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 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 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 interface.
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.
This page is part of release 3.14 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/.
