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Re: [Xen-devel] What is the state of blktap2?

To: Pasi Kärkkäinen <pasik@xxxxxx>
Subject: Re: [Xen-devel] What is the state of blktap2?
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Fri, 22 Jan 2010 10:43:28 -0800
Cc: "David P. Quigley" <dpquigl@xxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Ian Campbell <Ian.Campbell@xxxxxxxxxx>, Daniel Stodden <Daniel.Stodden@xxxxxxxxxx>
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On 01/21/2010 11:14 PM, Pasi Kärkkäinen wrote:
On Thu, Jan 21, 2010 at 06:13:46PM -0500, David P. Quigley wrote:
On Fri, 2010-01-22 at 00:59 +0200, Pasi Kärkkäinen wrote:
On Fri, Jan 22, 2010 at 12:55:52AM +0200, Pasi Kärkkäinen wrote:
On Thu, Jan 21, 2010 at 05:46:05PM -0500, David P. Quigley wrote:
On Fri, 2010-01-22 at 00:38 +0200, Pasi Kärkkäinen wrote:
On Thu, Jan 21, 2010 at 05:27:45PM -0500, David P. Quigley wrote:
I'm currently working on moving storage services into their own domain
and I've been looking at blktap2. I've been trying to get an image
mounted with blktap2 and for some odd reason and tapdisk2 keeps hanging
instead of quitting at the end. I haven't removed any of the storage
startup code at this point so everything should be as it normally is in
xen-unstable. Is this a known bug? Are there some requirements on
blktap2 that I'm possibly not meeting? Is there anything in particular
that I should be looking at to try to debug the problem?

What kernel are you using? pv_ops dom0 kernel doesn't have working blktap2 yet..
linux-2.6.18-xen has working blktap2 support.

-- Pasi
I'm using the patches maintained by Andrew Lyon that are applied to
2.6.31.10. These are supposedly based on the OpenSUSE patches and can be
found at http://code.google.com/p/gentoo-xen-kernel/downloads/list. I
need a more recent kernel version so the 2.6.18 dom0 kernel isn't an
option for me.

Ok. I'm not sure if those OpenSUSE patches have blktap2 support included?
I know that at least Citrix XenServer, XCP and XCI 2.6.27 kernels do have 
blktap2.

See:
http://wiki.xensource.com/xenwiki/XenDom0Kernels

More details about the pv_ops dom0 kernel (2.6.31.6 currently): It has initial 
version
of blktap2 patches, but they'd need some debugging, because they're not yet 
working.

-- Pasi

Looking under drivers through a make menuconfig on the pvops kernel I
don't see an entry for blktap2. I just see the entry for blktap. I know
that blktap2 was supposed to replace blktap but in the Novell patches
they are two separate config options and I don't seem to be seeing the
second on in the pvops kernel. Do I just enable blktap under drivers and
use tap:tapdisk:<type>  in the domU config to use blktap2?

See:
http://git.kernel.org/?p=linux/kernel/git/jeremy/xen.git;a=shortlog;h=xen/master

Commits like:

2009-12-10      Jeremy Fitzhardinge     Merge branch 'xen/dom0/backend/blktap2' 
into xen/master
2009-12-10      Jeremy Fitzhardinge     xen/blktap2: don't init on non-Xen 
system
2009-12-04      Ian Campbell    blktap: cleanup usage of sysfs
2009-12-04      Ian Campbell    blktap: wean off of use of the BlkBack pageflag.
2009-12-04      Ian Campbell    Port blktap2 from 2.6.18 to tip.
2009-12-04      Ian Campbell    Add build infrastrucuture for blktap2.
2009-12-04      Ian Campbell    patch 03-blktap2-patch
2009-12-04      Ian Campbell    patch 02-blkback-pagemap-patch
2009-12-04      Ian Campbell    patch 01-blktap-patch

I haven't tried it myself yet..

It is pretty broken at present, and I'll probably commit a change to disable it for now. Fortunately it looks like Daniel Stodden is going to have a crack at fixing it up.

    J

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