If a wait_queue_entry is passed in to epoll_wait(), then utilize this
new helper for reaping events and/or adding to the epoll waitqueue
rather than calling the potentially sleeping ep_poll(). It works like
ep_poll(), except it doesn't block - it either returns the events that
are already available, or it adds the specified entry to the struct
eventpoll waitqueue to get a callback when events are triggered. It
returns -EIOCBQUEUED for that case.
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
fs/eventpoll.c | 37 ++++++++++++++++++++++++++++++++++++-
1 file changed, 36 insertions(+), 1 deletion(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index ecaa5591f4be..a8be0c7110e4 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -2032,6 +2032,39 @@ static int ep_try_send_events(struct eventpoll *ep,
return res;
}
+static int ep_poll_queue(struct eventpoll *ep,
+ struct epoll_event __user *events, int maxevents,
+ struct wait_queue_entry *wait)
+{
+ int res, eavail;
+
+ /* See ep_poll() for commentary */
+ eavail = ep_events_available(ep);
+ while (1) {
+ if (eavail) {
+ res = ep_try_send_events(ep, events, maxevents);
+ if (res)
+ return res;
+ }
+
+ eavail = ep_busy_loop(ep, true);
+ if (eavail)
+ continue;
+
+ if (!list_empty_careful(&wait->entry))
+ return -EIOCBQUEUED;
+
+ write_lock_irq(&ep->lock);
+ eavail = ep_events_available(ep);
+ if (!eavail)
+ __add_wait_queue_exclusive(&ep->wq, wait);
+ write_unlock_irq(&ep->lock);
+
+ if (!eavail)
+ return -EIOCBQUEUED;
+ }
+}
+
/**
* ep_poll - Retrieves ready events, and delivers them to the caller-supplied
* event buffer.
@@ -2497,7 +2530,9 @@ int epoll_wait(struct file *file, struct epoll_event __user *events,
ep = file->private_data;
/* Time to fish for events ... */
- return ep_poll(ep, events, maxevents, to);
+ if (!wait)
+ return ep_poll(ep, events, maxevents, to);
+ return ep_poll_queue(ep, events, maxevents, wait);
}
/*
--
2.47.2
