Re: [Libvir] default hypervisor selection

While going though the ovirt installation steps I got annoyed with the need to add "-c qemu:///system" each time we are trying to start a virsh command if using KVM. The dfault setup is basically to assume a Xen hypervisor if the URI is not specified, this is glued in the do_open internal opening routine associated to the opening of connections: -------------------------------------- static virConnectPtr do_open (const char *name, virConnectAuthPtr auth, int flags) { int i, res; virConnectPtr ret = NULL; xmlURIPtr uri; /* Convert NULL or "" to xen:/// for back compat */ if (!name || name[0] == '\0') name = "xen:///"; -------------------------------------- In one hand this is the default behaviour of the library, but in my opinion it's not very smart. We should be able to be smarter than that, for example: - if /proc/xen doesn't exist (on linux, or /dev/xen on Solaris) well we should not do that we are pretty sure we will get an error when trying to connect - if /proc/vz is present, well it's very likely that if the kernel has been compiled with OpenVZ support, it's likely to be used as the default virtualization - if there is a kvm module loaded well we should probably use qemu:///system if running as root or qemu:///session otherwise I guess on Solaris an easy heuristic would allow to pick the right hypervisor by default too. At some point we may have multiple hypervisor support simultaneously on a linux system thanks to pv_ops, but right now it doesn't make too much sense to force a default Xen connection even when we know it won't work. For a virsh specific solution there is the VIRSH_DEFAULT_CONNECT_URI environment variable, but it's not really user friendly and not very generic,

What do people think ? I would be tempted to provide a patch to change do_open() behaviour on linux in the case name is NULL or "", and then check what hypervisor might be present and running,