EPOLL_CTL
Section: Linux Programmer's Manual (2)
Updated: 2010-08-29
NAME
epoll_ctl - control interface for an epoll descriptor
SYNOPSIS
#include <sys/epoll.h>
int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);
DESCRIPTION
This system call performs control operations on the epoll instance
referred to by the file descriptor
epfd.
It requests that the operation
op
be performed for the target file descriptor,
fd.
Valid values for the
op
argument are :
- EPOLL_CTL_ADD
-
Register the target file descriptor
fd
on the
epoll
instance referred to by the file descriptor
epfd
and associate the event
event
with the internal file linked to
fd.
- EPOLL_CTL_MOD
-
Change the event
event
associated with the target file descriptor
fd.
- EPOLL_CTL_DEL
-
Remove (deregister) the target file descriptor
fd
from the
epoll
instance referred to by
epfd.
The
event
is ignored and can be NULL (but see BUGS below).
The
event
argument describes the object linked to the file descriptor
fd.
The
struct epoll_event
is defined as :
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 */
};
The
events
member is a bit set composed using the following available event
types:
- EPOLLIN
-
The associated file is available for
read(2)
operations.
- EPOLLOUT
-
The associated file is available for
write(2)
operations.
- EPOLLRDHUP (since Linux 2.6.17)
-
Stream socket peer closed connection,
or shut down writing half of connection.
(This flag is especially useful for writing simple code to detect
peer shutdown when using Edge Triggered monitoring.)
- EPOLLPRI
-
There is urgent data available for
read(2)
operations.
- EPOLLERR
-
Error condition happened on the associated file descriptor.
epoll_wait(2)
will always wait for this event; it is not necessary to set it in
events.
- EPOLLHUP
-
Hang up happened on the associated file descriptor.
epoll_wait(2)
will always wait for this event; it is not necessary to set it in
events.
- EPOLLET
-
Sets the Edge Triggered behavior for the associated file descriptor.
The default behavior for
epoll
is Level Triggered.
See
epoll(7)
for more detailed information about Edge and Level Triggered event
distribution architectures.
- EPOLLONESHOT (since Linux 2.6.2)
-
Sets the one-shot behavior for the associated file descriptor.
This means that after an event is pulled out with
epoll_wait(2)
the associated file descriptor is internally disabled and no other events
will be reported by the
epoll
interface.
The user must call
epoll_ctl()
with
EPOLL_CTL_MOD
to rearm the file descriptor with a new event mask.
RETURN VALUE
When successful,
epoll_ctl()
returns zero.
When an error occurs,
epoll_ctl()
returns -1 and
errno
is set appropriately.
ERRORS
- EBADF
-
epfd
or
fd
is not a valid file descriptor.
- EEXIST
-
op
was
EPOLL_CTL_ADD,
and the supplied file descriptor
fd
is already registered with this epoll instance.
- EINVAL
-
epfd
is not an
epoll
file descriptor,
or
fd
is the same as
epfd,
or the requested operation
op
is not supported by this interface.
- ENOENT
-
op
was
EPOLL_CTL_MOD
or
EPOLL_CTL_DEL,
and
fd
is not registered with this epoll instance.
- ENOMEM
-
There was insufficient memory to handle the requested
op
control operation.
- ENOSPC
-
The limit imposed by
/proc/sys/fs/epoll/max_user_watches
was encountered while trying to register
(EPOLL_CTL_ADD)
a new file descriptor on an epoll instance.
See
epoll(7)
for further details.
- EPERM
-
The target file
fd
does not support
epoll.
CONFORMING TO
epoll_ctl()
is Linux-specific, and was introduced in kernel 2.5.44.
NOTES
The
epoll
interface supports all file descriptors that support
poll(2).
BUGS
In kernel versions before 2.6.9, the
EPOLL_CTL_DEL
operation required a non-NULL pointer in
event,
even though this argument is ignored.
Since Linux 2.6.9,
event
can be specified as NULL
when using
EPOLL_CTL_DEL.
Applications that need to be portable to kernels before 2.6.9
should specify a non-NULL pointer in
event.
SEE ALSO
epoll_create(2),
epoll_wait(2),
poll(2),
epoll(7)
COLOPHON
This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- BUGS
-
- SEE ALSO
-
- COLOPHON
-
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Time: 07:34:54 GMT, March 26, 2013