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Date: Fri, 03 May 2013 15:07:42 -0400 From: Peter Hurley <peter@...leysoftware.com> To: Neil Horman <nhorman@...driver.com> CC: Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org, David Miller <davem@...emloft.net> Subject: Re: netconsole fun 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 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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