Re: [PATCH 07/15] block: pass a maxlen argument to bio_iov_iter_bounce

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

On Wed, Jan 21, 2026 at 07:43:15AM +0100, Christoph Hellwig wrote:
> Allow the file system to limit the size processed in a single
> bounce operation.  This is needed when generating integrity data
> so that the size of a single integrity segment can't overflow.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  block/bio.c          | 17 ++++++++++-------
>  fs/iomap/direct-io.c |  2 +-
>  include/linux/bio.h  |  2 +-
>  3 files changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index da795b1df52a..e89b24dc0283 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1293,9 +1293,10 @@ static void bio_free_folios(struct bio *bio)
>  	}
>  }
>  
> -static int bio_iov_iter_bounce_write(struct bio *bio, struct iov_iter *iter)
> +static int bio_iov_iter_bounce_write(struct bio *bio, struct iov_iter *iter,
> +		size_t maxlen)
>  {
> -	size_t total_len = iov_iter_count(iter);
> +	size_t total_len = min(maxlen, iov_iter_count(iter));
>  
>  	if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
>  		return -EINVAL;
> @@ -1333,9 +1334,10 @@ static int bio_iov_iter_bounce_write(struct bio *bio, struct iov_iter *iter)
>  	return 0;
>  }
>  
> -static int bio_iov_iter_bounce_read(struct bio *bio, struct iov_iter *iter)
> +static int bio_iov_iter_bounce_read(struct bio *bio, struct iov_iter *iter,
> +		size_t maxlen)
>  {
> -	size_t len = min(iov_iter_count(iter), SZ_1M);
> +	size_t len = min3(iov_iter_count(iter), maxlen, SZ_1M);
>  	struct folio *folio;
>  
>  	folio = folio_alloc_greedy(GFP_KERNEL, &len);
> @@ -1372,6 +1374,7 @@ static int bio_iov_iter_bounce_read(struct bio *bio, struct iov_iter *iter)
>   * bio_iov_iter_bounce - bounce buffer data from an iter into a bio
>   * @bio:	bio to send
>   * @iter:	iter to read from / write into
> + * @maxlen:	maximum size to bounce
>   *
>   * Helper for direct I/O implementations that need to bounce buffer because
>   * we need to checksum the data or perform other operations that require
> @@ -1379,11 +1382,11 @@ static int bio_iov_iter_bounce_read(struct bio *bio, struct iov_iter *iter)
>   * copies the data into it.  Needs to be paired with bio_iov_iter_unbounce()
>   * called on completion.
>   */
> -int bio_iov_iter_bounce(struct bio *bio, struct iov_iter *iter)
> +int bio_iov_iter_bounce(struct bio *bio, struct iov_iter *iter, size_t maxlen)
>  {
>  	if (op_is_write(bio_op(bio)))
> -		return bio_iov_iter_bounce_write(bio, iter);
> -	return bio_iov_iter_bounce_read(bio, iter);
> +		return bio_iov_iter_bounce_write(bio, iter, maxlen);
> +	return bio_iov_iter_bounce_read(bio, iter, maxlen);
>  }
>  
>  static void bvec_unpin(struct bio_vec *bv, bool mark_dirty)
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 9c572de0d596..842fc7fecb2d 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -326,7 +326,7 @@ static ssize_t iomap_dio_bio_iter_one(struct iomap_iter *iter,
>  	bio->bi_end_io = iomap_dio_bio_end_io;
>  
>  	if (dio->flags & IOMAP_DIO_BOUNCE)
> -		ret = bio_iov_iter_bounce(bio, dio->submit.iter);
> +		ret = bio_iov_iter_bounce(bio, dio->submit.iter, UINT_MAX);

Nitpicking here, but shouldn't this be SIZE_MAX?

--D

>  	else
>  		ret = bio_iov_iter_get_pages(bio, dio->submit.iter,
>  					     alignment - 1);
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index 95cfc79b88b8..df0d7e71372a 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -479,7 +479,7 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty);
>  extern void bio_set_pages_dirty(struct bio *bio);
>  extern void bio_check_pages_dirty(struct bio *bio);
>  
> -int bio_iov_iter_bounce(struct bio *bio, struct iov_iter *iter);
> +int bio_iov_iter_bounce(struct bio *bio, struct iov_iter *iter, size_t maxlen);
>  void bio_iov_iter_unbounce(struct bio *bio, bool is_error, bool mark_dirty);
>  
>  extern void bio_copy_data_iter(struct bio *dst, struct bvec_iter *dst_iter,
> -- 
> 2.47.3
> 
>