Re: [PATCH 2/4] FIXUP: iomap: aligning to larger than fs block size doesn't make sense

Darrick J. Wong
2025-10-27T16:11:44Z

On Thu, Oct 23, 2025 at 03:55:43PM +0200, Christoph Hellwig wrote:
> All of the VFS and helpers assume that the file system block size must
> be larger or equal to the device block size. So doing a max of both
> doesn't really make much sense. Siplify the code in iomap_dio_bio_iter

Simplify

> to do a simple if/else.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

With that fixed,
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
> fs/iomap/direct-io.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index ce9cbd2bace0..8d094d6f5f3e 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -336,17 +336,19 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
> int nr_pages, ret = 0;
> u64 copied = 0;
> size_t orig_count;
> - unsigned int alignment = bdev_logical_block_size(iomap->bdev);
> + unsigned int alignment;
>
> if ((pos | length) & (bdev_logical_block_size(iomap->bdev) - 1))
> return -EINVAL;
>
> /*
> - * Align to the larger one of bdev and fs block size, to meet the
> - * alignment requirement of both layers.
> + * File systems that write out of place and always allocate new blocks
> + * need each bio to be block aligned as that's the unit of allocation.
> */
> if (dio->flags & IOMAP_DIO_FSBLOCK_ALIGNED)
> - alignment = max(alignment, fs_block_size);
> + alignment = fs_block_size;
> + else
> + alignment = bdev_logical_block_size(iomap->bdev);
>
> if (dio->flags & IOMAP_DIO_WRITE) {
> bio_opf |= REQ_OP_WRITE;
> --
> 2.47.3
>
>