linux-kernel - Re: [patch 1/3] timerfd: Implement show

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Date:	Tue, 8 Apr 2014 10:54:45 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
CC:	<linux-kernel@...r.kernel.org>, <shawn@...rchofgit.com>,
	<tglx@...utronix.de>, <akpm@...ux-foundation.org>,
	<avagin@...nvz.org>, <xemul@...allels.com>
Subject: Re: [patch 1/3] timerfd: Implement show_fdinfo method

On 04/08/2014 10:42 AM, Cyrill Gorcunov wrote:
> On Tue, Apr 08, 2014 at 10:17:14AM +0400, Vladimir Davydov wrote:
> ...
>>> +static int timerfd_show(struct seq_file *m, struct file *file)
>>> +{
>>> +	struct timerfd_ctx *ctx = file->private_data;
>>> +	struct itimerspec t;
>>> +
>>> +	spin_lock_irq(&ctx->wqh.lock);
>>> +	t.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
>>> +	t.it_interval = ktime_to_timespec(ctx->tintv);
>>> +	spin_unlock_irq(&ctx->wqh.lock);
>>> +
>>> +	return seq_printf(m,
>>> +			  "clockid: %d\n"
>>> +			  "ticks: %llu\n"
>>> +			  "settime flags: 0%o\n"
>>> +			  "it_value: (%llu, %llu)\n"
>>> +			  "it_interval: (%llu, %llu)\n",
>> IMO, one would expect to setup the timer on restore by passing the
>> values of settime_flags, it_value, and it_interval obtained from the
>> fdinfo to sys_timerfd_settime, but this will be incorrect, because AFAIU
>> the it_value you report here is always relative to the current time, no
>> matter whether TFD_TIMER_ABSTIME was set in settime_flags or not. Is it OK?
> Hi Vladimir! Well it_value returns remaining time so it's up to user to
> adjust this value when restore with abs time. That said one can examinate
> if abs flag was set and restore accordingly. If this is vague I'm open
> to change it to more clear way. Ideas?

If it's intended, it should be documented explicitly I think. Currently
in the doc patch I see nothing about whether expiration time is absolute
or relative:

> 'it_value' and 'it_interval' are the expiration time and interval for the timer.

Thanks.
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