linux-kernel - Re: Network Device Naming mechanism and policy

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Message-ID: <ac3eb2510903240928s6c42bc32pa0cd8a7f0e69b731@mail.gmail.com>
Date:	Tue, 24 Mar 2009 17:28:33 +0100
From:	Kay Sievers <kay.sievers@...y.org>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Matt Domsch <Matt_Domsch@...l.com>, netdev@...r.kernel.org,
	linux-hotplug@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Network Device Naming mechanism and policy

On Tue, Mar 24, 2009 at 17:21, Patrick McHardy <kaber@...sh.net> wrote:
> Matt Domsch wrote:
>>
>> 2) udev may have rules to change the device names.  This is most often
>>   seen in the '70-persistent-net.rules' file.  Here we have
>>   additional challenges:
>>
>> ...
>>
>>   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.

> 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.

Thanks,
Kay
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