Introduce a new in-core fork for storing copy-on-write delalloc
reservations and allocated extents that are in the process of being
written out.
v2: fix up bmapi_read so that we can query the CoW fork, and have it
return a "hole" extent if there's no CoW fork.
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
---
fs/xfs/Makefile | 1
fs/xfs/libxfs/xfs_bmap.c | 27 +++++++--
fs/xfs/libxfs/xfs_bmap.h | 22 +++++++-
fs/xfs/libxfs/xfs_bmap_btree.c | 1
fs/xfs/libxfs/xfs_inode_fork.c | 47 +++++++++++++++-
fs/xfs/libxfs/xfs_inode_fork.h | 28 ++++++++--
fs/xfs/libxfs/xfs_rmap.c | 15 +++--
fs/xfs/libxfs/xfs_types.h | 1
fs/xfs/xfs_icache.c | 5 ++
fs/xfs/xfs_inode.h | 4 +
fs/xfs/xfs_reflink.c | 114 ++++++++++++++++++++++++++++++++++++++++
fs/xfs/xfs_reflink.h | 23 ++++++++
fs/xfs/xfs_trace.h | 4 +
13 files changed, 264 insertions(+), 28 deletions(-)
create mode 100644 fs/xfs/xfs_reflink.c
create mode 100644 fs/xfs/xfs_reflink.h
diff --git a/fs/xfs/Makefile b/fs/xfs/Makefile
index 6afb228..26ef195 100644
--- a/fs/xfs/Makefile
+++ b/fs/xfs/Makefile
@@ -90,6 +90,7 @@ xfs-y += xfs_aops.o \
xfs_message.o \
xfs_mount.o \
xfs_mru_cache.o \
+ xfs_reflink.o \
xfs_stats.o \
xfs_super.o \
xfs_symlink.o \
diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index afedbc4..f745d7e 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -2924,6 +2924,7 @@ xfs_bmap_add_extent_hole_real(
ASSERT(!isnullstartblock(new->br_startblock));
ASSERT(!bma->cur ||
!(bma->cur->bc_private.b.flags & XFS_BTCUR_BPRV_WASDEL));
+ ASSERT(whichfork != XFS_COW_FORK);
XFS_STATS_INC(mp, xs_add_exlist);
@@ -4059,12 +4060,11 @@ xfs_bmapi_read(
int error;
int eof;
int n = 0;
- int whichfork = (flags & XFS_BMAPI_ATTRFORK) ?
- XFS_ATTR_FORK : XFS_DATA_FORK;
+ int whichfork = xfs_bmapi_whichfork(flags);
ASSERT(*nmap >= 1);
ASSERT(!(flags & ~(XFS_BMAPI_ATTRFORK|XFS_BMAPI_ENTIRE|
- XFS_BMAPI_IGSTATE)));
+ XFS_BMAPI_IGSTATE|XFS_BMAPI_COWFORK)));
ASSERT(xfs_isilocked(ip, XFS_ILOCK_SHARED|XFS_ILOCK_EXCL));
if (unlikely(XFS_TEST_ERROR(
@@ -4082,6 +4082,16 @@ xfs_bmapi_read(
ifp = XFS_IFORK_PTR(ip, whichfork);
+ /* No CoW fork? Return a hole. */
+ if (whichfork == XFS_COW_FORK && !ifp) {
+ mval->br_startoff = bno;
+ mval->br_startblock = HOLESTARTBLOCK;
+ mval->br_blockcount = len;
+ mval->br_state = XFS_EXT_NORM;
+ *nmap = 1;
+ return 0;
+ }
+
if (!(ifp->if_flags & XFS_IFEXTENTS)) {
error = xfs_iread_extents(NULL, ip, whichfork);
if (error)
@@ -4434,8 +4444,7 @@ xfs_bmapi_convert_unwritten(
xfs_filblks_t len,
int flags)
{
- int whichfork = (flags & XFS_BMAPI_ATTRFORK) ?
- XFS_ATTR_FORK : XFS_DATA_FORK;
+ int whichfork = xfs_bmapi_whichfork(flags);
struct xfs_ifork *ifp = XFS_IFORK_PTR(bma->ip, whichfork);
int tmp_logflags = 0;
int error;
@@ -4451,6 +4460,8 @@ xfs_bmapi_convert_unwritten(
(XFS_BMAPI_PREALLOC | XFS_BMAPI_CONVERT))
return 0;
+ ASSERT(whichfork != XFS_COW_FORK);
+
/*
* Modify (by adding) the state flag, if writing.
*/
@@ -4864,6 +4875,8 @@ xfs_bmap_del_extent(
if (whichfork == XFS_ATTR_FORK)
state |= BMAP_ATTRFORK;
+ else if (whichfork == XFS_COW_FORK)
+ state |= BMAP_COWFORK;
ifp = XFS_IFORK_PTR(ip, whichfork);
ASSERT((*idx >= 0) && (*idx < ifp->if_bytes /
@@ -5202,8 +5215,8 @@ __xfs_bunmapi(
trace_xfs_bunmap(ip, bno, len, flags, _RET_IP_);
- whichfork = (flags & XFS_BMAPI_ATTRFORK) ?
- XFS_ATTR_FORK : XFS_DATA_FORK;
+ whichfork = xfs_bmapi_whichfork(flags);
+ ASSERT(whichfork != XFS_COW_FORK);
ifp = XFS_IFORK_PTR(ip, whichfork);
if (unlikely(
XFS_IFORK_FORMAT(ip, whichfork) != XFS_DINODE_FMT_EXTENTS &&
diff --git a/fs/xfs/libxfs/xfs_bmap.h b/fs/xfs/libxfs/xfs_bmap.h
index 3b2a5b5..e686a1b 100644
--- a/fs/xfs/libxfs/xfs_bmap.h
+++ b/fs/xfs/libxfs/xfs_bmap.h
@@ -107,6 +107,9 @@ struct xfs_extent_free_item
*/
#define XFS_BMAPI_REMAP 0x100
+/* Map something in the CoW fork. */
+#define XFS_BMAPI_COWFORK 0x200
+
#define XFS_BMAPI_FLAGS \
{ XFS_BMAPI_ENTIRE, "ENTIRE" }, \
{ XFS_BMAPI_METADATA, "METADATA" }, \
@@ -116,12 +119,23 @@ struct xfs_extent_free_item
{ XFS_BMAPI_CONTIG, "CONTIG" }, \
{ XFS_BMAPI_CONVERT, "CONVERT" }, \
{ XFS_BMAPI_ZERO, "ZERO" }, \
- { XFS_BMAPI_REMAP, "REMAP" }
+ { XFS_BMAPI_REMAP, "REMAP" }, \
+ { XFS_BMAPI_COWFORK, "COWFORK" }
static inline int xfs_bmapi_aflag(int w)
{
- return (w == XFS_ATTR_FORK ? XFS_BMAPI_ATTRFORK : 0);
+ return (w == XFS_ATTR_FORK ? XFS_BMAPI_ATTRFORK :
+ (w == XFS_COW_FORK ? XFS_BMAPI_COWFORK : 0));
+}
+
+static inline int xfs_bmapi_whichfork(int bmapi_flags)
+{
+ if (bmapi_flags & XFS_BMAPI_COWFORK)
+ return XFS_COW_FORK;
+ else if (bmapi_flags & XFS_BMAPI_ATTRFORK)
+ return XFS_ATTR_FORK;
+ return XFS_DATA_FORK;
}
/*
@@ -142,13 +156,15 @@ static inline int xfs_bmapi_aflag(int w)
#define BMAP_LEFT_VALID (1 << 6)
#define BMAP_RIGHT_VALID (1 << 7)
#define BMAP_ATTRFORK (1 << 8)
+#define BMAP_COWFORK (1 << 9)
#define XFS_BMAP_EXT_FLAGS \
{ BMAP_LEFT_CONTIG, "LC" }, \
{ BMAP_RIGHT_CONTIG, "RC" }, \
{ BMAP_LEFT_FILLING, "LF" }, \
{ BMAP_RIGHT_FILLING, "RF" }, \
- { BMAP_ATTRFORK, "ATTR" }
+ { BMAP_ATTRFORK, "ATTR" }, \
+ { BMAP_COWFORK, "COW" }
/*
diff --git a/fs/xfs/libxfs/xfs_bmap_btree.c b/fs/xfs/libxfs/xfs_bmap_btree.c
index cd85274..37f0d9d 100644
--- a/fs/xfs/libxfs/xfs_bmap_btree.c
+++ b/fs/xfs/libxfs/xfs_bmap_btree.c
@@ -777,6 +777,7 @@ xfs_bmbt_init_cursor(
{
struct xfs_ifork *ifp = XFS_IFORK_PTR(ip, whichfork);
struct xfs_btree_cur *cur;
+ ASSERT(whichfork != XFS_COW_FORK);
cur = kmem_zone_zalloc(xfs_btree_cur_zone, KM_SLEEP);
diff --git a/fs/xfs/libxfs/xfs_inode_fork.c b/fs/xfs/libxfs/xfs_inode_fork.c
index 7699a03..d29954a 100644
--- a/fs/xfs/libxfs/xfs_inode_fork.c
+++ b/fs/xfs/libxfs/xfs_inode_fork.c
@@ -206,9 +206,14 @@ xfs_iformat_fork(
XFS_ERROR_REPORT("xfs_iformat(7)", XFS_ERRLEVEL_LOW, ip->i_mount);
return -EFSCORRUPTED;
}
- if (error) {
+ if (error)
return error;
+
+ if (xfs_is_reflink_inode(ip)) {
+ ASSERT(ip->i_cowfp == NULL);
+ xfs_ifork_init_cow(ip);
}
+
if (!XFS_DFORK_Q(dip))
return 0;
@@ -247,6 +252,9 @@ xfs_iformat_fork(
if (error) {
kmem_zone_free(xfs_ifork_zone, ip->i_afp);
ip->i_afp = NULL;
+ if (ip->i_cowfp)
+ kmem_zone_free(xfs_ifork_zone, ip->i_cowfp);
+ ip->i_cowfp = NULL;
xfs_idestroy_fork(ip, XFS_DATA_FORK);
}
return error;
@@ -761,6 +769,9 @@ xfs_idestroy_fork(
if (whichfork == XFS_ATTR_FORK) {
kmem_zone_free(xfs_ifork_zone, ip->i_afp);
ip->i_afp = NULL;
+ } else if (whichfork == XFS_COW_FORK) {
+ kmem_zone_free(xfs_ifork_zone, ip->i_cowfp);
+ ip->i_cowfp = NULL;
}
}
@@ -948,6 +959,19 @@ xfs_iext_get_ext(
}
}
+/* XFS_IEXT_STATE_TO_FORK() -- Convert BMAP state flags to an inode fork. */
+xfs_ifork_t *
+XFS_IEXT_STATE_TO_FORK(
+ struct xfs_inode *ip,
+ int state)
+{
+ if (state & BMAP_COWFORK)
+ return ip->i_cowfp;
+ else if (state & BMAP_ATTRFORK)
+ return ip->i_afp;
+ return &ip->i_df;
+}
+
/*
* Insert new item(s) into the extent records for incore inode
* fork 'ifp'. 'count' new items are inserted at index 'idx'.
@@ -960,7 +984,7 @@ xfs_iext_insert(
xfs_bmbt_irec_t *new, /* items to insert */
int state) /* type of extent conversion */
{
- xfs_ifork_t *ifp = (state & BMAP_ATTRFORK) ? ip->i_afp : &ip->i_df;
+ xfs_ifork_t *ifp = XFS_IEXT_STATE_TO_FORK(ip, state);
xfs_extnum_t i; /* extent record index */
trace_xfs_iext_insert(ip, idx, new, state, _RET_IP_);
@@ -1210,7 +1234,7 @@ xfs_iext_remove(
int ext_diff, /* number of extents to remove */
int state) /* type of extent conversion */
{
- xfs_ifork_t *ifp = (state & BMAP_ATTRFORK) ? ip->i_afp : &ip->i_df;
+ xfs_ifork_t *ifp = XFS_IEXT_STATE_TO_FORK(ip, state);
xfs_extnum_t nextents; /* number of extents in file */
int new_size; /* size of extents after removal */
@@ -1955,3 +1979,20 @@ xfs_iext_irec_update_extoffs(
ifp->if_u1.if_ext_irec[i].er_extoff += ext_diff;
}
}
+
+/*
+ * Initialize an inode's copy-on-write fork.
+ */
+void
+xfs_ifork_init_cow(
+ struct xfs_inode *ip)
+{
+ if (ip->i_cowfp)
+ return;
+
+ ip->i_cowfp = kmem_zone_zalloc(xfs_ifork_zone,
+ KM_SLEEP | KM_NOFS);
+ ip->i_cowfp->if_flags = XFS_IFEXTENTS;
+ ip->i_cformat = XFS_DINODE_FMT_EXTENTS;
+ ip->i_cnextents = 0;
+}
diff --git a/fs/xfs/libxfs/xfs_inode_fork.h b/fs/xfs/libxfs/xfs_inode_fork.h
index f95e072..44d38eb 100644
--- a/fs/xfs/libxfs/xfs_inode_fork.h
+++ b/fs/xfs/libxfs/xfs_inode_fork.h
@@ -92,7 +92,9 @@ typedef struct xfs_ifork {
#define XFS_IFORK_PTR(ip,w) \
((w) == XFS_DATA_FORK ? \
&(ip)->i_df : \
- (ip)->i_afp)
+ ((w) == XFS_ATTR_FORK ? \
+ (ip)->i_afp : \
+ (ip)->i_cowfp))
#define XFS_IFORK_DSIZE(ip) \
(XFS_IFORK_Q(ip) ? \
XFS_IFORK_BOFF(ip) : \
@@ -105,26 +107,38 @@ typedef struct xfs_ifork {
#define XFS_IFORK_SIZE(ip,w) \
((w) == XFS_DATA_FORK ? \
XFS_IFORK_DSIZE(ip) : \
- XFS_IFORK_ASIZE(ip))
+ ((w) == XFS_ATTR_FORK ? \
+ XFS_IFORK_ASIZE(ip) : \
+ 0))
#define XFS_IFORK_FORMAT(ip,w) \
((w) == XFS_DATA_FORK ? \
(ip)->i_d.di_format : \
- (ip)->i_d.di_aformat)
+ ((w) == XFS_ATTR_FORK ? \
+ (ip)->i_d.di_aformat : \
+ (ip)->i_cformat))
#define XFS_IFORK_FMT_SET(ip,w,n) \
((w) == XFS_DATA_FORK ? \
((ip)->i_d.di_format = (n)) : \
- ((ip)->i_d.di_aformat = (n)))
+ ((w) == XFS_ATTR_FORK ? \
+ ((ip)->i_d.di_aformat = (n)) : \
+ ((ip)->i_cformat = (n))))
#define XFS_IFORK_NEXTENTS(ip,w) \
((w) == XFS_DATA_FORK ? \
(ip)->i_d.di_nextents : \
- (ip)->i_d.di_anextents)
+ ((w) == XFS_ATTR_FORK ? \
+ (ip)->i_d.di_anextents : \
+ (ip)->i_cnextents))
#define XFS_IFORK_NEXT_SET(ip,w,n) \
((w) == XFS_DATA_FORK ? \
((ip)->i_d.di_nextents = (n)) : \
- ((ip)->i_d.di_anextents = (n)))
+ ((w) == XFS_ATTR_FORK ? \
+ ((ip)->i_d.di_anextents = (n)) : \
+ ((ip)->i_cnextents = (n))))
#define XFS_IFORK_MAXEXT(ip, w) \
(XFS_IFORK_SIZE(ip, w) / sizeof(xfs_bmbt_rec_t))
+xfs_ifork_t *XFS_IEXT_STATE_TO_FORK(struct xfs_inode *ip, int state);
+
int xfs_iformat_fork(struct xfs_inode *, struct xfs_dinode *);
void xfs_iflush_fork(struct xfs_inode *, struct xfs_dinode *,
struct xfs_inode_log_item *, int);
@@ -169,4 +183,6 @@ void xfs_iext_irec_update_extoffs(struct xfs_ifork *, int, int);
extern struct kmem_zone *xfs_ifork_zone;
+extern void xfs_ifork_init_cow(struct xfs_inode *ip);
+
#endif /* __XFS_INODE_FORK_H__ */
diff --git a/fs/xfs/libxfs/xfs_rmap.c b/fs/xfs/libxfs/xfs_rmap.c
index 73d0540..1c40b85 100644
--- a/fs/xfs/libxfs/xfs_rmap.c
+++ b/fs/xfs/libxfs/xfs_rmap.c
@@ -1263,9 +1263,10 @@ out_cur:
*/
static bool
xfs_rmap_update_is_needed(
- struct xfs_mount *mp)
+ struct xfs_mount *mp,
+ int whichfork)
{
- return xfs_sb_version_hasrmapbt(&mp->m_sb);
+ return xfs_sb_version_hasrmapbt(&mp->m_sb) && whichfork != XFS_COW_FORK;
}
/*
@@ -1311,7 +1312,7 @@ xfs_rmap_map_extent(
int whichfork,
struct xfs_bmbt_irec *PREV)
{
- if (!xfs_rmap_update_is_needed(mp))
+ if (!xfs_rmap_update_is_needed(mp, whichfork))
return 0;
return __xfs_rmap_add(mp, dfops, XFS_RMAP_MAP, ip->i_ino,
@@ -1327,7 +1328,7 @@ xfs_rmap_unmap_extent(
int whichfork,
struct xfs_bmbt_irec *PREV)
{
- if (!xfs_rmap_update_is_needed(mp))
+ if (!xfs_rmap_update_is_needed(mp, whichfork))
return 0;
return __xfs_rmap_add(mp, dfops, XFS_RMAP_UNMAP, ip->i_ino,
@@ -1343,7 +1344,7 @@ xfs_rmap_convert_extent(
int whichfork,
struct xfs_bmbt_irec *PREV)
{
- if (!xfs_rmap_update_is_needed(mp))
+ if (!xfs_rmap_update_is_needed(mp, whichfork))
return 0;
return __xfs_rmap_add(mp, dfops, XFS_RMAP_CONVERT, ip->i_ino,
@@ -1362,7 +1363,7 @@ xfs_rmap_alloc_extent(
{
struct xfs_bmbt_irec bmap;
- if (!xfs_rmap_update_is_needed(mp))
+ if (!xfs_rmap_update_is_needed(mp, XFS_DATA_FORK))
return 0;
bmap.br_startblock = XFS_AGB_TO_FSB(mp, agno, bno);
@@ -1386,7 +1387,7 @@ xfs_rmap_free_extent(
{
struct xfs_bmbt_irec bmap;
- if (!xfs_rmap_update_is_needed(mp))
+ if (!xfs_rmap_update_is_needed(mp, XFS_DATA_FORK))
return 0;
bmap.br_startblock = XFS_AGB_TO_FSB(mp, agno, bno);
diff --git a/fs/xfs/libxfs/xfs_types.h b/fs/xfs/libxfs/xfs_types.h
index 690d616..cf044c0 100644
--- a/fs/xfs/libxfs/xfs_types.h
+++ b/fs/xfs/libxfs/xfs_types.h
@@ -93,6 +93,7 @@ typedef __int64_t xfs_sfiloff_t; /* signed block number in a file */
*/
#define XFS_DATA_FORK 0
#define XFS_ATTR_FORK 1
+#define XFS_COW_FORK 2
/*
* Min numbers of data/attr fork btree root pointers.
diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index fb39a66..b5ccd20 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -76,6 +76,9 @@ xfs_inode_alloc(
ip->i_mount = mp;
memset(&ip->i_imap, 0, sizeof(struct xfs_imap));
ip->i_afp = NULL;
+ ip->i_cowfp = NULL;
+ ip->i_cnextents = 0;
+ ip->i_cformat = XFS_DINODE_FMT_EXTENTS;
memset(&ip->i_df, 0, sizeof(xfs_ifork_t));
ip->i_flags = 0;
ip->i_delayed_blks = 0;
@@ -101,6 +104,8 @@ xfs_inode_free_callback(
if (ip->i_afp)
xfs_idestroy_fork(ip, XFS_ATTR_FORK);
+ if (ip->i_cowfp)
+ xfs_idestroy_fork(ip, XFS_COW_FORK);
if (ip->i_itemp) {
ASSERT(!(ip->i_itemp->ili_item.li_flags & XFS_LI_IN_AIL));
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index 7283db3..7b2e858 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -47,6 +47,7 @@ typedef struct xfs_inode {
/* Extent information. */
xfs_ifork_t *i_afp; /* attribute fork pointer */
+ xfs_ifork_t *i_cowfp; /* copy on write extents */
xfs_ifork_t i_df; /* data fork */
/* operations vectors */
@@ -65,6 +66,9 @@ typedef struct xfs_inode {
struct xfs_icdinode i_d; /* most of ondisk inode */
+ xfs_extnum_t i_cnextents; /* # of extents in cow fork */
+ unsigned int i_cformat; /* format of cow fork */
+
/* VFS inode */
struct inode i_vnode; /* embedded VFS inode */
} xfs_inode_t;
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
new file mode 100644
index 0000000..7adbb83
--- /dev/null
+++ b/fs/xfs/xfs_reflink.c
@@ -0,0 +1,114 @@
+/*
+ * Copyright (C) 2016 Oracle. All Rights Reserved.
+ *
+ * Author: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
+ *
+ * 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; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * 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_mount.h"
+#include "xfs_defer.h"
+#include "xfs_da_format.h"
+#include "xfs_da_btree.h"
+#include "xfs_inode.h"
+#include "xfs_trans.h"
+#include "xfs_inode_item.h"
+#include "xfs_bmap.h"
+#include "xfs_bmap_util.h"
+#include "xfs_error.h"
+#include "xfs_dir2.h"
+#include "xfs_dir2_priv.h"
+#include "xfs_ioctl.h"
+#include "xfs_trace.h"
+#include "xfs_log.h"
+#include "xfs_icache.h"
+#include "xfs_pnfs.h"
+#include "xfs_refcount_btree.h"
+#include "xfs_refcount.h"
+#include "xfs_bmap_btree.h"
+#include "xfs_trans_space.h"
+#include "xfs_bit.h"
+#include "xfs_alloc.h"
+#include "xfs_quota_defs.h"
+#include "xfs_quota.h"
+#include "xfs_btree.h"
+#include "xfs_bmap_btree.h"
+#include "xfs_reflink.h"
+
+/*
+ * Copy on Write of Shared Blocks
+ *
+ * XFS must preserve "the usual" file semantics even when two files share
+ * the same physical blocks. This means that a write to one file must not
+ * alter the blocks in a different file; the way that we'll do that is
+ * through the use of a copy-on-write mechanism. At a high level, that
+ * means that when we want to write to a shared block, we allocate a new
+ * block, write the data to the new block, and if that succeeds we map the
+ * new block into the file.
+ *
+ * XFS provides a "delayed allocation" mechanism that defers the allocation
+ * of disk blocks to dirty-but-not-yet-mapped file blocks as long as
+ * possible. This reduces fragmentation by enabling the filesystem to ask
+ * for bigger chunks less often, which is exactly what we want for CoW.
+ *
+ * The delalloc mechanism begins when the kernel wants to make a block
+ * writable (write_begin or page_mkwrite). If the offset is not mapped, we
+ * create a delalloc mapping, which is a regular in-core extent, but without
+ * a real startblock. (For delalloc mappings, the startblock encodes both
+ * a flag that this is a delalloc mapping, and a worst-case estimate of how
+ * many blocks might be required to put the mapping into the BMBT.) delalloc
+ * mappings are a reservation against the free space in the filesystem;
+ * adjacent mappings can also be combined into fewer larger mappings.
+ *
+ * When dirty pages are being written out (typically in writepage), the
+ * delalloc reservations are converted into real mappings by allocating
+ * blocks and replacing the delalloc mapping with real ones. A delalloc
+ * mapping can be replaced by several real ones if the free space is
+ * fragmented.
+ *
+ * We want to adapt the delalloc mechanism for copy-on-write, since the
+ * write paths are similar. The first two steps (creating the reservation
+ * and allocating the blocks) are exactly the same as delalloc except that
+ * the mappings must be stored in a separate CoW fork because we do not want
+ * to disturb the mapping in the data fork until we're sure that the write
+ * succeeded. IO completion in this case is the process of removing the old
+ * mapping from the data fork and moving the new mapping from the CoW fork to
+ * the data fork. This will be discussed shortly.
+ *
+ * For now, unaligned directio writes will be bounced back to the page cache.
+ * Block-aligned directio writes will use the same mechanism as buffered
+ * writes.
+ *
+ * CoW remapping must be done after the data block write completes,
+ * because we don't want to destroy the old data fork map until we're sure
+ * the new block has been written. Since the new mappings are kept in a
+ * separate fork, we can simply iterate these mappings to find the ones
+ * that cover the file blocks that we just CoW'd. For each extent, simply
+ * unmap the corresponding range in the data fork, map the new range into
+ * the data fork, and remove the extent from the CoW fork.
+ *
+ * Since the remapping operation can be applied to an arbitrary file
+ * range, we record the need for the remap step as a flag in the ioend
+ * instead of declaring a new IO type. This is required for direct io
+ * because we only have ioend for the whole dio, and we have to be able to
+ * remember the presence of unwritten blocks and CoW blocks with a single
+ * ioend structure. Better yet, the more ground we can cover with one
+ * ioend, the better.
+ */
diff --git a/fs/xfs/xfs_reflink.h b/fs/xfs/xfs_reflink.h
new file mode 100644
index 0000000..820b151
--- /dev/null
+++ b/fs/xfs/xfs_reflink.h
@@ -0,0 +1,23 @@
+/*
+ * Copyright (C) 2016 Oracle. All Rights Reserved.
+ *
+ * Author: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
+ *
+ * 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; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * 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.
+ */
+#ifndef __XFS_REFLINK_H
+#define __XFS_REFLINK_H 1
+
+#endif /* __XFS_REFLINK_H */
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index 57ef0fa..73d92be 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -269,10 +269,10 @@ DECLARE_EVENT_CLASS(xfs_bmap_class,
__field(unsigned long, caller_ip)
),
TP_fast_assign(
- struct xfs_ifork *ifp = (state & BMAP_ATTRFORK) ?
- ip->i_afp : &ip->i_df;
+ struct xfs_ifork *ifp;
struct xfs_bmbt_irec r;
+ ifp = XFS_IEXT_STATE_TO_FORK(ip, state);
xfs_bmbt_get_all(xfs_iext_get_ext(ifp, idx), &r);
__entry->dev = VFS_I(ip)->i_sb->s_dev;
__entry->ino = ip->i_ino;
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