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Re: [Xen-devel] Xen 4.0.1, tap vs tap2, blktap2 documentation, and gento

To: "Fajar A. Nugraha" <list@xxxxxxxxx>
Subject: Re: [Xen-devel] Xen 4.0.1, tap vs tap2, blktap2 documentation, and gentoo-xen-kernel problem
From: Pasi Kärkkäinen <pasik@xxxxxx>
Date: Mon, 20 Sep 2010 09:25:28 +0300
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On Mon, Sep 20, 2010 at 10:02:17AM +0700, Fajar A. Nugraha wrote:
> Hi,
> I've been testing Xen 4.0.1 with kernel +
> http://gentoo-xen-kernel.googlecode.com/files/xen-patches-2.6.34-4.tar.bz2,
> and one of the things that I noticed immediately is there are two
> problems with tapdisk and this combination.
> First, the syntax "disk = ['tap:tapdisk:aio: ..."  no longer works.
> When tested with HVM domU, it boots, but there was no disk attched
> (and /sys/class/blktap2/devices stays empty). Changing it to
> tap2:tapdisk:aio works (sort of). I recall some discussion about tap
> vs tap2 compatibility on this list earlier, but no final conclusion.
> Shouldn't newer versions be backward compatible? Existing tap:aio and
> tap:tapdisk:aio should just work to minimize upgrade efforts.
> http://lxr.xensource.com/lxr/source/tools/blktap2/README also still
> mention tap:tapdisk, and not tap2:tapdisk.


The syntax was changed in Xen 4.0.1 .. which is a bit confusing..

> Second problem, using that combination, blktap2 devices was not
> cleanly freed. /sys/class/blktap2/devices and tapdisk devices keep
> increasing (tapdev0, tapdev1, etc.). The strange thing is, when using
> Xen 4.0.1 hypervisor but with Xen 4.0.0 userland, tap:tapdisk and
> blktap2 device cleanup works as expected.

Interesting. Did you try with a pvops dom0 kernel? Does that make a difference?

-- Pasi

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