[PATCH v9 7/8] xfs: Validate atomic writes

John Garry
2024-10-16T10:04:17Z

Validate that an atomic write adheres to length/offset rules. Currently
we can only write a single FS block.

For an IOCB with IOCB_ATOMIC set to get as far as xfs_file_write_iter(),
FMODE_CAN_ATOMIC_WRITE will need to be set for the file; for this,
ATOMICWRITES flags would also need to be set for the inode.

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
fs/xfs/xfs_file.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index b19916b11fd5..1ccbc1eb75c9 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -852,6 +852,20 @@ xfs_file_write_iter(
if (IS_DAX(inode))
return xfs_file_dax_write(iocb, from);

+ if (iocb->ki_flags & IOCB_ATOMIC) {
+ /*
+ * Currently only atomic writing of a single FS block is
+ * supported. It would be possible to atomic write smaller than
+ * a FS block, but there is no requirement to support this.
+ * Note that iomap also does not support this yet.
+ */
+ if (ocount != ip->i_mount->m_sb.sb_blocksize)
+ return -EINVAL;
+ ret = generic_atomic_write_valid(iocb, from);
+ if (ret)
+ return ret;
+ }
+
if (iocb->ki_flags & IOCB_DIRECT) {
/*
* Allow a directio write to fall back to a buffered
--
2.31.1