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Message-ID: <4AD33D6D.9020900@codemonkey.ws>
Date: Mon, 12 Oct 2009 09:30:05 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [PATCH] Add readonly flag to -drive command
References: <4AD32550.8040901@redhat.com> <4AD32DF6.4050100@redhat.com>
	<20091012135032.GA13560@shareable.org>
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To: Jamie Lokier <jamie@shareable.org>
Cc: Kevin Wolf <kwolf@redhat.com>, Naphtali Sprei <nsprei@redhat.com>, qemu-devel@nongnu.org

Jamie Lokier wrote:
> Kevin Wolf wrote:
>   
>> Am 12.10.2009 14:47, schrieb Naphtali Sprei:
>>     
>>> In order to safely share an image between guests (as read only drive), add a 'readonly' flag
>>> to the -drive command (qemu command line and monitor).
>>>       
>
> Heh.  I've been sharing images between guests for ages - using "chmod -r" :-)
>   

Were it not for backwards compatibility, I would remove that and have it 
error out.

I've had multiple people end up with strangely broken guests because 
they didn't realize the image was read only.

>>> Still missing passing the read only attribute to the guest, where possible. I don't know which device types supports
>>> read only, and don't know how to pass this information to guests.
>>>       
>
> This was discussed in a thread some months ago.  You might look it up.
> SCSI, USB, and floppy can pass the information to guests - see the
> Linux kernel for how the flag is read.  CD-ROMs are read-only already
> of course. I don't know if virtio-blk can; if not, it would be good to
> add it.
>   

virtio-blk can support read-only images now.

Regards,

Anthony Liguori