Re: kvm-ifup bug with complex default routes

["Dor Laor" <dor.laor-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

>Baruch Even wrote:
>> * Dor Laor <dor.laor-atKUWr5tajBWk0Htik3J/w@public.gmane.org> [070402 00:43]:
>>
>>>> A user just submitted a bug report against the kvm-18 debian
package.
>>>> You can find the bug report at
>>>> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=417151
>>>>
>>>> The user has a default route with extra features and the kvm-ifup
>>>>
>>> script
>>>
>>>> fails for him, his default route looks like:
>>>> default via 10.0.0.138 dev br0  metric 1 realm 10
>>>>
>>>> His suggestion to fix is:
>>>> -switch=$(/sbin/ip route list | awk '/^default / { print $NF }')
>>>> +switch=$(ip route ls | awk '/^default / { for(i=0;i<$NF;i++) { if
>>>>
>>> ($(i) ==
>>>
>>>> "dev") print $(i+1) }}')
>>>>
>>> Actually using the default route in order to get the bridge name is
a
>>> bad thing. The best is to use brctl show and pick the bridge that
has
>>> the interface attached.
>>>
>>
>> The current approach has its problems, especially if there is no
bridge
>> defined. But what if I have multiple bridges? You will need to figure
>> out which one of them to use.
>>
>> But then, this script can't take care of all situations, only of
simple
>> and common ones, the fix suggested above just improves coverage for a
>> few more cases.
>>
>
>I think the correct solution is to set up the bridge where and when
>networking is configured, using the regular configuration files and
>supported by the regular tools.  That's the only way we can deal with
>all the various options.  If there's only one bridge, qemu can use it;
>if there's more, qemu-ifup should read some configuration file to
select
>the bridge.
>
>Fedora has some support for bridging in initscripts: I have an
ifcfg-sw0
>with TYPE=Bridge and ifcfg-eth0 with BRIDGE=sw0.  Seems to work fine,
>and no need to transfer addresses and routes and dhcp client daemons
and
>whatnot.

In general you're right. The only problem is that the ifcfg-XX scripts 
do not work well while having bridge over bond interface.
If someone of our Redhat friends and also at debian will pick up the
glove 
and fix it we will do the same.
Anyway I think qemu guys use such call to external script because there
are
plenty of distributions.

So first the script should use the existing bridge, then the standard
bridge
creation tools can be used.


>
>--
>Do not meddle in the internals of kernels, for they are subtle and
quick to
>panic.


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