274 lines
6.6 KiB
Groff
274 lines
6.6 KiB
Groff
.\" $NetBSD: poll.2,v 1.3 1996/09/07 21:53:08 mycroft Exp $
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.\" Copyright (c) 1996 Charles M. Hannum. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by Charles M. Hannum.
|
|
.\" 4. The name of the author may not be used to endorse or promote products
|
|
.\" derived from this software without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
|
|
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
|
|
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
|
|
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
|
|
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
|
|
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
|
|
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
|
|
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
|
|
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
|
|
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
|
|
.\"
|
|
.Dd November 13, 2014
|
|
.Dt POLL 2
|
|
.Os
|
|
.Sh NAME
|
|
.Nm poll
|
|
.Nd synchronous I/O multiplexing
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In poll.h
|
|
.Ft int
|
|
.Fn poll "struct pollfd fds[]" "nfds_t nfds" "int timeout"
|
|
.Ft int
|
|
.Fo ppoll
|
|
.Fa "struct pollfd fds[]"
|
|
.Fa "nfds_t nfds"
|
|
.Fa "const struct timespec * restrict timeout"
|
|
.Fa "const sigset_t * restrict newsigmask"
|
|
.Fc
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn poll
|
|
system call
|
|
examines a set of file descriptors to see if some of them are ready for
|
|
I/O.
|
|
The
|
|
.Fa fds
|
|
argument is a pointer to an array of pollfd structures as defined in
|
|
.In poll.h
|
|
(shown below).
|
|
The
|
|
.Fa nfds
|
|
argument determines the size of the
|
|
.Fa fds
|
|
array.
|
|
.Bd -literal
|
|
struct pollfd {
|
|
int fd; /* file descriptor */
|
|
short events; /* events to look for */
|
|
short revents; /* events returned */
|
|
};
|
|
.Ed
|
|
.Pp
|
|
The fields of
|
|
.Fa struct pollfd
|
|
are as follows:
|
|
.Bl -tag -width XXXrevents
|
|
.It fd
|
|
File descriptor to poll.
|
|
If fd is equal to -1 then
|
|
.Fa revents
|
|
is cleared (set to zero), and that pollfd is not checked.
|
|
.It events
|
|
Events to poll for.
|
|
(See below.)
|
|
.It revents
|
|
Events which may occur.
|
|
(See below.)
|
|
.El
|
|
.Pp
|
|
The event bitmasks in
|
|
.Fa events
|
|
and
|
|
.Fa revents
|
|
have the following bits:
|
|
.Bl -tag -width XXXPOLLWRNORM
|
|
.It POLLIN
|
|
Data other than high priority data may be read without blocking.
|
|
.It POLLRDNORM
|
|
Normal data may be read without blocking.
|
|
.It POLLRDBAND
|
|
Data with a non-zero priority may be read without blocking.
|
|
.It POLLPRI
|
|
High priority data may be read without blocking.
|
|
.It POLLOUT
|
|
.It POLLWRNORM
|
|
Normal data may be written without blocking.
|
|
.It POLLWRBAND
|
|
Data with a non-zero priority may be written without blocking.
|
|
.It POLLERR
|
|
An exceptional condition has occurred on the device or socket.
|
|
This
|
|
flag is always checked, even if not present in the
|
|
.Fa events
|
|
bitmask.
|
|
.It POLLHUP
|
|
The device or socket has been disconnected.
|
|
This flag is always
|
|
checked, even if not present in the
|
|
.Fa events
|
|
bitmask.
|
|
Note that
|
|
POLLHUP
|
|
and
|
|
POLLOUT
|
|
should never be present in the
|
|
.Fa revents
|
|
bitmask at the same time.
|
|
.It POLLNVAL
|
|
The file descriptor is not open.
|
|
This flag is always checked, even
|
|
if not present in the
|
|
.Fa events
|
|
bitmask.
|
|
.El
|
|
.Pp
|
|
If
|
|
.Fa timeout
|
|
is neither zero nor INFTIM (-1), it specifies a maximum interval to
|
|
wait for any file descriptor to become ready, in milliseconds.
|
|
If
|
|
.Fa timeout
|
|
is INFTIM (-1), the poll blocks indefinitely.
|
|
If
|
|
.Fa timeout
|
|
is zero, then
|
|
.Fn poll
|
|
will return without blocking.
|
|
.Pp
|
|
The
|
|
.Fn ppoll
|
|
system call, unlike
|
|
.Fn poll ,
|
|
is used to safely wait until either a set of file descriptors becomes
|
|
ready or until a signal is caught.
|
|
The
|
|
.Fa fds
|
|
and
|
|
.Fa nfds
|
|
arguments are identical to the analogous arguments of
|
|
.Fn poll .
|
|
The
|
|
.Fa timeout
|
|
argument in
|
|
.Fn ppoll
|
|
points to a
|
|
.Vt "const struct timespec"
|
|
which is defined in
|
|
.In sys/timespec.h
|
|
(shown below) rather than the
|
|
.Vt "int timeout"
|
|
used by
|
|
.Fn poll .
|
|
A null pointer may be passed to indicate that
|
|
.Fn ppoll
|
|
should wait indefinitely.
|
|
Finally,
|
|
.Fa newsigmask
|
|
specifies a signal mask which is set while waiting for input.
|
|
When
|
|
.Fn ppoll
|
|
returns, the original signal mask is restored.
|
|
.Bd -literal
|
|
struct timespec {
|
|
time_t tv_sec; /* seconds */
|
|
long tv_nsec; /* and nanoseconds */
|
|
};
|
|
.Ed
|
|
.Sh RETURN VALUES
|
|
The
|
|
.Fn poll
|
|
system call
|
|
returns the number of descriptors that are ready for I/O, or -1 if an
|
|
error occurred.
|
|
If the time limit expires,
|
|
.Fn poll
|
|
returns 0.
|
|
If
|
|
.Fn poll
|
|
returns with an error,
|
|
including one due to an interrupted system call,
|
|
the
|
|
.Fa fds
|
|
array will be unmodified.
|
|
.Sh COMPATIBILITY
|
|
This implementation differs from the historical one in that a given
|
|
file descriptor may not cause
|
|
.Fn poll
|
|
to return with an error.
|
|
In cases where this would have happened in
|
|
the historical implementation (e.g.\& trying to poll a
|
|
.Xr revoke 2 Ns ed
|
|
descriptor), this implementation instead copies the
|
|
.Fa events
|
|
bitmask to the
|
|
.Fa revents
|
|
bitmask.
|
|
Attempting to perform I/O on this descriptor will then
|
|
return an error.
|
|
This behaviour is believed to be more useful.
|
|
.Sh ERRORS
|
|
An error return from
|
|
.Fn poll
|
|
indicates:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EFAULT
|
|
The
|
|
.Fa fds
|
|
argument
|
|
points outside the process's allocated address space.
|
|
.It Bq Er EINTR
|
|
A signal was delivered before the time limit expired and
|
|
before any of the selected events occurred.
|
|
.It Bq Er EINVAL
|
|
The specified time limit is invalid. One of its components is negative or too large.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr accept 2 ,
|
|
.Xr connect 2 ,
|
|
.Xr kqueue 2 ,
|
|
.Xr pselect 2 ,
|
|
.Xr read 2 ,
|
|
.Xr recv 2 ,
|
|
.Xr select 2 ,
|
|
.Xr send 2 ,
|
|
.Xr write 2
|
|
.Sh STANDARDS
|
|
The
|
|
.Fn poll
|
|
function conforms to
|
|
.St -p1003.1-2001 .
|
|
The
|
|
.Fn ppoll
|
|
is not specified by POSIX.
|
|
.Sh HISTORY
|
|
The
|
|
.Fn poll
|
|
function appeared in
|
|
.At V .
|
|
This manual page and the core of the implementation was taken from
|
|
.Nx .
|
|
The
|
|
.Fn ppoll
|
|
function first appeared in
|
|
.Fx 11.0
|
|
.Sh BUGS
|
|
The distinction between some of the fields in the
|
|
.Fa events
|
|
and
|
|
.Fa revents
|
|
bitmasks is really not useful without STREAMS.
|
|
The fields are
|
|
defined for compatibility with existing software.
|