Tribblix: manual page: chpoll.9e

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