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    SubjectRe: Network Device Naming mechanism and policy
    Kay Sievers wrote:
    > On Tue, Mar 24, 2009 at 17:21, Patrick McHardy <> 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.

     \ /
      Last update: 2009-03-24 17:43    [W:0.021 / U:13.836 seconds]
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