[libvirt] Support for qemu snapshot=on drives in libvirt

[Daniel P. Berrange]

On Fri, Oct 05, 2012 at 12:40:39PM +0100, Richard W.M. Jones wrote:
> 
> I notice that the qemu driver doesn't support snapshot drives
> (-drive file=foo,snapshot=on).  This is important for libguestfs.
> 
> Currently libguestfs hacks this using <qemu:arg>.  That works fine for
> static disks in the libvirt XML, but lack of direct support in libvirt
> is a blocker for adding hotplugging to libguestfs.
> 
> In qemu, the snapshot=on feature does several things:
> 
> (a) It creates a temporary qcow2 disk in $TMPDIR.

We really need to ask QEMU guys to add a config parameter to specify
the location of the snapshot disks. It is nuts to rely on TMPDIR for
this purpose.

No problem implementing the rest of the libvirt support in the
meantime though. We'll just add another XML attribute to configure
the snapshot location once QEMU is suitably functional


Daniel
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