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 - : send the line "unsubscribe linux-net" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
