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Re: [Xen-devel] [GIT PULL] for-2.6.32/bug-fixes

To: "Konrad Rzeszutek Wilk" <konrad.wilk@xxxxxxxxxx>
Subject: Re: [Xen-devel] [GIT PULL] for-2.6.32/bug-fixes
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Tue, 17 May 2011 10:48:00 +0100
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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>>> On 16.05.11 at 22:35, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:
> with xen-blkback wherein a barrier request would have been discarded (and an 
> error
> returned) b/c the sector provided via the request was -1. The -1 sector made
> vbd_translate return an error (it checked the sector number against the size 
> of
> the disk) and it would never go through trying to do a barrier. The second 
> bug-fix
> is also in my devel/xen-blkback-v3.2 upstream tree.

Is this really correct? You appear to assume that BLKIF_OP_WRITE_BARRIER
always has no data, but the rest of the code in the driver (and
the frontend) doesn't seem to imply that (see e.g. the check
immediately following the switch statement your patch modifies).
Hence shouldn't you clear the sector number only when
req->nr_segments is zero? Or alternatively, shouldn't
vbd_translate() simply not fail when req->nr_sects is zero?

Additionally, looking at the check in vbd_translate(), wouldn't you
think there ought to be overflow checking for the addition, too?


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