netdev - Re: [PATCH] ptp/ptp_clock.c: Correct input parameter range check

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Message-ID: <20190404031455.cn4cc5wxbn6izvwe@localhost>
Date:   Wed, 3 Apr 2019 20:14:55 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Siddaraju D H <siddarajudh@...il.com>
Cc:     john.stultz@...aro.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ptp/ptp_clock.c: Correct input parameter range check

On Thu, Apr 04, 2019 at 05:39:58AM +0530, Siddaraju D H wrote:
> From: Siddaraju DH <siddarajudh@...il.com>
> 
> The ealier implementaion used to return EINVAL for -ve adjustments
> in the range -1ns to -999999999ns as these -ve numbers will fail the
> unsigned comaparison against NSEC_PER_SEC. Since the tv_sec field
> will be ZERO in this range, the user will not be able to specify
> the signedness of adjustment through the tv_sec field.

NAK, the tv_sec field can be set to -1.  See the example, below.

Thanks,
Richard

void clockadj_step(clockid_t clkid, int64_t step)
{
	struct timex tx;
	int sign = 1;
	if (step < 0) {
		sign = -1;
		step *= -1;
	}
	memset(&tx, 0, sizeof(tx));
	tx.modes = ADJ_SETOFFSET | ADJ_NANO;
	tx.time.tv_sec  = sign * (step / NS_PER_SEC);
	tx.time.tv_usec = sign * (step % NS_PER_SEC);
	/*
	 * The value of a timeval is the sum of its fields, but the
	 * field tv_usec must always be non-negative.
	 */
	if (tx.time.tv_usec < 0) {
		tx.time.tv_sec  -= 1;
		tx.time.tv_usec += 1000000000;
	}
	if (clock_adjtime(clkid, &tx) < 0)
		pr_err("failed to step clock: %m");
}