linux-kernel - Re: [PATCH v5 6/7] xfs: Validate atomic writes

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Message-ID: <20240821171031.GL865349@frogsfrogsfrogs>
Date: Wed, 21 Aug 2024 10:10:31 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: John Garry <john.g.garry@...cle.com>
Cc: axboe@...nel.dk, brauner@...nel.org, viro@...iv.linux.org.uk,
	jack@...e.cz, chandan.babu@...cle.com, dchinner@...hat.com,
	hch@....de, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, hare@...e.de,
	martin.petersen@...cle.com, catherine.hoang@...cle.com,
	kbusch@...nel.org
Subject: Re: [PATCH v5 6/7] xfs: Validate atomic writes

On Sat, Aug 17, 2024 at 09:47:59AM +0000, John Garry wrote:
> Validate that an atomic write adheres to length/offset rules. Since we
> require extent alignment for atomic writes, this effectively also enforces
> that the BIO which iomap produces is aligned.
> 
> 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,
> FORCEALIGN and also ATOMICWRITES flags would also need to be set for the
> inode.
> 
> Signed-off-by: John Garry <john.g.garry@...cle.com>
> ---
>  fs/xfs/xfs_file.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 4cdc54dc9686..9b6530a4eb4a 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -684,9 +684,20 @@ xfs_file_dio_write(
>  	struct kiocb		*iocb,
>  	struct iov_iter		*from)
>  {
> -	struct xfs_inode	*ip = XFS_I(file_inode(iocb->ki_filp));
> +	struct inode		*inode = file_inode(iocb->ki_filp);
> +	struct xfs_inode	*ip = XFS_I(inode);
>  	struct xfs_buftarg      *target = xfs_inode_buftarg(ip);
>  	size_t			count = iov_iter_count(from);
> +	struct xfs_mount	*mp = ip->i_mount;
> +
> +	if (iocb->ki_flags & IOCB_ATOMIC) {
> +		if (count < i_blocksize(inode))
> +			return -EINVAL;
> +		if (count > XFS_FSB_TO_B(mp, ip->i_extsize))
> +			return -EINVAL;

Here's also the place to check the dynamic things like dalign/swidth
alignment.  Other than that, this looks good.

--D

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