linux-kernel - Re: [PATCH] xfs: fix the judgment of whether the file already has extents

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Message-ID: <ZyFJm7xg7Msd6eVr@dread.disaster.area>
Date: Wed, 30 Oct 2024 07:46:19 +1100
From: Dave Chinner <david@...morbit.com>
To: alexjlzheng@...il.com
Cc: cem@...nel.org, djwong@...nel.org, chandanbabu@...nel.org,
	dchinner@...hat.com, zhangjiachen.jaycee@...edance.com,
	linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jinliang Zheng <alexjlzheng@...cent.com>
Subject: Re: [PATCH] xfs: fix the judgment of whether the file already has
 extents

On Sun, Oct 27, 2024 at 02:01:16AM +0800, alexjlzheng@...il.com wrote:
> From: Jinliang Zheng <alexjlzheng@...cent.com>
> 
> When we call create(), lseek() and write() sequentially, offset != 0
> cannot be used as a judgment condition for whether the file already
> has extents.
> 
> This patch uses prev.br_startoff instead of offset != 0.
> 
> Signed-off-by: Jinliang Zheng <alexjlzheng@...cent.com>
> ---
>  fs/xfs/libxfs/xfs_bmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 36dd08d13293..94e7aeed9e95 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -3536,7 +3536,7 @@ xfs_bmap_btalloc_at_eof(
>  	 * or it's the first allocation in a file, just try for a stripe aligned
>  	 * allocation.
>  	 */
> -	if (ap->offset) {
> +	if (ap->prev.br_startoff != NULLFILEOFF) {
>  		xfs_extlen_t	nextminlen = 0;

Makes sense, but the logic is not correct. See xfs_bmap_adjacent()
on how it sets up the ap->blkno target for exact eof bno allocation.

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