Re: [PATCH v2] allow ifup bring up network manually even without netroot

[Dave Young <dyoung-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On 01/11/2012 05:48 PM, Cong Wang wrote:

> On 01/11/2012 10:05 AM, Dave Young wrote:
>> Hi, I have some additional comments
>>
>> On 01/10/2012 11:41 PM, Cong Wang wrote:
>>
>>> On Fri, 30 Dec 2011 at 08:38 GMT, Dave Young<dyoung-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>  wrote:
>>>> For kdump we need scp vmcore to remote machine, the nic to be used is
>>>> not limited to netroot one. we need a feature for manually bringing up
>>>>   network interface. Also it is useful for emergency shell with
>>>> ssh-client for recovery or test purpose
>>>>
>>>> I implement this by adding one argument to ifup script, user can use
>>>> `/sbin/ifup eth0 -m` to bring up eth0, note ifup will regard it a
>>>> manual operation for the nic specified in 1st argument if there's
>>>> the 2nd argument.
>>>>
>>>> If same nic is used for netroot the 2nd argument will be ignored,
>>>> in this case we will leave netroot bring up it automatically to
>>>> avoid side effect. And in this case hooks such as kdump will need to
>>>> execute after netroot mounted.
>>>>
>>>> `ifup eth0 -m` will create /tmp/net.eth0.manualup stamp file,
>>>> later dhclient-script can check this and pass $2 to netroot,
>>>> then netroot script will bring eth0 up
>>>>
>>>
>>> As we talked on IRC, we still need to discuss if this is really
>>> needed, from kdump perspective.
>>
>>
>> manually ifup nic also benefit to emergency shell use case. I want to
>> use dracut initramfs as a minimal system without real root for kernel
>> testing
> 
> 
> For emergency shell, yeah, it make senses.
> 
>>
>>> If we need to invoke `ifup` by
>>> ourselves, then we also need to determine which NIC we should bring
>>> up, this will make kdump code larger.
>>>
>>> So, I hope, we can have some kernel cmdline (like ip=...) to tell
>>> dracut which NIC we want to bring up in the second kernel, provided by
>>> either ssh-client module or nfs module.
>>
>>
>> If we need to pass the nic name to cmdline then we still need to
>> determine which one should be use.
> 
> 
> Sure, but this will go to ssh-client or nfs module, not kdump.


ssh-client does not pass any cmdline, instead the scripts of call dracut
to generate initrd do this. In case of kdump it's the kdump init scripts
or simplified mkdumprd, so we could not skip this step.

> 
>>
>> If we just bring up all nics, then use the manual ifup is also easy.
>>
> 
> 
> If there are lots of NIC, and we only use one (for remote kdump),
> bringing all NIC up is a waste. Nor to say when we only use eth0, you
> also bring up bond0, br0 etc...
> 
>> current dracut udev rules is: if there's no nic specified it will ifup
>> all possible nics, but all will be put in initqueue which finally be
>> brought up by netroot script.
> 
> 
> We need to specify at least one, the one that reach the remote dump server.
> 
> Thanks.



-- 
Thanks
Dave