linux-kernel - Re: [PATCH v2] firewire: Replace timeval with timespec64

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Date:	Thu, 22 Oct 2015 15:17:20 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Stefan Richter <stefanr@...6.in-berlin.de>
Cc:	outreachy-kernel@...glegroups.com,
	Amitoj Kaur Chawla <amitoj1606@...il.com>,
	linux1394-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, y2038@...ts.linaro.org
Subject: Re: [PATCH v2] firewire: Replace timeval with timespec64

On Thursday 22 October 2015 15:07:50 Stefan Richter wrote:
> Looks fine to me, but I have a question.  It was possibly already
> discussed at patch v1, though that was apparently not posted to an open
> list.
> 
> include/linux/timekeeping.h says:
> #define ktime_get_real_ts64(ts) getnstimeofday64(ts)
> 
> kernel/time/timekeeping.c says:
> /**
>   * do_gettimeofday - Returns the time of day in a timeval
>   * @tv:         pointer to the timeval to be set
>   *
>   * NOTE: Users should be converted to using getnstimeofday()
>   */
> 
> So what is the reason for calling ktime_get_real_ts64() instead of
> getnstimeofday[64]()?

They are identical in behavior, I don't know exactly why we have two
but I'm advocating the move to ktime_* functions for consistency
with ktime_get_seconds(), ktime_get_ns() and ktime_get() that don't
have another alias. Once all users of the old getnstimeofday()
and do_gettimeofday() have been converted, I might change over all
users of getnstimeofday64() to ktime_get_real_ts64() and remove
all of the get*timeofday*() family.

> PS, note to self:
> Independently of this patch, I need to check whether CLOCK_REALTIME was
> really the right clock here, in contrast to CLOCK_MONOTONIC.

Yes, good idea. I usually recommend changing to montonic time
(ktime_get_ts64()) in the same patch, but in this particular case that
would have been a user-visible change that we should not mix in
to a single commit.

	Arnd
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