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

From: Dmitry Monakhov
Date: Wed Mar 03 2010 - 14:42:32 EST

Mike Snitzer <snitzer@xxxxxxxxxx> 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
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