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Re: overriding udev rules



Am 10.09.2013 01:28, schrieb Uoti Urpala:
> Russ Allbery wrote:
>> Kay Sievers <kay@vrfy.org> writes:
>>> Hmm, why would upgrades break?
>>
>>> The old file would still be there, rename the devices (if you keep the
>>> patch to swap names, which upstream does not support any more), and take
>>> precedence over tht new names; the old rules file would just not be
>>> updated anymore when new devices appear.
>>
>> Manually-deployed /etc/network/interfaces files that assume a specific
>> device naming come to mind.  We have tons of those at work.
> 
> Why would those break? Just having a manually-deployed
> /etc/network/interfaces file that uses names like "eth0" should not
> break upgrades, because as mentioned in the part you quoted, the
> existing already-generated rules should still trigger and keep renaming
> the same card to eth0. So you need to assume something more to have an
> example of a problem case.

As I mentioned earlier, the problem is for those cases, where we
*didn't* generate persistent network interface names and used the kernel
provided names.
The conditions are listed at [1]. In such a case, the file
/etc/udev/rules.d/70-persistent-net.rules will *not* be created.
(There is also the case where an administrator decided to opt-out and
not use the persistent naming by running "echo : >
/etc/udev/rules.d/75-persistent-net-generator.rules")

Kay was kind enough to point out [2], that the new network interface
naming has similar rules where it skips the renaming but there might be
setups where those rules don't overlap, and there you would get a
network interface name change after an upgrade.
Kay expects this number to be very low.
The risk of breaking setups on upgrades made me uneasy though. We have
to be reasonably sure that the number of breakages is indeed very low
and ideally can detect such cases before we decide making the new
interface naming the default (at least for upgrades). So far nobody did
the analysis for that.


Michael


[1]
http://anonscm.debian.org/gitweb/?p=pkg-systemd/systemd.git;a=blob;f=debian/extra/rules/75-persistent-net-generator.rules;h=b6fcb917ee220b6ec6305b7170680caac3f0acdd;hb=refs/heads/debian-experimental#l23
[2] <CAPXgP11nncYSL1Xrwm+z2Ux5aUkOmkpODXOThqRO8dps1QiUDQ@mail.gmail.com>

-- 
Why is it that all of the instruments seeking intelligent life in the
universe are pointed away from Earth?

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