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Diffstat (limited to 'man2/poll.2')
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diff --git a/man2/poll.2 b/man2/poll.2 new file mode 100644 index 000000000..a04ea75e4 --- /dev/null +++ b/man2/poll.2 @@ -0,0 +1,145 @@ +.\" Hey Emacs! This file is -*- nroff -*- source. +.\" +.\" Copyright (C) 1997 Andries Brouwer (aeb@cwi.nl) +.\" +.\" Permission is granted to make and distribute verbatim copies of this +.\" manual provided the copyright notice and this permission notice are +.\" preserved on all copies. +.\" +.\" Permission is granted to copy and distribute modified versions of this +.\" manual under the conditions for verbatim copying, provided that the +.\" entire resulting derived work is distributed under the terms of a +.\" permission notice identical to this one. +.\" +.\" Since the Linux kernel and libraries are constantly changing, this +.\" manual page may be incorrect or out-of-date. The author(s) assume no +.\" responsibility for errors or omissions, or for damages resulting from +.\" the use of the information contained herein. The author(s) may not +.\" have taken the same level of care in the production of this manual, +.\" which is licensed free of charge, as they might when working +.\" professionally. +.\" +.\" Formatted or processed versions of this manual, if unaccompanied by +.\" the source, must acknowledge the copyright and authors of this work. +.\" +.\" Additions from Richard Gooch <rgooch@atnf.CSIRO.AU> and aeb, 971207 +.\" +.TH POLL 2 1997-12-07 "Linux 2.1.23" "Linux Programmer's Manual" +.SH NAME +poll \- wait for some event on a file descriptor +.SH SYNOPSIS +.B #include <sys/poll.h> +.sp +.BI "int poll(struct pollfd *" ufds ", unsigned int " nfds ", int " timeout ); +.SH DESCRIPTION +.B poll +is a variation on the theme of +.BR select . +It specifies an array of +.I nfds +structures of type +.br +.nf + struct pollfd { + int fd; /* file descriptor */ + short events; /* requested events */ + short revents; /* returned events */ + }; +.fi +and a +.I timeout +in milliseconds. A negative value means infinite timeout. +The field +.I fd +contains a file descriptor for an open file. +The field +.I events +is an input parameter, a bitmask specifying the events the application +is interested in. +The field +.I revents +is an output parameter, filled by the kernel with the events that +actually occurred, either of the type requested, or of one of the +types +.B POLLERR +or +.B POLLHUP +or +.BR POLLNVAL . +(These three bits are meaningless in the +.I events +field, and will be set in the +.I revents +field whenever the corresponding condition is true.) +If none of the events requested (and no error) has occurred for any +of the file descriptors, the kernel waits for +.I timeout +milliseconds for one of these events to occur. +The following possible bits in these masks are defined in <sys/poll.h> +.br +.nf + #define POLLIN 0x0001 /* There is data to read */ + #define POLLPRI 0x0002 /* There is urgent data to read */ + #define POLLOUT 0x0004 /* Writing now will not block */ + #define POLLERR 0x0008 /* Error condition */ + #define POLLHUP 0x0010 /* Hung up */ + #define POLLNVAL 0x0020 /* Invalid request: fd not open */ +.fi +When compiling XPG4.2 source one also has +.br +.nf +#ifdef _XOPEN_SOURCE + #define POLLRDNORM 0x0040 /* Normal data may be read */ + #define POLLRDBAND 0x0080 /* Priority data may be read */ + #define POLLWRNORM 0x0100 /* Writing now will not block */ + #define POLLWRBAND 0x0200 /* Priority data may be written */ +#endif +.fi +Finally, Linux knows about +.br +.nf +#ifdef _GNU_SOURCE + #define POLLMSG 0x0400 +#endif +.fi +.SH "RETURN VALUE" +On success, a positive number is returned, where the number returned +is the number of structures which have non-zero +.I revents +fields (in other words, those descriptors with events or errors reported). +A value of 0 indicates that the call timed out and no file +descriptors have been selected. On error, \-1 is returned, and +.I errno +is set appropriately. +.SH ERRORS +.TP +.B EBADF +An invalid file descriptor was given in one of the sets. +.TP +.B EFAULT +The array given as argument was not contained in the calling program's +address space. +.TP +.B EINTR +A signal occurred before any requested event. +.TP +.B EINVAL +The +.I nfds +value exceeds the RLIMIT_NOFILE value. +.TP +.B ENOMEM +There was no space to allocate file descriptor tables. +.SH BUGS +See the BUGS section of +.BR select (2). +.SH "CONFORMING TO" +XPG4-UNIX. +.SH AVAILABILITY +The poll() systemcall was introduced in Linux 2.1.23. +The poll() library call was introduced in libc 5.4.28 +(and provides emulation using select if your kernel does not +have a poll syscall). +.SH "SEE ALSO" +.BR select (2), +.BR select_tut (2) |