xfs_bmap_util.c

/*
 * Copyright (c) 2000-2006 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_format.h"
#include "xfs_bit.h"
#include "xfs_log.h"
#include "xfs_inum.h"
#include "xfs_trans.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_mount.h"
#include "xfs_da_btree.h"
#include "xfs_bmap_btree.h"
#include "xfs_alloc_btree.h"
#include "xfs_ialloc_btree.h"
#include "xfs_dinode.h"
#include "xfs_inode.h"
#include "xfs_btree.h"
#include "xfs_extfree_item.h"
#include "xfs_alloc.h"
#include "xfs_bmap.h"
#include "xfs_bmap_util.h"
#include "xfs_rtalloc.h"
#include "xfs_error.h"
#include "xfs_quota.h"
#include "xfs_trans_space.h"
#include "xfs_trace.h"

/* Kernel only BMAP related definitions and functions */

/*
 * Convert the given file system block to a disk block.  We have to treat it
 * differently based on whether the file is a real time file or not, because the
 * bmap code does.
 */
xfs_daddr_t
xfs_fsb_to_db(struct xfs_inode *ip, xfs_fsblock_t fsb)
{
	return (XFS_IS_REALTIME_INODE(ip) ? \
		 (xfs_daddr_t)XFS_FSB_TO_BB((ip)->i_mount, (fsb)) : \
		 XFS_FSB_TO_DADDR((ip)->i_mount, (fsb)));
}

/*
 * Routine to be called at transaction's end by xfs_bmapi, xfs_bunmapi
 * caller.  Frees all the extents that need freeing, which must be done
 * last due to locking considerations.  We never free any extents in
 * the first transaction.
 *
 * Return 1 if the given transaction was committed and a new one
 * started, and 0 otherwise in the committed parameter.
 */
int						/* error */
xfs_bmap_finish(
	xfs_trans_t		**tp,		/* transaction pointer addr */
	xfs_bmap_free_t		*flist,		/* i/o: list extents to free */
	int			*committed)	/* xact committed or not */
{
	xfs_efd_log_item_t	*efd;		/* extent free data */
	xfs_efi_log_item_t	*efi;		/* extent free intention */
	int			error;		/* error return value */
	xfs_bmap_free_item_t	*free;		/* free extent item */
	unsigned int		logres;		/* new log reservation */
	unsigned int		logcount;	/* new log count */
	xfs_mount_t		*mp;		/* filesystem mount structure */
	xfs_bmap_free_item_t	*next;		/* next item on free list */
	xfs_trans_t		*ntp;		/* new transaction pointer */

	ASSERT((*tp)->t_flags & XFS_TRANS_PERM_LOG_RES);
	if (flist->xbf_count == 0) {
		*committed = 0;
		return 0;
	}
	ntp = *tp;
	efi = xfs_trans_get_efi(ntp, flist->xbf_count);
	for (free = flist->xbf_first; free; free = free->xbfi_next)
		xfs_trans_log_efi_extent(ntp, efi, free->xbfi_startblock,
			free->xbfi_blockcount);
	logres = ntp->t_log_res;
	logcount = ntp->t_log_count;
	ntp = xfs_trans_dup(*tp);
	error = xfs_trans_commit(*tp, 0);
	*tp = ntp;
	*committed = 1;
	/*
	 * We have a new transaction, so we should return committed=1,
	 * even though we're returning an error.
	 */
	if (error)
		return error;

	/*
	 * transaction commit worked ok so we can drop the extra ticket
	 * reference that we gained in xfs_trans_dup()
	 */
	xfs_log_ticket_put(ntp->t_ticket);

	if ((error = xfs_trans_reserve(ntp, 0, logres, 0, XFS_TRANS_PERM_LOG_RES,
			logcount)))
		return error;
	efd = xfs_trans_get_efd(ntp, efi, flist->xbf_count);
	for (free = flist->xbf_first; free != NULL; free = next) {
		next = free->xbfi_next;
		if ((error = xfs_free_extent(ntp, free->xbfi_startblock,
				free->xbfi_blockcount))) {
			/*
			 * The bmap free list will be cleaned up at a
			 * higher level.  The EFI will be canceled when
			 * this transaction is aborted.
			 * Need to force shutdown here to make sure it
			 * happens, since this transaction may not be
			 * dirty yet.
			 */
			mp = ntp->t_mountp;
			if (!XFS_FORCED_SHUTDOWN(mp))
				xfs_force_shutdown(mp,
						   (error == EFSCORRUPTED) ?
						   SHUTDOWN_CORRUPT_INCORE :
						   SHUTDOWN_META_IO_ERROR);
			return error;
		}
		xfs_trans_log_efd_extent(ntp, efd, free->xbfi_startblock,
			free->xbfi_blockcount);
		xfs_bmap_del_free(flist, NULL, free);
	}
	return 0;
}

int
xfs_bmap_rtalloc(
	struct xfs_bmalloca	*ap)	/* bmap alloc argument struct */
{
	xfs_alloctype_t	atype = 0;	/* type for allocation routines */
	int		error;		/* error return value */
	xfs_mount_t	*mp;		/* mount point structure */
	xfs_extlen_t	prod = 0;	/* product factor for allocators */
	xfs_extlen_t	ralen = 0;	/* realtime allocation length */
	xfs_extlen_t	align;		/* minimum allocation alignment */
	xfs_rtblock_t	rtb;

	mp = ap->ip->i_mount;
	align = xfs_get_extsz_hint(ap->ip);
	prod = align / mp->m_sb.sb_rextsize;
	error = xfs_bmap_extsize_align(mp, &ap->got, &ap->prev,
					align, 1, ap->eof, 0,
					ap->conv, &ap->offset, &ap->length);
	if (error)
		return error;
	ASSERT(ap->length);
	ASSERT(ap->length % mp->m_sb.sb_rextsize == 0);

	/*
	 * If the offset & length are not perfectly aligned
	 * then kill prod, it will just get us in trouble.
	 */
	if (do_mod(ap->offset, align) || ap->length % align)
		prod = 1;
	/*
	 * Set ralen to be the actual requested length in rtextents.
	 */
	ralen = ap->length / mp->m_sb.sb_rextsize;
	/*
	 * If the old value was close enough to MAXEXTLEN that
	 * we rounded up to it, cut it back so it's valid again.
	 * Note that if it's a really large request (bigger than
	 * MAXEXTLEN), we don't hear about that number, and can't
	 * adjust the starting point to match it.
	 */
	if (ralen * mp->m_sb.sb_rextsize >= MAXEXTLEN)
		ralen = MAXEXTLEN / mp->m_sb.sb_rextsize;

	/*
	 * Lock out other modifications to the RT bitmap inode.
	 */
	xfs_ilock(mp->m_rbmip, XFS_ILOCK_EXCL);
	xfs_trans_ijoin(ap->tp, mp->m_rbmip, XFS_ILOCK_EXCL);

	/*
	 * If it's an allocation to an empty file at offset 0,
	 * pick an extent that will space things out in the rt area.
	 */
	if (ap->eof && ap->offset == 0) {
		xfs_rtblock_t uninitialized_var(rtx); /* realtime extent no */

		error = xfs_rtpick_extent(mp, ap->tp, ralen, &rtx);
		if (error)
			return error;
		ap->blkno = rtx * mp->m_sb.sb_rextsize;
	} else {
		ap->blkno = 0;
	}

	xfs_bmap_adjacent(ap);

	/*
	 * Realtime allocation, done through xfs_rtallocate_extent.
	 */
	atype = ap->blkno == 0 ?  XFS_ALLOCTYPE_ANY_AG : XFS_ALLOCTYPE_NEAR_BNO;
	do_div(ap->blkno, mp->m_sb.sb_rextsize);
	rtb = ap->blkno;
	ap->length = ralen;
	if ((error = xfs_rtallocate_extent(ap->tp, ap->blkno, 1, ap->length,
				&ralen, atype, ap->wasdel, prod, &rtb)))
		return error;
	if (rtb == NULLFSBLOCK && prod > 1 &&
	    (error = xfs_rtallocate_extent(ap->tp, ap->blkno, 1,
					   ap->length, &ralen, atype,
					   ap->wasdel, 1, &rtb)))
		return error;
	ap->blkno = rtb;
	if (ap->blkno != NULLFSBLOCK) {
		ap->blkno *= mp->m_sb.sb_rextsize;
		ralen *= mp->m_sb.sb_rextsize;
		ap->length = ralen;
		ap->ip->i_d.di_nblocks += ralen;
		xfs_trans_log_inode(ap->tp, ap->ip, XFS_ILOG_CORE);
		if (ap->wasdel)
			ap->ip->i_delayed_blks -= ralen;
		/*
		 * Adjust the disk quota also. This was reserved
		 * earlier.
		 */
		xfs_trans_mod_dquot_byino(ap->tp, ap->ip,
			ap->wasdel ? XFS_TRANS_DQ_DELRTBCOUNT :
					XFS_TRANS_DQ_RTBCOUNT, (long) ralen);
	} else {
		ap->length = 0;
	}
	return 0;
}

/*
 * Stack switching interfaces for allocation
 */
static void
xfs_bmapi_allocate_worker(
	struct work_struct	*work)
{
	struct xfs_bmalloca	*args = container_of(work,
						struct xfs_bmalloca, work);
	unsigned long		pflags;

	/* we are in a transaction context here */
	current_set_flags_nested(&pflags, PF_FSTRANS);

	args->result = __xfs_bmapi_allocate(args);
	complete(args->done);

	current_restore_flags_nested(&pflags, PF_FSTRANS);
}

/*
 * Some allocation requests often come in with little stack to work on. Push
 * them off to a worker thread so there is lots of stack to use. Otherwise just
 * call directly to avoid the context switch overhead here.
 */
int
xfs_bmapi_allocate(
	struct xfs_bmalloca	*args)
{
	DECLARE_COMPLETION_ONSTACK(done);

	if (!args->stack_switch)
		return __xfs_bmapi_allocate(args);


	args->done = &done;
	INIT_WORK_ONSTACK(&args->work, xfs_bmapi_allocate_worker);
	queue_work(xfs_alloc_wq, &args->work);
	wait_for_completion(&done);
	return args->result;
}

/*
 * Check if the endoff is outside the last extent. If so the caller will grow
 * the allocation to a stripe unit boundary.  All offsets are considered outside
 * the end of file for an empty fork, so 1 is returned in *eof in that case.
 */
int
xfs_bmap_eof(
	struct xfs_inode	*ip,
	xfs_fileoff_t		endoff,
	int			whichfork,
	int			*eof)
{
	struct xfs_bmbt_irec	rec;
	int			error;

	error = xfs_bmap_last_extent(NULL, ip, whichfork, &rec, eof);
	if (error || *eof)
		return error;

	*eof = endoff >= rec.br_startoff + rec.br_blockcount;
	return 0;
}

/*
 * Extent tree block counting routines.
 */

/*
 * Count leaf blocks given a range of extent records.
 */
STATIC void
xfs_bmap_count_leaves(
	xfs_ifork_t		*ifp,
	xfs_extnum_t		idx,
	int			numrecs,
	int			*count)
{
	int		b;

	for (b = 0; b < numrecs; b++) {
		xfs_bmbt_rec_host_t *frp = xfs_iext_get_ext(ifp, idx + b);
		*count += xfs_bmbt_get_blockcount(frp);
	}
}

/*
 * Count leaf blocks given a range of extent records originally
 * in btree format.
 */
STATIC void
xfs_bmap_disk_count_leaves(
	struct xfs_mount	*mp,
	struct xfs_btree_block	*block,
	int			numrecs,
	int			*count)
{
	int		b;
	xfs_bmbt_rec_t	*frp;

	for (b = 1; b <= numrecs; b++) {
		frp = XFS_BMBT_REC_ADDR(mp, block, b);
		*count += xfs_bmbt_disk_get_blockcount(frp);
	}
}

/*
 * Recursively walks each level of a btree
 * to count total fsblocks is use.
 */
STATIC int                                     /* error */
xfs_bmap_count_tree(
	xfs_mount_t     *mp,            /* file system mount point */
	xfs_trans_t     *tp,            /* transaction pointer */
	xfs_ifork_t	*ifp,		/* inode fork pointer */
	xfs_fsblock_t   blockno,	/* file system block number */
	int             levelin,	/* level in btree */
	int		*count)		/* Count of blocks */
{
	int			error;
	xfs_buf_t		*bp, *nbp;
	int			level = levelin;
	__be64			*pp;
	xfs_fsblock_t           bno = blockno;
	xfs_fsblock_t		nextbno;
	struct xfs_btree_block	*block, *nextblock;
	int			numrecs;

	error = xfs_btree_read_bufl(mp, tp, bno, 0, &bp, XFS_BMAP_BTREE_REF,
						&xfs_bmbt_buf_ops);
	if (error)
		return error;
	*count += 1;
	block = XFS_BUF_TO_BLOCK(bp);

	if (--level) {
		/* Not at node above leaves, count this level of nodes */
		nextbno = be64_to_cpu(block->bb_u.l.bb_rightsib);
		while (nextbno != NULLFSBLOCK) {
			error = xfs_btree_read_bufl(mp, tp, nextbno, 0, &nbp,
						XFS_BMAP_BTREE_REF,
						&xfs_bmbt_buf_ops);
			if (error)
				return error;
			*count += 1;
			nextblock = XFS_BUF_TO_BLOCK(nbp);
			nextbno = be64_to_cpu(nextblock->bb_u.l.bb_rightsib);
			xfs_trans_brelse(tp, nbp);
		}

		/* Dive to the next level */
		pp = XFS_BMBT_PTR_ADDR(mp, block, 1, mp->m_bmap_dmxr[1]);
		bno = be64_to_cpu(*pp);
		if (unlikely((error =
		     xfs_bmap_count_tree(mp, tp, ifp, bno, level, count)) < 0)) {
			xfs_trans_brelse(tp, bp);
			XFS_ERROR_REPORT("xfs_bmap_count_tree(1)",
					 XFS_ERRLEVEL_LOW, mp);
			return XFS_ERROR(EFSCORRUPTED);
		}
		xfs_trans_brelse(tp, bp);
	} else {
		/* count all level 1 nodes and their leaves */
		for (;;) {
			nextbno = be64_to_cpu(block->bb_u.l.bb_rightsib);
			numrecs = be16_to_cpu(block->bb_numrecs);
			xfs_bmap_disk_count_leaves(mp, block, numrecs, count);
			xfs_trans_brelse(tp, bp);
			if (nextbno == NULLFSBLOCK)
				break;
			bno = nextbno;
			error = xfs_btree_read_bufl(mp, tp, bno, 0, &bp,
						XFS_BMAP_BTREE_REF,
						&xfs_bmbt_buf_ops);
			if (error)
				return error;
			*count += 1;
			block = XFS_BUF_TO_BLOCK(bp);
		}
	}
	return 0;
}

/*
 * Count fsblocks of the given fork.
 */
int						/* error */
xfs_bmap_count_blocks(
	xfs_trans_t		*tp,		/* transaction pointer */
	xfs_inode_t		*ip,		/* incore inode */
	int			whichfork,	/* data or attr fork */
	int			*count)		/* out: count of blocks */
{
	struct xfs_btree_block	*block;	/* current btree block */
	xfs_fsblock_t		bno;	/* block # of "block" */
	xfs_ifork_t		*ifp;	/* fork structure */
	int			level;	/* btree level, for checking */
	xfs_mount_t		*mp;	/* file system mount structure */
	__be64			*pp;	/* pointer to block address */

	bno = NULLFSBLOCK;
	mp = ip->i_mount;
	ifp = XFS_IFORK_PTR(ip, whichfork);
	if ( XFS_IFORK_FORMAT(ip, whichfork) == XFS_DINODE_FMT_EXTENTS ) {
		xfs_bmap_count_leaves(ifp, 0,
			ifp->if_bytes / (uint)sizeof(xfs_bmbt_rec_t),
			count);
		return 0;
	}

	/*
	 * Root level must use BMAP_BROOT_PTR_ADDR macro to get ptr out.
	 */
	block = ifp->if_broot;
	level = be16_to_cpu(block->bb_level);
	ASSERT(level > 0);
	pp = XFS_BMAP_BROOT_PTR_ADDR(mp, block, 1, ifp->if_broot_bytes);
	bno = be64_to_cpu(*pp);
	ASSERT(bno != NULLDFSBNO);
	ASSERT(XFS_FSB_TO_AGNO(mp, bno) < mp->m_sb.sb_agcount);
	ASSERT(XFS_FSB_TO_AGBNO(mp, bno) < mp->m_sb.sb_agblocks);

	if (unlikely(xfs_bmap_count_tree(mp, tp, ifp, bno, level, count) < 0)) {
		XFS_ERROR_REPORT("xfs_bmap_count_blocks(2)", XFS_ERRLEVEL_LOW,
				 mp);
		return XFS_ERROR(EFSCORRUPTED);
	}

	return 0;
}

/*
 * returns 1 for success, 0 if we failed to map the extent.
 */
STATIC int
xfs_getbmapx_fix_eof_hole(
	xfs_inode_t		*ip,		/* xfs incore inode pointer */
	struct getbmapx		*out,		/* output structure */
	int			prealloced,	/* this is a file with
						 * preallocated data space */
	__int64_t		end,		/* last block requested */
	xfs_fsblock_t		startblock)
{
	__int64_t		fixlen;
	xfs_mount_t		*mp;		/* file system mount point */
	xfs_ifork_t		*ifp;		/* inode fork pointer */
	xfs_extnum_t		lastx;		/* last extent pointer */
	xfs_fileoff_t		fileblock;

	if (startblock == HOLESTARTBLOCK) {
		mp = ip->i_mount;
		out->bmv_block = -1;
		fixlen = XFS_FSB_TO_BB(mp, XFS_B_TO_FSB(mp, XFS_ISIZE(ip)));
		fixlen -= out->bmv_offset;
		if (prealloced && out->bmv_offset + out->bmv_length == end) {
			/* Came to hole at EOF. Trim it. */
			if (fixlen <= 0)
				return 0;
			out->bmv_length = fixlen;
		}
	} else {
		if (startblock == DELAYSTARTBLOCK)
			out->bmv_block = -2;
		else
			out->bmv_block = xfs_fsb_to_db(ip, startblock);
		fileblock = XFS_BB_TO_FSB(ip->i_mount, out->bmv_offset);
		ifp = XFS_IFORK_PTR(ip, XFS_DATA_FORK);
		if (xfs_iext_bno_to_ext(ifp, fileblock, &lastx) &&
		   (lastx == (ifp->if_bytes / (uint)sizeof(xfs_bmbt_rec_t))-1))
			out->bmv_oflags |= BMV_OF_LAST;
	}

	return 1;
}

/*
 * Get inode's extents as described in bmv, and format for output.
 * Calls formatter to fill the user's buffer until all extents
 * are mapped, until the passed-in bmv->bmv_count slots have
 * been filled, or until the formatter short-circuits the loop,
 * if it is tracking filled-in extents on its own.
 */
int						/* error code */
xfs_getbmap(
	xfs_inode_t		*ip,
	struct getbmapx		*bmv,		/* user bmap structure */
	xfs_bmap_format_t	formatter,	/* format to user */
	void			*arg)		/* formatter arg */
{
	__int64_t		bmvend;		/* last block requested */
	int			error = 0;	/* return value */
	__int64_t		fixlen;		/* length for -1 case */
	int			i;		/* extent number */
	int			lock;		/* lock state */
	xfs_bmbt_irec_t		*map;		/* buffer for user's data */
	xfs_mount_t		*mp;		/* file system mount point */
	int			nex;		/* # of user extents can do */
	int			nexleft;	/* # of user extents left */
	int			subnex;		/* # of bmapi's can do */
	int			nmap;		/* number of map entries */
	struct getbmapx		*out;		/* output structure */
	int			whichfork;	/* data or attr fork */
	int			prealloced;	/* this is a file with
						 * preallocated data space */
	int			iflags;		/* interface flags */
	int			bmapi_flags;	/* flags for xfs_bmapi */
	int			cur_ext = 0;

	mp = ip->i_mount;
	iflags = bmv->bmv_iflags;
	whichfork = iflags & BMV_IF_ATTRFORK ? XFS_ATTR_FORK : XFS_DATA_FORK;

	if (whichfork == XFS_ATTR_FORK) {
		if (XFS_IFORK_Q(ip)) {
			if (ip->i_d.di_aformat != XFS_DINODE_FMT_EXTENTS &&
			    ip->i_d.di_aformat != XFS_DINODE_FMT_BTREE &&
			    ip->i_d.di_aformat != XFS_DINODE_FMT_LOCAL)
				return XFS_ERROR(EINVAL);
		} else if (unlikely(
			   ip->i_d.di_aformat != 0 &&
			   ip->i_d.di_aformat != XFS_DINODE_FMT_EXTENTS)) {
			XFS_ERROR_REPORT("xfs_getbmap", XFS_ERRLEVEL_LOW,
					 ip->i_mount);
			return XFS_ERROR(EFSCORRUPTED);
		}

		prealloced = 0;
		fixlen = 1LL << 32;
	} else {
		if (ip->i_d.di_format != XFS_DINODE_FMT_EXTENTS &&
		    ip->i_d.di_format != XFS_DINODE_FMT_BTREE &&
		    ip->i_d.di_format != XFS_DINODE_FMT_LOCAL)
			return XFS_ERROR(EINVAL);

		if (xfs_get_extsz_hint(ip) ||
		    ip->i_d.di_flags & (XFS_DIFLAG_PREALLOC|XFS_DIFLAG_APPEND)){
			prealloced = 1;
			fixlen = mp->m_super->s_maxbytes;
		} else {
			prealloced = 0;
			fixlen = XFS_ISIZE(ip);
		}
	}

	if (bmv->bmv_length == -1) {
		fixlen = XFS_FSB_TO_BB(mp, XFS_B_TO_FSB(mp, fixlen));
		bmv->bmv_length =
			max_t(__int64_t, fixlen - bmv->bmv_offset, 0);
	} else if (bmv->bmv_length == 0) {
		bmv->bmv_entries = 0;
		return 0;
	} else if (bmv->bmv_length < 0) {
		return XFS_ERROR(EINVAL);
	}

	nex = bmv->bmv_count - 1;
	if (nex <= 0)
		return XFS_ERROR(EINVAL);
	bmvend = bmv->bmv_offset + bmv->bmv_length;


	if (bmv->bmv_count > ULONG_MAX / sizeof(struct getbmapx))
		return XFS_ERROR(ENOMEM);
	out = kmem_zalloc(bmv->bmv_count * sizeof(struct getbmapx), KM_MAYFAIL);
	if (!out) {
		out = kmem_zalloc_large(bmv->bmv_count *
					sizeof(struct getbmapx));
		if (!out)
			return XFS_ERROR(ENOMEM);
	}

	xfs_ilock(ip, XFS_IOLOCK_SHARED);
	if (whichfork == XFS_DATA_FORK && !(iflags & BMV_IF_DELALLOC)) {
		if (ip->i_delayed_blks || XFS_ISIZE(ip) > ip->i_d.di_size) {
			error = -filemap_write_and_wait(VFS_I(ip)->i_mapping);
			if (error)
				goto out_unlock_iolock;
		}
		/*
		 * even after flushing the inode, there can still be delalloc
		 * blocks on the inode beyond EOF due to speculative
		 * preallocation. These are not removed until the release
		 * function is called or the inode is inactivated. Hence we
		 * cannot assert here that ip->i_delayed_blks == 0.
		 */
	}

	lock = xfs_ilock_map_shared(ip);

	/*
	 * Don't let nex be bigger than the number of extents
	 * we can have assuming alternating holes and real extents.
	 */
	if (nex > XFS_IFORK_NEXTENTS(ip, whichfork) * 2 + 1)
		nex = XFS_IFORK_NEXTENTS(ip, whichfork) * 2 + 1;

	bmapi_flags = xfs_bmapi_aflag(whichfork);
	if (!(iflags & BMV_IF_PREALLOC))
		bmapi_flags |= XFS_BMAPI_IGSTATE;

	/*
	 * Allocate enough space to handle "subnex" maps at a time.
	 */
	error = ENOMEM;
	subnex = 16;
	map = kmem_alloc(subnex * sizeof(*map), KM_MAYFAIL | KM_NOFS);
	if (!map)
		goto out_unlock_ilock;

	bmv->bmv_entries = 0;

	if (XFS_IFORK_NEXTENTS(ip, whichfork) == 0 &&
	    (whichfork == XFS_ATTR_FORK || !(iflags & BMV_IF_DELALLOC))) {
		error = 0;
		goto out_free_map;
	}

	nexleft = nex;

	do {
		nmap = (nexleft > subnex) ? subnex : nexleft;
		error = xfs_bmapi_read(ip, XFS_BB_TO_FSBT(mp, bmv->bmv_offset),
				       XFS_BB_TO_FSB(mp, bmv->bmv_length),
				       map, &nmap, bmapi_flags);
		if (error)
			goto out_free_map;
		ASSERT(nmap <= subnex);

		for (i = 0; i < nmap && nexleft && bmv->bmv_length; i++) {
			out[cur_ext].bmv_oflags = 0;
			if (map[i].br_state == XFS_EXT_UNWRITTEN)
				out[cur_ext].bmv_oflags |= BMV_OF_PREALLOC;
			else if (map[i].br_startblock == DELAYSTARTBLOCK)
				out[cur_ext].bmv_oflags |= BMV_OF_DELALLOC;
			out[cur_ext].bmv_offset =
				XFS_FSB_TO_BB(mp, map[i].br_startoff);
			out[cur_ext].bmv_length =
				XFS_FSB_TO_BB(mp, map[i].br_blockcount);
			out[cur_ext].bmv_unused1 = 0;
			out[cur_ext].bmv_unused2 = 0;

			/*
			 * delayed allocation extents that start beyond EOF can
			 * occur due to speculative EOF allocation when the
			 * delalloc extent is larger than the largest freespace
			 * extent at conversion time. These extents cannot be
			 * converted by data writeback, so can exist here even
			 * if we are not supposed to be finding delalloc
			 * extents.
			 */
			if (map[i].br_startblock == DELAYSTARTBLOCK &&
			    map[i].br_startoff <= XFS_B_TO_FSB(mp, XFS_ISIZE(ip)))
				ASSERT((iflags & BMV_IF_DELALLOC) != 0);

                        if (map[i].br_startblock == HOLESTARTBLOCK &&
			    whichfork == XFS_ATTR_FORK) {
				/* came to the end of attribute fork */
				out[cur_ext].bmv_oflags |= BMV_OF_LAST;
				goto out_free_map;
			}

			if (!xfs_getbmapx_fix_eof_hole(ip, &out[cur_ext],
					prealloced, bmvend,
					map[i].br_startblock))
				goto out_free_map;

			bmv->bmv_offset =
				out[cur_ext].bmv_offset +
				out[cur_ext].bmv_length;
			bmv->bmv_length =
				max_t(__int64_t, 0, bmvend - bmv->bmv_offset);

			/*
			 * In case we don't want to return the hole,
			 * don't increase cur_ext so that we can reuse
			 * it in the next loop.
			 */
			if ((iflags & BMV_IF_NO_HOLES) &&
			    map[i].br_startblock == HOLESTARTBLOCK) {
				memset(&out[cur_ext], 0, sizeof(out[cur_ext]));
				continue;
			}

			nexleft--;
			bmv->bmv_entries++;
			cur_ext++;
		}
	} while (nmap && nexleft && bmv->bmv_length);

 out_free_map:
	kmem_free(map);
 out_unlock_ilock:
	xfs_iunlock_map_shared(ip, lock);
 out_unlock_iolock:
	xfs_iunlock(ip, XFS_IOLOCK_SHARED);

	for (i = 0; i < cur_ext; i++) {
		int full = 0;	/* user array is full */

		/* format results & advance arg */
		error = formatter(&arg, &out[i], &full);
		if (error || full)
			break;
	}

	if (is_vmalloc_addr(out))
		kmem_free_large(out);
	else
		kmem_free(out);
	return error;
}

/*
 * dead simple method of punching delalyed allocation blocks from a range in
 * the inode. Walks a block at a time so will be slow, but is only executed in
 * rare error cases so the overhead is not critical. This will alays punch out
 * both the start and end blocks, even if the ranges only partially overlap
 * them, so it is up to the caller to ensure that partial blocks are not
 * passed in.
 */
int
xfs_bmap_punch_delalloc_range(
	struct xfs_inode	*ip,
	xfs_fileoff_t		start_fsb,
	xfs_fileoff_t		length)
{
	xfs_fileoff_t		remaining = length;
	int			error = 0;

	ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));

	do {
		int		done;
		xfs_bmbt_irec_t	imap;
		int		nimaps = 1;
		xfs_fsblock_t	firstblock;
		xfs_bmap_free_t flist;

		/*
		 * Map the range first and check that it is a delalloc extent
		 * before trying to unmap the range. Otherwise we will be
		 * trying to remove a real extent (which requires a
		 * transaction) or a hole, which is probably a bad idea...
		 */
		error = xfs_bmapi_read(ip, start_fsb, 1, &imap, &nimaps,
				       XFS_BMAPI_ENTIRE);

		if (error) {
			/* something screwed, just bail */
			if (!XFS_FORCED_SHUTDOWN(ip->i_mount)) {
				xfs_alert(ip->i_mount,
			"Failed delalloc mapping lookup ino %lld fsb %lld.",
						ip->i_ino, start_fsb);
			}
			break;
		}
		if (!nimaps) {
			/* nothing there */
			goto next_block;
		}
		if (imap.br_startblock != DELAYSTARTBLOCK) {
			/* been converted, ignore */
			goto next_block;
		}
		WARN_ON(imap.br_blockcount == 0);

		/*
		 * Note: while we initialise the firstblock/flist pair, they
		 * should never be used because blocks should never be
		 * allocated or freed for a delalloc extent and hence we need
		 * don't cancel or finish them after the xfs_bunmapi() call.
		 */
		xfs_bmap_init(&flist, &firstblock);
		error = xfs_bunmapi(NULL, ip, start_fsb, 1, 0, 1, &firstblock,
					&flist, &done);
		if (error)
			break;

		ASSERT(!flist.xbf_count && !flist.xbf_first);
next_block:
		start_fsb++;
		remaining--;
	} while(remaining > 0);

	return error;
}