Re: [PATCH 2/3] iomap: don't lose a fiemap iteration error when emitting the last extent

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Sep 21, 2026 at 10:31:32AM +0200, Andrea Parri wrote:
> iomap_fiemap() emits extents one behind: iomap_fiemap_iter() flushes the
> previous extent and remembers the current one, and the remembered extent
> is written with FIEMAP_EXTENT_LAST after the iteration loop.
> 
> That final flush overwrites ret, so when ->iomap_begin() fails partway
> through the iteration the error is replaced by the result of
> iomap_to_fiemap() (zero on success) and iomap_fiemap() returns success
> with a truncated extent list whose last entry is wrongly marked as the
> last extent in the file.  The pre-iomap_iter code returned the error
> from inside the loop, before flushing the pending extent.
> 
> Check for the iteration error before flushing the pending extent, so
> that real errors are propagated and only a successful iteration emits
> the final FIEMAP_EXTENT_LAST extent.  -ENOENT (no mapping) is still not
> an error, and the pending extent is still emitted in that case.
> 
> Fixes: 7892386d35715 ("iomap: switch iomap_fiemap to use iomap_iter")
> Cc: stable@vger.kernel.org

Oooh, an oldie!

Cc: <stable@vger.kernel.org> # v5.15

> Assisted-by: LLM
> Signed-off-by: Andrea Parri <parri.andrea@gmail.com>

Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  fs/iomap/fiemap.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/iomap/fiemap.c b/fs/iomap/fiemap.c
> index d11dadff82865..54b824b7edb5c 100644
> --- a/fs/iomap/fiemap.c
> +++ b/fs/iomap/fiemap.c
> @@ -76,15 +76,15 @@ int iomap_fiemap(struct inode *inode, struct fiemap_extent_info *fi,
>  	while ((ret = iomap_iter(&iter, ops)) > 0)
>  		iter.status = iomap_fiemap_iter(&iter, fi, &prev);
>  
> +	/* inode with no (attribute) mapping will give ENOENT */
> +	if (ret < 0 && ret != -ENOENT)
> +		return ret;
> +
>  	if (prev.type != IOMAP_HOLE) {
>  		ret = iomap_to_fiemap(fi, &prev, FIEMAP_EXTENT_LAST);
>  		if (ret < 0)
>  			return ret;
>  	}
> -
> -	/* inode with no (attribute) mapping will give ENOENT */
> -	if (ret < 0 && ret != -ENOENT)
> -		return ret;
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(iomap_fiemap);
> -- 
> 2.53.0
>