For O_DIRECT writes to shared blocks, we have to CoW them just like
we would with buffered writes. For writes that are not block-aligned,
just bounce them to the page cache.
For block-aligned writes, however, we can do better than that. Use
the same mechanisms that we employ for buffered CoW to set up a
delalloc reservation, allocate all the blocks at once, issue the
writes against the new blocks and use the same ioend functions to
remap the blocks after the write. This should be fairly performant.
Christoph discovered that xfs_reflink_allocate_cow_range may stumble
over invalid entries in the extent array given that it drops the ilock
but still expects the index to be stable. Simple fixing it to a new
lookup for every iteration still isn't correct given that
xfs_bmapi_allocate will trigger a BUG_ON() if hitting a hole, and
there is nothing preventing a xfs_bunmapi_cow call removing extents
once we dropped the ilock either.
This patch duplicates the inner loop of xfs_bmapi_allocate into a
helper for xfs_reflink_allocate_cow_range so that it can be done under
the same ilock critical section as our CoW fork delayed allocation.
The directio CoW warts will be revisited in a later patch.
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
v2: Turns out that there's no way for xfs_end_io_direct_write to know
if the write completed successfully. Therefore, do /not/ use the
ioend for dio cow post-processing; instead, move it to xfs_vm_do_dio
where we *can* tell if the write succeeded or not.
v3: Update the file size if we do a directio CoW across EOF. This
can happen if the last block is shared, the cowextsize hint is set,
and we do a dio write past the end of the file.
v4: Christoph rewrote the allocate code to fix some concurrency
problems as part of migrating the code to support iomap.
---
fs/xfs/xfs_aops.c | 91 +++++++++++++++++++++++++++++++++++++++----
fs/xfs/xfs_file.c | 20 ++++++++-
fs/xfs/xfs_reflink.c | 107 +++++++++++++++++++++++++++++++++++++++++++++++++-
fs/xfs/xfs_reflink.h | 2 +
fs/xfs/xfs_trace.h | 1
5 files changed, 208 insertions(+), 13 deletions(-)
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 1d0435a..62a95e4 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -40,6 +40,7 @@
/* flags for direct write completions */
#define XFS_DIO_FLAG_UNWRITTEN (1 << 0)
#define XFS_DIO_FLAG_APPEND (1 << 1)
+#define XFS_DIO_FLAG_COW (1 << 2)
/*
* structure owned by writepages passed to individual writepage calls
@@ -1191,18 +1192,24 @@ xfs_map_direct(
struct inode *inode,
struct buffer_head *bh_result,
struct xfs_bmbt_irec *imap,
- xfs_off_t offset)
+ xfs_off_t offset,
+ bool is_cow)
{
uintptr_t *flags = (uintptr_t *)&bh_result->b_private;
xfs_off_t size = bh_result->b_size;
trace_xfs_get_blocks_map_direct(XFS_I(inode), offset, size,
- ISUNWRITTEN(imap) ? XFS_IO_UNWRITTEN : XFS_IO_OVERWRITE, imap);
+ ISUNWRITTEN(imap) ? XFS_IO_UNWRITTEN : is_cow ? XFS_IO_COW :
+ XFS_IO_OVERWRITE, imap);
if (ISUNWRITTEN(imap)) {
*flags |= XFS_DIO_FLAG_UNWRITTEN;
set_buffer_defer_completion(bh_result);
- } else if (offset + size > i_size_read(inode) || offset + size < 0) {
+ } else if (is_cow) {
+ *flags |= XFS_DIO_FLAG_COW;
+ set_buffer_defer_completion(bh_result);
+ }
+ if (offset + size > i_size_read(inode) || offset + size < 0) {
*flags |= XFS_DIO_FLAG_APPEND;
set_buffer_defer_completion(bh_result);
}
@@ -1248,6 +1255,44 @@ xfs_map_trim_size(
bh_result->b_size = mapping_size;
}
+/* Bounce unaligned directio writes to the page cache. */
+static int
+xfs_bounce_unaligned_dio_write(
+ struct xfs_inode *ip,
+ xfs_fileoff_t offset_fsb,
+ struct xfs_bmbt_irec *imap)
+{
+ struct xfs_bmbt_irec irec;
+ xfs_fileoff_t delta;
+ bool shared;
+ bool x;
+ int error;
+
+ irec = *imap;
+ if (offset_fsb > irec.br_startoff) {
+ delta = offset_fsb - irec.br_startoff;
+ irec.br_blockcount -= delta;
+ irec.br_startblock += delta;
+ irec.br_startoff = offset_fsb;
+ }
+ error = xfs_reflink_trim_around_shared(ip, &irec, &x, &shared);
+ if (error)
+ return error;
+ /*
+ * Are we doing a DIO write to a shared block? In
+ * the ideal world we at least would fork full blocks,
+ * but for now just fall back to buffered mode. Yuck.
+ * Use -EREMCHG ("remote address changed") to signal
+ * this, since in general XFS doesn't do this sort of
+ * fallback.
+ */
+ if (shared) {
+ trace_xfs_reflink_bounce_dio_write(ip, imap);
+ return -EREMCHG;
+ }
+ return 0;
+}
+
STATIC int
__xfs_get_blocks(
struct inode *inode,
@@ -1267,6 +1312,8 @@ __xfs_get_blocks(
xfs_off_t offset;
ssize_t size;
int new = 0;
+ bool is_cow = false;
+ bool need_alloc = false;
BUG_ON(create && !direct);
@@ -1292,8 +1339,27 @@ __xfs_get_blocks(
end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + size);
offset_fsb = XFS_B_TO_FSBT(mp, offset);
- error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
- &imap, &nimaps, XFS_BMAPI_ENTIRE);
+ if (create && direct) {
+ is_cow = xfs_reflink_find_cow_mapping(ip, offset, &imap,
+ &need_alloc);
+ }
+
+ if (!is_cow) {
+ error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
+ &imap, &nimaps, XFS_BMAPI_ENTIRE);
+ /*
+ * Truncate an overwrite extent if there's a pending CoW
+ * reservation before the end of this extent. This forces us
+ * to come back to writepage to take care of the CoW.
+ */
+ if (create && direct && nimaps &&
+ imap.br_startblock != HOLESTARTBLOCK &&
+ imap.br_startblock != DELAYSTARTBLOCK &&
+ !ISUNWRITTEN(&imap))
+ xfs_reflink_trim_irec_to_next_cow(ip, offset_fsb,
+ &imap);
+ }
+ ASSERT(!need_alloc);
if (error)
goto out_unlock;
@@ -1345,6 +1411,13 @@ __xfs_get_blocks(
if (imap.br_startblock != HOLESTARTBLOCK &&
imap.br_startblock != DELAYSTARTBLOCK &&
(create || !ISUNWRITTEN(&imap))) {
+ if (create && direct && !is_cow) {
+ error = xfs_bounce_unaligned_dio_write(ip, offset_fsb,
+ &imap);
+ if (error)
+ return error;
+ }
+
xfs_map_buffer(inode, bh_result, &imap, offset);
if (ISUNWRITTEN(&imap))
set_buffer_unwritten(bh_result);
@@ -1353,7 +1426,8 @@ __xfs_get_blocks(
if (dax_fault)
ASSERT(!ISUNWRITTEN(&imap));
else
- xfs_map_direct(inode, bh_result, &imap, offset);
+ xfs_map_direct(inode, bh_result, &imap, offset,
+ is_cow);
}
}
@@ -1479,7 +1553,10 @@ xfs_end_io_direct_write(
trace_xfs_end_io_direct_write_unwritten(ip, offset, size);
error = xfs_iomap_write_unwritten(ip, offset, size);
- } else if (flags & XFS_DIO_FLAG_APPEND) {
+ }
+ if (flags & XFS_DIO_FLAG_COW)
+ error = xfs_reflink_end_cow(ip, offset, size);
+ if (flags & XFS_DIO_FLAG_APPEND) {
trace_xfs_end_io_direct_write_append(ip, offset, size);
error = xfs_setfilesize(ip, offset, size);
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index f99d7fa..025d52f 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -38,6 +38,7 @@
#include "xfs_icache.h"
#include "xfs_pnfs.h"
#include "xfs_iomap.h"
+#include "xfs_reflink.h"
#include <linux/dcache.h>
#include <linux/falloc.h>
@@ -672,6 +673,13 @@ xfs_file_dio_aio_write(
trace_xfs_file_direct_write(ip, count, iocb->ki_pos);
+ /* If this is a block-aligned directio CoW, remap immediately. */
+ if (xfs_is_reflink_inode(ip) && !unaligned_io) {
+ ret = xfs_reflink_allocate_cow_range(ip, iocb->ki_pos, count);
+ if (ret)
+ goto out;
+ }
+
data = *from;
ret = __blockdev_direct_IO(iocb, inode, target->bt_bdev, &data,
xfs_get_blocks_direct, xfs_end_io_direct_write,
@@ -812,10 +820,18 @@ xfs_file_write_iter(
if (IS_DAX(inode))
ret = xfs_file_dax_write(iocb, from);
- else if (iocb->ki_flags & IOCB_DIRECT)
+ else if (iocb->ki_flags & IOCB_DIRECT) {
+ /*
+ * Allow DIO to fall back to buffered *only* in the case
+ * that we're doing a reflink CoW.
+ */
ret = xfs_file_dio_aio_write(iocb, from);
- else
+ if (ret == -EREMCHG)
+ goto buffered;
+ } else {
+buffered:
ret = xfs_file_buffered_aio_write(iocb, from);
+ }
if (ret > 0) {
XFS_STATS_ADD(ip->i_mount, xs_write_bytes, ret);
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index d913ad1..c95cdc3 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -246,7 +246,8 @@ static int
__xfs_reflink_reserve_cow(
struct xfs_inode *ip,
xfs_fileoff_t *offset_fsb,
- xfs_fileoff_t end_fsb)
+ xfs_fileoff_t end_fsb,
+ bool *skipped)
{
struct xfs_bmbt_irec got, prev, imap;
xfs_fileoff_t orig_end_fsb;
@@ -279,8 +280,10 @@ __xfs_reflink_reserve_cow(
end_fsb = orig_end_fsb = imap.br_startoff + imap.br_blockcount;
/* Not shared? Just report the (potentially capped) extent. */
- if (!shared)
+ if (!shared) {
+ *skipped = true;
goto done;
+ }
/*
* Fork all the shared blocks from our write offset until the end of
@@ -326,6 +329,7 @@ xfs_reflink_reserve_cow_range(
{
struct xfs_mount *mp = ip->i_mount;
xfs_fileoff_t offset_fsb, end_fsb;
+ bool skipped = false;
int error;
trace_xfs_reflink_reserve_cow_range(ip, offset, count);
@@ -335,7 +339,8 @@ xfs_reflink_reserve_cow_range(
xfs_ilock(ip, XFS_ILOCK_EXCL);
while (offset_fsb < end_fsb) {
- error = __xfs_reflink_reserve_cow(ip, &offset_fsb, end_fsb);
+ error = __xfs_reflink_reserve_cow(ip, &offset_fsb, end_fsb,
+ &skipped);
if (error) {
trace_xfs_reflink_reserve_cow_range_error(ip, error,
_RET_IP_);
@@ -347,6 +352,102 @@ xfs_reflink_reserve_cow_range(
return error;
}
+/* Allocate all CoW reservations covering a range of blocks in a file. */
+static int
+__xfs_reflink_allocate_cow(
+ struct xfs_inode *ip,
+ xfs_fileoff_t *offset_fsb,
+ xfs_fileoff_t end_fsb)
+{
+ struct xfs_mount *mp = ip->i_mount;
+ struct xfs_bmbt_irec imap;
+ struct xfs_defer_ops dfops;
+ struct xfs_trans *tp;
+ xfs_fsblock_t first_block;
+ xfs_fileoff_t next_fsb;
+ int nimaps = 1, error;
+ bool skipped = false;
+
+ xfs_defer_init(&dfops, &first_block);
+
+ error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, 0, 0,
+ XFS_TRANS_RESERVE, &tp);
+ if (error)
+ return error;
+
+ xfs_ilock(ip, XFS_ILOCK_EXCL);
+
+ next_fsb = *offset_fsb;
+ error = __xfs_reflink_reserve_cow(ip, &next_fsb, end_fsb, &skipped);
+ if (error)
+ goto out_trans_cancel;
+
+ if (skipped) {
+ *offset_fsb = next_fsb;
+ goto out_trans_cancel;
+ }
+
+ xfs_trans_ijoin(tp, ip, 0);
+ error = xfs_bmapi_write(tp, ip, *offset_fsb, next_fsb - *offset_fsb,
+ XFS_BMAPI_COWFORK, &first_block,
+ XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK),
+ &imap, &nimaps, &dfops);
+ if (error)
+ goto out_trans_cancel;
+
+ /* We might not have been able to map the whole delalloc extent */
+ *offset_fsb = min(*offset_fsb + imap.br_blockcount, next_fsb);
+
+ error = xfs_defer_finish(&tp, &dfops, NULL);
+ if (error)
+ goto out_trans_cancel;
+
+ error = xfs_trans_commit(tp);
+
+out_unlock:
+ xfs_iunlock(ip, XFS_ILOCK_EXCL);
+ return error;
+out_trans_cancel:
+ xfs_defer_cancel(&dfops);
+ xfs_trans_cancel(tp);
+ goto out_unlock;
+}
+
+/* Allocate all CoW reservations covering a part of a file. */
+int
+xfs_reflink_allocate_cow_range(
+ struct xfs_inode *ip,
+ xfs_off_t offset,
+ xfs_off_t count)
+{
+ struct xfs_mount *mp = ip->i_mount;
+ xfs_fileoff_t offset_fsb = XFS_B_TO_FSBT(mp, offset);
+ xfs_fileoff_t end_fsb = XFS_B_TO_FSB(mp, offset + count);
+ int error;
+
+ ASSERT(xfs_is_reflink_inode(ip));
+
+ trace_xfs_reflink_allocate_cow_range(ip, offset, count);
+
+ /*
+ * Make sure that the dquots are there.
+ */
+ error = xfs_qm_dqattach(ip, 0);
+ if (error)
+ return error;
+
+ while (offset_fsb < end_fsb) {
+ error = __xfs_reflink_allocate_cow(ip, &offset_fsb, end_fsb);
+ if (error) {
+ trace_xfs_reflink_allocate_cow_range_error(ip, error,
+ _RET_IP_);
+ break;
+ }
+ }
+
+ return error;
+}
+
/*
* Find the CoW reservation (and whether or not it needs block allocation)
* for a given byte offset of a file.
diff --git a/fs/xfs/xfs_reflink.h b/fs/xfs/xfs_reflink.h
index bffa4be..c0c989a 100644
--- a/fs/xfs/xfs_reflink.h
+++ b/fs/xfs/xfs_reflink.h
@@ -28,6 +28,8 @@ extern int xfs_reflink_trim_around_shared(struct xfs_inode *ip,
extern int xfs_reflink_reserve_cow_range(struct xfs_inode *ip,
xfs_off_t offset, xfs_off_t count);
+extern int xfs_reflink_allocate_cow_range(struct xfs_inode *ip,
+ xfs_off_t offset, xfs_off_t count);
extern bool xfs_reflink_find_cow_mapping(struct xfs_inode *ip, xfs_off_t offset,
struct xfs_bmbt_irec *imap, bool *need_alloc);
extern int xfs_reflink_trim_irec_to_next_cow(struct xfs_inode *ip,
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index 7612096..8e89223 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -3332,7 +3332,6 @@ DEFINE_INODE_IREC_EVENT(xfs_reflink_cow_enospc);
DEFINE_RW_EVENT(xfs_reflink_reserve_cow_range);
DEFINE_RW_EVENT(xfs_reflink_allocate_cow_range);
-DEFINE_INODE_IREC_EVENT(xfs_reflink_allocate_cow_extent);
DEFINE_INODE_IREC_EVENT(xfs_reflink_bounce_dio_write);
DEFINE_IOMAP_EVENT(xfs_reflink_find_cow_mapping);
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