Drivers: hv: Add state to manage batched reading

For the "read" side signaling optimization, the reader has to completely
drain the queue before exiting. Add state to manage this "batched"
reading.
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hv/channel_mgmt.c

@@ -275,6 +275,13 @@ static void vmbus_onoffer(struct vmbus_channel_message_header *hdr)
 		return;
 	}
 
+	/*
+	 * By default we setup state to enable batched
+	 * reading. A specific service can choose to
+	 * disable this prior to opening the channel.
+	 */
+	newchannel->batched_reading = true;
+
 	memcpy(&newchannel->offermsg, offer,
 	       sizeof(struct vmbus_channel_offer_channel));
 	newchannel->monitor_grp = (u8)offer->monitorid / 32;

include/linux/hyperv.h

@@ -882,8 +882,28 @@ struct vmbus_channel {
 
 	void (*onchannel_callback)(void *context);
 	void *channel_callback_context;
+
+	/*
+	 * A channel can be marked for efficient (batched)
+	 * reading:
+	 * If batched_reading is set to "true", we read until the
+	 * channel is empty and hold off interrupts from the host
+	 * during the entire read process.
+	 * If batched_reading is set to "false", the client is not
+	 * going to perform batched reading.
+	 *
+	 * By default we will enable batched reading; specific
+	 * drivers that don't want this behavior can turn it off.
+	 */
+
+	bool batched_reading;
 };
 
+static inline void set_channel_read_state(struct vmbus_channel *c, bool state)
+{
+	c->batched_reading = state;
+}
+
 void vmbus_onmessage(void *context);
 
 int vmbus_request_offers(void);