2fe8fb192f
There is important information about booting non-ack images in docs/UPDATING. ack/aout-format images can't be built any more, and booting clang/ELF-format ones is a little different. Updating to the new boot monitor is recommended. Changes in this commit: . drop boot monitor -> allowing dropping ack support . facility to copy ELF boot files to /boot so that old boot monitor can still boot fairly easily, see UPDATING . no more ack-format libraries -> single-case libraries . some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases . drop several ack toolchain commands, but not all support commands (e.g. aal is gone but acksize is not yet). . a few libc files moved to netbsd libc dir . new /bin/date as minix date used code in libc/ . test compile fix . harmonize includes . /usr/lib is no longer special: without ack, /usr/lib plays no kind of special bootstrapping role any more and bootstrapping is done exclusively through packages, so releases depend even less on the state of the machine making them now. . rename nbsd_lib* to lib* . reduce mtree
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6.1 KiB
Groff
246 lines
6.1 KiB
Groff
.\" $NetBSD: poll.2,v 1.28 2010/03/22 19:30:55 joerg Exp $
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.\"
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.\" Copyright (c) 1998, 2005 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Charles M. Hannum.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd September 8, 2006
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.Dt POLL 2
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.Os
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.Sh NAME
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.Nm poll, pollts
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.Nd synchronous I/O multiplexing
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In poll.h
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.Ft int
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.Fn poll "struct pollfd *fds" "nfds_t nfds" "int timeout"
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.In poll.h
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.In signal.h
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.In time.h
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.Ft int
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.Fn pollts "struct pollfd * restrict fds" "nfds_t nfds" "const struct timespec * restrict ts" "const sigset_t * restrict sigmask"
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.Sh DESCRIPTION
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.Fn poll
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and
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.Fn pollts
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examine a set of file descriptors to see if some of them are ready for
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I/O.
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The
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.Fa fds
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argument is a pointer to an array of pollfd structures as defined in
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.In poll.h
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(shown below).
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The
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.Fa nfds
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argument determines the size of the
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.Fa fds
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array.
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.Bd -literal
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struct pollfd {
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int fd; /* file descriptor */
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short events; /* events to look for */
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short revents; /* events returned */
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};
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.Ed
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.Pp
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The fields of
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.Fa struct pollfd
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are as follows:
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.Bl -tag -width XXXrevents
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.It fd
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File descriptor to poll.
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If the value in
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.Em fd
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is negative, the file descriptor is ignored and
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.Em revents
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is set to 0.
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.It events
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Events to poll for.
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(See below.)
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.It revents
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Events which may occur.
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(See below.)
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.El
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.Pp
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The event bitmasks in
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.Fa events
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and
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.Fa revents
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have the following bits:
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.Bl -tag -width XXXPOLLWRNORM
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.It POLLIN
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Data other than high priority data may be read without blocking.
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.It POLLRDNORM
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Normal data may be read without blocking.
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.It POLLRDBAND
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Data with a non-zero priority may be read without blocking.
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.It POLLPRI
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High priority data may be read without blocking.
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.It POLLOUT
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Normal data may be written without blocking.
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.It POLLWRNORM
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Equivalent to
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POLLOUT.
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.It POLLWRBAND
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Data with a non-zero priority may be written without blocking.
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.It POLLERR
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An exceptional condition has occurred on the device or socket.
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This flag is always checked, even if not present in the
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.Fa events
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bitmask.
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.It POLLHUP
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The device or socket has been disconnected.
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This flag is always
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checked, even if not present in the
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.Fa events
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bitmask.
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Note that
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POLLHUP
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and
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POLLOUT
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should never be present in the
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.Fa revents
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bitmask at the same time.
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If the remote end of a socket is closed,
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.Fn poll
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returns a
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POLLIN
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event, rather than a
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POLLHUP.
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.It POLLNVAL
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The file descriptor is not open.
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This flag is always checked, even
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if not present in the
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.Fa events
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bitmask.
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.El
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.Pp
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If
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.Fa timeout
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is neither zero nor INFTIM (\-1), it specifies a maximum interval to
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wait for any file descriptor to become ready, in milliseconds.
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If
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.Fa timeout
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is INFTIM (\-1), the poll blocks indefinitely.
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If
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.Fa timeout
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is zero, then
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.Fn poll
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will return without blocking.
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.Pp
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If
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.Fa ts
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is a non-null pointer, it references a timespec structure which specifies a
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maximum interval to wait for any file descriptor to become ready.
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If
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.Fa ts
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is a null pointer,
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.Fn pollts
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blocks indefinitely.
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If
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.Fa ts
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is a non-null pointer, referencing a zero-valued timespec structure, then
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.Fn pollts
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will return without blocking.
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.Pp
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If
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.Fa sigmask
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is a non-null pointer, then the
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.Fn pollts
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function shall replace the signal mask of the caller by the set of
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signals pointed to by
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.Fa sigmask
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before examining the descriptors, and shall restore the signal mask
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of the caller before returning.
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.Sh RETURN VALUES
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.Fn poll
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returns the number of descriptors that are ready for I/O, or \-1 if an
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error occurred.
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If the time limit expires,
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.Fn poll
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returns 0.
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If
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.Fn poll
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returns with an error,
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including one due to an interrupted call,
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the
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.Fa fds
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array will be unmodified.
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.Sh COMPATIBILITY
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This implementation differs from the historical one in that a given
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file descriptor may not cause
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.Fn poll
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to return with an error.
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In cases where this would have happened in the historical implementation
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(e.g. trying to poll a
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.Xr revoke 2 Ns d
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descriptor), this implementation instead copies the
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.Fa events
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bitmask to the
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.Fa revents
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bitmask.
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Attempting to perform I/O on this descriptor will then return an error.
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This behaviour is believed to be more useful.
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.Sh ERRORS
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An error return from
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.Fn poll
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indicates:
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.Bl -tag -width Er
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.It Bq Er EFAULT
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.Fa fds
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points outside the process's allocated address space.
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.It Bq Er EINTR
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A signal was delivered before the time limit expired and
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before any of the selected events occurred.
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.It Bq Er EINVAL
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The specified time limit is negative.
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.El
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.Sh SEE ALSO
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.Xr accept 2 ,
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.Xr connect 2 ,
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.Xr read 2 ,
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.Xr recv 2 ,
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.Xr select 2 ,
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.Xr send 2 ,
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.Xr write 2
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.Sh HISTORY
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The
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.Fn poll
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function appeared in
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.At V.3 .
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The
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.Fn pollts
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function first appeared in
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.Nx 3.0 .
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.Sh BUGS
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The distinction between some of the fields in the
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.Fa events
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and
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.Fa revents
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bitmasks is really not useful without STREAMS.
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The fields are defined for compatibility with existing software.
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