.\"
.\"  epoll by Davide Libenzi ( efficient event notification retrieval )
.\"  Copyright (C) 2003  Davide Libenzi
.\"
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.\"  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
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.\"  Davide Libenzi <davidel@xmailserver.org>
.\"
.\"
.TH EPOLL_CTL 2 "2002-10-23" Linux "Linux Programmer's Manual"
.SH NAME
epoll_ctl \- control interface for an epoll descriptor
.SH SYNOPSIS
.B #include <sys/epoll.h>
.sp
.BR "int epoll_ctl(int " epfd ", int " op ", int " fd ", struct epoll_event *" event )
.SH DESCRIPTION
Control an
.B epoll
descriptor,
.IR epfd ,
by requesting the operation
.IR op
be performed on the target file descriptor,
.IR fd .
The
.IR event
describes the object linked to the file descriptor
.IR fd .
The
.B struct epoll_event
is defined as :
.sp
.nf

	typedef union epoll_data {
		void *ptr;
		int fd;
		__uint32_t u32;
		__uint64_t u64;
	} epoll_data_t;

	struct epoll_event {
		__uint32_t events;	/* Epoll events */
		epoll_data_t data;	/* User data variable */
	};

.fi

The
.I events
member is a bit set composed using the following available event
types :
.TP
.B EPOLLIN
The associated file is available for
.BR read (2)
operations.
.TP
.B EPOLLOUT
The associated file is available for
.BR write (2)
operations.
.TP
.B EPOLLPRI
There is urgent data available for
.BR read (2)
operations.
.TP
.B EPOLLERR
Error condition happened on the associated file descriptor.
.TP
.B EPOLLHUP
Hang up happened on the associated file descriptor.
.TP
.B EPOLLET
Sets the Edge Triggered behaviour for the associated file descriptor.
The default behaviour for
.B epoll
is Level Triggered. See
.BR epoll (4)
for more detailed informations about Edge and Level Triggered event
distribution architectures.
.TP
.B EPOLLONESHOT
Sets the One-Shot behaviour for the associated file descriptor. It means
that after an event is pulled out with
.BR epoll_wait (2)
the associated file descriptor is internally disabled and no other events
will be reported by the
.B epoll
interface. The user must call
.BR epoll_ctl (2)
with
.B EPOLL_CTL_MOD
to re-enable the file descriptor with a new event mask.
.PP
.sp
The
.B epoll
interface supports all file descriptors that support
.BR poll (2).
Valid values for the
.IR op
parameter are :
.RS
.TP
.B EPOLL_CTL_ADD
Add the target file descriptor
.I fd
to the
.B epoll
descriptor
.I epfd
and associate the event
.I event
with the internal file linked to
.IR fd .
.TP
.B EPOLL_CTL_MOD
Change the event
.I event
associated to the target file descriptor
.IR fd .
.TP
.B EPOLL_CTL_DEL
Remove the target file descriptor
.I fd
from the
.B epoll
file descriptor,
.IR epfd .
.RE
.SH "RETURN VALUE"
When successful, 
.BR epoll_ctl (2)
returns zero. When an error occurs, 
.BR epoll_ctl (2)
returns \-1 and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EBADF
The
.I epfd
file descriptor is not a valid file descriptor.
.TP
.B EINVAL
The supplied file descriptor,
.IR epfd ,
is not an
.B epoll
file descriptor, or the requested operation
.I op
is not supported by this interface.
.TP
.B ENOMEM
There was insufficient memory to handle the requested
.I op
control operation.
.TP
.B EPERM
The target file
.I fd
is not supported by
.BR epoll .
.SH CONFORMING TO
.BR epoll_ctl (2)
is a new API introduced in Linux kernel 2.5.44.
The interface should be finalized by Linux kernel 2.5.66.
.SH "SEE ALSO"
.BR epoll_create (2),
.BR epoll_wait (2),
.BR epoll (4)