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Date: Tue, 16 Jun 2009 18:51:12 +0100
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [Qemu-devel] Regression opening read-only cdroms
Message-ID: <20090616175112.GB11893@shareable.org>
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To: Avi Kivity <avi@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>, qemu-devel <qemu-devel@nongnu.org>

Avi Kivity wrote:
> On 06/16/2009 06:54 PM, Jamie Lokier wrote:
> >read-only disk images don't make much sense.
> >   
> >
> >And yet "chmod 444 image; qemu ..." works.
> >If you're booting from a disk you don't need to write to, obviously.
> >Generally it'll need to be mounted read-only in the guest.
> >   
> 
> It will eventually fail.  Open the ext3 log, update atime, or 
> something.  The guest expects the disk to be writeable.

No.  Obviously if you _want_ to run a guest with the disk mounted
writable, you'll use snapshot=on instead because that's what it's for.

Otherwise, a read-only disk should works fine using virtio/SCSI/USB,
as the guest will mount it read-only, as those interfaces all have a
read-only media flag which Linux guests (at least) look at.

Which is the desired behaviour.

-- Jamie