5:54 a.m.
On Sun, Jan 17, 2010 at 12:31:07PM -0500, Philip Jameson wrote:
A little while ago I submitted a patch to add a snapshot API, but
I was informed that it got somewhat lost in the list. I have attached
a patch that implements this API at least for the qemu driver, and
it also added another function for screenshots, just because it
usually is nice to get a view of the screen with the snapshot.
Could you resubmit the virDomainTakeScreenshot() code as a separate
patch. That is quite a straightforward API addition, so we shouldn't
let snapshot discussions delay that.
The snapshot functions just take names, as I figure it should be up
to libvirt to figure out where the snapshots go. e.g. for qemu, they
just get stored with the drive using qemu's built in facilities. If
someone were using LVM, then that could be managed by libvirt, just
like it does for qemu monitors and such. The 'list snapshots' just
returns a list of names for now, as that's all I needed, but I think
it would probably be best to add a struct that would be name/time.
I've been taking a look at what VMWare and VirtualBox expose in their
respective APIs for snapshotting
VMWare
- There is a tree of snapshots. ie a snapshot can be against a
previous snapshot, rather than the base image, and you can
chain them together to arbitrary depth
- Copy of the domain configuration
- Creation time
- Name
- Description
- Quiesced (ie whether the guest filesystem had been told to
flush buffers & temporarily suspend I/O to get consistent state)
- VM State (whether it was running, or off when snapshotted)
- Current snapshot - the snapshot used for current execution
VirtualBox
- There is a tree of snapshots. The current impl does not allow
full use of this, restricting to a single branch / chain.
- UUID
- Name
- Description
- Timestamp
- Online. Whether it was running or off when snapshotted
- Copy of domain configuration.
- Current snapshot - the snapshot used for current execution
So this is all alot more advanced than current capabilities in either
Xen or QEMU/KVM. To cope with the level of complexity there I think
we need to go beyond a simple 'name' in the APIs, and have a real
object + an XML schema to record the metadata.
I don't know if it's of any use at the moment, but I needed
these
functions implemented, so I figured I'd at least submit my changes
+int virDomainTakeSnapshot (virDomainPtr
domain,
+ const char *name);
+int virDomainRestoreSnapshot(virDomainPtr domain,
+ const char *name);
+int virDomainDeleteSnapshot (virDomainPtr domain,
+ const char *name);
+int virDomainListSnapshots (virDomainPtr domain,
+ char** sslist, int listsize);
So thinking about things in terms of VMWare/VirtualBox capabilities, we
probably need to expand these APIs a little further to
typedef struct _virDomainSnapshot virDomainSnapshot;
/* Take a snapshot of the current VM state */
virDomainSnapshotPtr virDomainTakeSnapshot(virDomainPtr domain,
const char *name,
unsigned int flags);
/* Query all snapshots know for a VM */
int virDomainListSnapshotNames(virDomainPtr domain,
char** names, int nameslen);
/* Get a handle to a named snapshot */
virDomainSnapshotPtr virDomainSnapshotLookupByName(virDomainPtr domain,
const char *name);
/* Set this snapshot as the current one for a domain, to be
used next time domain is started */
int virDomainSnapshotActivate(virDomainSnapshotPtr snapshot,
unsigned int flags);
/* Delete a snapshot */
enum {
VIR_DOMAIN_SNAPSHOT_DELETE_MERGE,
VIR_DOMAIN_SNAPSHOT_DELETE_DISCARD,
};
int virDomainSnapshotDelete(virDomainSnapshotPtr snapshot,
unsigned int flags);
For XML to describe the metadata, I think we want to try something
like
<domainsnapshot>
<name>XYZ</name>
<creationdate>...</creationdate>
<description>
....blah....
</description>
<state>RUNNING</state>
<domain>
<uuid>XXXXX-XXXX-XXXX-XXXX-XXXXXXXXX</uuid>
</domain>
<parent>
<name>ABC</name>
</parent>
</domainsnapshot>
Regards,
Daniel
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