Re: console server and kernel prints

[Niels Möller]

Marcus Brinkmann <Marcus.Brinkmann@ruhr-uni-bochum.de> writes:

> We have a kernel log device to retrieve them.  It's just that if everything
> is going down, you probably want to see the last words of the kernel at the
> console, because that's your only chance.

Well, if the kernel doesn't know gfx hardware (which it shouldn't,
imo), it simply can't access the "raw" console. It can print out
messages on some serial port (if you have one) or other *simple*
communicatiosn hardware, or write message to some file or circular
buffer on disk. Or use morse code to the PC speaker ;-) But the screen
bitmap is off-limits.

But I think that limitation is something that it should be possible to
live with. There have been other OS:s where neither the kernel nor the
gfx hardware knows of any text-mode console (e.g. amigaos and probably
also macs), and I've not experienced or heard about any problems with
that. I was usually annoyed when I used SunOS or Solaris, where the
kernel *was* able to put random messages directly on the screen
corrupting my X windows.

For serious debugging of kernel panics, you'd want to use a gdb on the
serial line, or a real crash dump for post-mortem debugging (I'm not
very familiar with crash dump feature, but I think it means writing
the system state onto the swap partition, or some other partition
reserved for this very purpose).

Regards,
/Niels