Re: [Qemu-devel] [PATCH] Add readonly flag to -drive command

[Anthony Liguori]

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