Re: [Qemu-devel] Regression opening read-only cdroms

[Jamie Lokier <jamie@shareable.org>]

Richard W.M. Jones wrote:
> On Tue, Jun 16, 2009 at 03:33:00PM +0100, 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.
> 
> FWIW we went round the houses on this one for libguestfs and settled
> on using '-drive ...,snapshot=on' instead.  The guest sees the drive
> as writable, and any writes are discarded when libguestfs/qemu quits.

It's fine for CD-ROMs of course.

For disks, there's that slight problem of running out of RAM or disk
space for the /tmp snapshot files.  Better not to write anything.

It'd be nice to enforce it, instead of depending on good behaviour
from the guest.

-- Jamie