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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

       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 kernel 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 kernel 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 parameter 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
       kernel  2.6.9, event can be specified as NULL when using EPOLL_CTL_DEL.

SEE ALSO

       epoll_create(2), epoll_wait(2), poll(2), epoll(7)

COLOPHON

       This page is part of release 2.77 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/.