Re: [libvirt] [RFC] events scripts support

On Tue, Mar 23, 2010 at 12:12:57PM +0000, Daniel P. Berrange wrote: > On Tue, Mar 23, 2010 at 12:17:50PM +0100, Daniel Veillard wrote: > > We would like to introduce a way to configure system wide a script > > which would be called when some event happens. The script is a single > > executable set as a libvirtd option by the system administrator > > (assuming one runs the system libvirtd) or the user (assuming a > > user run libvirtd). > > The script could be invoked on daemon events, for example starting > > stopping, or reloading (SIGHUP), on domain events for example before > > a domain starts, or after its stops, and possibly on other kind of > > events detected by the daemon (storage or interface ...) > > I'd really like to avoid calling this events. This is really a means okay that's confusing and 'hook' is a better term > to insert synchronous hooks into certain key places like domain startup. > This is only really going to be usable for hypervisors/drivers where > libvirt is in total control of guest startup, which means QEMU, LXC & > UML. It'll never work for things like VMWare, Xen, VirtualBox, etc > and it will also be fairly limited in interactions with the network, > node device drivers, and possibly even storage. I would not presume too much about storage and network. I'm just opening the idea that some hooks may come from there in the future. > The synchronous hooks will also be limited in that they must be fast > to execute, and must not call back into libvirt - that would likely > deadlock since this is synchronous. The separate events daemon providing Yeah the deadlocking problem is something I raised in my mail. > I think we do need to support both approaches long term, but with the > async events being the general purpose option, and the sync hook here > being driver specific limited use cases. Still that's something I would like to see exposed for LXC too. > > My current thinking is to add the following two variables to > > libvirtd.conf: > > > > # Event scripts > > # An optional path to a script handling various kind of events like > > # domain start, domain end, pre and post migration, etc... > > # The events_script must be a path to the script or binary handling > > # the > > # events. > > # The events_set is a list of space separated name for the event type > > # the script should receive > > # > > # events_script="/etc/libvirt/events" > > # events_set="daemon domain" > > I think this really belongs in the QEMU driver, since I don't think this > can be generalized to other drivers. I disagree, this can be used for generic daemon events as I suggested like shutdown or restart, plus usable for lxc at least. > > The script aruguments would be > > > > - the object kind: e.g. "domain" > > If this is considered QEMU specific, we don't need 'domain' here I don't want this to be QEmu specific. But I think we need to provide the driver in case of qemu/lxc/... I think the first string should match one of the values registered in hooks_set="daemon domain"

> > - the object name: e.g. the domain name > > - the event itself: e.g. "start" > > - sub event qualifier: e.g. "before" > > - an optional extra information for example in case of migration > > the destination or source > > That sounds sufficient. Since this is synchronous we probably need the uuid of the object if available ('-' otherwise) and the driver name in case of a domain (or future network/storage) alternatively passing the object XML as the hook script stdin is probably the simplest way to convey a complete set of informations.