fs/xfs/libxfs/xfs_rmap_btree.c - kernel/msm-4.9 - Gitiles

 /*
  * Copyright (c) 2014 Red Hat, Inc.
  * All Rights Reserved.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
  * published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it would be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write the Free Software Foundation,
  * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
 #include "xfs.h"
 #include "xfs_fs.h"
 #include "xfs_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_defer.h"
 #include "xfs_inode.h"
 #include "xfs_trans.h"
 #include "xfs_alloc.h"
 #include "xfs_btree.h"
 #include "xfs_rmap.h"
 #include "xfs_rmap_btree.h"
 #include "xfs_trace.h"
 #include "xfs_cksum.h"
 #include "xfs_error.h"
 #include "xfs_extent_busy.h"
 #include "xfs_ag_resv.h"

 /*
  * Reverse map btree.
  *
  * This is a per-ag tree used to track the owner(s) of a given extent. With
  * reflink it is possible for there to be multiple owners, which is a departure
  * from classic XFS. Owner records for data extents are inserted when the
  * extent is mapped and removed when an extent is unmapped.  Owner records for
  * all other block types (i.e. metadata) are inserted when an extent is
  * allocated and removed when an extent is freed. There can only be one owner
  * of a metadata extent, usually an inode or some other metadata structure like
  * an AG btree.
  *
  * The rmap btree is part of the free space management, so blocks for the tree
  * are sourced from the agfl. Hence we need transaction reservation support for
  * this tree so that the freelist is always large enough. This also impacts on
  * the minimum space we need to leave free in the AG.
  *
  * The tree is ordered by [ag block, owner, offset]. This is a large key size,
  * but it is the only way to enforce unique keys when a block can be owned by
  * multiple files at any offset. There's no need to order/search by extent
  * size for online updating/management of the tree. It is intended that most
  * reverse lookups will be to find the owner(s) of a particular block, or to
  * try to recover tree and file data from corrupt primary metadata.
  */

 static struct xfs_btree_cur *
 xfs_rmapbt_dup_cursor(
 	struct xfs_btree_cur	*cur)
 {
 	return xfs_rmapbt_init_cursor(cur->bc_mp, cur->bc_tp,
 			cur->bc_private.a.agbp, cur->bc_private.a.agno);
 }

 STATIC void
 xfs_rmapbt_set_root(
 	struct xfs_btree_cur	*cur,
 	union xfs_btree_ptr	*ptr,
 	int			inc)
 {
 	struct xfs_buf		*agbp = cur->bc_private.a.agbp;
 	struct xfs_agf		*agf = XFS_BUF_TO_AGF(agbp);
 	xfs_agnumber_t		seqno = be32_to_cpu(agf->agf_seqno);
 	int			btnum = cur->bc_btnum;
 	struct xfs_perag	*pag = xfs_perag_get(cur->bc_mp, seqno);

 	ASSERT(ptr->s != 0);

 	agf->agf_roots[btnum] = ptr->s;
 	be32_add_cpu(&agf->agf_levels[btnum], inc);
 	pag->pagf_levels[btnum] += inc;
 	xfs_perag_put(pag);

 	xfs_alloc_log_agf(cur->bc_tp, agbp, XFS_AGF_ROOTS | XFS_AGF_LEVELS);
 }

 STATIC int
 xfs_rmapbt_alloc_block(
 	struct xfs_btree_cur	*cur,
 	union xfs_btree_ptr	*start,
 	union xfs_btree_ptr	*new,
 	int			*stat)
 {
 	struct xfs_buf		*agbp = cur->bc_private.a.agbp;
 	struct xfs_agf		*agf = XFS_BUF_TO_AGF(agbp);
 	int			error;
 	xfs_agblock_t		bno;

 	XFS_BTREE_TRACE_CURSOR(cur, XBT_ENTRY);

 	/* Allocate the new block from the freelist. If we can't, give up.  */
 	error = xfs_alloc_get_freelist(cur->bc_tp, cur->bc_private.a.agbp,
 				       &bno, 1);
 	if (error) {
 		XFS_BTREE_TRACE_CURSOR(cur, XBT_ERROR);
 		return error;
 	}

 	trace_xfs_rmapbt_alloc_block(cur->bc_mp, cur->bc_private.a.agno,
 			bno, 1);
 	if (bno == NULLAGBLOCK) {
 		XFS_BTREE_TRACE_CURSOR(cur, XBT_EXIT);
 		*stat = 0;
 		return 0;
 	}

 	xfs_extent_busy_reuse(cur->bc_mp, cur->bc_private.a.agno, bno, 1,
 			false);

 	xfs_trans_agbtree_delta(cur->bc_tp, 1);
 	new->s = cpu_to_be32(bno);
 	be32_add_cpu(&agf->agf_rmap_blocks, 1);
 	xfs_alloc_log_agf(cur->bc_tp, agbp, XFS_AGF_RMAP_BLOCKS);

 	XFS_BTREE_TRACE_CURSOR(cur, XBT_EXIT);
 	*stat = 1;
 	return 0;
 }

 STATIC int
 xfs_rmapbt_free_block(
 	struct xfs_btree_cur	*cur,
 	struct xfs_buf		*bp)
 {
 	struct xfs_buf		*agbp = cur->bc_private.a.agbp;
 	struct xfs_agf		*agf = XFS_BUF_TO_AGF(agbp);
 	xfs_agblock_t		bno;
 	int			error;

 	bno = xfs_daddr_to_agbno(cur->bc_mp, XFS_BUF_ADDR(bp));
 	trace_xfs_rmapbt_free_block(cur->bc_mp, cur->bc_private.a.agno,
 			bno, 1);
 	be32_add_cpu(&agf->agf_rmap_blocks, -1);
 	xfs_alloc_log_agf(cur->bc_tp, agbp, XFS_AGF_RMAP_BLOCKS);
 	error = xfs_alloc_put_freelist(cur->bc_tp, agbp, NULL, bno, 1);
 	if (error)
 		return error;

 	xfs_extent_busy_insert(cur->bc_tp, be32_to_cpu(agf->agf_seqno), bno, 1,
 			      XFS_EXTENT_BUSY_SKIP_DISCARD);
 	xfs_trans_agbtree_delta(cur->bc_tp, -1);

 	return 0;
 }

 STATIC int
 xfs_rmapbt_get_minrecs(
 	struct xfs_btree_cur	*cur,
 	int			level)
 {
 	return cur->bc_mp->m_rmap_mnr[level != 0];
 }

 STATIC int
 xfs_rmapbt_get_maxrecs(
 	struct xfs_btree_cur	*cur,
 	int			level)
 {
 	return cur->bc_mp->m_rmap_mxr[level != 0];
 }

 STATIC void
 xfs_rmapbt_init_key_from_rec(
 	union xfs_btree_key	*key,
 	union xfs_btree_rec	*rec)
 {
 	key->rmap.rm_startblock = rec->rmap.rm_startblock;
 	key->rmap.rm_owner = rec->rmap.rm_owner;
 	key->rmap.rm_offset = rec->rmap.rm_offset;
 }

 /*
  * The high key for a reverse mapping record can be computed by shifting
  * the startblock and offset to the highest value that would still map
  * to that record.  In practice this means that we add blockcount-1 to
  * the startblock for all records, and if the record is for a data/attr
  * fork mapping, we add blockcount-1 to the offset too.
  */
 STATIC void
 xfs_rmapbt_init_high_key_from_rec(
 	union xfs_btree_key	*key,
 	union xfs_btree_rec	*rec)
 {
 	__uint64_t		off;
 	int			adj;

 	adj = be32_to_cpu(rec->rmap.rm_blockcount) - 1;

 	key->rmap.rm_startblock = rec->rmap.rm_startblock;
 	be32_add_cpu(&key->rmap.rm_startblock, adj);
 	key->rmap.rm_owner = rec->rmap.rm_owner;
 	key->rmap.rm_offset = rec->rmap.rm_offset;
 	if (XFS_RMAP_NON_INODE_OWNER(be64_to_cpu(rec->rmap.rm_owner)) ||
 	    XFS_RMAP_IS_BMBT_BLOCK(be64_to_cpu(rec->rmap.rm_offset)))
 		return;
 	off = be64_to_cpu(key->rmap.rm_offset);
 	off = (XFS_RMAP_OFF(off) + adj) | (off & ~XFS_RMAP_OFF_MASK);
 	key->rmap.rm_offset = cpu_to_be64(off);
 }

 STATIC void
 xfs_rmapbt_init_rec_from_cur(
 	struct xfs_btree_cur	*cur,
 	union xfs_btree_rec	*rec)
 {
 	rec->rmap.rm_startblock = cpu_to_be32(cur->bc_rec.r.rm_startblock);
 	rec->rmap.rm_blockcount = cpu_to_be32(cur->bc_rec.r.rm_blockcount);
 	rec->rmap.rm_owner = cpu_to_be64(cur->bc_rec.r.rm_owner);
 	rec->rmap.rm_offset = cpu_to_be64(
 			xfs_rmap_irec_offset_pack(&cur->bc_rec.r));
 }

 STATIC void
 xfs_rmapbt_init_ptr_from_cur(
 	struct xfs_btree_cur	*cur,
 	union xfs_btree_ptr	*ptr)
 {
 	struct xfs_agf		*agf = XFS_BUF_TO_AGF(cur->bc_private.a.agbp);

 	ASSERT(cur->bc_private.a.agno == be32_to_cpu(agf->agf_seqno));
 	ASSERT(agf->agf_roots[cur->bc_btnum] != 0);

 	ptr->s = agf->agf_roots[cur->bc_btnum];
 }

 STATIC __int64_t
 xfs_rmapbt_key_diff(
 	struct xfs_btree_cur	*cur,
 	union xfs_btree_key	*key)
 {
 	struct xfs_rmap_irec	*rec = &cur->bc_rec.r;
 	struct xfs_rmap_key	*kp = &key->rmap;
 	__u64			x, y;
 	__int64_t		d;

 	d = (__int64_t)be32_to_cpu(kp->rm_startblock) - rec->rm_startblock;
 	if (d)
 		return d;

 	x = be64_to_cpu(kp->rm_owner);
 	y = rec->rm_owner;
 	if (x > y)
 		return 1;
 	else if (y > x)
 		return -1;

 	x = XFS_RMAP_OFF(be64_to_cpu(kp->rm_offset));
 	y = rec->rm_offset;
 	if (x > y)
 		return 1;
 	else if (y > x)
 		return -1;
 	return 0;
 }

 STATIC __int64_t
 xfs_rmapbt_diff_two_keys(
 	struct xfs_btree_cur	*cur,
 	union xfs_btree_key	*k1,
 	union xfs_btree_key	*k2)
 {
 	struct xfs_rmap_key	*kp1 = &k1->rmap;
 	struct xfs_rmap_key	*kp2 = &k2->rmap;
 	__int64_t		d;
 	__u64			x, y;

 	d = (__int64_t)be32_to_cpu(kp1->rm_startblock) -
 		       be32_to_cpu(kp2->rm_startblock);
 	if (d)
 		return d;

 	x = be64_to_cpu(kp1->rm_owner);
 	y = be64_to_cpu(kp2->rm_owner);
 	if (x > y)
 		return 1;
 	else if (y > x)
 		return -1;

 	x = XFS_RMAP_OFF(be64_to_cpu(kp1->rm_offset));
 	y = XFS_RMAP_OFF(be64_to_cpu(kp2->rm_offset));
 	if (x > y)
 		return 1;
 	else if (y > x)
 		return -1;
 	return 0;
 }

 static bool
 xfs_rmapbt_verify(
 	struct xfs_buf		*bp)
 {
 	struct xfs_mount	*mp = bp->b_target->bt_mount;
 	struct xfs_btree_block	*block = XFS_BUF_TO_BLOCK(bp);
 	struct xfs_perag	*pag = bp->b_pag;
 	unsigned int		level;

 	/*
 	 * magic number and level verification
 	 *
 	 * During growfs operations, we can't verify the exact level or owner as
 	 * the perag is not fully initialised and hence not attached to the
 	 * buffer.  In this case, check against the maximum tree depth.
 	 *
 	 * Similarly, during log recovery we will have a perag structure
 	 * attached, but the agf information will not yet have been initialised
 	 * from the on disk AGF. Again, we can only check against maximum limits
 	 * in this case.
 	 */
 	if (block->bb_magic != cpu_to_be32(XFS_RMAP_CRC_MAGIC))
 		return false;

 	if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
 		return false;
 	if (!xfs_btree_sblock_v5hdr_verify(bp))
 		return false;

 	level = be16_to_cpu(block->bb_level);
 	if (pag && pag->pagf_init) {
 		if (level >= pag->pagf_levels[XFS_BTNUM_RMAPi])
 			return false;
 	} else if (level >= mp->m_rmap_maxlevels)
 		return false;

 	return xfs_btree_sblock_verify(bp, mp->m_rmap_mxr[level != 0]);
 }

 static void
 xfs_rmapbt_read_verify(
 	struct xfs_buf	*bp)
 {
 	if (!xfs_btree_sblock_verify_crc(bp))
 		xfs_buf_ioerror(bp, -EFSBADCRC);
 	else if (!xfs_rmapbt_verify(bp))
 		xfs_buf_ioerror(bp, -EFSCORRUPTED);

 	if (bp->b_error) {
 		trace_xfs_btree_corrupt(bp, _RET_IP_);
 		xfs_verifier_error(bp);
 	}
 }

 static void
 xfs_rmapbt_write_verify(
 	struct xfs_buf	*bp)
 {
 	if (!xfs_rmapbt_verify(bp)) {
 		trace_xfs_btree_corrupt(bp, _RET_IP_);
 		xfs_buf_ioerror(bp, -EFSCORRUPTED);
 		xfs_verifier_error(bp);
 		return;
 	}
 	xfs_btree_sblock_calc_crc(bp);

 }

 const struct xfs_buf_ops xfs_rmapbt_buf_ops = {
 	.name			= "xfs_rmapbt",
 	.verify_read		= xfs_rmapbt_read_verify,
 	.verify_write		= xfs_rmapbt_write_verify,
 };

 #if defined(DEBUG) || defined(XFS_WARN)
 STATIC int
 xfs_rmapbt_keys_inorder(
 	struct xfs_btree_cur	*cur,
 	union xfs_btree_key	*k1,
 	union xfs_btree_key	*k2)
 {
 	__uint32_t		x;
 	__uint32_t		y;
 	__uint64_t		a;
 	__uint64_t		b;

 	x = be32_to_cpu(k1->rmap.rm_startblock);
 	y = be32_to_cpu(k2->rmap.rm_startblock);
 	if (x < y)
 		return 1;
 	else if (x > y)
 		return 0;
 	a = be64_to_cpu(k1->rmap.rm_owner);
 	b = be64_to_cpu(k2->rmap.rm_owner);
 	if (a < b)
 		return 1;
 	else if (a > b)
 		return 0;
 	a = XFS_RMAP_OFF(be64_to_cpu(k1->rmap.rm_offset));
 	b = XFS_RMAP_OFF(be64_to_cpu(k2->rmap.rm_offset));
 	if (a <= b)
 		return 1;
 	return 0;
 }

 STATIC int
 xfs_rmapbt_recs_inorder(
 	struct xfs_btree_cur	*cur,
 	union xfs_btree_rec	*r1,
 	union xfs_btree_rec	*r2)
 {
 	__uint32_t		x;
 	__uint32_t		y;
 	__uint64_t		a;
 	__uint64_t		b;

 	x = be32_to_cpu(r1->rmap.rm_startblock);
 	y = be32_to_cpu(r2->rmap.rm_startblock);
 	if (x < y)
 		return 1;
 	else if (x > y)
 		return 0;
 	a = be64_to_cpu(r1->rmap.rm_owner);
 	b = be64_to_cpu(r2->rmap.rm_owner);
 	if (a < b)
 		return 1;
 	else if (a > b)
 		return 0;
 	a = XFS_RMAP_OFF(be64_to_cpu(r1->rmap.rm_offset));
 	b = XFS_RMAP_OFF(be64_to_cpu(r2->rmap.rm_offset));
 	if (a <= b)
 		return 1;
 	return 0;
 }
 #endif	/* DEBUG */

 static const struct xfs_btree_ops xfs_rmapbt_ops = {
 	.rec_len		= sizeof(struct xfs_rmap_rec),
 	.key_len		= 2 * sizeof(struct xfs_rmap_key),

 	.dup_cursor		= xfs_rmapbt_dup_cursor,
 	.set_root		= xfs_rmapbt_set_root,
 	.alloc_block		= xfs_rmapbt_alloc_block,
 	.free_block		= xfs_rmapbt_free_block,
 	.get_minrecs		= xfs_rmapbt_get_minrecs,
 	.get_maxrecs		= xfs_rmapbt_get_maxrecs,
 	.init_key_from_rec	= xfs_rmapbt_init_key_from_rec,
 	.init_high_key_from_rec	= xfs_rmapbt_init_high_key_from_rec,
 	.init_rec_from_cur	= xfs_rmapbt_init_rec_from_cur,
 	.init_ptr_from_cur	= xfs_rmapbt_init_ptr_from_cur,
 	.key_diff		= xfs_rmapbt_key_diff,
 	.buf_ops		= &xfs_rmapbt_buf_ops,
 	.diff_two_keys		= xfs_rmapbt_diff_two_keys,
 #if defined(DEBUG) || defined(XFS_WARN)
 	.keys_inorder		= xfs_rmapbt_keys_inorder,
 	.recs_inorder		= xfs_rmapbt_recs_inorder,
 #endif
 };

 /*
  * Allocate a new allocation btree cursor.
  */
 struct xfs_btree_cur *
 xfs_rmapbt_init_cursor(
 	struct xfs_mount	*mp,
 	struct xfs_trans	*tp,
 	struct xfs_buf		*agbp,
 	xfs_agnumber_t		agno)
 {
 	struct xfs_agf		*agf = XFS_BUF_TO_AGF(agbp);
 	struct xfs_btree_cur	*cur;

 	cur = kmem_zone_zalloc(xfs_btree_cur_zone, KM_NOFS);
 	cur->bc_tp = tp;
 	cur->bc_mp = mp;
 	/* Overlapping btree; 2 keys per pointer. */
 	cur->bc_btnum = XFS_BTNUM_RMAP;
 	cur->bc_flags = XFS_BTREE_CRC_BLOCKS | XFS_BTREE_OVERLAPPING;
 	cur->bc_blocklog = mp->m_sb.sb_blocklog;
 	cur->bc_ops = &xfs_rmapbt_ops;
 	cur->bc_nlevels = be32_to_cpu(agf->agf_levels[XFS_BTNUM_RMAP]);

 	cur->bc_private.a.agbp = agbp;
 	cur->bc_private.a.agno = agno;

 	return cur;
 }

 /*
  * Calculate number of records in an rmap btree block.
  */
 int
 xfs_rmapbt_maxrecs(
 	struct xfs_mount	*mp,
 	int			blocklen,
 	int			leaf)
 {
 	blocklen -= XFS_RMAP_BLOCK_LEN;

 	if (leaf)
 		return blocklen / sizeof(struct xfs_rmap_rec);
 	return blocklen /
 		(2 * sizeof(struct xfs_rmap_key) + sizeof(xfs_rmap_ptr_t));
 }

 /* Compute the maximum height of an rmap btree. */
 void
 xfs_rmapbt_compute_maxlevels(
 	struct xfs_mount		*mp)
 {
 	/*
 	 * On a non-reflink filesystem, the maximum number of rmap
 	 * records is the number of blocks in the AG, hence the max
 	 * rmapbt height is log_$maxrecs($agblocks).  However, with
 	 * reflink each AG block can have up to 2^32 (per the refcount
 	 * record format) owners, which means that theoretically we
 	 * could face up to 2^64 rmap records.
 	 *
 	 * That effectively means that the max rmapbt height must be
 	 * XFS_BTREE_MAXLEVELS.  "Fortunately" we'll run out of AG
 	 * blocks to feed the rmapbt long before the rmapbt reaches
 	 * maximum height.  The reflink code uses ag_resv_critical to
 	 * disallow reflinking when less than 10% of the per-AG metadata
 	 * block reservation since the fallback is a regular file copy.
 	 */
 	if (xfs_sb_version_hasreflink(&mp->m_sb))
 		mp->m_rmap_maxlevels = XFS_BTREE_MAXLEVELS;
 	else
 		mp->m_rmap_maxlevels = xfs_btree_compute_maxlevels(mp,
 				mp->m_rmap_mnr, mp->m_sb.sb_agblocks);
 }

 /* Calculate the refcount btree size for some records. */
 xfs_extlen_t
 xfs_rmapbt_calc_size(
 	struct xfs_mount	*mp,
 	unsigned long long	len)
 {
 	return xfs_btree_calc_size(mp, mp->m_rmap_mnr, len);
 }

 /*
  * Calculate the maximum refcount btree size.
  */
 xfs_extlen_t
 xfs_rmapbt_max_size(
 	struct xfs_mount	*mp,
 	xfs_agblock_t		agblocks)
 {
 	/* Bail out if we're uninitialized, which can happen in mkfs. */
 	if (mp->m_rmap_mxr[0] == 0)
 		return 0;

 	return xfs_rmapbt_calc_size(mp, agblocks);
 }

 /*
  * Figure out how many blocks to reserve and how many are used by this btree.
  */
 int
 xfs_rmapbt_calc_reserves(
 	struct xfs_mount	*mp,
 	xfs_agnumber_t		agno,
 	xfs_extlen_t		*ask,
 	xfs_extlen_t		*used)
 {
 	struct xfs_buf		*agbp;
 	struct xfs_agf		*agf;
 	xfs_agblock_t		agblocks;
 	xfs_extlen_t		tree_len;
 	int			error;

 	if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
 		return 0;

 	error = xfs_alloc_read_agf(mp, NULL, agno, 0, &agbp);
 	if (error)
 		return error;

 	agf = XFS_BUF_TO_AGF(agbp);
 	agblocks = be32_to_cpu(agf->agf_length);
 	tree_len = be32_to_cpu(agf->agf_rmap_blocks);
 	xfs_buf_relse(agbp);

 	/* Reserve 1% of the AG or enough for 1 block per record. */
 	*ask += max(agblocks / 100, xfs_rmapbt_max_size(mp, agblocks));
 	*used += tree_len;

 	return error;
 }
	/*
	* Copyright (c) 2014 Red Hat, Inc.
	* All Rights Reserved.
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License as
	* published by the Free Software Foundation.
	*
	* This program is distributed in the hope that it would be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
	*/
	#include "xfs.h"
	#include "xfs_fs.h"
	#include "xfs_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_defer.h"
	#include "xfs_inode.h"
	#include "xfs_trans.h"
	#include "xfs_alloc.h"
	#include "xfs_btree.h"
	#include "xfs_rmap.h"
	#include "xfs_rmap_btree.h"
	#include "xfs_trace.h"
	#include "xfs_cksum.h"
	#include "xfs_error.h"
	#include "xfs_extent_busy.h"
	#include "xfs_ag_resv.h"

	/*
	* Reverse map btree.
	*
	* This is a per-ag tree used to track the owner(s) of a given extent. With
	* reflink it is possible for there to be multiple owners, which is a departure
	* from classic XFS. Owner records for data extents are inserted when the
	* extent is mapped and removed when an extent is unmapped. Owner records for
	* all other block types (i.e. metadata) are inserted when an extent is
	* allocated and removed when an extent is freed. There can only be one owner
	* of a metadata extent, usually an inode or some other metadata structure like
	* an AG btree.
	*
	* The rmap btree is part of the free space management, so blocks for the tree
	* are sourced from the agfl. Hence we need transaction reservation support for
	* this tree so that the freelist is always large enough. This also impacts on
	* the minimum space we need to leave free in the AG.
	*
	* The tree is ordered by [ag block, owner, offset]. This is a large key size,
	* but it is the only way to enforce unique keys when a block can be owned by
	* multiple files at any offset. There's no need to order/search by extent
	* size for online updating/management of the tree. It is intended that most
	* reverse lookups will be to find the owner(s) of a particular block, or to
	* try to recover tree and file data from corrupt primary metadata.
	*/

	static struct xfs_btree_cur *
	xfs_rmapbt_dup_cursor(
	struct xfs_btree_cur *cur)
	{
	return xfs_rmapbt_init_cursor(cur->bc_mp, cur->bc_tp,
	cur->bc_private.a.agbp, cur->bc_private.a.agno);
	}

	STATIC void
	xfs_rmapbt_set_root(
	struct xfs_btree_cur *cur,
	union xfs_btree_ptr *ptr,
	int inc)
	{
	struct xfs_buf *agbp = cur->bc_private.a.agbp;
	struct xfs_agf *agf = XFS_BUF_TO_AGF(agbp);
	xfs_agnumber_t seqno = be32_to_cpu(agf->agf_seqno);
	int btnum = cur->bc_btnum;
	struct xfs_perag *pag = xfs_perag_get(cur->bc_mp, seqno);

	ASSERT(ptr->s != 0);

	agf->agf_roots[btnum] = ptr->s;
	be32_add_cpu(&agf->agf_levels[btnum], inc);
	pag->pagf_levels[btnum] += inc;
	xfs_perag_put(pag);

	xfs_alloc_log_agf(cur->bc_tp, agbp, XFS_AGF_ROOTS \| XFS_AGF_LEVELS);
	}

	STATIC int
	xfs_rmapbt_alloc_block(
	struct xfs_btree_cur *cur,
	union xfs_btree_ptr *start,
	union xfs_btree_ptr *new,
	int *stat)
	{
	struct xfs_buf *agbp = cur->bc_private.a.agbp;
	struct xfs_agf *agf = XFS_BUF_TO_AGF(agbp);
	int error;
	xfs_agblock_t bno;

	XFS_BTREE_TRACE_CURSOR(cur, XBT_ENTRY);

	/* Allocate the new block from the freelist. If we can't, give up. */
	error = xfs_alloc_get_freelist(cur->bc_tp, cur->bc_private.a.agbp,
	&bno, 1);
	if (error) {
	XFS_BTREE_TRACE_CURSOR(cur, XBT_ERROR);
	return error;
	}

	trace_xfs_rmapbt_alloc_block(cur->bc_mp, cur->bc_private.a.agno,
	bno, 1);
	if (bno == NULLAGBLOCK) {
	XFS_BTREE_TRACE_CURSOR(cur, XBT_EXIT);
	*stat = 0;
	return 0;
	}

	xfs_extent_busy_reuse(cur->bc_mp, cur->bc_private.a.agno, bno, 1,
	false);

	xfs_trans_agbtree_delta(cur->bc_tp, 1);
	new->s = cpu_to_be32(bno);
	be32_add_cpu(&agf->agf_rmap_blocks, 1);
	xfs_alloc_log_agf(cur->bc_tp, agbp, XFS_AGF_RMAP_BLOCKS);

	XFS_BTREE_TRACE_CURSOR(cur, XBT_EXIT);
	*stat = 1;
	return 0;
	}

	STATIC int
	xfs_rmapbt_free_block(
	struct xfs_btree_cur *cur,
	struct xfs_buf *bp)
	{
	struct xfs_buf *agbp = cur->bc_private.a.agbp;
	struct xfs_agf *agf = XFS_BUF_TO_AGF(agbp);
	xfs_agblock_t bno;
	int error;

	bno = xfs_daddr_to_agbno(cur->bc_mp, XFS_BUF_ADDR(bp));
	trace_xfs_rmapbt_free_block(cur->bc_mp, cur->bc_private.a.agno,
	bno, 1);
	be32_add_cpu(&agf->agf_rmap_blocks, -1);
	xfs_alloc_log_agf(cur->bc_tp, agbp, XFS_AGF_RMAP_BLOCKS);
	error = xfs_alloc_put_freelist(cur->bc_tp, agbp, NULL, bno, 1);
	if (error)
	return error;

	xfs_extent_busy_insert(cur->bc_tp, be32_to_cpu(agf->agf_seqno), bno, 1,
	XFS_EXTENT_BUSY_SKIP_DISCARD);
	xfs_trans_agbtree_delta(cur->bc_tp, -1);

	return 0;
	}

	STATIC int
	xfs_rmapbt_get_minrecs(
	struct xfs_btree_cur *cur,
	int level)
	{
	return cur->bc_mp->m_rmap_mnr[level != 0];
	}

	STATIC int
	xfs_rmapbt_get_maxrecs(
	struct xfs_btree_cur *cur,
	int level)
	{
	return cur->bc_mp->m_rmap_mxr[level != 0];
	}

	STATIC void
	xfs_rmapbt_init_key_from_rec(
	union xfs_btree_key *key,
	union xfs_btree_rec *rec)
	{
	key->rmap.rm_startblock = rec->rmap.rm_startblock;
	key->rmap.rm_owner = rec->rmap.rm_owner;
	key->rmap.rm_offset = rec->rmap.rm_offset;
	}

	/*
	* The high key for a reverse mapping record can be computed by shifting
	* the startblock and offset to the highest value that would still map
	* to that record. In practice this means that we add blockcount-1 to
	* the startblock for all records, and if the record is for a data/attr
	* fork mapping, we add blockcount-1 to the offset too.
	*/
	STATIC void
	xfs_rmapbt_init_high_key_from_rec(
	union xfs_btree_key *key,
	union xfs_btree_rec *rec)
	{
	__uint64_t off;
	int adj;

	adj = be32_to_cpu(rec->rmap.rm_blockcount) - 1;

	key->rmap.rm_startblock = rec->rmap.rm_startblock;
	be32_add_cpu(&key->rmap.rm_startblock, adj);
	key->rmap.rm_owner = rec->rmap.rm_owner;
	key->rmap.rm_offset = rec->rmap.rm_offset;
	if (XFS_RMAP_NON_INODE_OWNER(be64_to_cpu(rec->rmap.rm_owner)) \|\|
	XFS_RMAP_IS_BMBT_BLOCK(be64_to_cpu(rec->rmap.rm_offset)))
	return;
	off = be64_to_cpu(key->rmap.rm_offset);
	off = (XFS_RMAP_OFF(off) + adj) \| (off & ~XFS_RMAP_OFF_MASK);
	key->rmap.rm_offset = cpu_to_be64(off);
	}

	STATIC void
	xfs_rmapbt_init_rec_from_cur(
	struct xfs_btree_cur *cur,
	union xfs_btree_rec *rec)
	{
	rec->rmap.rm_startblock = cpu_to_be32(cur->bc_rec.r.rm_startblock);
	rec->rmap.rm_blockcount = cpu_to_be32(cur->bc_rec.r.rm_blockcount);
	rec->rmap.rm_owner = cpu_to_be64(cur->bc_rec.r.rm_owner);
	rec->rmap.rm_offset = cpu_to_be64(
	xfs_rmap_irec_offset_pack(&cur->bc_rec.r));
	}

	STATIC void
	xfs_rmapbt_init_ptr_from_cur(
	struct xfs_btree_cur *cur,
	union xfs_btree_ptr *ptr)
	{
	struct xfs_agf *agf = XFS_BUF_TO_AGF(cur->bc_private.a.agbp);

	ASSERT(cur->bc_private.a.agno == be32_to_cpu(agf->agf_seqno));
	ASSERT(agf->agf_roots[cur->bc_btnum] != 0);

	ptr->s = agf->agf_roots[cur->bc_btnum];
	}

	STATIC __int64_t
	xfs_rmapbt_key_diff(
	struct xfs_btree_cur *cur,
	union xfs_btree_key *key)
	{
	struct xfs_rmap_irec *rec = &cur->bc_rec.r;
	struct xfs_rmap_key *kp = &key->rmap;
	__u64 x, y;
	__int64_t d;

	d = (__int64_t)be32_to_cpu(kp->rm_startblock) - rec->rm_startblock;
	if (d)
	return d;

	x = be64_to_cpu(kp->rm_owner);
	y = rec->rm_owner;
	if (x > y)
	return 1;
	else if (y > x)
	return -1;

	x = XFS_RMAP_OFF(be64_to_cpu(kp->rm_offset));
	y = rec->rm_offset;
	if (x > y)
	return 1;
	else if (y > x)
	return -1;
	return 0;
	}

	STATIC __int64_t
	xfs_rmapbt_diff_two_keys(
	struct xfs_btree_cur *cur,
	union xfs_btree_key *k1,
	union xfs_btree_key *k2)
	{
	struct xfs_rmap_key *kp1 = &k1->rmap;
	struct xfs_rmap_key *kp2 = &k2->rmap;
	__int64_t d;
	__u64 x, y;

	d = (__int64_t)be32_to_cpu(kp1->rm_startblock) -
	be32_to_cpu(kp2->rm_startblock);
	if (d)
	return d;

	x = be64_to_cpu(kp1->rm_owner);
	y = be64_to_cpu(kp2->rm_owner);
	if (x > y)
	return 1;
	else if (y > x)
	return -1;

	x = XFS_RMAP_OFF(be64_to_cpu(kp1->rm_offset));
	y = XFS_RMAP_OFF(be64_to_cpu(kp2->rm_offset));
	if (x > y)
	return 1;
	else if (y > x)
	return -1;
	return 0;
	}

	static bool
	xfs_rmapbt_verify(
	struct xfs_buf *bp)
	{
	struct xfs_mount *mp = bp->b_target->bt_mount;
	struct xfs_btree_block *block = XFS_BUF_TO_BLOCK(bp);
	struct xfs_perag *pag = bp->b_pag;
	unsigned int level;

	/*
	* magic number and level verification
	*
	* During growfs operations, we can't verify the exact level or owner as
	* the perag is not fully initialised and hence not attached to the
	* buffer. In this case, check against the maximum tree depth.
	*
	* Similarly, during log recovery we will have a perag structure
	* attached, but the agf information will not yet have been initialised
	* from the on disk AGF. Again, we can only check against maximum limits
	* in this case.
	*/
	if (block->bb_magic != cpu_to_be32(XFS_RMAP_CRC_MAGIC))
	return false;

	if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
	return false;
	if (!xfs_btree_sblock_v5hdr_verify(bp))
	return false;

	level = be16_to_cpu(block->bb_level);
	if (pag && pag->pagf_init) {
	if (level >= pag->pagf_levels[XFS_BTNUM_RMAPi])
	return false;
	} else if (level >= mp->m_rmap_maxlevels)
	return false;

	return xfs_btree_sblock_verify(bp, mp->m_rmap_mxr[level != 0]);
	}

	static void
	xfs_rmapbt_read_verify(
	struct xfs_buf *bp)
	{
	if (!xfs_btree_sblock_verify_crc(bp))
	xfs_buf_ioerror(bp, -EFSBADCRC);
	else if (!xfs_rmapbt_verify(bp))
	xfs_buf_ioerror(bp, -EFSCORRUPTED);

	if (bp->b_error) {
	trace_xfs_btree_corrupt(bp, _RET_IP_);
	xfs_verifier_error(bp);
	}
	}

	static void
	xfs_rmapbt_write_verify(
	struct xfs_buf *bp)
	{
	if (!xfs_rmapbt_verify(bp)) {
	trace_xfs_btree_corrupt(bp, _RET_IP_);
	xfs_buf_ioerror(bp, -EFSCORRUPTED);
	xfs_verifier_error(bp);
	return;
	}
	xfs_btree_sblock_calc_crc(bp);

	}

	const struct xfs_buf_ops xfs_rmapbt_buf_ops = {
	.name = "xfs_rmapbt",
	.verify_read = xfs_rmapbt_read_verify,
	.verify_write = xfs_rmapbt_write_verify,
	};

	#if defined(DEBUG) \|\| defined(XFS_WARN)
	STATIC int
	xfs_rmapbt_keys_inorder(
	struct xfs_btree_cur *cur,
	union xfs_btree_key *k1,
	union xfs_btree_key *k2)
	{
	__uint32_t x;
	__uint32_t y;
	__uint64_t a;
	__uint64_t b;

	x = be32_to_cpu(k1->rmap.rm_startblock);
	y = be32_to_cpu(k2->rmap.rm_startblock);
	if (x < y)
	return 1;
	else if (x > y)
	return 0;
	a = be64_to_cpu(k1->rmap.rm_owner);
	b = be64_to_cpu(k2->rmap.rm_owner);
	if (a < b)
	return 1;
	else if (a > b)
	return 0;
	a = XFS_RMAP_OFF(be64_to_cpu(k1->rmap.rm_offset));
	b = XFS_RMAP_OFF(be64_to_cpu(k2->rmap.rm_offset));
	if (a <= b)
	return 1;
	return 0;
	}

	STATIC int
	xfs_rmapbt_recs_inorder(
	struct xfs_btree_cur *cur,
	union xfs_btree_rec *r1,
	union xfs_btree_rec *r2)
	{
	__uint32_t x;
	__uint32_t y;
	__uint64_t a;
	__uint64_t b;

	x = be32_to_cpu(r1->rmap.rm_startblock);
	y = be32_to_cpu(r2->rmap.rm_startblock);
	if (x < y)
	return 1;
	else if (x > y)
	return 0;
	a = be64_to_cpu(r1->rmap.rm_owner);
	b = be64_to_cpu(r2->rmap.rm_owner);
	if (a < b)
	return 1;
	else if (a > b)
	return 0;
	a = XFS_RMAP_OFF(be64_to_cpu(r1->rmap.rm_offset));
	b = XFS_RMAP_OFF(be64_to_cpu(r2->rmap.rm_offset));
	if (a <= b)
	return 1;
	return 0;
	}
	#endif /* DEBUG */

	static const struct xfs_btree_ops xfs_rmapbt_ops = {
	.rec_len = sizeof(struct xfs_rmap_rec),
	.key_len = 2 * sizeof(struct xfs_rmap_key),

	.dup_cursor = xfs_rmapbt_dup_cursor,
	.set_root = xfs_rmapbt_set_root,
	.alloc_block = xfs_rmapbt_alloc_block,
	.free_block = xfs_rmapbt_free_block,
	.get_minrecs = xfs_rmapbt_get_minrecs,
	.get_maxrecs = xfs_rmapbt_get_maxrecs,
	.init_key_from_rec = xfs_rmapbt_init_key_from_rec,
	.init_high_key_from_rec = xfs_rmapbt_init_high_key_from_rec,
	.init_rec_from_cur = xfs_rmapbt_init_rec_from_cur,
	.init_ptr_from_cur = xfs_rmapbt_init_ptr_from_cur,
	.key_diff = xfs_rmapbt_key_diff,
	.buf_ops = &xfs_rmapbt_buf_ops,
	.diff_two_keys = xfs_rmapbt_diff_two_keys,
	#if defined(DEBUG) \|\| defined(XFS_WARN)
	.keys_inorder = xfs_rmapbt_keys_inorder,
	.recs_inorder = xfs_rmapbt_recs_inorder,
	#endif
	};

	/*
	* Allocate a new allocation btree cursor.
	*/
	struct xfs_btree_cur *
	xfs_rmapbt_init_cursor(
	struct xfs_mount *mp,
	struct xfs_trans *tp,
	struct xfs_buf *agbp,
	xfs_agnumber_t agno)
	{
	struct xfs_agf *agf = XFS_BUF_TO_AGF(agbp);
	struct xfs_btree_cur *cur;

	cur = kmem_zone_zalloc(xfs_btree_cur_zone, KM_NOFS);
	cur->bc_tp = tp;
	cur->bc_mp = mp;
	/* Overlapping btree; 2 keys per pointer. */
	cur->bc_btnum = XFS_BTNUM_RMAP;
	cur->bc_flags = XFS_BTREE_CRC_BLOCKS \| XFS_BTREE_OVERLAPPING;
	cur->bc_blocklog = mp->m_sb.sb_blocklog;
	cur->bc_ops = &xfs_rmapbt_ops;
	cur->bc_nlevels = be32_to_cpu(agf->agf_levels[XFS_BTNUM_RMAP]);

	cur->bc_private.a.agbp = agbp;
	cur->bc_private.a.agno = agno;

	return cur;
	}

	/*
	* Calculate number of records in an rmap btree block.
	*/
	int
	xfs_rmapbt_maxrecs(
	struct xfs_mount *mp,
	int blocklen,
	int leaf)
	{
	blocklen -= XFS_RMAP_BLOCK_LEN;

	if (leaf)
	return blocklen / sizeof(struct xfs_rmap_rec);
	return blocklen /
	(2 * sizeof(struct xfs_rmap_key) + sizeof(xfs_rmap_ptr_t));
	}

	/* Compute the maximum height of an rmap btree. */
	void
	xfs_rmapbt_compute_maxlevels(
	struct xfs_mount *mp)
	{
	/*
	* On a non-reflink filesystem, the maximum number of rmap
	* records is the number of blocks in the AG, hence the max
	* rmapbt height is log_$maxrecs($agblocks). However, with
	* reflink each AG block can have up to 2^32 (per the refcount
	* record format) owners, which means that theoretically we
	* could face up to 2^64 rmap records.
	*
	* That effectively means that the max rmapbt height must be
	* XFS_BTREE_MAXLEVELS. "Fortunately" we'll run out of AG
	* blocks to feed the rmapbt long before the rmapbt reaches
	* maximum height. The reflink code uses ag_resv_critical to
	* disallow reflinking when less than 10% of the per-AG metadata
	* block reservation since the fallback is a regular file copy.
	*/
	if (xfs_sb_version_hasreflink(&mp->m_sb))
	mp->m_rmap_maxlevels = XFS_BTREE_MAXLEVELS;
	else
	mp->m_rmap_maxlevels = xfs_btree_compute_maxlevels(mp,
	mp->m_rmap_mnr, mp->m_sb.sb_agblocks);
	}

	/* Calculate the refcount btree size for some records. */
	xfs_extlen_t
	xfs_rmapbt_calc_size(
	struct xfs_mount *mp,
	unsigned long long len)
	{
	return xfs_btree_calc_size(mp, mp->m_rmap_mnr, len);
	}

	/*
	* Calculate the maximum refcount btree size.
	*/
	xfs_extlen_t
	xfs_rmapbt_max_size(
	struct xfs_mount *mp,
	xfs_agblock_t agblocks)
	{
	/* Bail out if we're uninitialized, which can happen in mkfs. */
	if (mp->m_rmap_mxr[0] == 0)
	return 0;

	return xfs_rmapbt_calc_size(mp, agblocks);
	}

	/*
	* Figure out how many blocks to reserve and how many are used by this btree.
	*/
	int
	xfs_rmapbt_calc_reserves(
	struct xfs_mount *mp,
	xfs_agnumber_t agno,
	xfs_extlen_t *ask,
	xfs_extlen_t *used)
	{
	struct xfs_buf *agbp;
	struct xfs_agf *agf;
	xfs_agblock_t agblocks;
	xfs_extlen_t tree_len;
	int error;

	if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
	return 0;

	error = xfs_alloc_read_agf(mp, NULL, agno, 0, &agbp);
	if (error)
	return error;

	agf = XFS_BUF_TO_AGF(agbp);
	agblocks = be32_to_cpu(agf->agf_length);
	tree_len = be32_to_cpu(agf->agf_rmap_blocks);
	xfs_buf_relse(agbp);

	/* Reserve 1% of the AG or enough for 1 block per record. */
	*ask += max(agblocks / 100, xfs_rmapbt_max_size(mp, agblocks));
	*used += tree_len;

	return error;
	}