Re: [Qemu-devel] [PATCH] block: do not allow read-only=on and snapshot=on to be used together

[Jeff Cody <jcody@redhat.com>]

On Wed, Mar 12, 2014 at 12:16:04PM +0100, Kevin Wolf wrote:
> Am 24.01.2014 um 14:48 hat Jeff Cody geschrieben:
> > On Fri, Jan 24, 2014 at 02:33:19PM +0100, Kevin Wolf wrote:
> > > Am 14.01.2014 um 20:12 hat Jeff Cody geschrieben:
> > > > Having both read-only=on and snapshot=on together does not make sense;
> > > > currently, the read-only argument is effectively ignored for the
> > > > temporary snapshot.  To prevent confusion, disallow the usage of both
> > > > 'snapshot=on' and 'read-only=on'.
> > > > 
> > > > Signed-off-by: Jeff Cody <jcody@redhat.com>
> > > 
> > > This breaks in a surprising way:
> > > 
> > > $ softmmu/qemu-system-x86_64 -drive file=~/images/hd.img,snapshot=on
> > > ... works fine ...
> > > 
> > > $ qemu-system-x86_64 -drive file=~/images/hd.img -snapshot
> > > qemu-system-x86_64: invalid option combination: read-only and snapshot
> > > 
> > > qemu-iotests case 051 catches this. I'll have to remove this patch and
> > > the follow-up from the queue for now.
> > >
> > 
> > Odd - OK, I'll follow up on this and submit a series with both patches
> > (well, likely squashed together), and whatever is needed to fix this
> > as well.
> 
> Jeff, what happened with this? I found the two patches in an old git
> branch and wondered why they didn't disappear in the rebase. But
> apparently we still allow read-only and snapshot at the same time.
>

The test case 051 failed because when -snapshot was specified, it was
enabled for all the default drives as well, which included
default_cdrom.

The solutions for that seemed a little hacky, and I wasn't sure it was
actually worth it, given that this is probably not a real problem to
begin with.  If you think it is worth it, I can resurrect the patch
and make sure it works with both snapshot=on and -snapshot.