Date:	Sat, 04 May 2013 20:59:15 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org,
	David Miller <davem@...emloft.net>
Subject: Re: netconsole fun

Thanks for clarifying.  Glad to hear you got it working.  If your doing a lot of custom initramfs work, a distro dump package would be worth your investigation, as they have likely covered a lot of ground that you're traversing.

Best
Neil


Peter Hurley <peter@...leysoftware.com> wrote:

>On 04/29/2013 02:21 PM, Neil Horman wrote:
>> On Mon, Apr 29, 2013 at 01:28:45PM -0400, Peter Hurley wrote:
>>> On Mon, 2012-12-17 at 09:20 -0500, Neil Horman wrote:
>>>> On Sat, Dec 15, 2012 at 09:13:58AM -0500, Peter Hurley wrote:
>>>>> On Fri, 2012-12-14 at 09:20 -0500, Neil Horman wrote:
>>>>>> Ah!  I'm sorry, I didn't realize this was really about getting netconsole up
>>>>>> early in the boot, rather than just getting it up robustly using the startup
>>>>>> script.
>>>>>
>>>>> Well, it's both but I should have been clearer here. Sorry about that.
>>>>>
>>>>>> If thats the case, then I would recommend that you modify the initramfs
>>>>>> to do something simmilar to the startup script (since thats where the netconsole
>>>>>> module will get loaded anyway).  You can write a script there that will let you
>>>>>> specify the destination ip address and figure out the output dev based on the
>>>>>> routing tables.  If you're using dracut to build your initramfs, then this
>>>>>> should be pretty straightforward.
>>>>>
>>>>> When I get some more free time I'll experiment with this approach.
>>>>>
>>>>> Just to clarify something from earlier in the discussion:
>>>>>
>>>>> On Thu, 2012-12-13 at 13:08 -0500, Neil Horman wrote:
>>>>>> On Thu, Dec 13, 2012 at 09:49:31AM -0500, Peter Hurley wrote:
>>>>> ....
>>>>>>> There is an unforeseen consequence of the patch: it breaks device
>>>>>>> renaming because the device will already be in use by netconsole. Which
>>>>>>> is the whole problem with userspace device renaming to begin with...
>>>>>>>
>>>>>> That is bad, but see above, the netconsole service can work around this for you,
>>>>>> allowing you to never have to specify a particular device at all.
>>>>>
>>>>> The breakage is a normal consequence of being able to load netconsole
>>>>> before the udev rules that do device renaming. The same thing would
>>>>> happen modifying initramfs.
>>>>>
>>>>> Basically, once netconsole attaches to a device, that device cannot be
>>>>> renamed. Unfortunately, the default udev behavior messes things up
>>>>> further because it will try to do this:
>>>>>    eth0->eth1
>>>>>    eth1->eth0
>>>>> which means neither device will be renamed.
>>>>>
>>>>> Maybe the net core should just implement persistent device names ;)
>>>>>
>>>> Theres no good way for the kernel to do that, as persistent naming in this case
>>>> is a matter of user policy, not kernel hardware management (i.e. do you want a
>>>> network name to follow a mac address, a pci slot, or the network its connected
>>>> to)?  You can use smbios to get some modicum of persistent device naming
>>>> currently, but I don't recall if that requires udev rules to implement as well
>>>>
>>>> You're best bet is to simply make your initramfs more robust.  I understand what
>>>> you're saying regarding renaming after you've taken a reference on a device not
>>>> being possible, but you can run udev within the initramfs, and do your renaming
>>>> prior to your netconsole load.
>>>
>>> Hi Neil,
>>>
>>> I plan to re-submit 'netconsole: allow mac addr to specify local
>>> interface device' which you originally objected to because you asserted
>>> that the same effect could be obtained through udev scripts in the
>>> initramfs.
>>>
>>> When you shot down this patch, did you actually try what you suggested
>>> in the initramfs or were you just hypothesizing that it would possible?
>>>
>> I've not tried specifically what want to do, no, but I've done interface
>> renaming plenty of times in the initramfs back when I did kdump work (we had to
>> rename devices in the initramfs to align them with whatever udev renamed them to
>> once we pivot_root-ed to the rootfs).
>>
>> I presume you're sending me this note because you've for some reason decided
>> that doing this in the initramfs isn't feasible?  I'm happy to help you through
>> it if you like.
>
>Neil,
>
>I owe you an apology.
>
>Performing the udev device renaming and modprobing netconsole
>with the renamed device interface is indeed possible within initramfs.
>Once I had managed to get udev device renaming working in the initramfs,
>I had confused myself regarding which interface went with which MAC address.
>
>Have a good weekend.
>
>Regards,
>Peter Hurley
>
>

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