linux-kernel - Re: [PATCH v2 09/14] block: Add an explicit bio flag for bios that own their bvec

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Message-ID: <20120525164914.GE3855@redhat.com>
Date:	Fri, 25 May 2012 12:49:14 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	Boaz Harrosh <bharrosh@...asas.com>, linux-kernel@...r.kernel.org,
	linux-bcache@...r.kernel.org, dm-devel@...hat.com,
	linux-fsdevel@...r.kernel.org, tj@...nel.org, axboe@...nel.dk,
	agk@...hat.com, neilb@...e.de, drbd-dev@...ts.linbit.com,
	mpatocka@...hat.com, sage@...dream.net, yehuda@...newdream.net
Subject: Re: [PATCH v2 09/14] block: Add an explicit bio flag for bios that
 own their bvec

On Thu, May 24, 2012 at 02:31:58PM -0700, Kent Overstreet wrote:
> On Thu, May 24, 2012 at 07:57:34PM +0300, Boaz Harrosh wrote:
> > How do you insure that the original bio which owns the
> > bvec is not freed before the split-out bio.
> > 
> > Perhaps calling code needs to make sure by taking an extra
> > ref on the original bio, or something. If so a big fat comment
> > at bio_split is do.
> 
> Yeah, just added that.
> 
> > 
> > And I understand you did not like my suggestion of negating
> > the meaning of the flag, so the default is zero?
> > Please say why?
> 
> I liked it at first, but I think I prefer having the flag be set
> if bio_free() must take some action; i.e. you set the flag when you
> allocate bi_io_vec. Also, I think bio_alloc_bioset() getting
> reimplemented is less likely than people open coding bio splitting or
> something that shares bi_io_vec in the future, so it's slightlry less
> likely to be used wrong this way.

Even if you keep it as it is, I thought BIO_OWNS_BVEC probably communicates
the idea better than BIO_HAS_BVEC.

Thanks
Vivek
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