epoll_ctl


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  opera-
       tion 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 descrip-
              tor 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 sim-
              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  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  inter-
              face.

       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.

VERSIONS
       epoll_ctl() was added to the kernel in version 2.6.

CONFORMING TO
       epoll_ctl() is Linux-specific.  Library support is  provided  in  glibc
       starting with version 2.3.2.

NOTES
       The epoll interface supports all file descriptors that support poll(2).
       This  page  is  part of release 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://man7.org/linux/man-pages/.



Linux                             2010-12-03                      EPOLL_CTL(2)
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