ddi_enter_critical, ddi_exit_critical - enter and exit a critical region of
unsigned int ddi_enter_critical(void);
void ddi_exit_critical(unsignedint ddic);
illumos DDI specific (illumos DDI).
The returned value from the call to
ddi_enter_critical() must be passed to
Nearly all driver operations can be done without any special synchronization and
protection mechanisms beyond those provided by, for example, 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
The ddi_enter_critical() function returns an opaque unsigned integer
which must be used in the subsequent call to ddi_exit_critical().
This function can be called from user, interrupt, or kernel context.
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.