input: evdev: only allow reading events if a full packet is present

Without this, it was possible for the reader to get ahead of packet_head.
If the the input device generated a partial packet *right* after the
reader got ahead, then we can get into a situation where the device is
marked readable but read always returns 0 until the next packet is
finished (i.e a SYN is generated by the input driver).

This situation can also happen if we overflow the buffer while a reader
is trying to read an event out.

Change-Id: If01ab371bc7de1bf1f90c122dcc5a29242b01a09
Signed-off-by: Dima Zavin <dima@android.com>

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index 07b6c81..13a741a 100644 (file)
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c
@@ -381,7 +381,7 @@ static int evdev_fetch_next_event(struct evdev_client *client,
 
        spin_lock_irq(&client->buffer_lock);
 
-       have_event = client->head != client->tail;
+       have_event = client->packet_head != client->tail;
        if (have_event) {
                *event = client->buffer[client->tail++];
                client->tail &= client->bufsize - 1;