minix/lib/libc/sys/poll.2
Ben Gras 2fe8fb192f Full switch to clang/ELF. Drop ack. Simplify.
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
2012-02-14 14:52:02 +01:00

246 lines
6.1 KiB
Groff

.\" $NetBSD: poll.2,v 1.28 2010/03/22 19:30:55 joerg Exp $
.\"
.\" Copyright (c) 1998, 2005 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Charles M. Hannum.
.\"
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.\" 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.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``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 FOUNDATION OR CONTRIBUTORS
.\" 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
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\"
.Dd September 8, 2006
.Dt POLL 2
.Os
.Sh NAME
.Nm poll, pollts
.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"
.In poll.h
.In signal.h
.In time.h
.Ft int
.Fn pollts "struct pollfd * restrict fds" "nfds_t nfds" "const struct timespec * restrict ts" "const sigset_t * restrict sigmask"
.Sh DESCRIPTION
.Fn poll
and
.Fn pollts
examine 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 the value in
.Em fd
is negative, the file descriptor is ignored and
.Em revents
is set to 0.
.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
Normal data may be written without blocking.
.It POLLWRNORM
Equivalent to
POLLOUT.
.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.
If the remote end of a socket is closed,
.Fn poll
returns a
POLLIN
event, rather than a
POLLHUP.
.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
If
.Fa ts
is a non-null pointer, it references a timespec structure which specifies a
maximum interval to wait for any file descriptor to become ready.
If
.Fa ts
is a null pointer,
.Fn pollts
blocks indefinitely.
If
.Fa ts
is a non-null pointer, referencing a zero-valued timespec structure, then
.Fn pollts
will return without blocking.
.Pp
If
.Fa sigmask
is a non-null pointer, then the
.Fn pollts
function shall replace the signal mask of the caller by the set of
signals pointed to by
.Fa sigmask
before examining the descriptors, and shall restore the signal mask
of the caller before returning.
.Sh RETURN VALUES
.Fn poll
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 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 d
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
.Fa fds
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 negative.
.El
.Sh SEE ALSO
.Xr accept 2 ,
.Xr connect 2 ,
.Xr read 2 ,
.Xr recv 2 ,
.Xr select 2 ,
.Xr send 2 ,
.Xr write 2
.Sh HISTORY
The
.Fn poll
function appeared in
.At V.3 .
The
.Fn pollts
function first appeared in
.Nx 3.0 .
.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.