Bug#800845: autopkgtest: Add support for nested VMs

[Christian Seiler]

On 07.03.2016 10:21, Martin Pitt wrote:
> However, there's still one major issue left: Despite the
> "readonly=on", one can actually mount /dev/vdb1 in the VM and write
> files into it! This sounds like a QEMU bug (running
> 1:2.5+dfsg-5ubuntu4 here), but as long as that exists this is
> dangerous as this alters your pristine base images. I already tried to
> add the "readonly=on" to the "device_add", but that's just an "unknown
> property". Unfortunately this stuff isn't documented very well..

So I just tried this on an Ubuntu Wily box, both with the QEMU from
Wily and with the QEMU from Xenial (only upgraded QEMU + deps, didn't
upgrade the entire OS) - and I really cannot reproduce this.

Host kernel: 4.2.0-30-generic
QEMU: 1:2.3+dfsg-5ubuntu9.2 and 1:2.5+dfsg-5ubuntu4
Image: adt-sid.img as generated per adt-virt-qemu(1) manpage
       instructions with vmdebootstrap (exactly, no changes!)
       Tried both writable to user executing QEMU and not
       writable to user executing QEMU.

My Debian machine with which I tried that earlier had:

Host kernel: 4.4.2-3 (from sid)
QEMU: 1:2.5+dfsg-4~bpo8+1
Image: see above

I consistently get (via adt-run --shell, autopkgtest git master, no
changes) in _any_ of these setups:

mount: /dev/vdb1 is write-protected, mounting read-only

(Now I haven't tried the newest kernel on the Ubuntu side, but I'd
_really_ be surprised if that changed anything - especially since
I did try with a recent kernel on Debian with basically the same
QEMU version.)

Regards,
Christian

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