Print a formatted message to the kernel console, much like the
printf
function of the stdio library. Normally, the message is written to the
physical console device of the computer, although this behavior can be
changed with the
register_console
function. Messages are also stored in a message log book.
The generated string may also start with a message priority code,
which sets the priority of the message. The priority code strings are
of the form
<n>
where n is a number from 0 - 7. The following macros are defined in
the
<linux/kernel.h>
header file:
KERN_EMERG
System is unuseable
KERN_ALERT
Action must be taken immediately
KERN_CRIT
Critical conditions
KERN_ERR
Error conditions
KERN_WARNING
Warning conditions
KERN_NOTICE
Normal but significant condition
KERN_INFO
Informational
KERN_DEBUG
Debug-level messages
For example
printk(KERN_NOTICE "Hello, world.\n");
does the expected thing.
RETURN VALUE
Returns the number of characters written to the log.
float and double formats are not supported. Floats and doubles do not
belong inside the kernel anyhow.
The
printk
implementation protects itself from interruption, so in principle it
can be used in interrupts handlers and critical sections. However,
there are no guarantees about the console function that is registered.
