Hello Mr. Torokhov,

Hope you are doing great!

Could you please help to update about below version of the patch?

--
Copying text about last two problems in v8:

Problem 1: Handle EVIOCG[type] for queue empty case
--> Done
Queue empty condition needs to be added before calling evdev_queue_syn_dropped.
Since there is a rare chance that new packet gets inserted between buffer_lock
mutex unlocking and copying events to user space, so I will check whether queue
is empty or not before __evdev_flush_queue and then use it before invoking
evdev_queue_syn_dropped.
And if queue is not empty then there is no problem as after flushing some
events we always have atleast one SYN_REPORT event left in queue.

Problem 2: We try to pass full packets to clients, but there is no guarantee.
--> Done

From my earlier patch discussion regarding dropping syn_report in between a

single packet it was deduced that since no driver is currently using that code
so there is no impact. Hence for this problem too, we are good to go.~
(Although from code reading/learning perspective, I would still suggest to not
have code of forceful sun_report event addition even if no driver using that
code :-) )

Have a good day!

Best Regards,
Aniroop Mathur

On Wed, Oct 5, 2016 at 12:42 AM, Aniroop Mathur [off-list ref] wrote:

quoted

If last event dropped in the old queue was EV_SYN/SYN_REPORT, then lets
generate EV_SYN/SYN_REPORT immediately after queing EV_SYN/SYN_DROPPED
so that clients would not ignore next valid full packet events.

Signed-off-by: Aniroop Mathur <redacted>

Difference from v8:
Added check for handling EVIOCG[type] ioctl for queue empty case
---
 drivers/input/evdev.c | 52 ++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 39 insertions(+), 13 deletions(-)

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index e9ae3d5..69407ff 100644
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c

@@ -156,7 +156,12 @@ 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 *last_ev;
        ktime_t time;
+       unsigned int mask = client->bufsize - 1;
+
+       /* capture last event stored in the buffer */
+       last_ev = &client->buffer[(client->head - 1) & mask];

        time = client->clk_type == EV_CLK_REAL ?
                        ktime_get_real() :

@@ -170,13 +175,28 @@ 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 was completely stored, then queue SYN_REPORT
+        * so that clients would not ignore next valid full packet
+        */
+       if (last_ev->type == EV_SYN && last_ev->code == SYN_REPORT) {
+               last_ev->time = ev.time;
+               client->buffer[client->head++] = *last_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;
+       }
 }

 static void evdev_queue_syn_dropped(struct evdev_client *client)

@@ -218,7 +238,7 @@ static int evdev_set_clk_type(struct evdev_client *client, unsigned int clkid)
                spin_lock_irqsave(&client->buffer_lock, flags);

                if (client->head != client->tail) {
-                       client->packet_head = client->head = client->tail;
+                       client->packet_head = client->tail = client->head;
                        __evdev_queue_syn_dropped(client);
                }

@@ -231,22 +251,24 @@ static int evdev_set_clk_type(struct evdev_client *client, unsigned int clkid)
 static void __pass_event(struct evdev_client *client,
                         const struct input_event *event)
 {
+       unsigned int mask = client->bufsize - 1;
+
        client->buffer[client->head++] = *event;
-       client->head &= client->bufsize - 1;
+       client->head &= mask;

        if (unlikely(client->head == client->tail)) {
                /*
                 * This effectively "drops" all unconsumed events, leaving
-                * EV_SYN/SYN_DROPPED plus the newest event in the queue.
+                * EV_SYN/SYN_DROPPED, EV_SYN/SYN_REPORT (if required) and
+                * 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->head = (client->head - 1) & mask;
+               client->packet_head = client->tail = client->head;
+               __evdev_queue_syn_dropped(client);

-               client->packet_head = client->tail;
+               client->buffer[client->head++] = *event;
+               client->head &= mask;
+               /* No need to check for buffer overflow as it just occurred */
        }

        if (event->type == EV_SYN && event->code == SYN_REPORT) {

@@ -920,6 +942,7 @@ static int evdev_handle_get_val(struct evdev_client *client,
        int ret;
        unsigned long *mem;
        size_t len;
+       bool is_queue_empty;

        len = BITS_TO_LONGS(maxbit) * sizeof(unsigned long);
        mem = kmalloc(len, GFP_KERNEL);

@@ -933,12 +956,15 @@ static int evdev_handle_get_val(struct evdev_client *client,

        spin_unlock(&dev->event_lock);

+       if (client->head == client->tail)
+               is_queue_empty = true;
+
        __evdev_flush_queue(client, type);

        spin_unlock_irq(&client->buffer_lock);

        ret = bits_to_user(mem, maxbit, maxlen, p, compat);
-       if (ret < 0)
+       if (ret < 0 && !is_queue_empty)
                evdev_queue_syn_dropped(client);

        kfree(mem);
--

2.6.2