[PATCH 3/7] poll: POLL_ENQUEUE_EXCLUSIVE

[Peter Xu]

Add a flag for poll_wait() showing that the caller wants the enqueue to be
exclusive.  It is similar to EPOLLEXCLUSIVE for epoll() but grants kernel
poll users to opt-in with more efficient exclusive queuing where applicable.

Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
 fs/select.c          |  5 ++++-
 include/linux/poll.h | 20 ++++++++++++++++++--
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/fs/select.c b/fs/select.c
index 0433448481e9..a3c9088e8d76 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -231,7 +231,10 @@ static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
 	entry->key = p->_key;
 	init_waitqueue_func_entry(&entry->wait, pollwake);
 	entry->wait.private = pwq;
-	add_wait_queue(wait_address, &entry->wait);
+	if (flags & POLL_ENQUEUE_EXCLUSIVE)
+		add_wait_queue_exclusive(wait_address, &entry->wait);
+	else
+		add_wait_queue(wait_address, &entry->wait);
 }
 
 static int poll_schedule_timeout(struct poll_wqueues *pwq, int state,
diff --git a/include/linux/poll.h b/include/linux/poll.h
index cbad520fc65c..11af98ae579c 100644
--- a/include/linux/poll.h
+++ b/include/linux/poll.h
@@ -29,6 +29,8 @@
 
 typedef unsigned int poll_flags;
 
+#define POLL_ENQUEUE_EXCLUSIVE  BIT(0)
+
 struct poll_table_struct;
 
 /* 
@@ -46,10 +48,24 @@ typedef struct poll_table_struct {
 	__poll_t _key;
 } poll_table;
 
-static inline void poll_wait(struct file * filp, wait_queue_head_t * wait_address, poll_table *p)
+static inline void __poll_wait(struct file *filp, wait_queue_head_t *wait_address,
+			       poll_table *p, poll_flags flags)
 {
 	if (p && p->_qproc && wait_address)
-		p->_qproc(filp, wait_address, p, 0);
+		p->_qproc(filp, wait_address, p, flags);
+}
+
+static inline void poll_wait(struct file *filp, wait_queue_head_t *wait_address,
+			     poll_table *p)
+{
+	__poll_wait(filp, wait_address, p, 0);
+}
+
+static inline void poll_wait_exclusive(struct file *filp,
+				       wait_queue_head_t *wait_address,
+				       poll_table *p)
+{
+	__poll_wait(filp, wait_address, p, POLL_ENQUEUE_EXCLUSIVE);
 }
 
 /*
-- 
2.41.0