man2/epoll_ctl.2

   1 .\"  Copyright (C) 2003  Davide Libenzi
   2 .\"  Davide Libenzi <davidel@xmailserver.org>
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  19 .\"
  20 .TH EPOLL_CTL 2 2012-04-15 "Linux" "Linux Programmer's Manual"
  21 .SH NAME
  22 epoll_ctl \- control interface for an epoll descriptor
  23 .SH SYNOPSIS
  24 .B #include <sys/epoll.h>
  25 .sp
  26 .BI "int epoll_ctl(int " epfd ", int " op ", int " fd \
  27 ", struct epoll_event *" event );
  28 .SH DESCRIPTION
  29 This system call performs control operations on the
  30 .BR epoll (7)
  31 instance
  32 referred to by the file descriptor
  33 .IR epfd .
  34 It requests that the operation
  35 .I op
  36 be performed for the target file descriptor,
  37 .IR fd .
  38
  39 Valid values for the
  40 .I op
  41 argument are :
  42 .TP
  43 .B EPOLL_CTL_ADD
  44 Register the target file descriptor
  45 .I fd
  46 on the
  47 .B epoll
  48 instance referred to by the file descriptor
  49 .I epfd
  50 and associate the event
  51 .I event
  52 with the internal file linked to
  53 .IR fd .
  54 .TP
  55 .B EPOLL_CTL_MOD
  56 Change the event
  57 .I event
  58 associated with the target file descriptor
  59 .IR fd .
  60 .TP
  61 .B EPOLL_CTL_DEL
  62 Remove (deregister) the target file descriptor
  63 .I fd
  64 from the
  65 .B epoll
  66 instance referred to by
  67 .IR epfd .
  68 The
  69 .I event
  70 is ignored and can be NULL (but see BUGS below).
  71 .PP
  72 The
  73 .I event
  74 argument describes the object linked to the file descriptor
  75 .IR fd .
  76 The
  77 .I struct epoll_event
  78 is defined as :
  79 .sp
  80 .in +4n
  81 .nf
  82 typedef union epoll_data {
  83     void        *ptr;
  84     int          fd;
  85     uint32_t     u32;
  86     uint64_t     u64;
  87 } epoll_data_t;
  88
  89 struct epoll_event {
  90     uint32_t     events;      /* Epoll events */
  91     epoll_data_t data;        /* User data variable */
  92 };
  93 .fi
  94 .in
  95
  96 The
  97 .I events
  98 member is a bit set composed using the following available event
  99 types:
 100 .TP
 101 .B EPOLLIN
 102 The associated file is available for
 103 .BR read (2)
 104 operations.
 105 .TP
 106 .B EPOLLOUT
 107 The associated file is available for
 108 .BR write (2)
 109 operations.
 110 .TP
 111 .BR EPOLLRDHUP " (since Linux 2.6.17)"
 112 Stream socket peer closed connection,
 113 or shut down writing half of connection.
 114 (This flag is especially useful for writing simple code to detect
 115 peer shutdown when using Edge Triggered monitoring.)
 116 .TP
 117 .B EPOLLPRI
 118 There is urgent data available for
 119 .BR read (2)
 120 operations.
 121 .TP
 122 .B EPOLLERR
 123 Error condition happened on the associated file descriptor.
 124 .BR epoll_wait (2)
 125 will always wait for this event; it is not necessary to set it in
 126 .IR events .
 127 .TP
 128 .B EPOLLHUP
 129 Hang up happened on the associated file descriptor.
 130 .BR epoll_wait (2)
 131 will always wait for this event; it is not necessary to set it in
 132 .IR events .
 133 .TP
 134 .B EPOLLET
 135 Sets the Edge Triggered behavior for the associated file descriptor.
 136 The default behavior for
 137 .B epoll
 138 is Level Triggered.
 139 See
 140 .BR epoll (7)
 141 for more detailed information about Edge and Level Triggered event
 142 distribution architectures.
 143 .TP
 144 .BR EPOLLONESHOT " (since Linux 2.6.2)"
 145 Sets the one-shot behavior for the associated file descriptor.
 146 This means that after an event is pulled out with
 147 .BR epoll_wait (2)
 148 the associated file descriptor is internally disabled and no other events
 149 will be reported by the
 150 .B epoll
 151 interface.
 152 The user must call
 153 .BR epoll_ctl ()
 154 with
 155 .B EPOLL_CTL_MOD
 156 to rearm the file descriptor with a new event mask.
 157 .TP
 158 .BR EPOLLWAKEUP " (since Linux 3.5)"
 159 .\" commit 4d7e30d98939a0340022ccd49325a3d70f7e0238
 160 If
 161 .B EPOLLONESHOT
 162 and
 163 .B EPOLLET
 164 are clear and the process has the
 165 .B CAP_BLOCK_SUSPEND
 166 capability,
 167 ensure that the system does not enter "suspend" or
 168 "hibernate" while this event is pending or being processed.
 169 The event is considered as being "processed" from the time
 170 when it is returned by a call to
 171 .BR epoll_wait (2)
 172 until the next call to
 173 .BR epoll_wait (2)
 174 on the same
 175 .BR epoll (7)
 176 file descriptor.
 177 .SH RETURN VALUE
 178 When successful,
 179 .BR epoll_ctl ()
 180 returns zero.
 181 When an error occurs,
 182 .BR epoll_ctl ()
 183 returns \-1 and
 184 .I errno
 185 is set appropriately.
 186 .SH ERRORS
 187 .TP
 188 .B EBADF
 189 .I epfd
 190 or
 191 .I fd
 192 is not a valid file descriptor.
 193 .TP
 194 .B EEXIST
 195 .I op
 196 was
 197 .BR EPOLL_CTL_ADD ,
 198 and the supplied file descriptor
 199 .I fd
 200 is already registered with this epoll instance.
 201 .TP
 202 .B EINVAL
 203 .I epfd
 204 is not an
 205 .B epoll
 206 file descriptor,
 207 or
 208 .I fd
 209 is the same as
 210 .IR epfd ,
 211 or the requested operation
 212 .I op
 213 is not supported by this interface.
 214 .TP
 215 .B ENOENT
 216 .I op
 217 was
 218 .B EPOLL_CTL_MOD
 219 or
 220 .BR EPOLL_CTL_DEL ,
 221 and
 222 .I fd
 223 is not registered with this epoll instance.
 224 .TP
 225 .B ENOMEM
 226 There was insufficient memory to handle the requested
 227 .I op
 228 control operation.
 229 .TP
 230 .B ENOSPC
 231 The limit imposed by
 232 .I /proc/sys/fs/epoll/max_user_watches
 233 was encountered while trying to register
 234 .RB ( EPOLL_CTL_ADD )
 235 a new file descriptor on an epoll instance.
 236 See
 237 .BR epoll (7)
 238 for further details.
 239 .TP
 240 .B EPERM
 241 The target file
 242 .I fd
 243 does not support
 244 .BR epoll .
 245 .SH VERSIONS
 246 .BR epoll_ctl ()
 247 was added to the kernel in version 2.6.
 248 .\" To be precise: kernel 2.5.44.
 249 .\" The interface should be finalized by Linux kernel 2.5.66.
 250 .SH CONFORMING TO
 251 .BR epoll_ctl ()
 252 is Linux-specific.
 253 Library support is provided in glibc starting with version 2.3.2.
 254 .SH NOTES
 255 The
 256 .B epoll
 257 interface supports all file descriptors that support
 258 .BR poll (2).
 259 .SH BUGS
 260 In kernel versions before 2.6.9, the
 261 .B EPOLL_CTL_DEL
 262 operation required a non-null pointer in
 263 .IR event ,
 264 even though this argument is ignored.
 265 Since Linux 2.6.9,
 266 .I event
 267 can be specified as NULL
 268 when using
 269 .BR EPOLL_CTL_DEL .
 270 Applications that need to be portable to kernels before 2.6.9
 271 should specify a non-null pointer in
 272 .IR event .
 273 .SH SEE ALSO
 274 .BR epoll_create (2),
 275 .BR epoll_wait (2),
 276 .BR poll (2),
 277 .BR epoll (7)