- whenever a kernel panic occurs, the message is saved
(this is actually the case since the "buf" string
in panic() is declared static).
- when RightAlt-SysRq-D is pressed, if there has been
a panic previously, then the system reboots to real
mode, waits for the user to insert a diskette in the
first drive and hit a key, then dumps a copy of the
last message onto the first sectors by using bios
int 13h.
Rebooting to real mode and using int 13h is essential
because it enhances the chances to obtain a valid dump
even under very unstable crash situations where the
floppy driver may not work.
At first I even wanted to immediately force a reboot
to real mode after a solid lock (when possible) to
get more chances to catch keyboard keys used to initiate the dump, but
this would prevent EMERG_SYNC
from working anymore. Anyway, I don't think there are
so many cases where RightAlt-SysRq doesn't work.
If you have suggestions (reinitializing screen to
text mode, getting more info than just the panic
dump, etc ...), they're welcome.
Of course, if you have any objections such as "don't
do this, it's too risky and/or too dirty", they're
welcome too !
Willy Tarreau
willy@meta-x.org
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