RE: Capturing dmesg upon system crash on 6.3

I'm facing a system reboot upon loading of the driver, and

I could use

a tool for capturing dmesg upon system crash (such as

netconsole

on Linux).

Your kernel isn't setup for driver development:
http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-ha
ndbook/kerneldebug.html
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kern
elconfig.html

Basically, your system is rebooting cause the kernel
panics and
you're not setup for crash dumps, or anything that could help
you diagnose the panic.
--
Mel

I've setup the dumpdev/dumpdir and I get a vmcore image

upon a crash.

I don't really understand how to use kgdb in order to read

it but more

than that - I don't need that much of data. I only want
the dmesg
report at the moment, see at what point my driver went

crazy. Is it possible?


Uhm, no. Fundamental logic flaw: when a kernel is
stopped, you can't
issue userland commands. All you have when you use ddb, is the
contents of the registers, ram and backtrace.

You really want ddb in the kernel: when a kernel panics,
it'll drop
to ddb and you can examine registers and do a backtrace,
instead of
dumping core and rebooting. It should point exactly to where your
driver went crazy.
--
Mel

I meant making the dmesg log sent over the network/serial
console to a
linux machine. I just found out about syslogd, I'm trying to figure
out how to use it.
DDB sounds like a great option for deeper debugging, I'll use it.

Ooh, sorry, totally got your question wrong.
Serial should really be the way to go. But it depends when
you load your driver. If your driver panics the kernel before
it gets to loading syslogd, there may not be much sent.
You could help this by not loading the network interface on
bootup, but via cron instead, so that you're sure syslogd is
up and running when you load the driver. Of course this
assumes a working main network interface and that the driver
isn't loaded automatically by /boot/loader.conf.
--
Mel


Thanks Mel, DDB is a great help.



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