linux-kernel - Re: [PATCH v6 08/13] block: Add an explicit bio flag for bios that own their bvec

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Message-ID: <20120828172336.GA25749@google.com>
Date:	Tue, 28 Aug 2012 10:23:36 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Adrian Bunk <bunk@...nel.org>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, tj@...nel.org, vgoyal@...hat.com,
	mpatocka@...hat.com, bharrosh@...asas.com,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v6 08/13] block: Add an explicit bio flag for bios that
 own their bvec

On Wed, Aug 22, 2012 at 11:00:38PM +0300, Adrian Bunk wrote:
> On Wed, Aug 22, 2012 at 12:22:41PM -0700, Kent Overstreet wrote:
> > On Wed, Aug 22, 2012 at 08:43:52PM +0300, Adrian Bunk wrote:
> > > On Wed, Aug 22, 2012 at 10:04:05AM -0700, Kent Overstreet wrote:
> > > >...
> > > > --- a/include/linux/blk_types.h
> > > > +++ b/include/linux/blk_types.h
> > > > @@ -117,6 +117,7 @@ struct bio {
> > > >   * BIO_POOL_IDX()
> > > >   */
> > > >  #define BIO_RESET_BITS	12
> > > > +#define BIO_OWNS_VEC	12	/* bio_free() should free bvec */
> > > >...
> > > 
> > > This doesn't look right.
> > 
> > Well, the first 12 bits are reset, so bit 12 will get preserved... I
> > guess it's unusual to have a duplicated enum value like that but
> > BIO_RESET_BITS is just a marker, not a real bit.
> 
> Wouldn't a BIO_RESET_MASK be better than BIO_RESET_BITS?

Ehh... Might be good to have BIO_RESET_MASK too, but we really want
BIO_RESET_BITS with the flags as that makes it explicit which flags get
cleared and which don't. At first I was going to add BIO_RESET_MASK too,
but it just seemed to get ugly and verbose and didn't fit nicely
anywhere, so I'm dithering and not doing anything with it for now.
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