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Date: Tue, 16 Jun 2009 19:56:46 +0100
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [Qemu-devel] Regression opening read-only cdroms
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To: Avi Kivity <avi@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>, qemu-devel <qemu-devel@nongnu.org>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>

Avi Kivity wrote:
> On 06/16/2009 08:46 PM, Jamie Lokier wrote:
> >Users who expect things to just work will be even more surprised that
> >"-hda image" where image is read-only does not give any error from
> >QEMU, but their guest crashes.  Or that "-hda image" works as usual,
> >and their guest crashes, and eventually they discover it's because
> >their disk image is not writable, and it's always worked before
> >because they were using -snapshot or something like that, and QEMU
> >didn't warn them it would be a problem...
> 
> I agree, for non-cdroms/floppies, non-backing store files we should 
> require write access.

Did you miss that read-only disks exist, as seen through
SCSI/USB/virtio, and that guests will mount them read-only automatically?

There are real physical storage devices like that.  Just think of your
favourite USB flash drive with a write-protection switch.  It's just a
SCSI disk with the read-only flag set, to the guest.  Modern guests
know about them.

-- Jamie