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    Command:

    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(7) 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
                  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

    
    

    Linux 2012-04-15 EPOLL_CTL(2)

    
    
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