Re: [PATCH v6 6/7] xfs: Validate atomic writes

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Sep 30, 2024 at 12:54:37PM +0000, John Garry wrote:
> 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_dio_write(),
> 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 | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 412b1d71b52b..fa6a44b88ecc 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -688,6 +688,13 @@ xfs_file_dio_write(
>  	struct xfs_buftarg      *target = xfs_inode_buftarg(ip);
>  	size_t			count = iov_iter_count(from);
>  
> +	if (iocb->ki_flags & IOCB_ATOMIC) {
> +		if (count != ip->i_mount->m_sb.sb_blocksize)
> +			return -EINVAL;
> +		if (!generic_atomic_write_valid(iocb, from))
> +			return -EINVAL;
> +	}

Does xfs_file_write_iter need a catch-all so that we don't fall back to
buffered write for a directio write that returns ENOTBLK?

	if (iocb->ki_flags & IOCB_DIRECT) {
		/*
		 * Allow a directio write to fall back to a buffered
		 * write *only* in the case that we're doing a reflink
		 * CoW.  In all other directio scenarios we do not
		 * allow an operation to fall back to buffered mode.
		 */
		ret = xfs_file_dio_write(iocb, from);
		if (ret != -ENOTBLK || (iocb->ki_flags & IOCB_ATOMIC))
			return ret;
	}

IIRC iomap_dio_rw can return ENOTBLK if pagecache invalidation fails for
the region that we're trying to directio write.

--D

> +
>  	/* direct I/O must be aligned to device logical sector size */
>  	if ((iocb->ki_pos | count) & target->bt_logical_sectormask)
>  		return -EINVAL;
> -- 
> 2.31.1
> 
>