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

illumos DDI specific (illumos 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 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
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

January 16, 2006 DDI_ENTER_CRITICAL(9F)