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Re: [Xen-devel] xen 4.1.1 + 3.0.0-rc5 dom0 + blktap2

To: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Subject: Re: [Xen-devel] xen 4.1.1 + 3.0.0-rc5 dom0 + blktap2
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Date: Thu, 30 Jun 2011 11:55:12 +0100
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Madjik <madjik@xxxxxxxxxxxxxxxx>
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On Thu, 30 Jun 2011, Ian Campbell wrote:
> On Wed, 2011-06-29 at 03:06 +0100, Madjik wrote:
> > Hi,
> > 
> > I'm currently trying xen 4.1.1 with the 3.0.0-rc5 (heard that it now 
> > contains the xen code to run as front or back xen domain).
> > 
> > Everything seems to run fine, except that I am trying since a  few hours 
> > to mount a .vhd file in the dom0.
> Everything needed to run a guest is upstream but not everything needed
> to run any guest, if you see what I mean. In particular the upstream
> kernel contains blkback but not blktap so using a vhd would not be
> expected to work today.
> I'm afraid blktap is unlikely to be accepted upstream as it is. There is
> a plan to remove the kernel component and have guests communicate
> directly with the tapdisk process in userspace (via /dev/xen/gtndev et
> al). There is no real downside to this since everything goes through
> tapdisk anyway. I don't know how advanced that plan is currently.
> With the 4.1 release you might be able to use the qdisk (qemu based
> backend) to run a VHD but it is known not to perform all that well (and
> I don't know off-hand how you enable it). Performance is, AIUI, better
> with the upstream qemu port.

If you want to run 3.0.0-rc5 as dom0 your best bet would be to convert
your vhd file to a raw file, setup LVM, then dd the raw file into a new
LVM volume. This in order to get the best performances.

Otherwise the easiest thing to do would be to clone a kernel tree that
contains blktap2, I believe Daniel has one based on 3.0, see the thread
"xen 4.1.1 + 3.0.0-rc5 dom0 + blktap2".

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