opensolaris man page for ddi_enter_critical

ddi_enter_critical(9F)					   Kernel Functions for Drivers 				    ddi_enter_critical(9F)

NAME
       ddi_enter_critical, ddi_exit_critical - enter and exit a critical region of control

SYNOPSIS
       #include <sys/conf.h>
       #include <sys/ddi.h>
       #include <sys/sunddi.h>

       unsigned int ddi_enter_critical(void);

       void ddi_exit_critical(unsignedint ddic);

INTERFACE LEVEL
       Solaris DDI specific (Solaris DDI).

PARAMETERS
       ddic    The returned value from the call to ddi_enter_critical() must be passed to ddi_exit_critical().

DESCRIPTION
       Nearly  all driver operations can be done without any special synchronization and protection mechanisms beyond those provided by, for exam-
       ple, mutexes (see mutex(9F)). However, for certain devices there can exist a very short critical region of code which must  be  allowed	to
       run  uninterrupted. The function ddi_enter_critical() provides a mechanism by which a driver can ask the system to guarantee to the best of
       its ability that the current thread of execution will neither be preempted nor interrupted. This stays in effect until a bracketing call to
       ddi_exit_critical() is made (with an argument which was the returned value from ddi_enter_critical()).

       The  driver  may  not  call  any  functions  external  to  itself  in  between the time it calls ddi_enter_critical() and the time it calls
       ddi_exit_critical().

RETURN VALUES
       The ddi_enter_critical() function returns an opaque unsigned integer which must be used in the subsequent call to ddi_exit_critical().

CONTEXT
       This function can be called from user, interrupt, or kernel context.

WARNINGS
       Driver writers should note that in a multiple processor system  this function does not temporarily suspend other processors from executing.
       This  function  also cannot guarantee to actually block the hardware from doing such things as interrupt acknowledge cycles. What it can do
       is guarantee that the currently executing thread will not be preempted.

       Do not write code  bracketed by ddi_enter_critical() and ddi_exit_critical() that can get caught in an infinite loop, as  the  machine  may
       crash if you do.

SEE ALSO
       mutex(9F)

       Writing Device Drivers

SunOS 5.11							    16 Jan 2006 					    ddi_enter_critical(9F)