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[Xen-devel] Xen 4.0.1, tap vs tap2, blktap2 documentation, and gentoo-xe

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Subject: [Xen-devel] Xen 4.0.1, tap vs tap2, blktap2 documentation, and gentoo-xen-kernel problem
From: "Fajar A. Nugraha" <list@xxxxxxxxx>
Date: Mon, 20 Sep 2010 10:02:17 +0700
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I've been testing Xen 4.0.1 with kernel +
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.

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.


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