Messages in this thread | | | Date | Tue, 24 Mar 2009 17:38:49 +0100 | From | Patrick McHardy <> | Subject | Re: Network Device Naming mechanism and policy |
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Kay Sievers wrote: > On Tue, Mar 24, 2009 at 17:21, Patrick McHardy <kaber@trash.net> wrote: >> Matt Domsch wrote: >>> c) udev may not always be able to change a device's name. If udev >>> uses the kernel assignment namespace (ethN), then a rename of >>> eth0->eth1 may require renaming eth1->eth0 (or something else). >>> Udev operates on a single device instance at a time, it becomes >>> difficult to switch names around for multiple devices, within >>> the single namespace. >> I would classify this as a bug, especially the fact that udev doesn't >> undo a failed rename, so you end up with ethX_rename. Virtual devices >> using the same MAC address trigger this reliably unless you add >> exceptions to the udev rules. > > This is handled in most cases. Virtual interfaces claiming a > configured name and created before the "hardware" interface are not > handled, that's right, but pretty uncommon.
I don't remember the exact circumstances, but I've seen it quite a few times. I'll gather some information next time.
>> You state that it only operates on one device at a time. If that is >> correct, I'm not sure why the _rename suffix is used at all instead >> of simply trying to assign the final name, which would avoid this >> problem. > > How? The kernel assignes the names and the configured names may > conflict. So you possibly can not rename a device to the target name > when it's name is already taken. I don't see how to avoid this.
Sure, you can't rename it when the name is taken. But what udev apparently does when renaming a device is:
- rename eth0 to eth0_rename - rename eth0_rename to eth2 - rename returns -EEXISTS: udev keeps eth0_rename
What it could do is:
- rename eth0 to eth2 - rename returns -EEXISTS: device at least still has a proper name
Alternatively it should unroll the rename and hope that the old name is still free. But I don't see why the _rename step would do any good, assuming only a single device is handled at a time, it can't prevent clashes.
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