linux-kernel - Re: [RFE PATCH 2/2] rtc, add write functionality to sysfs

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Date:	Sun, 24 Feb 2013 12:03:01 -0500
From:	Prarit Bhargava <prarit@...hat.com>
To:	Alessandro Zummo <a.zummo@...ertech.it>
CC:	John Stultz <john.stultz@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>,
	Matt Fleming <matt.fleming@...el.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...ux.intel.com>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>
Subject: Re: [RFE PATCH 2/2] rtc, add write functionality to sysfs



On 02/23/2013 06:11 PM, Alessandro Zummo wrote:
> On 22/feb/2013, at 22:05, John Stultz <john.stultz@...aro.org> wrote:
> 
>> On 02/22/2013 12:55 PM, Prarit Bhargava wrote:
>>>
>>> On 02/22/2013 03:43 PM, John Stultz wrote:
>>>> On 02/14/2013 09:02 AM, Prarit Bhargava wrote:
>>>>> /sys/class/rtc/rtcX/date and /sys/class/rtc/rtcX/time currently have
>>>>> read-only access.  This patch introduces write functionality which will
>>>>> set the rtc time.
>>>>>
>>>>> Usage: echo YYYY-MM-DD > /sys/class/rtc/rtcX/date
>>>>>         echo HH:MM:SS > /sys/class/rtc/rtcX/time
>>>> Why do we want to add a new interface here?
>>> John,
>>>
>>> I'm not adding a new interface.  The current date/time interface only handles
>>> read and I'm introducing write.
>>>
>>
>> Right, but what benefit does that provide?
>> (I'm not saying there isn't any, its just not clear from your patch why this is a good thing.)
>>

Sorry John, I misunderstood your question.

>> Also CC'ing Alessandro for his input.
> 
> I'd like to keep the interfaces as simple as possible but I'm open to improvements if there are good use cases.
> 

AFAICT there is no way for me to "test" or use the write from userspace.
hwclock uses the SET_TIME ioctl, which is a different code path AFAICT.

I'd like to be at least able to test this stuff when we make changes to it so I
think having write functionality for date & time is worthwhile.

For me, I'm using these to heavily test ntp and ntpdate over system reboots.

OOC, Alessandro, why is the date & time split into two fields?

P.
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