linux-kernel - Re: [PATCH 26/27] block: Add an explicit bio flag for bios that own their bvec

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Message-ID: <20130326194237.GA24935@google.com>
Date:	Tue, 26 Mar 2013 12:42:37 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, axboe@...nel.dk
Subject: Re: [PATCH 26/27] block: Add an explicit bio flag for bios that own
 their bvec

On Tue, Mar 26, 2013 at 11:11:06AM -0700, Andrew Morton wrote:
> On Tue, 19 Feb 2013 16:22:40 -0800 Kent Overstreet <koverstreet@...gle.com> wrote:
> 
> > This is for the new bio splitting code. When we split a bio, if the
> > split occured on a bvec boundry we reuse the bvec for the new bio. But
> > that means bio_free() can't free it, hence the explicit flag.
> > 
> > --- 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 */
> >  
> >  #define bio_flagged(bio, flag)	((bio)->bi_flags & (1 << (flag)))
> 
> The BIO_OWNS_VEC definition seems to be in the wrong place - it should
> be grouped with the "bio flags" group above?

No - BIO_OWNS_VEC is set by bio_alloc_bioset() and is used by bio_free()
to determine if it should free the biovec, so it's something we don't
want cleared if driver code uses bio_reset().
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