Re: [Qemu-devel] [PATCH 1/4] rtc: fix 12-hour mode

[Paolo Bonzini <pbonzini@redhat.com>]

On 01/01/2012 03:53 PM, Avi Kivity wrote:
> On 11/21/2011 08:00 PM, Paolo Bonzini wrote:
>> Hours in 12-hour mode are in the 1-12 range, not 0-11.
>>
>> @@ -320,7 +324,8 @@ static void rtc_copy_date(RTCState *s)
>>           s->cmos_data[RTC_HOURS] = rtc_to_bcd(s, tm->tm_hour);
>>       } else {
>>           /* 12 hour format */
>> -        s->cmos_data[RTC_HOURS] = rtc_to_bcd(s, tm->tm_hour % 12);
>> +        int h = (tm->tm_hour % 12) ? tm->tm_hour % 12 : 12;
>> +        s->cmos_data[RTC_HOURS] = rtc_to_bcd(s, h);
>>           if (tm->tm_hour>= 12)
>>               s->cmos_data[RTC_HOURS] |= 0x80;
>>       }
>
> Nitpick, don't update patch on this account:
>
> I dislike seeing int-to-bool conversion on anything that is not a
> true/false or count value.  Things like if (has_some_property) or if
> (!nr_items) read well and are easily understood.  But here, you're not
> checking for "are there any tm_hours, if yes, use them, if not, use
> 12".  You're testing against the value 0 which has a special encoding in
> 12 hour mode.
>
> The is usually manifested in
>
>     if (!strcmp(a, b)) ...
>
> strcmp() does not return a bool or a count, and in fact it reads exactly
> the opposite of the intent: "if not string compare".  strcmp() returns
> an enumeration, or perhaps a mapping of string trichotomy to integer
> trichotomy.
>
> Sorry about the pontification, back to the regularly scheduled
> whitespace discussion.

Yeah, I probably would have remarked the same if it was someone else's 
patch. :)

BTW, I have kvm-unit-tests tests for these and other RTC emulation 
problems.  Long term perhaps they should become qtests, but for now 
kvm-unit-tests is the best place.  However, without these four patches 
they hang which is a bit too heavy.  So I'll submit as soon as these are in.

Paolo