epoll.7: Document EPOLLWAKEUP

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/man7/epoll.7 b/man7/epoll.7
index a372d9727..31b1a8c8c 100644
--- a/man7/epoll.7
+++ b/man7/epoll.7
@@ -173,6 +173,35 @@ it is the caller's responsibility to rearm the file descriptor using
 .BR epoll_ctl (2)
 with
 .BR EPOLL_CTL_MOD .
+.SS Interaction with autosleep
+If the system is in
+.B autosleep
+mode via
+.I /sys/power/autosleep
+and an event happens which wakes the device from sleep, the device
+driver will only keep the device awake until that event is queued.  To
+keep the device awake until the event has been processed it is
+necessary to use
+.B epoll
+and the
+.B EPOLLWAKEUP
+flag.
+
+When this flag is set in the
+.B events
+field for a
+.I struct epoll_event
+then system will be kept awake from the moment the event is queued,
+through the
+.IR epoll_wait (2)
+call which returns the event until the subsequent
+.IR epoll_wait (2)
+call.  If the event should keep the system awake beyond that time,
+the a separate
+.I wake_lock
+should be taken before the second
+.IR epoll_wait (2)
+call.
 .SS /proc interfaces
 The following interfaces can be used to limit the amount of
 kernel memory consumed by epoll: