linux-kernel - Re: [PATCH 1/8] posix clocks: introduce a syscall for clock tuning.

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Date:	Thu, 23 Sep 2010 12:48:51 -0700
From:	john stultz <johnstul@...ibm.com>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	linux-kernel@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	linux-api@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>,
	Christoph Lameter <cl@...ux.com>,
	David Miller <davem@...emloft.net>,
	Krzysztof Halasa <khc@...waw.pl>,
	Peter Zijlstra <peterz@...radead.org>,
	Rodolfo Giometti <giometti@...ux.it>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/8] posix clocks: introduce a syscall for clock tuning.

On Thu, 2010-09-23 at 19:31 +0200, Richard Cochran wrote:
> A new syscall is introduced that allows tuning of a POSIX clock. The
> syscall is implemented for four architectures: arm, blackfin, powerpc,
> and x86.
> 
> The new syscall, clock_adjtime, takes two parameters, the clock ID,
> and a pointer to a struct timex. The semantics of the timex struct
> have been expanded by one additional mode flag, which allows an
> absolute offset correction. When specificied, the clock offset is
> immediately corrected by adding the given time value to the current
> time value.


So I'd still split this patch up a little bit more.

1) Patch that implements the ADJ_SETOFFSET  (*and its implementation*)
in do_adjtimex.

2) Patch that adds the new syscall and clock_id multiplexing.

3) Patches that wire it up to the rest of the architectures (there's
still a bunch missing here).



And one little nit in the code:

> diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
> index 9ca4973..446b566 100644
> --- a/kernel/posix-timers.c
> +++ b/kernel/posix-timers.c
> @@ -197,6 +197,14 @@ static int common_timer_create(struct k_itimer *new_timer)
>  	return 0;
>  }
> 
> +static inline int common_clock_adj(const clockid_t which_clock, struct timex *t)
> +{
> +	if (CLOCK_REALTIME == which_clock)
> +		return do_adjtimex(t);
> +	else
> +		return -EOPNOTSUPP;
> +}


Would it make sense to point to the do_adjtimex() in the k_clock
definition for CLOCK_REALTIME rather then conditionalizing it here?



thanks
-john

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