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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.

       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  behaviour  for  the  associated file
              descriptor.  The default behaviour for epoll is Level Triggered.
              See  epoll(4) for more detailed information about Edge and Level
              Triggered event distribution architectures.

       EPOLLONESHOT
              Sets the one-shot behaviour 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(2) 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(2)  returns  zero.  When  an error occurs,
       epoll_ctl(2) returns -1 and errno is set appropriately.

ERRORS

       EBADF  epfd 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(2) is a new API  introduced  in  Linux  kernel  2.5.44.   The
       interface should be finalized by Linux kernel 2.5.66.

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), epoll(4)