Re: [PATCH 03/14] iov_iter: extract a iov_iter_extract_bvecs helper from bio code

[Christoph Hellwig <hch@lst.de>]

On Thu, Jan 22, 2026 at 11:09:33PM -0800, Darrick J. Wong wrote:
> On Fri, Jan 23, 2026 at 06:44:48AM +0100, Christoph Hellwig wrote:
> > On Thu, Jan 22, 2026 at 09:47:03AM -0800, Darrick J. Wong wrote:
> > > > -	struct page **pages = (struct page **)bv;
> > > 
> > > Huh.  We type-abuse an array of bio_vec's as an array of struct page
> > > pointers??
> > > 
> > > As a straight hoist the patch looks correct but I'm confused about this.
> > 
> > Yes.  This uses the larger space allocated for bio_vecs to first
> > place the pages at the end, and then filling in the bio_vecs from the
> > beginning.  I think the comments describe it pretty well, but if you
> > have ideas for enhancement, this might be a good time to update them.
> 
> I'm not sure, since the alternative is to wrap the whole mess in a
> union, which makes the type-abuse more explicit but then is still pretty
> ugly.  The only improvement I can really think of would be a huge
> comment wherever we start this, which I think Kent's original code from
> 2011 had ("deep magic", etc).

I don't think a union would be good here.  It primarily operates on
the bio_vecs embedded in the bio, which certainly should not be a
union.