[libvirt] [RFC] Design executing commands from within domains

Dear list, while wiring qemu-ga into libvirt I've noticed that it has ability to spawn commands inside guest. I haven't paid much attention to it then as implementing libvirt <-> qemu-ga communication was more important. But lately couple of requests on the list showed up where ability to spawn various commands inside guests would be much appreciated (e.g. when fetching some stats that HV can't know or has no support for yet - free/df/..). When it comes to spawning commands we distinguish two modes: sync and async. I think we should stick to this on the public API level too. Yet better, we can have async APIs and the sync API would just be a wrapper around async then. One picture instead of thousand words: /* obtain conn and dom somehow */ const char argv[] = {"argv1", "argv2", "argv3", ...} size_t argc = ARRAY_CARDINALITY(argv); unsigned int flags = 0; virDomainCommandPtr cmd = virDomainCommandNew("/path/to/binary", argv, argc, flags); /* Should we care about env too? */ virStreamPtr st = virSreamNew(conn, VIR_STREAM_NONBLOCK); virDomainCommandRun(dom, cmd, st, VIR_COMMAND_STRING_IO); virStreamEventAddCallback(st, VIR_STREAM_EVENT_READABLE, domainCommandCallback, ...); /* ... */ virDomainCommandJoin(dom, cmd); virStreamEventRemoveCallback(con->st) virDomainCommandFree(cmd); While qemu-ga can handle input for a binary its executing, this must be put right into JSON when constructing the qemu-ga command. It's not common that by that time users know the input they want to enter. So I have to figure out something. Opinions? Michal