man-pages/man2/epoll_create.2

.\"
.\"  epoll by Davide Libenzi ( efficient event notification retrieval )
.\"  Copyright (C) 2003  Davide Libenzi
.\"
.\"  This program is free software; you can redistribute it and/or modify
.\"  it under the terms of the GNU General Public License as published by
.\"  the Free Software Foundation; either version 2 of the License, or
.\"  (at your option) any later version.
.\"
.\"  This program is distributed in the hope that it will be useful,
.\"  but WITHOUT ANY WARRANTY; without even the implied warranty of
.\"  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
.\"  GNU General Public License for more details.
.\"
.\"  You should have received a copy of the GNU General Public License
.\"  along with this program; if not, write to the Free Software
.\"  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
.\"
.\"  Davide Libenzi <davidel@xmailserver.org>
.\"
.\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com>
.\" Modified 2005-04-04 by Marko Kohtala <marko.kohtala@gmail.com>
.\" 2008-10-10, mtk: add description of epoll_create1()
.\"
.TH EPOLL_CREATE 2 2009-01-17 "Linux" "Linux Programmer's Manual"
.SH NAME
epoll_create, epoll_create1 \- open an epoll file descriptor
.SH SYNOPSIS
.nf
.B #include <sys/epoll.h>
.sp
.BI "int epoll_create(int " size );
.BI "int epoll_create1(int " flags );
.fi
.SH DESCRIPTION
.BR epoll_create ()
creates an epoll "instance",
requesting the kernel to allocate an event backing store dimensioned for
.I size
descriptors.
The
.I size
is not the maximum size of the backing store but
just a hint to the kernel about how to dimension internal structures.
(Nowadays,
.I size
is ignored; see NOTES below.)

.BR epoll_create ()
returns a file descriptor referring to the new epoll instance.
This file descriptor is used for all the subsequent calls to the
.B epoll
interface.
When no longer required, the file descriptor returned by
.BR epoll_create ()
should be closed by using
.BR close (2).
When all file descriptors referring to an epoll instance have been closed,
the kernel destroys the instance
and releases the associated resources for re-use.

If
.I flags
is 0, then, other than the fact that the obsolete
.I flags
argument is dropped,
.BR epoll_create1 ()
is the same as
.BR epoll_create ().
The following value can be included in
.IR flags
to obtain different behavior:
.TP
.B EPOLL_CLOEXEC
Set the close-on-exec
.RB ( FD_CLOEXEC )
flag on the new file descriptor.
See the description of the
.B O_CLOEXEC
flag in
.BR open (2)
for reasons why this may be useful.
.SH "RETURN VALUE"
On success,
these system calls
return a non-negative file descriptor.
On error, \-1 is returned, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EINVAL
.I size
is not positive.
.TP
.B EINVAL
.RB ( epoll_create1 ())
Invalid value specified in
.IR flags .
.TP
.B EMFILE
The per-user limit on the number of epoll instances imposed by
.I /proc/sys/fs/epoll/max_user_instances
was encountered.
See
.BR epoll (7)
for further details.
.TP
.B ENFILE
The system limit on the total number of open files has been reached.
.TP
.B ENOMEM
There was insufficient memory to create the kernel object.
.SH CONFORMING TO
.BR epoll_create ()
is Linux-specific, and was introduced in kernel 2.5.44.
.\" The interface should be finalized by Linux kernel 2.5.66.
.SH NOTES
Since Linux 2.6.8, the
.I size
argument is unused.
(The kernel dynamically sizes the required data structures
without needing this initial hint.)
.SH "SEE ALSO"
.BR close (2),
.BR epoll_ctl (2),
.BR epoll_wait (2),
.BR epoll (7)