Re: [PATCH[ RTC: Add rtc_year_days() to calculate tm_yday

From: H. Peter Anvin
Date: Wed Jun 07 2006 - 18:48:02 EST


Followup to: <20060607193311.GH13165@xxxxxxxxxxxxxxxxxxxxxx>
By author: Russell King <rmk+lkml@xxxxxxxxxxxxxxxx>
In newsgroup: linux.dev.kernel
>
> On Wed, Jun 07, 2006 at 08:26:09PM +0200, Andrew Victor wrote:
> > RTC: Add exported function rtc_year_days() to calculate the tm_yday
> > value.
>
> Is there a good reason for this? I ask the question because the x86
> /dev/rtc driver says:
>
> * Only the values that we read from the RTC are set. We leave
> * tm_wday, tm_yday and tm_isdst untouched. Note that while the
> * RTC has RTC_DAY_OF_WEEK, we should usually ignore it, as it is
> * only updated by the RTC when initially set to a non-zero value.
>
> So it seems the established modus operandi for RTC interfaces is "don't
> trust wday, yday and isdst".
>

"Be conservative in what you send, liberal in what you accept."

- Mr. Protocol

In this case it seems a good idea to set these fields correctly, but
not rely upon them, unless there are known cases where that causes
trouble.

-hpa
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