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Re: [patch] netconsole - log kernel messages over the network. 2.4.10.

To: Ingo Molnar <mingo@xxxxxxx>
Subject: Re: [patch] netconsole - log kernel messages over the network. 2.4.10.
From: Marcelo Tosatti <marcelo@xxxxxxxxxxxxxxxx>
Date: Wed, 26 Sep 2001 16:36:20 -0300 (BRT)
Cc: linux-kernel@xxxxxxxxxxxxxxx, linux-net@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxx
In-reply-to: <Pine.LNX.4.33.0109262128320.8277-100000@xxxxxxxxxxxxxxxxxxxxx>
Sender: owner-netdev@xxxxxxxxxxx
Ingo, 

Don't you think it would be useful to have some reserved memory for the
netconsole use ?

It would be nice to have a guarantee that messages are sent over network
even if the system is under real OOM. 

On Wed, 26 Sep 2001, Ingo Molnar wrote:

> 
> this is the first public release of the 'netconsole patch', a debugging
> patch that implements kernel-level network logging via UDP packets.
> 
> the special thing about this approach is the ability to send 'emergency'
> network packets even from IRQ handlers. This enables the netconsole to
> send enough info even if we crash in init or in an interrupt handler.
> 
> another property of netconsole is that it's able to share the networking
> device with other kernel subsystems, like the TCP/IP stack. So the
> networking device is not dedicated for netconsole use, it's transparently
> shared.
> 
> netconsole is also designed to be robust, it goes straight to the network
> driver, so it does not depend on the networking stack to log messages.
> 
> kernel-level netlogging is useful in a number of scenarios:
> 
>  - if remotely managed systems with no serial cable logging keep crashing
>    without any trace of an oops message in the userspace log. (the patch
>    was written to debug such a crash. Original idea of sending an
>    emergency packet from IRQ handlers comes from Daniel Veillard who's
>    system produced the crash - thanks Daniel!)
> 
>  - if for whatever reason the amount of logging is so high that a serial
>    console cannot hold it and disks can not keep up - or in cases where
>    logged messages disturb the debugged subsystem. I'm sure fellow VM
>    hackers will find this useful :-)
> 
>  - the netconsole can be used to emit crashdumps over the network, without
>    any delay between the point of crash and start of netlogging.
> 
> the kernel patch (against 2.4.10 or 2.4.9-ac), and a simple user-space
> tool to display netconsole messages can be found at:
> 
>       http://redhat.com/~mingo/netconsole-patches/
> 
> sample startup of the netconsole on the server:
> 
>      insmod netconsole dev=eth1 target_ip=0x0a000701 \
>                   source_port=6666 \
>                   target_port=6666 \
>                   target_eth_byte0=0x00 \
>                   target_eth_byte1=0x90\
>                   target_eth_byte2=0x27 \
>                   target_eth_byte3=0x8C \
>                   target_eth_byte4=0xA0 \
>                   target_eth_byte5=0xA8
> 
> and on the client:
> 
>       # ./netconsole-client -server 10.0.7.5 -client 10.0.7.1 -port 6666
>         [...network console startup...]
>         netconsole: network logging started up successfully!
>         SysRq : Loglevel set to 9
> 
> more about features and limitations can be found under:
> 
>       Documentation/networking/netlogging.txt
> 
> reports, comments, suggestions welcome.
> 
>       Ingo
> 
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