mirror of https://github.com/mkerrisk/man-pages
235 lines
4.9 KiB
Groff
235 lines
4.9 KiB
Groff
.\"
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.\" epoll by Davide Libenzi ( efficient event notification retrieval )
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.\" Copyright (C) 2003 Davide Libenzi
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.\"
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.\" This program is free software; you can redistribute it and/or modify
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.\" it under the terms of the GNU General Public License as published by
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.\" the Free Software Foundation; either version 2 of the License, or
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.\" (at your option) any later version.
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.\"
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.\" This program is distributed in the hope that it will be useful,
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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" GNU General Public License for more details.
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.\"
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.\" You should have received a copy of the GNU General Public License
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.\" along with this program; if not, write to the Free Software
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.\" Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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.\"
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.\" Davide Libenzi <davidel@xmailserver.org>
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.\"
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.TH EPOLL_CTL 2 "2002-10-23" Linux "Linux Programmer's Manual"
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.SH NAME
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epoll_ctl \- control interface for an epoll descriptor
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.SH SYNOPSIS
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.B #include <sys/epoll.h>
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.sp
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.BI "int epoll_ctl(int " epfd ", int " op ", int " fd ", struct epoll_event *" event )
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.SH DESCRIPTION
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Control an
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.B epoll
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descriptor,
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.IR epfd ,
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by requesting that the operation
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.IR op
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be performed on the target file descriptor,
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.IR fd .
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The
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.IR event
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describes the object linked to the file descriptor
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.IR fd .
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The
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.I struct epoll_event
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is defined as :
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.sp
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.in +0.5i
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.nf
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typedef union epoll_data {
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void *ptr;
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int fd;
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__uint32_t u32;
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__uint64_t u64;
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} epoll_data_t;
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struct epoll_event {
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__uint32_t events; /* Epoll events */
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epoll_data_t data; /* User data variable */
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};
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.fi
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.in -0.5i
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The
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.I events
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member is a bit set composed using the following available event
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types :
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.TP
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.B EPOLLIN
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The associated file is available for
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.BR read (2)
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operations.
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.TP
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.B EPOLLOUT
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The associated file is available for
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.BR write (2)
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operations.
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.TP
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.BR EPOLLRDHUP " (since kernel 2.6.17)"
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Stream socket peer closed connection,
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or shut down writing half of connection.
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(This flag is especially useful for writing simple code to detect
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peer shutdown when using Edge Triggered monitoring.)
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.TP
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.B EPOLLPRI
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There is urgent data available for
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.BR read (2)
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operations.
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.TP
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.B EPOLLERR
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Error condition happened on the associated file descriptor.
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.BR epoll_wait (2)
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will always wait for this event; it is not necessary to set it in
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.IR events .
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.TP
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.B EPOLLHUP
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Hang up happened on the associated file descriptor.
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.BR epoll_wait (2)
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will always wait for this event; it is not necessary to set it in
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.IR events .
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.TP
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.B EPOLLET
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Sets the Edge Triggered behaviour for the associated file descriptor.
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The default behaviour for
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.B epoll
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is Level Triggered.
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See
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.BR epoll (7)
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for more detailed information about Edge and Level Triggered event
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distribution architectures.
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.TP
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.BR EPOLLONESHOT " (since kernel 2.6.2)"
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Sets the one-shot behaviour for the associated file descriptor.
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This means that after an event is pulled out with
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.BR epoll_wait (2)
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the associated file descriptor is internally disabled and no other events
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will be reported by the
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.B epoll
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interface.
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The user must call
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.BR epoll_ctl (2)
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with
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.B EPOLL_CTL_MOD
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to re-enable the file descriptor with a new event mask.
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.PP
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The
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.B epoll
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interface supports all file descriptors that support
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.BR poll (2).
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Valid values for the
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.IR op
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parameter are :
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.RS
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.TP
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.B EPOLL_CTL_ADD
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Add the target file descriptor
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.I fd
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to the
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.B epoll
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descriptor
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.I epfd
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and associate the event
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.I event
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with the internal file linked to
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.IR fd .
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.TP
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.B EPOLL_CTL_MOD
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Change the event
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.I event
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associated with the target file descriptor
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.IR fd .
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.TP
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.B EPOLL_CTL_DEL
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Remove the target file descriptor
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.I fd
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from the
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.B epoll
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file descriptor,
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.IR epfd .
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The
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.IR event
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is ignored and can be NULL (but see BUGS below).
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.RE
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.SH "RETURN VALUE"
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When successful,
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.BR epoll_ctl (2)
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returns zero.
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When an error occurs,
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.BR epoll_ctl (2)
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returns \-1 and
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.I errno
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is set appropriately.
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.SH ERRORS
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.TP
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.B EBADF
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.I epfd
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or
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.I fd
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is not a valid file descriptor.
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.TP
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.B EEXIST
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.I op
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was EPOLL_CTL_ADD, and the supplied file descriptor
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.IR fd
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is already in
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.IR epfd .
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.TP
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.B EINVAL
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.IR epfd
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is not an
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.B epoll
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file descriptor,
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or
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.IR fd
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is the same as
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.IR epfd ,
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or the requested operation
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.I op
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is not supported by this interface.
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.TP
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.B ENOENT
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.I op
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was EPOLL_CTL_MOD or EPOLL_CTL_DEL, and
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.IR fd
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is not in
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.IR epfd .
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.TP
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.B ENOMEM
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There was insufficient memory to handle the requested
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.I op
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control operation.
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.TP
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.B EPERM
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The target file
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.I fd
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does not support
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.BR epoll .
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.SH CONFORMING TO
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.BR epoll_ctl (2)
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is Linux specific, and was introduced in kernel 2.5.44.
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.\" The interface should be finalized by Linux kernel 2.5.66.
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.SH BUGS
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In kernel versions before 2.6.9, the
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.B EPOLL_CTL_DEL
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operation required a non-NULL pointer in
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.IR event ,
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even though this argument is ignored.
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Since kernel 2.6.9,
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.I event
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can be specified as NULL
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when using
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.BR EPOLL_CTL_DEL .
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.SH "SEE ALSO"
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.BR epoll_create (2),
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.BR epoll_wait (2),
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.BR poll (2),
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.BR epoll (7)
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