[PATCH] [v4]Input: evdev - drop partial events after emptying the buffer

[Aniroop Mathur]

This patch introduces concept to drop partial events in evdev handler
itself after emptying the buffer which are dropped by all evdev
clients in userspace after SYN_DROPPED occurs and this in turn reduces
evdev client reading requests plus saves memory space filled by partial
events in evdev handler buffer.
Also, this patch prevents dropping of full packet by evdev client after
SYN_DROPPED occurs in case last stored event was SYN_REPORT.
(like after clock change request)

--
Please ignore v3.

Signed-off-by: Aniroop Mathur <a.mathur@xxxxxxxxxxx>
---
 drivers/input/evdev.c | 53 ++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 40 insertions(+), 13 deletions(-)

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index e9ae3d5..15b6eb2 100644
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c
@@ -58,6 +58,7 @@ struct evdev_client {
 	struct list_head node;
 	unsigned int clk_type;
 	bool revoked;
+	bool drop_pevent; /* specifies if partial events need to be dropped */
 	unsigned long *evmasks[EV_CNT];
 	unsigned int bufsize;
 	struct input_event buffer[];
@@ -156,7 +157,12 @@ static void __evdev_flush_queue(struct evdev_client *client, unsigned int type)
 static void __evdev_queue_syn_dropped(struct evdev_client *client)
 {
 	struct input_event ev;
+	struct input_event *prev_ev;
 	ktime_t time;
+	unsigned int mask = client->bufsize - 1;
+
+	/* Store previous event */
+	prev_ev = &client->buffer[(client->head - 1) & mask];
 
 	time = client->clk_type == EV_CLK_REAL ?
 			ktime_get_real() :
@@ -170,13 +176,33 @@ static void __evdev_queue_syn_dropped(struct evdev_client *client)
 	ev.value = 0;
 
 	client->buffer[client->head++] = ev;
-	client->head &= client->bufsize - 1;
+	client->head &= mask;
 
 	if (unlikely(client->head == client->tail)) {
 		/* drop queue but keep our SYN_DROPPED event */
-		client->tail = (client->head - 1) & (client->bufsize - 1);
+		client->tail = (client->head - 1) & mask;
 		client->packet_head = client->tail;
 	}
+
+	/*
+	 * If last packet is NOT fully stored, set drop_pevent to true to
+	 * ignore partial events and if last packet is fully stored, queue
+	 * SYN_REPORT so that clients would not ignore next full packet.
+	 */
+	if (prev_ev->type != EV_SYN && prev_ev->code != SYN_REPORT) {
+		client->drop_pevent = true;
+	} else if (prev_ev->type == EV_SYN && prev_ev->code == SYN_REPORT) {
+		prev_ev->time = ev.time;
+		client->buffer[client->head++] = *prev_ev;
+		client->head &= mask;
+		client->packet_head = client->head;
+
+		/* drop queue but keep our SYN_DROPPED & SYN_REPORT event */
+		if (unlikely(client->head == client->tail)) {
+			client->tail = (client->head - 2) & mask;
+			client->packet_head = client->tail;
+		}
+	}
 }
 
 static void evdev_queue_syn_dropped(struct evdev_client *client)
@@ -235,18 +261,8 @@ static void __pass_event(struct evdev_client *client,
 	client->head &= client->bufsize - 1;
 
 	if (unlikely(client->head == client->tail)) {
-		/*
-		 * This effectively "drops" all unconsumed events, leaving
-		 * EV_SYN/SYN_DROPPED plus the newest event in the queue.
-		 */
-		client->tail = (client->head - 2) & (client->bufsize - 1);
-
-		client->buffer[client->tail].time = event->time;
-		client->buffer[client->tail].type = EV_SYN;
-		client->buffer[client->tail].code = SYN_DROPPED;
-		client->buffer[client->tail].value = 0;
-
 		client->packet_head = client->tail;
+		__evdev_queue_syn_dropped(client);
 	}
 
 	if (event->type == EV_SYN && event->code == SYN_REPORT) {
@@ -284,6 +300,17 @@ static void evdev_pass_values(struct evdev_client *client,
 			wakeup = true;
 		}
 
+		/*
+		 * drop partial events of last packet but queue SYN_REPORT
+		 * so that clients would not ignore extra full packet.
+		 */
+		if (client->drop_pevent) {
+			if (v->type == EV_SYN && v->code == SYN_REPORT)
+				client->drop_pevent = false;
+			else
+				continue;
+		}
+
 		event.type = v->type;
 		event.code = v->code;
 		event.value = v->value;
-- 
2.6.2

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