Re: [libvirt] [PATCH] virNetDevVethCreate: assign names based on mac address by default

On 08/29/2013 04:20 PM, Oskari Saarenmaa wrote: > On Thu, Aug 29, 2013 at 10:10:36AM +0200, Michal Privoznik wrote: >> On 28.08.2013 23:05, Oskari Saarenmaa wrote: >>> Interface names do not have to be numerical (or veth + number) and trying to >>> assign them to that format is susceptible to race conditions. Instead, >>> assign the parent interface name according to the mac address (the last >>> three bytes) if no name was given by the caller and use the parent interface >>> name plus 'p' for the container name. >> I don't think it is a good idea. What it user defines MAC addresses in a >> way that the last three bytes are the same? E.g. >> >> 00:11:22:33:44:55 >> 00:22:11:33:44:55 >> >> (there are plenty of possibilities). With your code we would create >> veth334455 for the first domain and there's nothing left for the other >> one but eyes to cry. > > Sure, it's possible for the user to assign addresses like this, but I > believe most mac addresses are assigned randomly, that's what libvirt does > by default, no? Also, it's possible for the user to override the interface > name if they want to. Currently it's only possible to set the first > interface name, but there's no way to set the name of the second interface > which causes failures because of races. In any case it makes sense to set > the second interface's name based on the first interface's name so we don't > have to try to come up with two different unique names. > >> Moreover, there's no race now, as we use global lock to mutually exclude >> call to virNetDevVethCreate. Although, I must admit it's only within a >> single driver, I think. So if there are two domains starting (one in >> qemu driver the other one in lxc, for instance) there can be race. But >> this should be solved in a different way then. The virNetDevVethCreate >> should be turned into virObjectLockable and a veth should be allocated >> by calling a method. > > I ran into this issue repeatedly when I tried to start multiple LXC domains > simultaneously from my application (https://github.com/melor/poni) which > runs libvirt operations in their own threads. > It's easy to be resolved. give the parentVeth and containerVeth a name by default.