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EPOLL_CTL(2)		   Linux Programmer's Manual		  EPOLL_CTL(2)

       epoll_ctl - control interface for an epoll descriptor

       #include <sys/epoll.h>

       int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);

       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 :

	      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.

	      Change  the event event associated with the target file descrip‐
	      tor fd.

	      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:

	      The associated file is available for read(2) operations.

	      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‐
	      ple code to detect peer shutdown when using Edge Triggered moni‐

	      There is urgent data available for read(2) operations.

	      Error  condition	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.

	      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.

	      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.

       When  successful,  epoll_ctl()  returns	zero.	When  an error occurs,
       epoll_ctl() returns -1 and errno is set appropriately.

       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‐

       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

       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

       EPERM  The target file fd does not support epoll.

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

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

       The epoll interface supports all file descriptors that support poll(2).

       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.

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

       This  page  is  part of release 3.65 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/.

Linux				  2012-04-15			  EPOLL_CTL(2)

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