PRINTK(9)                                 Driver Basics                                 PRINTK(9)



NAME
       printk - print a kernel message

SYNOPSIS
       __visible 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 4.8.                 January 2017                                 PRINTK(9)