1 files changed, 31 insertions, 6 deletions

diff --git a/include/linux/poll.h b/include/linux/poll.h
index cf40010ce0cd..48fe8bc398d1 100644
--- a/include/linux/poll.h
+++ b/include/linux/poll.h
@@ -32,21 +32,46 @@ struct poll_table_struct;
  */
 typedef void (*poll_queue_proc)(struct file *, wait_queue_head_t *, struct poll_table_struct *);
 
+/*
+ * Do not touch the structure directly, use the access functions
+ * poll_does_not_wait() and poll_requested_events() instead.
+ */
 typedef struct poll_table_struct {
-	poll_queue_proc qproc;
-	unsigned long key;
+	poll_queue_proc _qproc;
+	unsigned long _key;
 } poll_table;
 
 static inline void poll_wait(struct file * filp, wait_queue_head_t * wait_address, poll_table *p)
 {
-	if (p && wait_address)
-		p->qproc(filp, wait_address, p);
+	if (p && p->_qproc && wait_address)
+		p->_qproc(filp, wait_address, p);
+}
+
+/*
+ * Return true if it is guaranteed that poll will not wait. This is the case
+ * if the poll() of another file descriptor in the set got an event, so there
+ * is no need for waiting.
+ */
+static inline bool poll_does_not_wait(const poll_table *p)
+{
+	return p == NULL || p->_qproc == NULL;
+}
+
+/*
+ * Return the set of events that the application wants to poll for.
+ * This is useful for drivers that need to know whether a DMA transfer has
+ * to be started implicitly on poll(). You typically only want to do that
+ * if the application is actually polling for POLLIN and/or POLLOUT.
+ */
+static inline unsigned long poll_requested_events(const poll_table *p)
+{
+	return p ? p->_key : ~0UL;
 }
 
 static inline void init_poll_funcptr(poll_table *pt, poll_queue_proc qproc)
 {
-	pt->qproc = qproc;
-	pt->key   = ~0UL; /* all events enabled */
+	pt->_qproc = qproc;
+	pt->_key   = ~0UL; /* all events enabled */
 }
 
 struct poll_table_entry {