From 9fb0f14e31b6101a0cc69a333b43541044f9b0a6 Mon Sep 17 00:00:00 2001 From: Jeff Brown Date: Tue, 12 Apr 2011 23:29:38 -0700 Subject: 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 [dtor@mail.ru: Implement Henrik's suggestion and drop old events in case of overflow.] Signed-off-by: Dmitry Torokhov --- drivers/input/evdev.c | 33 +++++++++++++++++++++------------ 1 file changed, 21 insertions(+), 12 deletions(-) (limited to 'drivers/input/evdev.c') diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c index 7f42d3a454d2..88d8e4cb419a 100644 --- a/drivers/input/evdev.c +++ b/drivers/input/evdev.c @@ -39,13 +39,13 @@ struct evdev { }; 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 DEFINE_MUTEX(evdev_table_mutex); 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) -- cgit v1.2.3