poll.7 (2010 09)

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poll(7) poll(7)

NAME

poll - monitor I/O conditions on multiple ﬁle descriptors

SYNOPSIS

#include <sys/devpoll.h> #include <fcntl.h>

int open("/dev/poll", O_RDWR);

int write(int filedes, const struct pollfd *buf, size_t nbyte);

int ioctl(int filedes, DP_POLL, struct dvpoll *arg);

int ioctl(int filedes, DP_ISPOLLED, struct pollfd *arg);

DESCRIPTION

/dev/poll provides an interface to the event port driver allowing a user to synchronously monitor a

speciﬁc set of conditions associated with a registered set of ﬁle descriptors. Poll conditions include the

ability to read or write data without blocking and certain exceptional conditions.

Access to

/dev/poll is provided through the

open(), write(), and ioctl() system calls.

The

/dev/poll event port provides functionality comparable to the

select(2) and poll(2)

system

calls and supports the following types of ﬁle descriptors: network (

AF_INET) and Unix Domain

(

AF_UNIX) sockets, named FIFO ﬁles and pipes, XTI endpoints, and STREAMS devices.

General operations supported by the event port driver are:

-- Opening an event port.

-- Registering and deregistering ﬁle descriptors on an event port.

-- Polling registered ﬁle descriptors on an event port.

-- Retrieving registered poll conditions for a ﬁle descriptor.

-- Closing an event port.

Opening An Event Port

Each open of the /dev/poll device enables an event port from which a different set of ﬁle descriptors

can be polled. The ﬁle descriptor returned by the open() system call represents the event port. Users

wishing to monitor multiple sets of ﬁle descriptors should open the /dev/poll device multiple times.

For example:

int evpfd;

evpfd = open("/dev/poll", O_RDWR);

Only the process that performed the open() on /dev/poll can perform general event port operations.

Speciﬁcally, any event port ﬁle descriptor inherited by a child from its parent or that is received from

another process using the Unix Domain Sockets access rights can only be closed. (See sendmsg in the

send(2) man page or the STREAMS I_FDINSERT ioctl request in the streamio (7) man page.)

Registering and Deregistering File Descriptors

An interest set of ﬁle descriptors and poll conditions is registered with an event port by using the

write() system call. By writing an array of pollfd structures to an event port the user can register

multiple ﬁle descriptors in one write() service call. The pollfd structure and related poll conditions

are deﬁned in <poll.h>, (included by <sys/devpoll.h>). Other ﬂags are deﬁned in the

<sys/devpoll.h> ﬁle. See the poll (2) man page for the deﬁnition of the poll conditions.

To register a ﬁle descriptor, the

fd ﬁeld is set to the ﬁle descriptor to be registered, and the events ﬁeld

is set to one or more poll conditions, such as POLLIN. Multiple poll conditions can be ORed together. A

given ﬁle descriptor can be registered with multiple event ports. Re-registering a ﬁle descriptor with the

same event port will cause the the speciﬁed poll conditions to join the previous conditions for the given

ﬁle descriptor.

To deregister,

fd is set to the ﬁle descriptor to be deregistered, and events is set to POLLREMOVE.

POLLREMOVE is deﬁned in <sys/devpoll.h>. POLLREMOVE must not be ORed together with any

other poll conditions.

When a polled ﬁle descriptor is closed, it is automatically deregistered.

Continuing our example, the following registers two ﬁle descriptors on the opened event port,

fd1 and

fd2:

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (6 pages)

PAGE 1
poll(7) poll(7) NAME poll - monitor I/O conditions on multiple file descriptors SYNOPSIS #include #include
PAGE 2
poll(7) poll(7) struct pollfd pfd[2]; int err; pfd[0].fd = fd1; pfd[0].events = POLLIN; pfd[1].fd = fd2; pfd[1].events = (POLLIN | POLLRDBAND); err = write(evpfd, pfd, sizeof(pfd)); Polling File Descriptors Polling an event port’s interest set is initiated by calling ioctl() specifying the DP_POLL request . The ioctl arg parameter is a pointer to a dvpoll structure, defined in .
PAGE 3
poll(7) poll(7) If ioctl() returns -1, errno is set to the error condition. ERRORS The following errors are returned by the event port driver. If open() fails, errno is set to one of the following values. [EACCES] [EAGAIN] The minor number of the device file name passed to open() is not 0. Allocation of internal data structures failed due to a temporary condition. Calling open() again might succeed. [EMFILE] The maximum number of file descriptors allowed for the process is already open.
PAGE 4
poll(7) poll(7) After the last non-blocking write succeeds, the following should be used to deregister for POLLOUT, but continue to be registered for input notifications. Note that POLLREMOVE must be used in order to remove the POLLOUT registration. struct pollfd regpfd[2]; int err; regpfd[0].fd = sd; regpfd[0].events = POLLREMOVE; regpfd[1].fd = sd; regpfd[1].
PAGE 5
poll(7) poll(7) SEE ALSO ioctl(2), mknod(2), open(2), pipe(2), poll(2), select(2), send(2), socket(2), socketpair(2), write(2), t_open(3).
PAGE 6
(Notes) A (Notes) pA 6 Hewlett-Packard Company −1− HP-UX 11i Version 3: September 2010