Revert "Revert "Add API for channel frame deferral.""

This reverts commit 6b5a7ced13.

Change-Id: I61d1dbb2e69e1977f684b7dfc8e98211024e1cd1

include/asterisk/channel.h

@@ -966,6 +966,11 @@ enum {
 	 * The channel is executing a subroutine or macro
 	 */
 	AST_FLAG_SUBROUTINE_EXEC = (1 << 27),
+	/*!
+	 * The channel is currently in an operation where
+	 * frames should be deferred.
+	 */
+	AST_FLAG_DEFER_FRAMES = (1 << 28),
 };
 
 /*! \brief ast_bridge_config flags */
@@ -4681,4 +4686,37 @@ enum ast_channel_error {
  */
 enum ast_channel_error ast_channel_errno(void);
 
+/*!
+ * \brief Retrieve the deferred read queue.
+ */
+struct ast_readq_list *ast_channel_deferred_readq(struct ast_channel *chan);
+
+/*!
+ * \brief Start deferring deferrable frames on this channel
+ *
+ * Sometimes, a channel gets entered into a mode where a "main" application
+ * is tasked with servicing frames on the channel, but that application does
+ * not need to act on those frames. However, it would be imprudent to simply
+ * drop important frames. This function can be called so that important frames
+ * will be deferred, rather than placed in the channel frame queue as normal.
+ *
+ * \pre chan MUST be locked before calling
+ *
+ * \param chan The channel on which frames should be deferred
+ */
+void ast_channel_start_defer_frames(struct ast_channel *chan);
+
+/*!
+ * \brief Stop deferring deferrable frames on this channel
+ *
+ * When it is time to stop deferring frames on the channel, all deferred frames
+ * will be queued onto the channel's read queue so that the next servicer of
+ * the channel can handle those frames as necessary.
+ *
+ * \pre chan MUST be locked before calling
+ *
+ * \param chan The channel on which to stop deferring frames.
+ */
+void ast_channel_stop_defer_frames(struct ast_channel *chan);
+
 #endif /* _ASTERISK_CHANNEL_H */