Re: [PATCH 04/15] iov_iter: extract a iov_iter_extract_bvecs helper from bio code

[Christoph Hellwig <hch@lst.de>]

On Mon, Jan 26, 2026 at 03:27:16PM +0900, Damien Le Moal wrote:
> On 1/26/26 2:53 PM, Christoph Hellwig wrote:
> > Massage __bio_iov_iter_get_pages so that it doesn't need the bio, and
> > move it to lib/iov_iter.c so that it can be used by block code for
> > other things than filling a bio and by other subsystems like netfs.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> 
> > +ssize_t iov_iter_extract_bvecs(struct iov_iter *iter, struct bio_vec *bv,
> > +		size_t max_size, unsigned short *nr_vecs,
> > +		unsigned short max_vecs, iov_iter_extraction_t extraction_flags)
> > +{
> > +	unsigned short entries_left = max_vecs - *nr_vecs;
> 
> Do we need to check that *nrvecs > 0 && *nrvecs < max_vecs ?
> Also, if *nr_vecs == max_vecs, we should warn and return 0, no ?

*nr_vecs = 0 is fine, and in fact the most common case.

We could add a protection for *nrvecs < max_vecs, but this is a very
low-level API, so we should be able to expect some sanity from the
users.  Especially as it will blow up instantly, including with KASAN
splats.