linux-kernel - Re: [PATCH] xfs: Do not fallback to buffered-io for DIO atomic write

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Message-ID: <878qu8m5r6.fsf@gmail.com>
Date: Tue, 29 Oct 2024 00:09:25 +0530
From: Ritesh Harjani (IBM) <ritesh.list@...il.com>
To: linux-xfs@...r.kernel.org
Cc: "Darrick J . Wong" <djwong@...nel.org>, Christoph Hellwig <hch@...radead.org>, John Garry <john.g.garry@...cle.com>, Ojaswin Mujoo <ojaswin@...ux.ibm.com>, Dave Chinner <david@...morbit.com>, Carlos Maiolino <cem@...nel.org>, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] xfs: Do not fallback to buffered-io for DIO atomic write

We need not pick this patch up. As after the careful review of the code,
it seems XFS can never fallback to buffered-io for DIO atomic writes. 

Hence we don't need this patch. More details in [1]. 

[1]: https://lore.kernel.org/linux-xfs/cover.1729825985.git.ritesh.list@gmail.com/T/#m9dbecc11bed713ed0d7a486432c56b105b555f04

(Sorry for the noise).

"Ritesh Harjani (IBM)" <ritesh.list@...il.com> writes:

> iomap can return -ENOTBLK if pagecache invalidation fails.
> Let's make sure if -ENOTBLK is ever returned for atomic
> writes than we fail the write request (-EIO) instead of
> fallback to buffered-io.
>
> Suggested-by: Darrick J. Wong <djwong@...nel.org>
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
> ---
>
> This should be on top of John's atomic write series [1].
> [1]: https://lore.kernel.org/linux-xfs/20241019125113.369994-1-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 ca47cae5a40a..b819a9273511 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -876,6 +876,14 @@ xfs_file_write_iter(
>  		ret = xfs_file_dio_write(iocb, from);
>  		if (ret != -ENOTBLK)
>  			return ret;
> +		/*
> +		 * iomap can return -ENOTBLK if pagecache invalidation fails.
> +		 * Let's make sure if -ENOTBLK is ever returned for atomic
> +		 * writes than we fail the write request instead of fallback
> +		 * to buffered-io.
> +		 */
> +		if (iocb->ki_flags & IOCB_ATOMIC)
> +			return -EIO;
>  	}
>
>  	return xfs_file_buffered_write(iocb, from);
> --
> 2.39.5