[libvirt] Executing gdb/gcore as an on_crash action

Hi, Right now, the actions coredump-[destroy|restart] for on_crash work in a similar way as "virsh dump", requesting a dump of Guest's memory contents to QEMU. I think it'd be nice to have the ability for executing gdb/gcore to produce a full core dump of QEMU. This would be especially useful for debugging hard/soft lockups on the Guest. Of course, this should be implemented in a completely optional way, checking if the gdb binary is present, to avoid creating a direct dependency between libvirt and gdb. I'm willing to work on a patch implementing this feature myself, but first I'd like to know if this sounds good to you. Also, if it does, do you think the behavior of coredump-[destroy|restart] should be changed to use gdb if available, falling back to qemuDomainCoreDump if it isn't, or just implement another action for on_crash? -- Sergio