Re: [dm-devel] [PATCH 1/2] blkdev: fix merge_bvec_fn return value checks

[Dmitry Monakhov <dmonakhov openvz org>]

Mike Snitzer <snitzer redhat com> writes:

> Linux has all sorts of internal interfaces that are "odd"... the current
> 'q->merge_bvec_fn' interface included.  But odd is not a problem (nor is
> it "broken") unless you make changes that don't consider how the current
> interface is defined.
Ok. then cant you please explain more historical questions
1) Why bio_add_page() can not add less data than requested?
   Seems that it doesn't make caller's code much complicate
   Off course barrier bio is special case. I don't consider it here.
   
2) What statement "bio_add_page() must accept at least one page"
   exactly means?
   IMHO this means that bio_add_page() must accept at least
   one page with len (PAGE_SIZE - offset). Or more restricted
   statemnt that first bio_add_page() must be always successfull.

   But currently in some places this rule treated as what all bio
   which has size less whan PAGE_SIZE are accepted. And in x86 such
   bio may has up to 8 pages/bvecs.
>
> But I digress...
>
> Mike