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 | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 412b1d71b52b..3a0a35e7826a 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -822,6 +822,14 @@ xfs_file_write_iter(
 	if (IS_DAX(inode))
 		return xfs_file_dax_write(iocb, from);
 
+	if (iocb->ki_flags & IOCB_ATOMIC) {
+		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

On Tue, Oct 15, 2024 at 09:01:41AM +0000, John Garry wrote:
> Validate that an atomic write adheres to length/offset rules. Currently
> we can only write a single FS block.

> +	if (iocb->ki_flags & IOCB_ATOMIC) {
> +		if (ocount != ip->i_mount->m_sb.sb_blocksize)
> +			return -EINVAL;

Maybe throw in a comment here why we are currently limited to atomic
writes of exactly the file system block size and don't allow smaller
values.

Otherwise this looks good to me.

On 15/10/2024 13:16, Christoph Hellwig wrote:
> On Tue, Oct 15, 2024 at 09:01:41AM +0000, John Garry wrote:
>> Validate that an atomic write adheres to length/offset rules. Currently
>> we can only write a single FS block.
>> +	if (iocb->ki_flags & IOCB_ATOMIC) {
>> +		if (ocount != ip->i_mount->m_sb.sb_blocksize)
>> +			return -EINVAL;
> Maybe throw in a comment here why we are currently limited to atomic
> writes of exactly the file system block size and don't allow smaller
> values.
> 

ok

> Otherwise this looks good to me.

cheers