centos man page for printk

PRINTK(9)							   Driver Basics							 PRINTK(9)

NAME
       printk - print a kernel message

SYNOPSIS
       int printk(const char * fmt, ...);

ARGUMENTS
       fmt
	   format string

       ...
	   variable arguments

DESCRIPTION
       This is printk. It can be called from any context. We want it to work.

       We try to grab the console_lock. If we succeed, it's easy - we log the output and call the console drivers. If we fail to get the
       semaphore, we place the output into the log buffer and return. The current holder of the console_sem will notice the new output in
       console_unlock; and will send it to the consoles before releasing the lock.

       One effect of this deferred printing is that code which calls printk and then changes console_loglevel may break. This is because
       console_loglevel is inspected when the actual printing occurs.

SEE ALSO
       printf(3)

       See the vsnprintf documentation for format string extensions over C99.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014								 PRINTK(9)