On Tue, Mar 22, 2011 at 06:04:03PM -0700, Jeff Brown wrote:
> From: Jeff Brown <jeffbrown@xxxxxxxxxx>
>
> 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.
>
I like it.
> Signed-off-by: jeffbrown@xxxxxxxxxxx
> ---
> drivers/input/evdev.c | 18 ++++++++++++------
> include/linux/input.h | 1 +
> 2 files changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
> index 7f42d3a..203ed70 100644
> --- a/drivers/input/evdev.c
> +++ b/drivers/input/evdev.c
> @@ -57,14 +57,20 @@ static void evdev_pass_event(struct evdev_client *client,
> {
> /*
> * Interrupts are disabled, just acquire the lock.
> - * Make sure we don't leave with the client buffer
> - * "empty" by having client->head == client->tail.
> + * When the client buffer is full, replace the tail with SYN_DROPPED
> + * to let the client know that events were dropped. Ensure that the
> + * head and tail never coincide so the buffer does not appear "empty".
> */
> 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 (client->head == client->tail) {
Do you think this should be unlikely()?
> + client->tail = (client->tail + 1) & (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 056ae8a..65d253e 100644
> --- a/include/linux/input.h
> +++ b/include/linux/input.h
> @@ -167,6 +167,7 @@ struct input_keymap_entry {
> #define SYN_REPORT 0
> #define SYN_CONFIG 1
> #define SYN_MT_REPORT 2
> +#define SYN_DROPPED 3
>
> /*
> * Keys and buttons
Thanks.
--
Dmitry
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