linux-kernel - Re: [dm-devel] [PATCH v3 06/26] block: Add bio_end

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Message-ID: <20121002202026.GN26488@google.com>
Date:	Tue, 2 Oct 2012 13:20:26 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, axboe@...nel.dk, linux-s390@...r.kernel.org,
	Chris Mason <chris.mason@...ionio.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Alasdair Kergon <agk@...hat.com>, tj@...nel.org,
	Steven Whitehouse <swhiteho@...hat.com>,
	Lars Ellenberg <drbd-dev@...ts.linbit.com>
Subject: Re: [dm-devel] [PATCH v3 06/26] block: Add bio_end_sector()

On Tue, Oct 02, 2012 at 02:10:01PM -0400, Vivek Goyal wrote:
> On Mon, Sep 24, 2012 at 03:34:46PM -0700, Kent Overstreet wrote:
> 
> [..]
> > diff --git a/include/linux/bio.h b/include/linux/bio.h
> > index 4e32be1..d985e90 100644
> > --- a/include/linux/bio.h
> > +++ b/include/linux/bio.h
> > @@ -67,6 +67,7 @@
> >  #define bio_offset(bio)		bio_iovec((bio))->bv_offset
> >  #define bio_segments(bio)	((bio)->bi_vcnt - (bio)->bi_idx)
> >  #define bio_sectors(bio)	((bio)->bi_size >> 9)
> > +#define bio_end_sector(bio)	((bio)->bi_sector + bio_sectors(bio))
> 
> May be it is just me. But bio_end_sector() kind of sounds that it will
> calculate to the last sector of bio. So I thought of it more as
> bio_last_sector() and not the sector which is next to the last sector.
> 
> Will it make sense to introduce bio_last_sector() and use +1 everywhere.
> Or may be we need a better name. Can't think of one though.

Ugh, that sounds like it'd be just begging for fencepost errors. I've
never ran into a situation where I needed bio->bi_sector +
bio_sectors(bio) - 1, either.

I kind of see your point... it seems like there should be a name for
this concept (same as a pointer to the end of an array), but I can't
think of one.
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