[PATCH RFC 08/10] xfs: Commit CoW-based atomic writes atomically

John Garry
2025-02-04T12:02:20Z

When completing a CoW-based write, each extent range mapping update is
covered by a separate transaction.

For a CoW-based atomic write, all mappings must be changed at once, so
change to use a single transaction.

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
fs/xfs/xfs_file.c | 5 ++++-
fs/xfs/xfs_reflink.c | 48 ++++++++++++++++++++++++++++++++++++++++++++
fs/xfs/xfs_reflink.h | 3 +++
3 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 12af5cdc3094..170d7891f90d 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -527,7 +527,10 @@ xfs_dio_write_end_io(
nofs_flag = memalloc_nofs_save();

if (flags & IOMAP_DIO_COW) {
- error = xfs_reflink_end_cow(ip, offset, size);
+ if (iocb->ki_flags & IOCB_ATOMIC)
+ error = xfs_reflink_end_atomic_cow(ip, offset, size);
+ else
+ error = xfs_reflink_end_cow(ip, offset, size);
if (error)
goto out;
}
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index dbce333b60eb..60c986300faa 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -990,6 +990,54 @@ xfs_reflink_end_cow(
trace_xfs_reflink_end_cow_error(ip, error, _RET_IP_);
return error;
}
+int
+xfs_reflink_end_atomic_cow(
+ struct xfs_inode *ip,
+ xfs_off_t offset,
+ xfs_off_t count)
+{
+ xfs_fileoff_t offset_fsb;
+ xfs_fileoff_t end_fsb;
+ int error = 0;
+ struct xfs_mount *mp = ip->i_mount;
+ struct xfs_trans *tp;
+ unsigned int resblks;
+ bool commit = false;
+
+ trace_xfs_reflink_end_cow(ip, offset, count);
+
+ offset_fsb = XFS_B_TO_FSBT(ip->i_mount, offset);
+ end_fsb = XFS_B_TO_FSB(ip->i_mount, offset + count);
+
+ resblks = XFS_NEXTENTADD_SPACE_RES(ip->i_mount,
+ (unsigned int)(end_fsb - offset_fsb),
+ XFS_DATA_FORK);
+
+ error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0,
+ XFS_TRANS_RESERVE, &tp);
+ if (error)
+ return error;
+
+ xfs_ilock(ip, XFS_ILOCK_EXCL);
+ xfs_trans_ijoin(tp, ip, 0);
+
+ while (end_fsb > offset_fsb && !error)
+ error = xfs_reflink_end_cow_extent_locked(ip, &offset_fsb,
+ end_fsb, tp, &commit);
+
+ if (error || !commit)
+ goto out_cancel;
+
+ if (error)
+ trace_xfs_reflink_end_cow_error(ip, error, _RET_IP_);
+ error = xfs_trans_commit(tp);
+ xfs_iunlock(ip, XFS_ILOCK_EXCL);
+ return error;
+out_cancel:
+ xfs_trans_cancel(tp);
+ xfs_iunlock(ip, XFS_ILOCK_EXCL);
+ return error;
+}

/*
* Free all CoW staging blocks that are still referenced by the ondisk refcount
diff --git a/fs/xfs/xfs_reflink.h b/fs/xfs/xfs_reflink.h
index ef5c8b2398d8..2c3b096c1386 100644
--- a/fs/xfs/xfs_reflink.h
+++ b/fs/xfs/xfs_reflink.h
@@ -45,6 +45,9 @@ extern int xfs_reflink_cancel_cow_range(struct xfs_inode *ip, xfs_off_t offset,
xfs_off_t count, bool cancel_real);
extern int xfs_reflink_end_cow(struct xfs_inode *ip, xfs_off_t offset,
xfs_off_t count);
+ int
+xfs_reflink_end_atomic_cow(struct xfs_inode *ip, xfs_off_t offset,
+ xfs_off_t count);
extern int xfs_reflink_recover_cow(struct xfs_mount *mp);
extern loff_t xfs_reflink_remap_range(struct file *file_in, loff_t pos_in,
struct file *file_out, loff_t pos_out, loff_t len,
--
2.31.1