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Kernel Functions for Driversddi_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 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

 

ddi_enter_critical() 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 or interrupt 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 5.9Go To TopLast Changed 4 Nov 1991

 
      
      
Copyright 2002 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.