ddi_enter_critical(9f) [opensolaris man page]

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)

Check Out this Related Man Page

CRITICAL_ENTER(9)                                          BSD Kernel Developer's Manual                                         CRITICAL_ENTER(9)

NAME

     critical_enter, critical_exit -- enter and exit a critical region

SYNOPSIS

     #include <sys/param.h>
     #include <sys/systm.h>

     void
     critical_enter(void);

     void
     critical_exit(void);

DESCRIPTION

     These functions are used to prevent preemption in a critical region of code.  All that is guaranteed is that the thread currently executing
     on a CPU will not be preempted.  Specifically, a thread in a critical region will not migrate to another CPU while it is in a critical
     region.  The current CPU may still trigger faults and exceptions during a critical section; however, these faults are usually fatal.

     The critical_enter() and critical_exit() functions manage a per-thread counter to handle nested critical sections.  If a thread is made
     runnable that would normally preempt the current thread while the current thread is in a critical section, then the preemption will be
     deferred until the current thread exits the outermost critical section.

     Note that these functions are not required to provide any inter-CPU synchronization, data protection, or memory ordering guarantees and thus
     should not be used to protect shared data structures.

     These functions should be used with care as an infinite loop within a critical region will deadlock the CPU.  Also, they should not be inter-
     locked with operations on mutexes, sx locks, semaphores, or other synchronization primitives.  One exception to this is that spin mutexes
     include a critical section, so in certain cases critical sections may be interlocked with spin mutexes.

HISTORY

     These functions were introduced in FreeBSD 5.0.

BSD                                                               October 5, 2005                                                              BSD

Linux and UNIX Man Pages

ddi_enter_critical(9f) [opensolaris man page]

Check Out this Related Man Page