Tribblix: manual page: ddi_periodic

DDI_PERIODIC_DELETE(9F) Kernel Functions for Drivers

NAME

ddi_periodic_delete - cancel periodic function invocation requests

SYNOPSIS

#include <sys/dditypes.h>
#include <sys/sunddi.h>

void ddi_periodic_delete(ddi_periodic_t request);

INTERFACE LEVEL

illumos DDI specific (illumos DDI)

PARAMETERS

request
ddi_periodic_t opaque value returned by ddi_periodic_add(9F)

DESCRIPTION

The ddi_periodic_delete() function cancels a periodic invocation
request previously established with ddi_periodic_add(9F).

It is not possible to cancel a periodic invocation request from
within the periodic callback itself; to do so is a programming error
that will panic the system. Instead, requests must be cancelled from
some other user or kernel context routine, such as the detach(9E)
entry point of a module.

If the callback function is already executing (for instance, on
another CPU) when the request is cancelled, ddi_periodic_delete()
will block until it finishes executing and is completely
unregistered. Because of this, locks acquired by the callback
function must not be held across the call to ddi_periodic_delete() or
a deadlock may result.

The callback will not be invoked again after the call to
ddi_periodic_delete() returns.

CONTEXT

The ddi_periodic_delete() function may be called from user or kernel
context.

EXAMPLES

Example 1: Cancelling a periodic invocation request

In the following example, the device driver cancels the request by
calling ddi_periodic_delete() and passing the opaque request
identifier returned by a previous call to ddi_periodic_add(9F).

/*
* Stop the periodic timer.
*/
static void
stop_periodic_timer(struct my_state *statep)
{
ddi_periodic_delete(statep->periodic_id);
mutex_destroy(&statep->lock);
}

static void
start_periodic_timer(struct my_state *statep)
{
hrtime_t interval = CHECK_INTERVAL;

mutex_init(&statep->lock, NULL, MUTEX_DRIVER, DDI_IPL_0);

/*
* Register my_callback which is invoked periodically
* in CHECK_INTERVAL in kernel context.
*/
statep->periodic_id = ddi_periodic_add(my_periodic_func,
statep, interval, DDI_IPL_0);
}

static void
my_periodic_func(void *arg)
{
/*
* This handler is invoked periodically.
*/
struct my_state *statep = (struct my_state *)arg;

mutex_enter(&statep->lock);
if (load_unbalanced(statep)) {
balance_tasks(statep);
}
mutex_exit(&statep->lock);
}

NOTES

Historically this interface was advertised as safe for use from
within the periodic callback function. In order to ensure the
correct operation of the system, and as reflected in the
documentation above, this unlikely (and unsafe) usage pattern is no
longer allowed.

February 12, 2014 DDI_PERIODIC_DELETE(9F)