Provided by: freebsd-manpages_7.2-1_all bug

NAME

     ithread_add_handler, ithread_create, ithread_destroy, ithread_priority,
     ithread_remove_handler, ithread_schedule - kernel interrupt threads

SYNOPSIS

     #include <sys/param.h>
     #include <sys/bus.h>
     #include <sys/interrupt.h>

     int
     ithread_add_handler(struct ithd *ithread, const char *name,
             driver_intr_t handler, void *arg, u_char pri,
             enum intr_type flags, void **cookiep);

     int
     ithread_create(struct ithd **ithread, int vector, int flags,
             void (*disable)(int), void (*enable)(int), const char *fmt, ...);

     int
     ithread_destroy(struct ithd *ithread);

     u_char
     ithread_priority(enum intr_type flags);

     int
     ithread_remove_handler(void *cookie);

     int
     ithread_schedule(struct ithd *ithread, int do_switch);

DESCRIPTION

     Interrupt threads are kernel threads that run a list of handlers when
     triggered by either a hardware or software interrupt.  Each interrupt
     handler has a name, handler function, handler argument, priority, and
     various flags.  Each interrupt thread maintains a list of handlers sorted
     by priority.  This results in higher priority handlers being executed
     prior to lower priority handlers.  Each thread assumes the priority of
     its highest priority handler for its process priority, or PRIO_MAX if it
     has no handlers.  Interrupt threads are also associated with a single
     interrupt source, represented as a vector number.

     The ithread_create() function creates a new interrupt thread.  The
     ithread argument points to an struct ithd pointer that will point to the
     newly created thread upon success.  The vector argument specifies the
     interrupt source to associate this thread with.  The flags argument is a
     mask of properties of this thread.  The only valid flag currently for
     ithread_create() is IT_SOFT to specify that this interrupt thread is a
     software interrupt.  The enable and disable arguments specify optional
     functions used to enable and disable this interrupt thread’s interrupt
     source.  The functions receive the vector corresponding to the thread’s
     interrupt source as their only argument.  The remaining arguments form a
     printf(9) argument list that is used to build the base name of the new
     ithread.  The full name of an interrupt thread is formed by concatenating
     the base name of an interrupt thread with the names of all of its
     interrupt handlers.

     The ithread_destroy() function destroys a previously created interrupt
     thread by releasing its resources and arranging for the backing kernel
     thread to terminate.  An interrupt thread can only be destroyed if it has
     no handlers remaining.

     The ithread_add_handler() function adds a new handler to an existing
     interrupt thread specified by ithread.  The name argument specifies a
     name for this handler.  The handler and arg arguments provide the
     function to execute for this handler and an argument to pass to it.  The
     pri argument specifies the priority of this handler and is used both in
     sorting it in relation to the other handlers for this thread and to
     specify the priority of the backing kernel thread.  The flags argument
     can be used to specify properties of this handler as defined in If
     cookiep is not NULL, then it will be assigned a cookie that can be used
     later to remove this handler.

     The ithread_remove_handler() removes a handler from an interrupt thread.
     The cookie argument specifies the handler to remove from its thread.

     The ithread_schedule() function schedules an interrupt thread to run.  If
     the do_switch argument is non-zero and the interrupt thread is idle, then
     a context switch will be forced after putting the interrupt thread on the
     run queue.

     The ithread_priority() function translates the INTR_TYPE_* interrupt
     flags into interrupt handler priorities.

     The interrupt flags not related to the type of a particular interrupt
     (INTR_TYPE_*) can be used to specify additional properties of both
     hardware and software interrupt handlers.  The INTR_EXCL flag specifies
     that this handler cannot share an interrupt thread with another handler.
     The INTR_FAST flag specifies that when this handler is executed, it
     should be run immediately rather than being run asynchronously when its
     interrupt thread is scheduled to run.  The INTR_FAST flag implies
     INTR_EXCL.  The INTR_MPSAFE flag specifies that this handler is MP safe
     in that it does not need the Giant mutex to be held while it is executed.
     The INTR_ENTROPY flag specifies that the interrupt source this handler is
     tied to is a good source of entropy, and thus that entropy should be
     gathered when an interrupt from the handler’s source triggers.
     Presently, the INTR_FAST and INTR_ENTROPY flags are not valid for
     software interrupt handlers.

     It is not permitted to sleep in an interrupt thread; hence, any memory or
     zone allocations in an interrupt thread should be specified with the
     M_NOWAIT flag set.  Any allocation errors must be handled thereafter.

RETURN VALUES

     The ithread_add_handler(), ithread_create(), ithread_destroy(),
     ithread_remove_handler(), and ithread_schedule() functions return zero on
     success and non-zero on failure.  The ithread_priority() function returns
     a process priority corresponding to the passed in interrupt flags.

EXAMPLES

     The swi_add() function demonstrates the use of ithread_create() and
     ithread_add_handler().

           int
           swi_add(struct ithd **ithdp, const char *name, driver_intr_t handler,
                       void *arg, int pri, enum intr_type flags, void **cookiep)
           {
                   struct proc *p;
                   struct ithd *ithd;
                   int error;

                   if (flags & (INTR_FAST | INTR_ENTROPY))
                           return (EINVAL);

                   ithd = (ithdp != NULL) ? *ithdp : NULL;

                   if (ithd != NULL) {
                           if ((ithd->it_flags & IT_SOFT) == 0)
                                   return(EINVAL);
                   } else {
                           error = ithread_create(&ithd, pri, IT_SOFT, NULL, NULL,
                               "swi%d:", pri);
                           if (error)
                                   return (error);

                           if (ithdp != NULL)
                                   *ithdp = ithd;
                   }
                   return (ithread_add_handler(ithd, name, handler, arg, pri + PI_SOFT,
                               flags, cookiep));
           }

ERRORS

     The ithread_add_handler() function will fail if:

     [EINVAL]           Any of the ithread, handler, or name arguments are
                        NULL.

     [EINVAL]           The INTR_EXCL flag is specified and the interrupt
                        thread ithread already has at least one handler, or
                        the interrupt thread ithread already has an exclusive
                        handler.

     [ENOMEM]           Could not allocate needed memory for this handler.

     The ithread_create() function will fail if:

     [EAGAIN]           The system-imposed limit on the total number of
                        processes under execution would be exceeded.  The
                        limit is given by the sysctl(3) MIB variable
                        KERN_MAXPROC.

     [EINVAL]           A flag other than IT_SOFT was specified in the flags
                        parameter.

     [ENOMEM]           Could not allocate needed memory for this interrupt
                        thread.

     The ithread_destroy() function will fail if:

     [EINVAL]           The ithread argument is NULL.

     [EINVAL]           The interrupt thread pointed to by ithread has at
                        least one handler.

     The ithread_remove_handler() function will fail if:

     [EINVAL]           The cookie argument is NULL.

     The ithread_schedule() function will fail if:

     [EINVAL]           The ithread argument is NULL.

     [EINVAL]           The interrupt thread pointed to by ithread has no
                        interrupt handlers.

SEE ALSO

     kthread(9), malloc(9), swi(9), uma(9)

HISTORY

     Interrupt threads and their corresponding API first appeared in
     FreeBSD 5.0.

BUGS

     Currently struct ithd represents both an interrupt source and an
     interrupt thread.  There should be a separate struct isrc that contains a
     vector number, enable and disable functions, etc. that an ithread holds a
     reference to.