1epoll_ctl(2)                  System Calls Manual                 epoll_ctl(2)
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NAME

6       epoll_ctl - control interface for an epoll file descriptor
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LIBRARY

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <sys/epoll.h>
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14       int epoll_ctl(int epfd, int op, int fd,
15                     struct epoll_event *_Nullable event);
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DESCRIPTION

18       This  system  call is used to add, modify, or remove entries in the in‐
19       terest list of the epoll(7) instance referred to by the file descriptor
20       epfd.   It  requests  that the operation op be performed for the target
21       file descriptor, fd.
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23       Valid values for the op argument are:
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25       EPOLL_CTL_ADD
26              Add an entry to the interest list of the epoll file  descriptor,
27              epfd.   The  entry includes the file descriptor, fd, a reference
28              to the corresponding open file  description  (see  epoll(7)  and
29              open(2)), and the settings specified in event.
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31       EPOLL_CTL_MOD
32              Change  the  settings associated with fd in the interest list to
33              the new settings specified in event.
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35       EPOLL_CTL_DEL
36              Remove (deregister) the target file descriptor fd from  the  in‐
37              terest list.  The event argument is ignored and can be NULL (but
38              see BUGS below).
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40       The event argument describes the object linked to the  file  descriptor
41       fd.  The struct epoll_event is described in epoll_event(3type).
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43       The  data  member  of the epoll_event structure specifies data that the
44       kernel should save and then return (via epoll_wait(2)) when  this  file
45       descriptor becomes ready.
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47       The  events  member of the epoll_event structure is a bit mask composed
48       by ORing together zero or more event types, returned by  epoll_wait(2),
49       and  input flags, which affect its behaviour, but aren't returned.  The
50       available event types are:
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52       EPOLLIN
53              The associated file is available for read(2) operations.
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55       EPOLLOUT
56              The associated file is available for write(2) operations.
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58       EPOLLRDHUP (since Linux 2.6.17)
59              Stream socket peer closed connection, or shut down writing  half
60              of connection.  (This flag is especially useful for writing sim‐
61              ple code to detect peer shutdown when using edge-triggered moni‐
62              toring.)
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64       EPOLLPRI
65              There  is  an exceptional condition on the file descriptor.  See
66              the discussion of POLLPRI in poll(2).
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68       EPOLLERR
69              Error condition happened  on  the  associated  file  descriptor.
70              This event is also reported for the write end of a pipe when the
71              read end has been closed.
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73              epoll_wait(2) will always report for this event; it is not  nec‐
74              essary to set it in events when calling epoll_ctl().
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76       EPOLLHUP