linux-kernel - Re: [PATCH] specific do_timer

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Message-ID: <alpine.LFD.2.02.1109022155080.2723@ionos>
Date:	Fri, 2 Sep 2011 21:57:59 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dimitri Sivanich <sivanich@....com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	John Stultz <johnstul@...ibm.com>
Subject: Re: [PATCH] specific do_timer_cpu value for nohz off mode

On Fri, 2 Sep 2011, Dimitri Sivanich wrote:
> On Fri, Sep 02, 2011 at 10:19:36AM +0200, Thomas Gleixner wrote:
> +#ifdef CONFIG_SYSFS
> +/**
> + * sysfs_show_do_timer_cpu - sysfs interface for tick_do_timer_cpu
> + * @dev:        unused
> + * @buf:        char buffer where value of tick_do_timer_cpu is copied
> + *
> + * Provides sysfs interface for showing the current tick_do_timer_cpu.
> + */
> +static ssize_t
> +sysfs_show_do_timer_cpu(struct sys_device *dev,
> +				struct sysdev_attribute *attr, char *buf)
> +{
> +	ssize_t count = 0;
> +
> +	count = snprintf(buf, PAGE_SIZE, "%d\n", tick_do_timer_cpu);
> +
> +	return count;
> +}
> +
> +/**
> + * sysfs_override_do_timer_cpu - manually override tick_do_timer_cpu
> + * @dev:        unused
> + * @buf:        cpu number of desired tick_do_timer_cpu
> + * @count:      length of buffer
> + *
> + * Takes input from sysfs interface for manually overriding the selected
> + * tick_do_timer_cpu.  Only applicable when not running in nohz mode.
> + */
> +static ssize_t
> +sysfs_override_do_timer_cpu(struct sys_device *dev,
> +					struct sysdev_attribute *attr,
> +					const char *buf, size_t count)
> +{
> +	char b[16];
> +	size_t ret = count;
> +	int c;
> +
> +#ifdef CONFIG_NO_HZ
> +	/* nohz mode not supported */
> +	if (tick_nohz_enabled)
> +		return -EINVAL;
> +#endif
> +	/* strings from sysfs write are not 0 terminated! */
> +	if (count >= sizeof(b))
> +		return -EINVAL;
> +
> +	/* strip off \n: */
> +	if (buf[count-1] == '\n')
> +		count--;
> +	if (count < 1)
> +		return -EINVAL;
> +
> +	memcpy(b, buf, count);
> +	b[count] = 0;
> +
> +	if (sscanf(b, "%d", &c) != 1)
> +		return -EINVAL;

Isn't there a function which parses sysfs writes into an integer ?

Thanks,

	tglx
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