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

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] [GIT PULL] for-2.6.32/bug-fixes
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Wed, 18 May 2011 10:56:44 -0400
Cc: jeremy@xxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx
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On Wed, May 18, 2011 at 03:31:35PM +0100, Jan Beulich wrote:
> >>> On 18.05.11 at 15:24, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 
> >>> wrote:
> >> >Well, req->ns_segments = 0, so nseg is zero, which means all
> >> >of those for loops never get executed.
> >> 
> >> This you say is the case for the request you saw the failure with, or
> >> *all* barrier requests? In the latter case, what do you conclude this
> > 
> > Good question. It was the first barrier request sent when guest tried to
> > mount the filesystem. I will instrument the code to see what the other
> > barriers contained when they were sent.
> That wouldn't tell you anything if they're all empty, as there's nothing
> preventing other guests (including other guest OSes) to still send
> non-empty ones - after all the protocol allows for this.

Aha! That is what you been trying to tell me. I will make a patch to make
sure to not overwrite the req->sector_number blindly. What other guest OSes
use barriers? I looked at Solaris (it uses 'feature-flush-cache'), NetBSD
('feature-flush-cache') and Linux ('feature-barrier' and now in 2.6.40

The GPLV Windows drivers have no barrier implementation - do you know if
the Novell ones are using barriers?

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