linux-kernel - Re: [PATCH v2 14/14] fs: xfs: Support setting FMODE_CAN_ATOMIC

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Message-ID: <ZejhNMW5o0JSCgqW@dread.disaster.area>
Date: Thu, 7 Mar 2024 08:33:40 +1100
From: Dave Chinner <david@...morbit.com>
To: John Garry <john.g.garry@...cle.com>
Cc: djwong@...nel.org, hch@....de, viro@...iv.linux.org.uk,
	brauner@...nel.org, jack@...e.cz, chandan.babu@...cle.com,
	axboe@...nel.dk, martin.petersen@...cle.com,
	linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
	ojaswin@...ux.ibm.com, ritesh.list@...il.com,
	linux-block@...r.kernel.org
Subject: Re: [PATCH v2 14/14] fs: xfs: Support setting FMODE_CAN_ATOMIC_WRITE

On Mon, Mar 04, 2024 at 01:04:28PM +0000, John Garry wrote:
> For when an inode is enabled for atomic writes, set FMODE_CAN_ATOMIC_WRITE
> flag. We check for direct I/O and also check that the bdev can actually
> support atomic writes.
> 
> We rely on the block layer to reject atomic writes which exceed the bdev
> request_queue limits, so don't bother checking any such thing here.
> 
> Signed-off-by: John Garry <john.g.garry@...cle.com>
> ---
>  fs/xfs/xfs_file.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index cecc5428fd7c..e63851be6c15 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -1234,6 +1234,25 @@ xfs_file_remap_range(
>  	return remapped > 0 ? remapped : ret;
>  }
>  
> +static bool xfs_file_open_can_atomicwrite(
> +	struct inode		*inode,
> +	struct file		*file)
> +{
> +	struct xfs_inode	*ip = XFS_I(inode);
> +	struct xfs_buftarg	*target = xfs_inode_buftarg(ip);
> +
> +	if (!(file->f_flags & O_DIRECT))
> +		return false;
> +
> +	if (!xfs_inode_atomicwrites(ip))
> +		return false;
> +
> +	if (!bdev_can_atomic_write(target->bt_bdev))
> +		return false;

Again, this is static blockdev information - the inode atomic write
flag should not be set if the bdev cannot do atomic writes. It
should be checked at mount time - the filesystem probably should
only mount read-only if it is configured to allow atomic writes and
the underlying blockdev does not support atomic writes...

-Dave.
-- 
Dave Chinner
david@...morbit.com