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epoll_ctl.2: Various minor additions and clarifications
And add self to copyright, since, by now, I'm the author of substantial parts of the page. Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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Michael Kerrisk
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@ -1,5 +1,6 @@
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.\" Copyright (C) 2003 Davide Libenzi
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.\" Davide Libenzi <davidel@xmailserver.org>
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.\" and Copyright 2009, 2014, 2016, 2018, 2019 Michael Kerrisk <tk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(GPLv2+_SW_3_PARA)
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.\" This program is free software; you can redistribute it and/or modify
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@ -42,13 +43,16 @@ Valid values for the
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argument are:
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.TP
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.B EPOLL_CTL_ADD
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Add
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.I fd
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to the interest list
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and associate the settings specified in
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.I event
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with the internal file linked to
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.IR fd .
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Add an entry to the interest list of the epoll file descriptor,
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.IR epfd .
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The entry includes the file descriptor,
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.IR fd ,
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a reference to the corresponding open file description (see
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.BR epoll (7)
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and
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.BR open (2)),
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and the settings specified in
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.IR event .
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.TP
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.B EPOLL_CTL_MOD
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Change the settings associated with
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@ -89,8 +93,18 @@ struct epoll_event {
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.in
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.PP
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The
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.I data
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member of the
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.I epoll_event
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structure specifies data that the kernel should save and then return (via
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.BR epoll_wait (2))
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when this file descriptor becomes ready.
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.PP
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The
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.I events
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member is a bit mask composed by ORing together zero or more of
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member of the
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.I epoll_event
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structure is a bit mask composed by ORing together zero or more of
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the following available event types:
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.TP
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.B EPOLLIN
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@ -107,7 +121,7 @@ operations.
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Stream socket peer closed connection,
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or shut down writing half of connection.
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(This flag is especially useful for writing simple code to detect
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peer shutdown when using Edge Triggered monitoring.)
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peer shutdown when using edge-triggered monitoring.)
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.TP
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.B EPOLLPRI
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There is an exceptional condition on the file descriptor.
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@ -120,15 +134,21 @@ in
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Error condition happened on the associated file descriptor.
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This event is also reported for the write end of a pipe when the read end
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has been closed.
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.IP
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.BR epoll_wait (2)
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will always report for this event; it is not necessary to set it in
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.IR events .
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.IR events
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when calling
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.BR epoll_ctl ().
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.TP
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.B EPOLLHUP
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Hang up happened on the associated file descriptor.
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.IP
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.BR epoll_wait (2)
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will always wait for this event; it is not necessary to set it in
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.IR events .
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.IR events
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when calling
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.BR epoll_ctl ().
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.IP
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Note that when reading from a channel such as a pipe or a stream socket,
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this event merely indicates that the peer closed its end of the channel.
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@ -136,20 +156,27 @@ Subsequent reads from the channel will return 0 (end of file)
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only after all outstanding data in the channel has been consumed.
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.TP
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.B EPOLLET
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Sets the Edge Triggered behavior for the associated file descriptor.
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Requests edge-triggered notification for the associated file descriptor.
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The default behavior for
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.B epoll
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is Level Triggered.
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is level-triggered.
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See
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.BR epoll (7)
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for more detailed information about Edge and Level Triggered event
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distribution architectures.
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for more detailed information about edge-triggered and
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level-triggered notification.
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.IP
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This flag is an input flag for the
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.I event.events
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field when calling
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.BR epoll_ctl ();
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it is never returned by
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.BR epoll_wait (2).
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.TP
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.BR EPOLLONESHOT " (since Linux 2.6.2)"
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Sets the one-shot behavior for the associated file descriptor.
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This means that after an event is pulled out with
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.BR epoll_wait (2)
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the associated file descriptor is internally disabled and no other events
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Requests one-shot notification for the associated file descriptor.
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This means that after an event notified for the file descriptor by
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.BR epoll_wait (2),
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the file descriptor is disabled in the interest list and no other events
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will be reported by the
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.B epoll
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interface.
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@ -158,6 +185,13 @@ The user must call
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with
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.B EPOLL_CTL_MOD
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to rearm the file descriptor with a new event mask.
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.IP
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This flag is an input flag for the
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.I event.events
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field when calling
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.BR epoll_ctl ();
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it is never returned by
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.BR epoll_wait (2).
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.TP
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.BR EPOLLWAKEUP " (since Linux 3.5)"
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.\" commit 4d7e30d98939a0340022ccd49325a3d70f7e0238
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@ -186,6 +220,13 @@ or the clearing of
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for the event file descriptor with
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.BR EPOLL_CTL_MOD .
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See also BUGS.
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.IP
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This flag is an input flag for the
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.I event.events
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field when calling
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.BR epoll_ctl ();
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it is never returned by
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.BR epoll_wait (2).
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.TP
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.BR EPOLLEXCLUSIVE " (since Linux 4.5)"
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Sets an exclusive wakeup mode for the epoll file descriptor that is being
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@ -256,6 +297,15 @@ and specifies the target file descriptor
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as an epoll instance will likewise fail.
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The error in all of these cases is
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.BR EINVAL .
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.IP
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The
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.BR EPOLLEXCLUSIVE
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flag is an input flag for the
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.I event.events
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field when calling
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.BR epoll_ctl ();
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it is never returned by
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.BR epoll_wait (2).
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.SH RETURN VALUE
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When successful,
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.BR epoll_ctl ()
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