1;
  		okalloc = 0;
  	}
  
  	/*
  	 * Loop until we find an allocation group that either has free inodes
  	 * or in which we can allocate some inodes.  Iterate through the
  	 * allocation groups upward, wrapping at the end.
  	 */
  	agno = start_agno;
  	for (;;) {
  		pag = xfs_perag_get(mp, agno);
  		if (!pag->pagi_inodeok) {
  			xfs_ialloc_next_ag(mp);
  			goto nextag;
  		}
  
  		if (!pag->pagi_init) {
  			error = xfs_ialloc_pagi_init(mp, tp, agno);
  			if (error)
  				goto out_error;
  		}
  
  		/*
  		 * Do a first racy fast path check if this AG is usable.
  		 */
  		if (!pag->pagi_freecount && !okalloc)
  			goto nextag;
  
  		/*
  		 * Then read in the AGI buffer and recheck with the AGI buffer
  		 * lock held.
  		 */
  		error = xfs_ialloc_read_agi(mp, tp, agno, &agbp);
  		if (error)
  			goto out_error;
  
  		if (pag->pagi_freecount) {
  			xfs_perag_put(pag);
  			goto out_alloc;
  		}
  
  		if (!okalloc)
  			goto nextag_relse_buffer;
  
  
  		error = xfs_ialloc_ag_alloc(tp, agbp, &ialloced);
  		if (error) {
  			xfs_trans_brelse(tp, agbp);
  
  			if (error != -ENOSPC)
  				goto out_error;
  
  			xfs_perag_put(pag);
  			*inop = NULLFSINO;
  			return 0;
  		}
  
  		if (ialloced) {
  			/*
  			 * We successfully allocated some inodes, return
  			 * the current context to the caller so that it
  			 * can commit the current transaction and call
  			 * us again where we left off.
  			 */
  			ASSERT(pag->pagi_freecount > 0);
  			xfs_perag_put(pag);
  
  			*IO_agbp = agbp;
  			*inop = NULLFSINO;
  			return 0;
  		}
  
  nextag_relse_buffer:
  		xfs_trans_brelse(tp, agbp);
  nextag:
  		xfs_perag_put(pag);
  		if (++agno == mp->m_sb.sb_agcount)
  			agno = 0;
  		if (agno == start_agno) {
  			*inop = NULLFSINO;
  			return noroom ? -ENOSPC : 0;
  		}
  	}
  
  out_alloc:
  	*IO_agbp = NULL;
  	return xfs_dialloc_ag(tp, agbp, parent, inop);
  out_error:
  	xfs_perag_put(pag);
  	return error;
  }
  
  /*
   * Free the blocks of an inode chunk. We must consider that the inode chunk
   * might be sparse and only free the regions that are allocated as part of the
   * chunk.
   */
  STATIC void
  xfs_difree_inode_chunk(
  	struct xfs_mount		*mp,
  	xfs_agnumber_t			agno,
  	struct xfs_inobt_rec_incore	*rec,
  	struct xfs_bmap_free		*flist)
  {
  	xfs_agblock_t	sagbno = XFS_AGINO_TO_AGBNO(mp, rec->ir_startino);
  	int		startidx, endidx;
  	int		nextbit;
  	xfs_agblock_t	agbno;
  	int		contigblk;
  	DECLARE_BITMAP(holemask, XFS_INOBT_HOLEMASK_BITS);
  
  	if (!xfs_inobt_issparse(rec->ir_holemask)) {
  		/* not sparse, calculate extent info directly */
  		xfs_bmap_add_free(XFS_AGB_TO_FSB(mp, agno,
  				  XFS_AGINO_TO_AGBNO(mp, rec->ir_startino)),
  				  mp->m_ialloc_blks, flist, mp);
  		return;
  	}
  
  	/* holemask is only 16-bits (fits in an unsigned long) */
  	ASSERT(sizeof(rec->ir_holemask) <= sizeof(holemask[0]));
  	holemask[0] = rec->ir_holemask;
  
  	/*
  	 * Find contiguous ranges of zeroes (i.e., allocated regions) in the
  	 * holemask and convert the start/end index of each range to an extent.
  	 * We start with the start and end index both pointing at the first 0 in
  	 * the mask.
  	 */
  	startidx = endidx = find_first_zero_bit(holemask,
  						XFS_INOBT_HOLEMASK_BITS);
  	nextbit = startidx + 1;
  	while (startidx < XFS_INOBT_HOLEMASK_BITS) {
  		nextbit = find_next_zero_bit(holemask, XFS_INOBT_HOLEMASK_BITS,
  					     nextbit);
  		/*
  		 * If the next zero bit is contiguous, update the end index of
  		 * the current range and continue.
  		 */
  		if (nextbit != XFS_INOBT_HOLEMASK_BITS &&
  		    nextbit == endidx + 1) {
  			endidx = nextbit;
  			goto next;
  		}
  
  		/*
  		 * nextbit is not contiguous with the current end index. Convert
  		 * the current start/end to an extent and add it to the free
  		 * list.
  		 */
  		agbno = sagbno + (startidx * XFS_INODES_PER_HOLEMASK_BIT) /
  				  mp->m_sb.sb_inopblock;
  		contigblk = ((endidx - startidx + 1) *
  			     XFS_INODES_PER_HOLEMASK_BIT) /
  			    mp->m_sb.sb_inopblock;
  
  		ASSERT(agbno % mp->m_sb.sb_spino_align == 0);
  		ASSERT(contigblk % mp->m_sb.sb_spino_align == 0);
  		xfs_bmap_add_free(XFS_AGB_TO_FSB(mp, agno, agbno), contigblk,
  				  flist, mp);
  
  		/* reset range to current bit and carry on... */
  		startidx = endidx = nextbit;
  
  next:
  		nextbit++;
  	}
  }
  
  STATIC int
  xfs_difree_inobt(
  	struct xfs_mount		*mp,
  	struct xfs_trans		*tp,
  	struct xfs_buf			*agbp,
  	xfs_agino_t			agino,
  	struct xfs_bmap_free		*flist,
  	struct xfs_icluster		*xic,
  	struct xfs_inobt_rec_incore	*orec)
  {
  	struct xfs_agi			*agi = XFS_BUF_TO_AGI(agbp);
  	xfs_agnumber_t			agno = be32_to_cpu(agi->agi_seqno);
  	struct xfs_perag		*pag;
  	struct xfs_btree_cur		*cur;
  	struct xfs_inobt_rec_incore	rec;
  	int				ilen;
  	int				error;
  	int				i;
  	int				off;
  
  	ASSERT(agi->agi_magicnum == cpu_to_be32(XFS_AGI_MAGIC));
  	ASSERT(XFS_AGINO_TO_AGBNO(mp, agino) < be32_to_cpu(agi->agi_length));
  
  	/*
  	 * Initialize the cursor.
  	 */
  	cur = xfs_inobt_init_cursor(mp, tp, agbp, agno, XFS_BTNUM_INO);
  
  	error = xfs_check_agi_freecount(cur, agi);
  	if (error)
  		goto error0;
  
  	/*
  	 * Look for the entry describing this inode.
  	 */
  	if ((error = xfs_inobt_lookup(cur, agino, XFS_LOOKUP_LE, &i))) {
  		xfs_warn(mp, "%s: xfs_inobt_lookup() returned error %d.",
  			__func__, error);
  		goto error0;
  	}
  	XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
  	error = xfs_inobt_get_rec(cur, &rec, &i);
  	if (error) {
  		xfs_warn(mp, "%s: xfs_inobt_get_rec() returned error %d.",
  			__func__, error);
  		goto error0;
  	}
  	XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
  	/*
  	 * Get the offset in the inode chunk.
  	 */
  	off = agino - rec.ir_startino;
  	ASSERT(off >= 0 && off < XFS_INODES_PER_CHUNK);
  	ASSERT(!(rec.ir_free & XFS_INOBT_MASK(off)));
  	/*
  	 * Mark the inode free & increment the count.
  	 */
  	rec.ir_free |= XFS_INOBT_MASK(off);
  	rec.ir_freecount++;
  
  	/*
  	 * When an inode chunk is free, it becomes eligible for removal. Don't
  	 * remove the chunk if the block size is large enough for multiple inode
  	 * chunks (that might not be free).
  	 */
  	if (!(mp->m_flags & XFS_MOUNT_IKEEP) &&
  	    rec.ir_free == XFS_INOBT_ALL_FREE &&
  	    mp->m_sb.sb_inopblock <= XFS_INODES_PER_CHUNK) {
  		xic->deleted = 1;
  		xic->first_ino = XFS_AGINO_TO_INO(mp, agno, rec.ir_startino);
  		xic->alloc = xfs_inobt_irec_to_allocmask(&rec);
  
  		/*
  		 * Remove the inode cluster from the AGI B+Tree, adjust the
  		 * AGI and Superblock inode counts, and mark the disk space
  		 * to be freed when the transaction is committed.
  		 */
  		ilen = rec.ir_freecount;
  		be32_add_cpu(&agi->agi_count, -ilen);
  		be32_add_cpu(&agi->agi_freecount, -(ilen - 1));
  		xfs_ialloc_log_agi(tp, agbp, XFS_AGI_COUNT | XFS_AGI_FREECOUNT);
  		pag = xfs_perag_get(mp, agno);
  		pag->pagi_freecount -= ilen - 1;
  		xfs_perag_put(pag);
  		xfs_trans_mod_sb(tp, XFS_TRANS_SB_ICOUNT, -ilen);
  		xfs_trans_mod_sb(tp, XFS_TRANS_SB_IFREE, -(ilen - 1));
  
  		if ((error = xfs_btree_delete(cur, &i))) {
  			xfs_warn(mp, "%s: xfs_btree_delete returned error %d.",
  				__func__, error);
  			goto error0;
  		}
  
  		xfs_difree_inode_chunk(mp, agno, &rec, flist);
  	} else {
  		xic->deleted = 0;
  
  		error = xfs_inobt_update(cur, &rec);
  		if (error) {
  			xfs_warn(mp, "%s: xfs_inobt_update returned error %d.",
  				__func__, error);
  			goto error0;
  		}
  
  		/* 
  		 * Change the inode free counts and log the ag/sb changes.
  		 */
  		be32_add_cpu(&agi->agi_freecount, 1);
  		xfs_ialloc_log_agi(tp, agbp, XFS_AGI_FREECOUNT);
  		pag = xfs_perag_get(mp, agno);
  		pag->pagi_freecount++;
  		xfs_perag_put(pag);
  		xfs_trans_mod_sb(tp, XFS_TRANS_SB_IFREE, 1);
  	}
  
  	error = xfs_check_agi_freecount(cur, agi);
  	if (error)
  		goto error0;
  
  	*orec = rec;
  	xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
  	return 0;
  
  error0:
  	xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
  	return error;
  }
  
  /*
   * Free an inode in the free inode btree.
   */
  STATIC int
  xfs_difree_finobt(
  	struct xfs_mount		*mp,
  	struct xfs_trans		*tp,
  	struct xfs_buf			*agbp,
  	xfs_agino_t			agino,
  	struct xfs_inobt_rec_incore	*ibtrec) /* inobt record */
  {
  	struct xfs_agi			*agi = XFS_BUF_TO_AGI(agbp);
  	xfs_agnumber_t			agno = be32_to_cpu(agi->agi_seqno);
  	struct xfs_btree_cur		*cur;
  	struct xfs_inobt_rec_incore	rec;
  	int				offset = agino - ibtrec->ir_startino;
  	int				error;
  	int				i;
  
  	cur = xfs_inobt_init_cursor(mp, tp, agbp, agno, XFS_BTNUM_FINO);
  
  	error = xfs_inobt_lookup(cur, ibtrec->ir_startino, XFS_LOOKUP_EQ, &i);
  	if (error)
  		goto error;
  	if (i == 0) {
  		/*
  		 * If the record does not exist in the finobt, we must have just
  		 * freed an inode in a previously fully allocated chunk. If not,
  		 * something is out of sync.
  		 */
  		XFS_WANT_CORRUPTED_GOTO(mp, ibtrec->ir_freecount == 1, error);
  
  		error = xfs_inobt_insert_rec(cur, ibtrec->ir_holemask,
  					     ibtrec->ir_count,
  					     ibtrec->ir_freecount,
  					     ibtrec->ir_free, &i);
  		if (error)
  			goto error;
  		ASSERT(i == 1);
  
  		goto out;
  	}
  
  	/*
  	 * Read and update the existing record. We could just copy the ibtrec
  	 * across here, but that would defeat the purpose of having redundant
  	 * metadata. By making the modifications independently, we can catch
  	 * corruptions that we wouldn't see if we just copied from one record
  	 * to another.
  	 */
  	error = xfs_inobt_get_rec(cur, &rec, &i);
  	if (error)
  		goto error;
  	XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error);
  
  	rec.ir_free |= XFS_INOBT_MASK(offset);
  	rec.ir_freecount++;
  
  	XFS_WANT_CORRUPTED_GOTO(mp, (rec.ir_free == ibtrec->ir_free) &&
  				(rec.ir_freecount == ibtrec->ir_freecount),
  				error);
  
  	/*
  	 * The content of inobt records should always match between the inobt
  	 * and finobt. The lifecycle of records in the finobt is different from
  	 * the inobt in that the finobt only tracks records with at least one
  	 * free inode. Hence, if all of the inodes are free and we aren't
  	 * keeping inode chunks permanently on disk, remove the record.
  	 * Otherwise, update the record with the new information.
  	 *
  	 * Note that we currently can't free chunks when the block size is large
  	 * enough for multiple chunks. Leave the finobt record to remain in sync
  	 * with the inobt.
  	 */
  	if (rec.ir_free == XFS_INOBT_ALL_FREE &&
  	    mp->m_sb.sb_inopblock <= XFS_INODES_PER_CHUNK &&
  	    !(mp->m_flags & XFS_MOUNT_IKEEP)) {
  		error = xfs_btree_delete(cur, &i);
  		if (error)
  			goto error;
  		ASSERT(i == 1);
  	} else {
  		error = xfs_inobt_update(cur, &rec);
  		if (error)
  			goto error;
  	}
  
  out:
  	error = xfs_check_agi_freecount(cur, agi);
  	if (error)
  		goto error;
  
  	xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
  	return 0;
  
  error:
  	xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
  	return error;
  }
  
  /*
   * Free disk inode.  Carefully avoids touching the incore inode, all
   * manipulations incore are the caller's responsibility.
   * The on-disk inode is not changed by this operation, only the
   * btree (free inode mask) is changed.
   */
  int
  xfs_difree(
  	struct xfs_trans	*tp,		/* transaction pointer */
  	xfs_ino_t		inode,		/* inode to be freed */
  	struct xfs_bmap_free	*flist,		/* extents to free */
  	struct xfs_icluster	*xic)	/* cluster info if deleted */
  {
  	/* REFERENCED */
  	xfs_agblock_t		agbno;	/* block number containing inode */
  	struct xfs_buf		*agbp;	/* buffer for allocation group header */
  	xfs_agino_t		agino;	/* allocation group inode number */
  	xfs_agnumber_t		agno;	/* allocation group number */
  	int			error;	/* error return value */
  	struct xfs_mount	*mp;	/* mount structure for filesystem */
  	struct xfs_inobt_rec_incore rec;/* btree record */
  
  	mp = tp->t_mountp;
  
  	/*
  	 * Break up inode number into its components.
  	 */
  	agno = XFS_INO_TO_AGNO(mp, inode);
  	if (agno >= mp->m_sb.sb_agcount)  {
  		xfs_warn(mp, "%s: agno >= mp->m_sb.sb_agcount (%d >= %d).",
  			__func__, agno, mp->m_sb.sb_agcount);
  		ASSERT(0);
  		return -EINVAL;
  	}
  	agino = XFS_INO_TO_AGINO(mp, inode);
  	if (inode != XFS_AGINO_TO_INO(mp, agno, agino))  {
  		xfs_warn(mp, "%s: inode != XFS_AGINO_TO_INO() (%llu != %llu).",
  			__func__, (unsigned long long)inode,
  			(unsigned long long)XFS_AGINO_TO_INO(mp, agno, agino));
  		ASSERT(0);
  		return -EINVAL;
  	}
  	agbno = XFS_AGINO_TO_AGBNO(mp, agino);
  	if (agbno >= mp->m_sb.sb_agblocks)  {
  		xfs_warn(mp, "%s: agbno >= mp->m_sb.sb_agblocks (%d >= %d).",
  			__func__, agbno, mp->m_sb.sb_agblocks);
  		ASSERT(0);
  		return -EINVAL;
  	}
  	/*
  	 * Get the allocation group header.
  	 */
  	error = xfs_ialloc_read_agi(mp, tp, agno, &agbp);
  	if (error) {
  		xfs_warn(mp, "%s: xfs_ialloc_read_agi() returned error %d.",
  			__func__, error);
  		return error;
  	}
  
  	/*
  	 * Fix up the inode allocation btree.
  	 */
  	error = xfs_difree_inobt(mp, tp, agbp, agino, flist, xic, &rec);
  	if (error)
  		goto error0;
  
  	/*
  	 * Fix up the free inode btree.
  	 */
  	if (xfs_sb_version_hasfinobt(&mp->m_sb)) {
  		error = xfs_difree_finobt(mp, tp, agbp, agino, &rec);
  		if (error)
  			goto error0;
  	}
  
  	return 0;
  
  error0:
  	return error;
  }
  
  STATIC int
  xfs_imap_lookup(
  	struct xfs_mount	*mp,
  	struct xfs_trans	*tp,
  	xfs_agnumber_t		agno,
  	xfs_agino_t		agino,
  	xfs_agblock_t		agbno,
  	xfs_agblock_t		*chunk_agbno,
  	xfs_agblock_t		*offset_agbno,
  	int			flags)
  {
  	struct xfs_inobt_rec_incore rec;
  	struct xfs_btree_cur	*cur;
  	struct xfs_buf		*agbp;
  	int			error;
  	int			i;
  
  	error = xfs_ialloc_read_agi(mp, tp, agno, &agbp);
  	if (error) {
  		xfs_alert(mp,
  			"%s: xfs_ialloc_read_agi() returned error %d, agno %d",
  			__func__, error, agno);
  		return error;
  	}
  
  	/*
  	 * Lookup the inode record for the given agino. If the record cannot be
  	 * found, then it's an invalid inode number and we should abort. Once
  	 * we have a record, we need to ensure it contains the inode number
  	 * we are looking up.
  	 */
  	cur = xfs_inobt_init_cursor(mp, tp, agbp, agno, XFS_BTNUM_INO);
  	error = xfs_inobt_lookup(cur, agino, XFS_LOOKUP_LE, &i);
  	if (!error) {
  		if (i)
  			error = xfs_inobt_get_rec(cur, &rec, &i);
  		if (!error && i == 0)
  			error = -EINVAL;
  	}
  
  	xfs_trans_brelse(tp, agbp);
  	xfs_btree_del_cursor(cur, error ? XFS_BTREE_ERROR : XFS_BTREE_NOERROR);
  	if (error)
  		return error;
  
  	/* check that the returned record contains the required inode */
  	if (rec.ir_startino > agino ||
  	    rec.ir_startino + mp->m_ialloc_inos <= agino)
  		return -EINVAL;
  
  	/* for untrusted inodes check it is allocated first */
  	if ((flags & XFS_IGET_UNTRUSTED) &&
  	    (rec.ir_free & XFS_INOBT_MASK(agino - rec.ir_startino)))
  		return -EINVAL;
  
  	*chunk_agbno = XFS_AGINO_TO_AGBNO(mp, rec.ir_startino);
  	*offset_agbno = agbno - *chunk_agbno;
  	return 0;
  }
  
  /*
   * Return the location of the inode in imap, for mapping it into a buffer.
   */
  int
  xfs_imap(
  	xfs_mount_t	 *mp,	/* file system mount structure */
  	xfs_trans_t	 *tp,	/* transaction pointer */
  	xfs_ino_t	ino,	/* inode to locate */
  	struct xfs_imap	*imap,	/* location map structure */
  	uint		flags)	/* flags for inode btree lookup */
  {
  	xfs_agblock_t	agbno;	/* block number of inode in the alloc group */
  	xfs_agino_t	agino;	/* inode number within alloc group */
  	xfs_agnumber_t	agno;	/* allocation group number */
  	int		blks_per_cluster; /* num blocks per inode cluster */
  	xfs_agblock_t	chunk_agbno;	/* first block in inode chunk */
  	xfs_agblock_t	cluster_agbno;	/* first block in inode cluster */
  	int		error;	/* error code */
  	int		offset;	/* index of inode in its buffer */
  	xfs_agblock_t	offset_agbno;	/* blks from chunk start to inode */
  
  	ASSERT(ino != NULLFSINO);
  
  	/*
  	 * Split up the inode number into its parts.
  	 */
  	agno = XFS_INO_TO_AGNO(mp, ino);
  	agino = XFS_INO_TO_AGINO(mp, ino);
  	agbno = XFS_AGINO_TO_AGBNO(mp, agino);
  	if (agno >= mp->m_sb.sb_agcount || agbno >= mp->m_sb.sb_agblocks ||
  	    ino != XFS_AGINO_TO_INO(mp, agno, agino)) {
  #ifdef DEBUG
  		/*
  		 * Don't output diagnostic information for untrusted inodes
  		 * as they can be invalid without implying corruption.
  		 */
  		if (flags & XFS_IGET_UNTRUSTED)
  			return -EINVAL;
  		if (agno >= mp->m_sb.sb_agcount) {
  			xfs_alert(mp,
  				"%s: agno (%d) >= mp->m_sb.sb_agcount (%d)",
  				__func__, agno, mp->m_sb.sb_agcount);
  		}
  		if (agbno >= mp->m_sb.sb_agblocks) {
  			xfs_alert(mp,
  		"%s: agbno (0x%llx) >= mp->m_sb.sb_agblocks (0x%lx)",
  				__func__, (unsigned long long)agbno,
  				(unsigned long)mp->m_sb.sb_agblocks);
  		}
  		if (ino != XFS_AGINO_TO_INO(mp, agno, agino)) {
  			xfs_alert(mp,
  		"%s: ino (0x%llx) != XFS_AGINO_TO_INO() (0x%llx)",
  				__func__, ino,
  				XFS_AGINO_TO_INO(mp, agno, agino));
  		}
  		xfs_stack_trace();
  #endif /* DEBUG */
  		return -EINVAL;
  	}
  
  	blks_per_cluster = xfs_icluster_size_fsb(mp);
  
  	/*
  	 * For bulkstat and handle lookups, we have an untrusted inode number
  	 * that we have to verify is valid. We cannot do this just by reading
  	 * the inode buffer as it may have been unlinked and removed leaving
  	 * inodes in stale state on disk. Hence we have to do a btree lookup
  	 * in all cases where an untrusted inode number is passed.
  	 */
  	if (flags & XFS_IGET_UNTRUSTED) {
  		error = xfs_imap_lookup(mp, tp, agno, agino, agbno,
  					&chunk_agbno, &offset_agbno, flags);
  		if (error)
  			return error;
  		goto out_map;
  	}
  
  	/*
  	 * If the inode cluster size is the same as the blocksize or
  	 * smaller we get to the buffer by simple arithmetics.
  	 */
  	if (blks_per_cluster == 1) {
  		offset = XFS_INO_TO_OFFSET(mp, ino);
  		ASSERT(offset < mp->m_sb.sb_inopblock);
  
  		imap->im_blkno = XFS_AGB_TO_DADDR(mp, agno, agbno);
  		imap->im_len = XFS_FSB_TO_BB(mp, 1);
  		imap->im_boffset = (ushort)(offset << mp->m_sb.sb_inodelog);
  		return 0;
  	}
  
  	/*
  	 * If the inode chunks are aligned then use simple maths to
  	 * find the location. Otherwise we have to do a btree
  	 * lookup to find the location.
  	 */
  	if (mp->m_inoalign_mask) {
  		offset_agbno = agbno & mp->m_inoalign_mask;
  		chunk_agbno = agbno - offset_agbno;
  	} else {
  		error = xfs_imap_lookup(mp, tp, agno, agino, agbno,
  					&chunk_agbno, &offset_agbno, flags);
  		if (error)
  			return error;
  	}
  
  out_map:
  	ASSERT(agbno >= chunk_agbno);
  	cluster_agbno = chunk_agbno +
  		((offset_agbno / blks_per_cluster) * blks_per_cluster);
  	offset = ((agbno - cluster_agbno) * mp->m_sb.sb_inopblock) +
  		XFS_INO_TO_OFFSET(mp, ino);
  
  	imap->im_blkno = XFS_AGB_TO_DADDR(mp, agno, cluster_agbno);
  	imap->im_len = XFS_FSB_TO_BB(mp, blks_per_cluster);
  	imap->im_boffset = (ushort)(offset << mp->m_sb.sb_inodelog);
  
  	/*
  	 * If the inode number maps to a block outside the bounds
  	 * of the file system then return NULL rather than calling
  	 * read_buf and panicing when we get an error from the
  	 * driver.
  	 */
  	if ((imap->im_blkno + imap->im_len) >
  	    XFS_FSB_TO_BB(mp, mp->m_sb.sb_dblocks)) {
  		xfs_alert(mp,
  	"%s: (im_blkno (0x%llx) + im_len (0x%llx)) > sb_dblocks (0x%llx)",
  			__func__, (unsigned long long) imap->im_blkno,
  			(unsigned long long) imap->im_len,
  			XFS_FSB_TO_BB(mp, mp->m_sb.sb_dblocks));
  		return -EINVAL;
  	}
  	return 0;
  }
  
  /*
   * Compute and fill in value of m_in_maxlevels.
   */
  void
  xfs_ialloc_compute_maxlevels(
  	xfs_mount_t	*mp)		/* file system mount structure */
  {
  	int		level;
  	uint		maxblocks;
  	uint		maxleafents;
  	int		minleafrecs;
  	int		minnoderecs;
  
  	maxleafents = (1LL << XFS_INO_AGINO_BITS(mp)) >>
  		XFS_INODES_PER_CHUNK_LOG;
  	minleafrecs = mp->m_alloc_mnr[0];
  	minnoderecs = mp->m_alloc_mnr[1];
  	maxblocks = (maxleafents + minleafrecs - 1) / minleafrecs;
  	for (level = 1; maxblocks > 1; level++)
  		maxblocks = (maxblocks + minnoderecs - 1) / minnoderecs;
  	mp->m_in_maxlevels = level;
  }
  
  /*
   * Log specified fields for the ag hdr (inode section). The growth of the agi
   * structure over time requires that we interpret the buffer as two logical
   * regions delineated by the end of the unlinked list. This is due to the size
   * of the hash table and its location in the middle of the agi.
   *
   * For example, a request to log a field before agi_unlinked and a field after
   * agi_unlinked could cause us to log the entire hash table and use an excessive
   * amount of log space. To avoid this behavior, log the region up through
   * agi_unlinked in one call and the region after agi_unlinked through the end of
   * the structure in another.
   */
  void
  xfs_ialloc_log_agi(
  	xfs_trans_t	*tp,		/* transaction pointer */
  	xfs_buf_t	*bp,		/* allocation group header buffer */
  	int		fields)		/* bitmask of fields to log */
  {
  	int			first;		/* first byte number */
  	int			last;		/* last byte number */
  	static const short	offsets[] = {	/* field starting offsets */
  					/* keep in sync with bit definitions */
  		offsetof(xfs_agi_t, agi_magicnum),
  		offsetof(xfs_agi_t, agi_versionnum),
  		offsetof(xfs_agi_t, agi_seqno),
  		offsetof(xfs_agi_t, agi_length),
  		offsetof(xfs_agi_t, agi_count),
  		offsetof(xfs_agi_t, agi_root),
  		offsetof(xfs_agi_t, agi_level),
  		offsetof(xfs_agi_t, agi_freecount),
  		offsetof(xfs_agi_t, agi_newino),
  		offsetof(xfs_agi_t, agi_dirino),
  		offsetof(xfs_agi_t, agi_unlinked),
  		offsetof(xfs_agi_t, agi_free_root),
  		offsetof(xfs_agi_t, agi_free_level),
  		sizeof(xfs_agi_t)
  	};
  #ifdef DEBUG
  	xfs_agi_t		*agi;	/* allocation group header */
  
  	agi = XFS_BUF_TO_AGI(bp);
  	ASSERT(agi->agi_magicnum == cpu_to_be32(XFS_AGI_MAGIC));
  #endif
  
  	xfs_trans_buf_set_type(tp, bp, XFS_BLFT_AGI_BUF);
  
  	/*
  	 * Compute byte offsets for the first and last fields in the first
  	 * region and log the agi buffer. This only logs up through
  	 * agi_unlinked.
  	 */
  	if (fields & XFS_AGI_ALL_BITS_R1) {
  		xfs_btree_offsets(fields, offsets, XFS_AGI_NUM_BITS_R1,
  				  &first, &last);
  		xfs_trans_log_buf(tp, bp, first, last);
  	}
  
  	/*
  	 * Mask off the bits in the first region and calculate the first and
  	 * last field offsets for any bits in the second region.
  	 */
  	fields &= ~XFS_AGI_ALL_BITS_R1;
  	if (fields) {
  		xfs_btree_offsets(fields, offsets, XFS_AGI_NUM_BITS_R2,
  				  &first, &last);
  		xfs_trans_log_buf(tp, bp, first, last);
  	}
  }
  
  #ifdef DEBUG
  STATIC void
  xfs_check_agi_unlinked(
  	struct xfs_agi		*agi)
  {
  	int			i;
  
  	for (i = 0; i < XFS_AGI_UNLINKED_BUCKETS; i++)
  		ASSERT(agi->agi_unlinked[i]);
  }
  #else
  #define xfs_check_agi_unlinked(agi)
  #endif
  
  static bool
  xfs_agi_verify(
  	struct xfs_buf	*bp)
  {
  	struct xfs_mount *mp = bp->b_target->bt_mount;
  	struct xfs_agi	*agi = XFS_BUF_TO_AGI(bp);
  
  	if (xfs_sb_version_hascrc(&mp->m_sb)) {
  		if (!uuid_equal(&agi->agi_uuid, &mp->m_sb.sb_meta_uuid))
  			return false;
  		if (!xfs_log_check_lsn(mp,
  				be64_to_cpu(XFS_BUF_TO_AGI(bp)->agi_lsn)))
  			return false;
  	}
  
  	/*
  	 * Validate the magic number of the agi block.
  	 */
  	if (agi->agi_magicnum != cpu_to_be32(XFS_AGI_MAGIC))
  		return false;
  	if (!XFS_AGI_GOOD_VERSION(be32_to_cpu(agi->agi_versionnum)))
  		return false;
  
  	if (be32_to_cpu(agi->agi_level) > XFS_BTREE_MAXLEVELS)
  		return false;
  	/*
  	 * during growfs operations, the perag is not fully initialised,
  	 * so we can't use it for any useful checking. growfs ensures we can't
  	 * use it by using uncached buffers that don't have the perag attached
  	 * so we can detect and avoid this problem.
  	 */
  	if (bp->b_pag && be32_to_cpu(agi->agi_seqno) != bp->b_pag->pag_agno)
  		return false;
  
  	xfs_check_agi_unlinked(agi);
  	return true;
  }
  
  static void
  xfs_agi_read_verify(
  	struct xfs_buf	*bp)
  {
  	struct xfs_mount *mp = bp->b_target->bt_mount;
  
  	if (xfs_sb_version_hascrc(&mp->m_sb) &&
  	    !xfs_buf_verify_cksum(bp, XFS_AGI_CRC_OFF))
  		xfs_buf_ioerror(bp, -EFSBADCRC);
  	else if (XFS_TEST_ERROR(!xfs_agi_verify(bp), mp,
  				XFS_ERRTAG_IALLOC_READ_AGI,
  				XFS_RANDOM_IALLOC_READ_AGI))
  		xfs_buf_ioerror(bp, -EFSCORRUPTED);
  
  	if (bp->b_error)
  		xfs_verifier_error(bp);
  }
  
  static void
  xfs_agi_write_verify(
  	struct xfs_buf	*bp)
  {
  	struct xfs_mount *mp = bp->b_target->bt_mount;
  	struct xfs_buf_log_item	*bip = bp->b_fspriv;
  
  	if (!xfs_agi_verify(bp)) {
  		xfs_buf_ioerror(bp, -EFSCORRUPTED);
  		xfs_verifier_error(bp);
  		return;
  	}
  
  	if (!xfs_sb_version_hascrc(&mp->m_sb))
  		return;
  
  	if (bip)
  		XFS_BUF_TO_AGI(bp)->agi_lsn = cpu_to_be64(bip->bli_item.li_lsn);
  	xfs_buf_update_cksum(bp, XFS_AGI_CRC_OFF);
  }
  
  const struct xfs_buf_ops xfs_agi_buf_ops = {
  	.name = "xfs_agi",
  	.verify_read = xfs_agi_read_verify,
  	.verify_write = xfs_agi_write_verify,
  };
  
  /*
   * Read in the allocation group header (inode allocation section)
   */
  int
  xfs_read_agi(
  	struct xfs_mount	*mp,	/* file system mount structure */
  	struct xfs_trans	*tp,	/* transaction pointer */
  	xfs_agnumber_t		agno,	/* allocation group number */
  	struct xfs_buf		**bpp)	/* allocation group hdr buf */
  {
  	int			error;
  
  	trace_xfs_read_agi(mp, agno);
  
  	ASSERT(agno != NULLAGNUMBER);
  	error = xfs_trans_read_buf(mp, tp, mp->m_ddev_targp,
  			XFS_AG_DADDR(mp, agno, XFS_AGI_DADDR(mp)),
  			XFS_FSS_TO_BB(mp, 1), 0, bpp, &xfs_agi_buf_ops);
  	if (error)
  		return error;
  
  	xfs_buf_set_ref(*bpp, XFS_AGI_REF);
  	return 0;
  }
  
  int
  xfs_ialloc_read_agi(
  	struct xfs_mount	*mp,	/* file system mount structure */
  	struct xfs_trans	*tp,	/* transaction pointer */
  	xfs_agnumber_t		agno,	/* allocation group number */
  	struct xfs_buf		**bpp)	/* allocation group hdr buf */
  {
  	struct xfs_agi		*agi;	/* allocation group header */
  	struct xfs_perag	*pag;	/* per allocation group data */
  	int			error;
  
  	trace_xfs_ialloc_read_agi(mp, agno);
  
  	error = xfs_read_agi(mp, tp, agno, bpp);
  	if (error)
  		return error;
  
  	agi = XFS_BUF_TO_AGI(*bpp);
  	pag = xfs_perag_get(mp, agno);
  	if (!pag->pagi_init) {
  		pag->pagi_freecount = be32_to_cpu(agi->agi_freecount);
  		pag->pagi_count = be32_to_cpu(agi->agi_count);
  		pag->pagi_init = 1;
  	}
  
  	/*
  	 * It's possible for these to be out of sync if
  	 * we are in the middle of a forced shutdown.
  	 */
  	ASSERT(pag->pagi_freecount == be32_to_cpu(agi->agi_freecount) ||
  		XFS_FORCED_SHUTDOWN(mp));
  	xfs_perag_put(pag);
  	return 0;
  }
  
  /*
   * Read in the agi to initialise the per-ag data in the mount structure
   */
  int
  xfs_ialloc_pagi_init(
  	xfs_mount_t	*mp,		/* file system mount structure */
  	xfs_trans_t	*tp,		/* transaction pointer */
  	xfs_agnumber_t	agno)		/* allocation group number */
  {
  	xfs_buf_t	*bp = NULL;
  	int		error;
  
  	error = xfs_ialloc_read_agi(mp, tp, agno, &bp);
  	if (error)
  		return error;
  	if (bp)
  		xfs_trans_brelse(tp, bp);
  	return 0;
  }
  