Description of problem:
Please add ability to set snapshot mode for virtual harddisks. There is an excellent parameter of qemu, which can run virtual machine in mode, where all changes are stored in separate file and original image is not touched.
This parameter can be well used by developers or testers, which need to test any software without reinstallation of his machine. User can install anything and then simply poweroff this virtual machine, after next boot everything will be back in original state.
This can be done in qemu 2 ways:
1. add -snapshot parameter, which set snapshot mode for all harddisks (not best way)
2. add ",snapshot=on" for "-drive" parameter. By this way each partition can be set separately.
There are other options, which can be useful too, for example these:
snapshot is "on" or "off" and allows to enable snapshot for
given drive (see -snapshot).
cache is "none", "writeback", or "writethrough" and controls
how the host cache is used to access block data.
boot if "on" enables extboot for a given drive so it can be
used as a boot drive.
Moving this to libvirt's upstream bug tracker - it's a common request, but there are no immediate plans to implement it
(Not, cache= and boot= are already available through libvirt)
The XML is in place as of 0.9.5 (the <transient/> attribute of a <disk> in domain xml), but has not yet been wired up to qemu.
*** Bug 832194 has been marked as a duplicate of this bug. ***