Re: [PATCH] block: Make __bio_clone_fast() copy bi_vcnt

Kent Overstreet
2018-06-30T23:38:30Z

On Fri, Jun 29, 2018 at 01:00:33PM -0700, Bart Van Assche wrote:
> On 06/28/18 17:04, Kent Overstreet wrote:
> > On Thu, Jun 28, 2018 at 04:54:44PM -0700, Bart Van Assche wrote:
> > > Thanks for chiming in. The linux-block mailing list is archived by multiple
> > > websites. The entire e-mail thread is available on e.g.
> > > https://www.mail-archive.com/linux-block@vger.kernel.org/msg23006.html.
> > >
> > > I have a question for you: at least in kernel v4.17 bio_clone_bioset()
> > > copies bi_vcnt from the source to the destination bio. However,
> > > __bio_clone_fast() doesn't copy bi_vcnt. Isn't that an inconsistency?
> >
> > No - when you use bio_clone_bioset() you get a bio that you own and can do
> > whatever you want with, so it does make sense for it to initialize bi_vcnt.
> >
> > e.g. you could use bio_clone_bioset() when you're going to be bouncing a bio,
> > iterating over each bvec and allocating a new page and copying data from the old
> > page to the new page.
>
> Hello Kent,
>
> Have you considered to explain this in a comment above __bio_clone_fast() to
> avoid that the next person who reads that function gets confused?

Well, there is a large comment in bio_clone_bioset() that you must have found...