Re: [PATCH 07/14] iomap: simplify iomap_dio_bio_iter

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

On Wed, Jan 14, 2026 at 08:41:05AM +0100, Christoph Hellwig wrote:
> Use iov_iter_count to check if we need to continue as that just reads
> a field in the iov_iter, and only use bio_iov_vecs_to_alloc to calculate
> the actual number of vectors to allocate for the bio.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Huh, interesting.  bio_iov_vecs_to_alloc returns 0 if the iov_iter is of
type bvec, so I guess we'd only run the loop body once before, and with
zero pages?  Hrmm, that doesn't seem right.

Does that mean that we could always construct a bio for the entire bvec?
Or does that just mean that directio doesn't get called with a bvec
iterator?

Or, basic question: what the heck is a bvec?  A bio_vec?  So perhaps
iomap_dio_bio_iter can't be called with a bio_vec because we're
constructing a bio, not dealing with an existing one?

<have the cold meds kicked in yet?>

--D

> ---
>  fs/iomap/direct-io.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 6ec4940e019c..1acdab7cf5f1 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -311,7 +311,7 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
>  	blk_opf_t bio_opf = REQ_SYNC | REQ_IDLE;
>  	struct bio *bio;
>  	bool need_zeroout = false;
> -	int nr_pages, ret = 0;
> +	int ret = 0;
>  	u64 copied = 0;
>  	size_t orig_count;
>  	unsigned int alignment;
> @@ -439,7 +439,6 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
>  			goto out;
>  	}
>  
> -	nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter, BIO_MAX_VECS);
>  	do {
>  		size_t n;
>  
> @@ -452,7 +451,9 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
>  			goto out;
>  		}
>  
> -		bio = iomap_dio_alloc_bio(iter, dio, nr_pages, bio_opf);
> +		bio = iomap_dio_alloc_bio(iter, dio,
> +				bio_iov_vecs_to_alloc(dio->submit.iter,
> +						BIO_MAX_VECS), bio_opf);
>  		fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
>  					  GFP_KERNEL);
>  		bio->bi_iter.bi_sector = iomap_sector(iomap, pos);
> @@ -494,16 +495,14 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
>  		dio->size += n;
>  		copied += n;
>  
> -		nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter,
> -						 BIO_MAX_VECS);
>  		/*
>  		 * We can only poll for single bio I/Os.
>  		 */
> -		if (nr_pages)
> +		if (iov_iter_count(dio->submit.iter))
>  			dio->iocb->ki_flags &= ~IOCB_HIPRI;
>  		iomap_dio_submit_bio(iter, dio, bio, pos);
>  		pos += n;
> -	} while (nr_pages);
> +	} while (iov_iter_count(dio->submit.iter));
>  
>  	/*
>  	 * We need to zeroout the tail of a sub-block write if the extent type
> -- 
> 2.47.3
> 
>