man2/epoll_create.2

   1 .\"  Copyright (C) 2003  Davide Libenzi
   2 .\" and Copyright 2008, 2009, 2012 Michael Kerrisk <tk.manpages@gmail.com>
   3 .\"  Davide Libenzi <davidel@xmailserver.org>
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  21 .\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com>
  22 .\" Modified 2005-04-04 by Marko Kohtala <marko.kohtala@gmail.com>
  23 .\" 2008-10-10, mtk: add description of epoll_create1()
  24 .\"
  25 .TH EPOLL_CREATE 2 2020-04-11 "Linux" "Linux Programmer's Manual"
  26 .SH NAME
  27 epoll_create, epoll_create1 \- open an epoll file descriptor
  28 .SH SYNOPSIS
  29 .nf
  30 .B #include <sys/epoll.h>
  31 .PP
  32 .BI "int epoll_create(int " size );
  33 .BI "int epoll_create1(int " flags );
  34 .fi
  35 .SH DESCRIPTION
  36 .BR epoll_create ()
  37 creates a new
  38 .BR epoll (7)
  39 instance.
  40 Since Linux 2.6.8, the
  41 .I size
  42 argument is ignored, but must be greater than zero; see NOTES.
  43 .PP
  44 .BR epoll_create ()
  45 returns a file descriptor referring to the new epoll instance.
  46 This file descriptor is used for all the subsequent calls to the
  47 .B epoll
  48 interface.
  49 When no longer required, the file descriptor returned by
  50 .BR epoll_create ()
  51 should be closed by using
  52 .BR close (2).
  53 When all file descriptors referring to an epoll instance have been closed,
  54 the kernel destroys the instance
  55 and releases the associated resources for reuse.
  56 .SS epoll_create1()
  57 If
  58 .I flags
  59 is 0, then, other than the fact that the obsolete
  60 .I size
  61 argument is dropped,
  62 .BR epoll_create1 ()
  63 is the same as
  64 .BR epoll_create ().
  65 The following value can be included in
  66 .IR flags
  67 to obtain different behavior:
  68 .TP
  69 .B EPOLL_CLOEXEC
  70 Set the close-on-exec
  71 .RB ( FD_CLOEXEC )
  72 flag on the new file descriptor.
  73 See the description of the
  74 .B O_CLOEXEC
  75 flag in
  76 .BR open (2)
  77 for reasons why this may be useful.
  78 .SH RETURN VALUE
  79 On success,
  80 these system calls
  81 return a file descriptor (a nonnegative integer).
  82 On error, \-1 is returned, and
  83 .I errno
  84 is set to indicate the error.
  85 .SH ERRORS
  86 .TP
  87 .B EINVAL
  88 .I size
  89 is not positive.
  90 .TP
  91 .B EINVAL
  92 .RB ( epoll_create1 ())
  93 Invalid value specified in
  94 .IR flags .
  95 .TP
  96 .B EMFILE
  97 The per-user limit on the number of epoll instances imposed by
  98 .I /proc/sys/fs/epoll/max_user_instances
  99 was encountered.
 100 See
 101 .BR epoll (7)
 102 for further details.
 103 .TP
 104 .B EMFILE
 105 The per-process limit on the number of open file descriptors has been reached.
 106 .TP
 107 .B ENFILE
 108 The system-wide limit on the total number of open files has been reached.
 109 .TP
 110 .B ENOMEM
 111 There was insufficient memory to create the kernel object.
 112 .SH VERSIONS
 113 .BR epoll_create ()
 114 was added to the kernel in version 2.6.
 115 Library support is provided in glibc starting with version 2.3.2.
 116 .PP
 117 .\" To be precise: kernel 2.5.44.
 118 .\" The interface should be finalized by Linux kernel 2.5.66.
 119 .BR epoll_create1 ()
 120 was added to the kernel in version 2.6.27.
 121 Library support is provided in glibc starting with version 2.9.
 122 .SH CONFORMING TO
 123 .BR epoll_create ()
 124 is Linux-specific.
 125 .SH NOTES
 126 In the initial
 127 .BR epoll_create ()
 128 implementation, the
 129 .I size
 130 argument informed the kernel of the number of file descriptors
 131 that the caller expected to add to the
 132 .B epoll
 133 instance.
 134 The kernel used this information as a hint for the amount of
 135 space to initially allocate in internal data structures describing events.
 136 (If necessary, the kernel would allocate more space
 137 if the caller's usage exceeded the hint given in
 138 .IR size .)
 139 Nowadays,
 140 this hint is no longer required
 141 (the kernel dynamically sizes the required data structures
 142 without needing the hint), but
 143 .I size
 144 must still be greater than zero,
 145 in order to ensure backward compatibility when new
 146 .B epoll
 147 applications are run on older kernels.
 148 .SH SEE ALSO
 149 .BR close (2),
 150 .BR epoll_ctl (2),
 151 .BR epoll_wait (2),
 152 .BR epoll (7)