On Mon, 2010-06-14 at 18:49 +0200, Jan Kiszka wrote: > Alex Williamson wrote: > > On Mon, 2010-06-14 at 18:00 +0200, Jan Kiszka wrote: > >> And instead of introducing another hierarchy level with the bus address, > >> I would also prefer to add this as prefix or suffix to the device name, > >> e.g. <driver>.<busaddr>. > > > > That's what I had started with. The first post in this thread has > > "pci.0,addr=09.0" as a single hierarchy level. The "addr=" may be > > unnecessary there, but I also prefer something along those lines. For > > PCI it'd make sense to have <name>:<addr>, which comes out to > > "pci.0:09.0". (Maybe rather than flagging properties as being relevant > > to the path and printing them generically, we should extract specific > > properties based on the bus type.) > > Not bus.addr, driver.addr. We only have one PCI bus here, not as many as > there are slots on that bus. Ok, I can get it down to something like: /i440FX-pcihost/pci.0/virtio-blk-pci,09.0 The addr on the device is initially a little non-intuitive to me since it's a property of the bus, but I guess it make sense if we think of that level as slot, which includes an address and driver. > >>>> For busses that don't have a consistent addressing scheme then some sort of > >>>> instance ID is unavoidable. I guess it may be possible to invent something > >>>> based on other device properties (e.g. address of the first IO port/memory > >>>> region). > >>> Instance IDs aren't always bad, we just run into trouble with hotplug > >>> and maybe creating unique ramblock names. But, such busses typically > >>> don't support hotplug and don't have multiple instances of the same > >>> device on the bus, so I don't expect us to hit many issues there as long > >>> as we can get a stable address path. Thanks, > >>> > >> If stable instance numbers are required, we could simply keep them in > >> DeviceState and search for the smallest free one on additions. Actually, > >> I'm more in favor of this direction than including the bus address. That > >> way we could keep a canonical format across all buses and do not have to > >> provide possibly complex ID generation rules for each of them. > > > > I started down that path, but it still breaks for hotplug. If we start > > a VM with two e1000 NICs, then remove the first, we can no longer > > migrate because the target can't represent having a single e1000 with a > > non-zero instance ID. > > That's indeed a good point. > > Still, I'm worried about having to define numbering schemes for all the > buses qemu supports. Maybe we can run a mixture: address-based for > hotplug-capably buses (they tend to be cooperative in this regard) and > simple instance numbers for the rest, likely the majority. Yep, I share that concern, which is I say instance numbers aren't always bad. If we have devices that we don't care about doing hotplug on, we can live with instance numbers. Thanks, Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
