Date:	Thu, 13 Dec 2012 07:36:11 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Subject: Re: netconsole fun

On Wed, Dec 12, 2012 at 03:59:17PM -0500, Peter Hurley wrote:
> On Tue, 2012-12-11 at 11:45 -0500, Neil Horman wrote:
> > On Tue, Dec 11, 2012 at 10:16:51AM -0500, Peter Hurley wrote:
> > > On Tue, 2012-12-11 at 09:30 -0500, Neil Horman wrote:
> > > > On Tue, Dec 11, 2012 at 09:19:52AM -0500, Peter Hurley wrote:
> > > > > On Tue, 2012-12-11 at 04:51 +0000, Cong Wang wrote:
> > > > > > On Mon, 10 Dec 2012 at 14:17 GMT, Peter Hurley <peter@...leysoftware.com> wrote:
> > > > > > > Now that netpoll has been disabled for slaved devices, is there a
> > > > > > > recommended method of running netconsole on a machine that has a slaved
> > > > > > > device?
> > > > > > >
> > > > > > 
> > > > > > Yes, running it on the master device instead.
> > > > > 
> > > > > Thanks for the suggestion, but:
> > > > > 
> > > > > [ 0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.7.0-rc8-xeon ...... netconsole=@....168.10.99/br0,30000@....168.10.100/xx:xx:xx:xx:xx:xx
> > > > > ...
> > > > > [ 5.289869] netpoll: netconsole: local port 6665
> > > > > [ 5.289885] netpoll: netconsole: local IP 192.168.10.99
> > > > > [ 5.289892] netpoll: netconsole: interface 'br0'
> > > > > [ 5.289898] netpoll: netconsole: remote port 30000
> > > > > [ 5.289907] netpoll: netconsole: remote IP 192.168.10.100
> > > > > [ 5.289914] netpoll: netconsole: remote ethernet address xx:xx:xx:xx:xx:xx
> > > > > [ 5.289922] netpoll: netconsole: br0 doesn't exist, aborting
> > > > > [ 5.289929] netconsole: cleaning up
> > > > > ...
> > > > > [ 9.392291] Bridge firewalling registered
> > > > > [ 9.396805] device eth1 entered promiscuous mode
> > > > > [ 9.418350] eth1:  setting full-duplex.
> > > > > [ 9.421268] br0: port 1(eth1) entered forwarding state
> > > > > [ 9.423354] br0: port 1(eth1) entered forwarding state
> > > > > 
> > > > > 
> > > > > Is there a way to control or associate network device names prior to
> > > > > udev renaming?
> > > > > 
> > > > That looks like a systemd problem (or more specifically a boot dependency
> > > > problem).  You need to modify your netconsole unit/service file to start after
> > > > all your networking is up.  NetworkManager provides a dummy service file for
> > > > this purpose, called networkmanager-wait-online.service
> > > 
> > > Ok. So with a single physical network interface that will be bridged,
> > > netconsole cannot used for kernel boot messages.
> > > 
> > > With a machine with multiple nics, is there a way to control device
> > > naming so that the interface name to be used by netconsole specified on
> > > the boot command line will actually corresponding to the intended
> > > device. For example,
> > > 
> > > [ 0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.7.0-rc8-xeon ...... netconsole=@....168.1.123/eth0,30000@....168.1.139/xx:xx:xx:xx:xx:xx
> > > ....
> > > [ 4.092184] 3c59x: Donald Becker and others.
> > > [ 4.092204] 0000:07:05.0: 3Com PCI 3c905C Tornado at ffffc9000186cf80.
> > > [ 4.094035] tg3.c:v3.125 (September 26, 2012)
> > > ....
> > > [ 4.125038] tg3 0000:08:00.0 eth1: Tigon3 [partno(BCM95754) rev b002] (PCI Express) MAC address xx:xx:xx:xx:xx:xx
> > > [ 4.125055] tg3 0000:08:00.0 eth1: attached PHY is 5787 (10/100/1000Base-T Ethernet) (WireSpeed[1], EEE[0])
> > > [ 4.125062] tg3 0000:08:00.0 eth1: RXcsums[1] LinkChgREG[0] MIirq[0] ASF[0] TSOcap[1]
> > > [ 4.125068] tg3 0000:08:00.0 eth1: dma_rwctrl[76180000] dma_mask[64-bit]
> > > 
> > > This is attaching netconsole to the wrong device because bus
> > > enumeration, and therefore load order, is not consistent from boot to
> > > boot.
> > > 
> > No, theres no way to do that.  As you note device ennumeration isn't consistent
> > accross boots, thats why udev creates rules to rename devices based on immutable
> > (or semi-immutable) data, like mac addresses, or pci bus locations).  Once that
> > happens, you'll have consistent names for your interfaces, and that work will be
> > guaranteed to be done after networkmanager has finished opening all the
> > interfaces that it needs (hence my suggestion to make netconsole service
> > dependent on networkmanager service startup completing).
> 
> Just wondering if you think something like the patch below is
> suitable/acceptable for insulating netconsole from inconsistent device
> name scenarios without changing the existing semantics. The basic idea
> is to allow an ethernet MAC address in the <dev> field of the
> netconsole= options, and if a MAC address was specified rather than a
> device name, to do the dev lookup from the MAC address instead.
> 
> This doesn't extend to, but also doesn't interfere with, the dynamic
> config of netconsole via configfs.
> 
> Would you mind reviewing it?
> 
> Regards,
> Peter
> 
This looks like a pretty good idea to me.  That said, something occured to me
when you wrote your summary above.  Have you looked at the netconsole service
scripts that most distros provide in their packaging?  I'm almost positive Red
Hat/Fedora (and also like Suse and Ubuntu), already implement this functionality
from user space.  Basically, instead of people just modprobing netconsole, they
create a service script that parses a config file that has contains all the
options needed to load the netconsole module, and it has the intellegence to see
if you specified a mac address rather than a device.  If you did that it finds
the corresponding device mac address and uses that as the device.  I'm sorry, I
don't know why I didn't think of that before.  Check that out though, that will
likey give you exactly what you need

Neil

P.S. Actually looking at it, I think it does one better, it lets you specify the
destinaition netconsole address, and then dynamically looks up the routing table
entry that gets you there, and uses the output device specified in the routing
table.

http://www.cyberciti.biz/tips/linux-netconsole-log-management-tutorial.html

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