EPOLL_CTL(2) Linux Programmers Manual EPOLL_CTL(2)
NAME
epoll_ctl - control interface for an epoll descriptor
SYNOPSIS
#include
int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);
DESCRIPTION
Control an epoll descriptor, epfd, by requesting that the operation op
be performed on the target file descriptor, fd. The event 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 sim
ple code to detect peer shutdown when using Edge Triggered moni
toring.)
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 neces
sary 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 neces
sary 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 re-enable the file
descriptor with a new event mask.
The epoll interface supports all file descriptors that support poll(2).
Valid values for the op argument are :
EPOLL_CTL_ADD
Add the target file descriptor fd to the epoll 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 the target file descriptor fd from the epoll file
descriptor, epfd. The event is ignored and can be NULL
(but see BUGS below).
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 in epfd.
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 inter
face.
ENOENT op was EPOLL_CTL_MOD or EPOLL_CTL_DEL, and fd is not in epfd.
ENOMEM There was insufficient memory to handle the requested op control
operation.
EPERM The target file fd does not support epoll.
CONFORMING TO
epoll_ctl() is Linux-specific, and was introduced in kernel 2.5.44.
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 3.05 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/.
Linux 2008-04-25 EPOLL_CTL(2)
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