Input: evdev - indicate buffer overrun with SYN_DROPPED
Add a new EV_SYN code, SYN_DROPPED, to inform the client when input
events have been dropped from the evdev input buffer due to a
buffer overrun. The client should use this event as a hint to
reset its state or ignore all following events until the next
packet begins.
Signed-off-by: Jeff Brown <jeffbrown@android.com>
[dtor@mail.ru: Implement Henrik's suggestion and drop old events in
case of overflow.]
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
diff --git a/Documentation/input/event-codes.txt b/Documentation/input/event-codes.txt
index f13aee5..23fcb05 100644
--- a/Documentation/input/event-codes.txt
+++ b/Documentation/input/event-codes.txt
@@ -85,6 +85,12 @@
- Used to synchronize and separate touch events. See the
multi-touch-protocol.txt document for more information.
+* SYN_DROPPED:
+ - Used to indicate buffer overrun in the evdev client's event queue.
+ Client should ignore all events up to and including next SYN_REPORT
+ event and query the device (using EVIOCG* ioctls) to obtain its
+ current state.
+
EV_KEY:
----------
EV_KEY events take the form KEY_<name> or BTN_<name>. For example, KEY_A is used
diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index 7f42d3a..88d8e4c 100644
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c
@@ -39,13 +39,13 @@
};
struct evdev_client {
- int head;
- int tail;
+ unsigned int head;
+ unsigned int tail;
spinlock_t buffer_lock; /* protects access to buffer, head and tail */
struct fasync_struct *fasync;
struct evdev *evdev;
struct list_head node;
- int bufsize;
+ unsigned int bufsize;
struct input_event buffer[];
};
@@ -55,16 +55,25 @@
static void evdev_pass_event(struct evdev_client *client,
struct input_event *event)
{
- /*
- * Interrupts are disabled, just acquire the lock.
- * Make sure we don't leave with the client buffer
- * "empty" by having client->head == client->tail.
- */
+ /* Interrupts are disabled, just acquire the lock. */
spin_lock(&client->buffer_lock);
- do {
- client->buffer[client->head++] = *event;
- client->head &= client->bufsize - 1;
- } while (client->head == client->tail);
+
+ client->buffer[client->head++] = *event;
+ 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;
+ }
+
spin_unlock(&client->buffer_lock);
if (event->type == EV_SYN)
diff --git a/include/linux/input.h b/include/linux/input.h
index 0cc25e4..73a8c6e 100644
--- a/include/linux/input.h
+++ b/include/linux/input.h
@@ -167,6 +167,7 @@
#define SYN_REPORT 0
#define SYN_CONFIG 1
#define SYN_MT_REPORT 2
+#define SYN_DROPPED 3
/*
* Keys and buttons
