CHPOLL(9E) Driver Entry Points CHPOLL(9E)
NAME
chpoll - poll entry point for a non-STREAMS character driver
SYNOPSIS
#include <sys/types.h>
#include <sys/poll.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>
int prefixchpoll(
dev_t dev,
short events,
int anyyet,
short *reventsp,
struct pollhead **phpp);
INTERFACE LEVEL
This entry point is optional. Architecture independent level 1 (DDI/DKI).
PARAMETERS
dev The device number for the device to be polled.
events The events that may occur. Valid events are:
POLLIN Data other than high priority data may be read
without blocking.
POLLOUT Normal data may be written without blocking.
POLLPRI High priority data may be received without
blocking.
POLLHUP A device hangup has occurred.
POLLERR An error has occurred on the device.
POLLRDNORM Normal data (priority band = 0) may be read
without blocking.
POLLRDBAND Data from a non-zero priority band may be read
without blocking
POLLWRNORM The same as
POLLOUT.
POLLWRBAND Priority data (priority band > 0) may be
written.
POLLET The desired event is to be edge-triggered;
calls to
pollwakeup(9F) should not be
suppressed, even if the event is pending at the
time of call to the
chpoll() function.
anyyet A flag that is non-zero if any other file descriptors in the
pollfd array have events pending. The
poll(2) system call
takes a pointer to an array of
pollfd structures as one of
its arguments. See the
poll(2) reference page for more
details.
reventsp A pointer to a bitmask of the returned events satisfied.
phpp A pointer to a pointer to a
pollhead structure.
DESCRIPTION
The
chpoll() entry point routine is used by non-STREAMS character device
drivers that wish to support polling. The driver must implement the
polling discipline itself. The following rules must be followed when
implementing the polling discipline:
1. Implement the following algorithm when the
chpoll() entry
point is called:
if (specified_events_are_satisfied_now) {
*reventsp = satisfied_events & events;
} else {
*reventsp = 0;
}
if ((*reventsp == 0 && !anyyet) || (events & POLLET))
*phpp = &my_local_pollhead_structure;
return (0);
Note: Prior to the integration of
epoll(7), which included
edge-triggering via the
POLLET flag, standard chpoll
mechanisms would only provide a pollhead in
phpp if there were
no matching events. Edge-triggered polling requires that
pollwakeup() always be called for a resource, so if
POLLET is
set in the
events of interest, the chpoll method must yield a
pollhead and prepare to issue
pollwakeup() calls on it.
Drivers which are not wired up to make
pollwakeup() calls on a
pollhead when their status changes should emit one from their
chpoll routine. This will exclude the resource from caching
by pollers, since it cannot alert them to new events without
pollwakeup() notification.
2. Allocate an instance of the
pollhead structure. This instance
may be tied to the per-minor data structure defined by the
driver. The
pollhead structure should be treated as a "black
box" by the driver. Initialize the
pollhead structure by
filling it with zeroes. The size of this structure is
guaranteed to remain the same across releases.
3. Call the
pollwakeup() function with
events listed above
whenever pollable
events which the driver should monitor
occur. This function can be called with multiple events at one
time. The
pollwakup() can be called regardless of whether or
not the
chpoll() entry is called; it should be called every
time the driver detects the pollable event. The driver must
not hold any mutex across the call to
pollwakeup(9F) that is
acquired in its
chpoll() entry point, or a deadlock may
result. Note that if
POLLET is set in the specified events,
the driver must call
pollwakeup(9F) on subsequent events, even
if events are pending at the time of the call to
chpoll().
4. In the
close(9E) entry point, the driver should call
pollwakeup() on the
pollhead structure that corresponds to the
closing software state, specifying
POLLERR for the events.
Further, upon return from
pollwakeup(), the driver's
close(9E) entry point should call the
pollhead_clean(9F) function,
specifying the
pollhead that corresponds to the structure that
will be deallocated:
static int
mydriver_close(dev_t dev, int flag, int otyp, cred_t *cp)
{
minor_t minor = getminor(dev);
mydriver_state_t *state;
state = ddi_get_soft_state(mydriver_softstate, minor);
pollwakeup(&state->mydriver_pollhd, POLLERR);
pollhead_clean(&state->mydriver_pollhd);
...
This step is necessary to inform other kernel subsystems that
the memory associated with the
pollhead is about to be
deallocated by the
close(9E) entry point.
RETURN VALUES
chpoll() should return
0 for success, or the appropriate error number.
SEE ALSO
poll(2),
epoll(7),
nochpoll(9F),
pollwakeup(9F) Writing Device Drivers January 18, 2017
CHPOLL(9E)