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

NAME

     swi_add, swi_remove, swi_sched -- register and schedule software interrupt handlers

SYNOPSIS

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

     extern struct intr_event *tty_intr_event;
     extern struct intr_event *clk_intr_event;
     extern void *vm_ih;

     int
     swi_add(struct intr_event **eventp, const char *name, driver_intr_t handler, void *arg, int pri, enum intr_type flags, void **cookiep);

     int
     swi_remove(void *cookie);

     void
     swi_sched(void *cookie, int flags);

DESCRIPTION

     These functions are used to register and schedule software interrupt handlers.  Software interrupt handlers are attached to a software inter-
     rupt thread, just as hardware interrupt handlers are attached to a hardware interrupt thread.  Multiple handlers can be attached to the same
     thread.  Software interrupt handlers can be used to queue up less critical processing inside of hardware interrupt handlers so that the work
     can be done at a later time.  Software interrupt threads are different from other kernel threads in that they are treated as an interrupt
     thread.  This means that time spent executing these threads is counted as interrupt time, and that they can be run via a lightweight context
     switch.

     The swi_add() function is used to add a new software interrupt handler to a specified interrupt event.  The eventp argument is an optional
     pointer to a struct intr_event pointer.  If this argument points to an existing event that holds a list of interrupt handlers, then this han-
     dler will be attached to that event.  Otherwise a new event will be created, and if eventp is not NULL, then the pointer at that address to
     will be modified to point to the newly created event.  The name argument is used to associate a name with a specific handler.  This name is
     appended to the name of the software interrupt thread that this handler is attached to.  The handler argument is the function that will be
     executed when the handler is scheduled to run.  The arg parameter will be passed in as the only parameter to handler when the function is
     executed.	The pri value specifies the priority of this interrupt handler relative to other software interrupt handlers.  If an interrupt
     event is created, then this value is used as the vector, and the flags argument is used to specify the attributes of a handler such as
     INTR_MPSAFE.  The cookiep argument points to a void * cookie.  This cookie will be set to a value that uniquely identifies this handler, and
     is used to schedule the handler for execution later on.

     The swi_remove() function is used to teardown an interrupt handler pointed to by the cookie argument.  It detaches the interrupt handler from
     the associated interrupt event and frees its memory.

     The swi_sched() function is used to schedule an interrupt handler and its associated thread to run.  The cookie argument specifies which
     software interrupt handler should be scheduled to run.  The flags argument specifies how and when the handler should be run and is a mask of
     one or more of the following flags:

     SWI_DELAY	Specifies that the kernel should mark the specified handler as needing to run, but the kernel should not schedule the software
		interrupt thread to run.  Instead, handler will be executed the next time that the software interrupt thread runs after being
		scheduled by another event.  Attaching a handler to the clock software interrupt thread and using this flag when scheduling a
		software interrupt handler can be used to implement the functionality performed by setdelayed() in earlier versions of FreeBSD.

     The tty_intr_event and clk_intr_event variables contain pointers to the software interrupt handlers for the tty and clock software inter-
     rupts, respectively.  tty_intr_event is used to hang tty software interrupt handlers off of the same thread.  clk_intr_event is used to hang
     delayed handlers off of the clock software interrupt thread so that the functionality of setdelayed() can be obtained in conjunction with
     SWI_DELAY.  The vm_ih handler cookie is used to schedule software interrupt threads to run for the VM subsystem.

RETURN VALUES

     The swi_add() and swi_remove() functions return zero on success and non-zero on failure.

ERRORS

     The swi_add() 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]		The flags argument specifies INTR_ENTROPY.

     [EINVAL]		The eventp argument points to a hardware interrupt thread.

     [EINVAL]		Either of the name or handler arguments are NULL.

     [EINVAL]		The INTR_EXCL flag is specified and the interrupt event pointed to by eventp already has at least one handler, or the
			interrupt event already has an exclusive handler.

     The swi_remove() function will fail if:

     [EINVAL]		A software interrupt handler pointed to by cookie is NULL.

SEE ALSO

     ithread(9), taskqueue(9)

HISTORY

     The swi_add() and swi_sched() functions first appeared in FreeBSD 5.0.  They replaced the register_swi() function which appeared in
     FreeBSD 3.0 and the setsoft*(), and schedsoft*() functions which date back to at least 4.4BSD.  The swi_remove() function first appeared in
     FreeBSD 6.1.

BUGS

     Most of the global variables described in this manual page should not be global, or at the very least should not be declared in
     <sys/interrupt.h>.

BSD
								  April 19, 2012							       BSD