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Date: Tue, 16 Jun 2009 15:54:55 +0100
From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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Subject: Re: [Qemu-devel] Regression opening read-only cdroms
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	<20090616143259.GA29040@shareable.org>
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To: Jamie Lokier <jamie@shareable.org>
Cc: qemu-devel <qemu-devel@nongnu.org>, Avi Kivity <avi@redhat.com>, Christoph Hellwig <hch@lst.de>

Jamie Lokier wrote:

> Avi Kivity wrote:
>> qemu used to be quite happy opening read-only cdrom images, and I was 
>> quite happy feeding kvm-autotest a library of read-only iso images.
> 
> 1. While we're here, an _option_ to open an image read-only even when
>    you have write permission would be useful, for those occasions when
>    you want to boot from some valuable image and be certain you aren't
>    modifying it - without having to chmod back and forth in
>    Qemu-wrapper scripts, or copy the image first.


Indeed.
I have a patch that adds bdrv_set_read_only that set bs->read_only = 1
so that bdrv_open2 can check if the flag is set and act accordingly.
The problem is that in xen we read whether the device should be opened
read only in the VM config file, I don't think the user can specify to
open a drive read-only in qemu.

 
> 2. Would it make sense to open CD-ROM images read-only all the time,
>    when they are opened with media=cdrom, or can QEMU's CD-ROM devices
>    write to the images?
> 

not at the moment, it may  be possible in the future.