linux-kernel - Re: [patch 1/2]block: handle merged discard request

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Message-ID: <20120820135739.GB28570@redhat.com>
Date:	Mon, 20 Aug 2012 09:57:39 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	"Martin K. Petersen" <martin.petersen@...cle.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Shaohua Li <shli@...nel.org>, Vivek Goyal <vgoyal@...hat.com>,
	axboe@...nel.dk, linux-kernel@...r.kernel.org, neilb@...e.de,
	linux-scsi@...r.kernel.org
Subject: Re: [patch 1/2]block: handle merged discard request

On Fri, Aug 17 2012 at 11:47pm -0400,
Martin K. Petersen <martin.petersen@...cle.com> wrote:

> >>>>> "Mike" == Mike Snitzer <snitzer@...hat.com> writes:
> 
> Mike> Could be I've wasted a few hours by rebasing these patches...
> Mike> regardless, it would be great if you could share what your plans
> Mike> are.
> 
> Heh, I worked on syncing my patch queue up to Jens' and James' trees
> this afternoon. But I didn't quite finish the block stuff, mainly due to
> some conflicts with a few topology changes I also have pending.
> 
> I'll take a look at your series. Maybe I'll swap things around and put
> the topology changes on top instead of below. Leverage some of the work
> you did...

OK, just FYI, I had to change bio_has_data() to test bio->bi_vcnt
(rather than bio->bi_io_vec != NULL) because a discard bio has a
non-NULL bio->bi_io_vec (likely points to the bio->bi_inline_vecs but I
didn't check yet).

But I haven't put my finger on _why_ a discard bio has bio->bi_io_vec
(but given my use of DM, bio comes from bio_alloc_bioset, and DM passes
original bio->bi_max_vecs for nr_iovecs).

Anyway, this bio_has_data() change seemed reasonable considering
bio_data() checks bio->bi_vcnt.
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