What should I have to fix a bug?
- Bug. Well knowed, particular bug.
- Version of "bugged" kernel.
- Bit of luck.
Note: Repeated bug is more then 50% of success.
printk is very useful function similar to printf(). This function work evrywhere and at any time(apart from early stage of booting kernel when video isn't initialized).It use loglevels to tell console how important is message.
Full list of levels:
KERN_EMERG <-- the most important
KERN_DEBUG <-- the less important
Console will print messages olny with level higher than console_loglevel. And default printk use DEFAULT_MESSAGE_LOGLEVEL == KERN_WARNING (but it mey changed in the future).
printk() use cyclic buffer to manage with messages. Next klogd read messages (by /proc/kmsg) from buffer and give it to syslogd with write them to /var/log/messages. (You can configure syslogd by /etc/syslog.conf).
oops is error caused by uncorrectly worked kernel. Kernel write on console what registers contain and "back trace". Only when kernel is in user space oops kill program and system can steel work. In other spaces kernel do panic error and stop running.By default back trace contain adresses of functions with were called. But you can use ksymoops file_with_oops.txt to see names of this functions or you can compile your kernel with CONFIG_KALLSYMS that give you this same effect.