linux-kernel - Re: [PATCH] Input: evdev: avoid storing newest SYN

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Date:	Mon, 28 Dec 2015 15:41:25 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Aniroop Mathur <a.mathur@...sung.com>
Cc:	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Aniroop Mathur <aniroop.mathur@...il.com>
Subject: Re: [PATCH] Input: evdev: avoid storing newest SYN_REPORT when
 dropping all events

Hi Aniroop,

On Thu, Dec 24, 2015 at 11:25 AM, Aniroop Mathur <a.mathur@...sung.com> wrote:
> The newest event can be SYN_REPORT in case of dropping all old events when
> buffer is full, but as now there is no device data available to read so
> lets drop SYN_REPORT as well and store only SYN_DROPPED.
>

We can not drop the SYN_REPORT event in this case as userspace needs
it to determine if the events that are coming after SYN_DROPPED are
part of a full packet or if they belong to a partial packet. From
Documentation/input/event-codes.txt:

* 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.

Thanks.

-- 
Dmitry
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