[libvirt] [PATCH] Libvirt Snapshot API
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. 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 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 Philip Jameson
Sorry, looks like I missed the message about the new error handling functions, and I messed up a regex. Attached are the changes. Philip Jameson On Jan 17, 2010, at 12:31 PM, 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.
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 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
Philip Jameson <snapshot-diff.txt.2>-- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
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 -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://ovirt.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|
On Jan 20, 2010, at 6:54 AM, Daniel P. Berrange wrote:
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.
Will do, just need to separate it out from the other code.
+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);
I think that's probably a good modification to allow for storing more information on the snapshots, however, did you remove the restore function, or is that what you're wanting the 'virDomainSnapshotActivate' to be? If so, that doesn't make as much sense at least for qemu, as it can do restoration of snapshots while online. If this was intended to replace the restore function, I suppose online/immediate restoration could be one of the 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>
That's probably a fair layout. The only thing I might add is that for qemu/kvm support, since it is stored on the first block device, I believe, we would need to keep track of any shuffling of drives. So, maybe add a <blockdev>/path/to/hd</blockdev> tag so we know whether you can actually restore a snapshot at the time. Philip Jameson
participants (2)
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Daniel P. Berrange -
Philip Jameson