epoll_ctl(2)

1EPOLL_CTL(2)               Linux Programmer's Manual              EPOLL_CTL(2)
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NAME

6       epoll_ctl - control interface for an epoll descriptor
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SYNOPSIS

9       #include <sys/epoll.h>
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11       int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event)
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DESCRIPTION

14       Control  an epoll descriptor, epfd, by requesting that the operation op
15       be performed on the target file descriptor, fd.   The  event  describes
16       the object linked to the file descriptor fd.  The struct epoll_event is
17       defined as :
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19           typedef union epoll_data {
20               void *ptr;
21               int fd;
22               __uint32_t u32;
23               __uint64_t u64;
24           } epoll_data_t;
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26           struct epoll_event {
27               __uint32_t events;      /* Epoll events */
28               epoll_data_t data;      /* User data variable */
29           };
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31       The events member is a bit set composed using the  following  available
32       event types :
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34       EPOLLIN
35              The associated file is available for read(2) operations.
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37       EPOLLOUT
38              The associated file is available for write(2) operations.
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40       EPOLLRDHUP (since kernel 2.6.17)
41              Stream  socket peer closed connection, or shut down writing half
42              of connection.  (This flag is especially useful for writing sim‐
43              ple code to detect peer shutdown when using Edge Triggered moni‐
44              toring.)
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46       EPOLLPRI
47              There is urgent data available for read(2) operations.
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49       EPOLLERR
50              Error condition happened  on  the  associated  file  descriptor.
51              epoll_wait(2)  will always wait for this event; it is not neces‐
52              sary to set it in events.
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54       EPOLLHUP
55              Hang  up   happened   on   the   associated   file   descriptor.
56              epoll_wait(2)  will always wait for this event; it is not neces‐
57              sary to set it in events.
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59       EPOLLET
60              Sets the  Edge  Triggered  behaviour  for  the  associated  file
61              descriptor.  The default behaviour for epoll is Level Triggered.
62              See epoll(7) for more detailed information about Edge and  Level
63              Triggered event distribution architectures.
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65       EPOLLONESHOT (since kernel 2.6.2)
66              Sets  the one-shot behaviour for the associated file descriptor.
67              This means that after an event is pulled out with  epoll_wait(2)
68              the  associated  file  descriptor  is internally disabled and no
69              other events will be reported by the epoll interface.  The  user
70              must  call epoll_ctl(2) with EPOLL_CTL_MOD to re-enable the file
71              descriptor with a new event mask.
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73       The epoll interface supports all file descriptors that support poll(2).
74       Valid values for the op parameter are :
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76              EPOLL_CTL_ADD
77                     Add the target file descriptor fd to the epoll descriptor
78                     epfd and associate the event event with the internal file
79                     linked to fd.
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81              EPOLL_CTL_MOD
82                     Change  the  event  event associated with the target file
83                     descriptor fd.
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85              EPOLL_CTL_DEL
86                     Remove the target file descriptor fd from the epoll  file
87                     descriptor,  epfd.   The event is ignored and can be NULL
88                     (but see BUGS below).
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RETURN VALUE

91       When successful, epoll_ctl(2)  returns  zero.  When  an  error  occurs,
92       epoll_ctl(2) returns -1 and errno is set appropriately.
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ERRORS

95       EBADF  epfd or fd is not a valid file descriptor.
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97       EEXIST op  was  EPOLL_CTL_ADD,  and  the supplied file descriptor fd is
98              already in epfd.
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100       EINVAL epfd is not an epoll file descriptor, or fd is the same as epfd,
101              or  the  requested  operation op is not supported by this inter‐
102              face.
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104       ENOENT op was EPOLL_CTL_MOD or EPOLL_CTL_DEL, and fd is not in epfd.
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106       ENOMEM There was insufficient memory to handle the requested op control
107              operation.
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109       EPERM  The target file fd does not support epoll.
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CONFORMING TO

112       epoll_ctl(2) is Linux specific, and was introduced in kernel 2.5.44.
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BUGS

115       In kernel versions before 2.6.9, the EPOLL_CTL_DEL operation required a
116       non-NULL pointer in event, even though this argument is ignored.  Since
117       kernel 2.6.9, event can be specified as NULL when using EPOLL_CTL_DEL.
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