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

From: Dave Chinner
Date: Tue Oct 29 2024 - 16:48:48 EST


On Sun, Oct 27, 2024 at 02:01:16AM +0800, alexjlzheng@xxxxxxxxx wrote:
> From: Jinliang Zheng <alexjlzheng@xxxxxxxxxxx>
>
> 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@xxxxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxx