linux-kernel - Re: [Y2038] [PATCH v4 1/4] uinput: Use monotonic times for uinput timestamps.

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Date:   Thu, 14 Dec 2017 21:18:52 +0000
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Deepa Dinamani <deepa.kernel@...il.com>, dmitry.torokhov@...il.com,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     y2038@...ts.linaro.org, peter.hutterer@...-t.net, arnd@...db.de
Subject: Re: [Y2038] [PATCH v4 1/4] uinput: Use monotonic times for uinput
 timestamps.

On Thu, 2017-12-14 at 21:17 +0000, Ben Hutchings wrote:
> On Thu, 2017-12-07 at 10:13 -0800, Deepa Dinamani wrote:
> > struct timeval which is part of struct input_event to
> > maintain the event times is not y2038 safe.
> > 
> > Real time timestamps are also not ideal for input_event
> > as this time can go backwards as noted in the patch
> > a80b83b7b8 by John Stultz.
> > 
> > The patch switches the timestamps to use monotonic time
> > from realtime time. This is assuming no one is using
> > absolute times from these timestamps.
> 
> Why is this change not opt-in, as for evdev?  I assume there were
> compatibility reasons for not changing evdev's clock by default, so I
> would expect them to apply to uinput as well.  (But I'm also prepared
> to believe that user-space is now generally compatible with and would
> prefer monotonic time from all input devices.)

Never mind, I've gone back and seen Arnd's comments about compatibility
on v3.  It might be worth copying those into the commit message though.

Ben.

> Ben.
> 
> > The structure to maintain input events will be changed
> > in a different patch.
> > 
> > Signed-off-by: Deepa Dinamani <deepa.kernel@...il.com>
> > ---
> >  drivers/input/misc/uinput.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/input/misc/uinput.c
> > b/drivers/input/misc/uinput.c
> > index 39ddd9a73feb..d521aecbc078 100644
> > --- a/drivers/input/misc/uinput.c
> > +++ b/drivers/input/misc/uinput.c
> > @@ -84,11 +84,14 @@ static int uinput_dev_event(struct input_dev
> > *dev,
> > >  			    unsigned int type, unsigned int
> > > code, int value)
> > 
> >  {
> >  	struct uinput_device	*udev =
> > input_get_drvdata(dev);
> > +	struct timespec64	ts;
> >  
> >  	udev->buff[udev->head].type = type;
> >  	udev->buff[udev->head].code = code;
> >  	udev->buff[udev->head].value = value;
> > -	do_gettimeofday(&udev->buff[udev->head].time);
> > +	ktime_get_ts64(&ts);
> > +	udev->buff[udev->head].time.tv_sec = ts.tv_sec;
> > +	udev->buff[udev->head].time.tv_usec = ts.tv_nsec /
> > NSEC_PER_USEC;
> >  	udev->head = (udev->head + 1) % UINPUT_BUFFER_SIZE;
> >  
> >  	wake_up_interruptible(&udev->waitq);
-- 
Ben Hutchings
Software Developer, Codethink Ltd.