Re: [libvirt] RFC: virInterface change transaction API

On Thu, Apr 14, 2011 at 04:03:03PM +0300, Dan Kenigsberg wrote: > On Fri, Apr 08, 2011 at 03:31:05PM -0400, Laine Stump wrote: > > I've been asked to implement what some people have termed as a > > "transaction-oriented" API for host interface configuration (ie > > virInterface*()). > > The basic intent is to allow rollback to a known-good config if > > anything goes > > wrong when changing around the host network config with virInterface*() > > functions. > > > > The most straightforward way to achieve this is that prior to calling > > virInterfaceDefine/virInterfaceUndefine, the current state of the > > host's network configuration (ie the /etc/sysconfig/network-scripts/ifcfg-* > > files in the case of Fedora and RHEL) would be saved off somewhere, and > > kept around until we're sure the new config is good; once we know that, > > we can just eliminate the backup. If, however, the user of virInterface*() > > explicitly requests, we could copy the files back; alternately if the system > > is rebooted without these known-good files being erased, we would assume > > that something went wrong and restore the original config. > > > > As with all other virInterface functions, the details of all this will > > be handled by netcf (and below), but since libvirt is the main consumer > > of netcf, I figure this is the appropriate place to discuss how it > > gets done, > > so please let me know any opinions on any piece of this. I plan to start > > the implementation "soon", as I want to be finished before the end of > > May. > > I like the idea, and think that virtInterface* users will benefit from it. > Few comments are inline. > > > > > I see 3 layers to this: > > > > 1) libvirt > > > > At the libvirt layer, this feature just requires 3 new APIs, which > > are directly passed through to netcf: > > > > virInterfaceChangeStart(virConnectPtr conn, unsigned int flags); > > virInterfaceChangeCommit(virConnectPtr conn, unsigned int flags); > > virInterfaceChangeRollback(virConnectPtr conn, unsigned int flags); > > > > For the initial implementation, these will be simple passthroughs > > to similarly named netcf functions. (in the future, it would be > > useful for the server side of libvirt to determine if client<->server > > connectivity was lost due to the network changes, and automatically > > tell netcf to do a rollback). > > When such a feature is added, we should make it dependent on FLAG_AUTO_ROLLBACK > passed to ChangeStart. Higher levels on the management stack may want full > controll over when rollback happens. I don't think a AUTO_ROLLBACK flag is sufficient. You'd almost certainly want to pass some info such as hostname/port number to test, and perhaps a test timeout in milliseconds, and perhaps a retry count.

I suggest a separate API that is invoked just after starting the TXN, to provide auto-rollback data. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|