Re: [Xen-devel] [PATCH] hvm: Correct RTC time offset update error due to tm->tm_year

[annie li <annie.li@xxxxxxxxxx>]

On 2012-2-22 21:58, Ian Campbell wrote:
> Yes, this looks plausible to me (although I'm no expert on this code).
> Something similar happens in rtc_next_second. 
>
> Perhaps it would be better to add a function or macro to do the
> conversion, such that it is somewhat self documenting? Or at least make
> the 1900 a #define with a suitable name.
>   
I changed the 1900 to a macro and added a new function get_year. The new 
patch is attached.
Thanks
Annie

# HG changeset patch
# Parent f2543f449a49b8979becbf6888e009973427089a
hvm: correct RTC time offset update error due to tm->tm_year

tm->tm_year in rtc.c is year number offsetting from 1900. So it is necessary to 
add the offset 1900 when calling mktime funtion in Xen. Otherwise, the 
calculation result of mktime is incorrect.

Signed-off-by: Annie Li <annie.li@xxxxxxxxxx>

diff -r f2543f449a49 xen/arch/x86/hvm/rtc.c
--- a/xen/arch/x86/hvm/rtc.c    Mon Feb 13 17:57:47 2012 +0000
+++ b/xen/arch/x86/hvm/rtc.c    Thu Feb 23 18:21:19 2012 +0800
@@ -33,6 +33,8 @@
 #define vrtc_domain(x) (container_of((x), struct domain, \
                                      arch.hvm_domain.pl_time.vrtc))
 #define vrtc_vcpu(x)   (pt_global_vcpu_target(vrtc_domain(x)))
+#define epoch_year     1900
+#define get_year(x)    (x + epoch_year)
 
 static void rtc_periodic_cb(struct vcpu *v, void *opaque)
 {
@@ -165,7 +167,7 @@ static void rtc_set_time(RTCState *s)
       
     ASSERT(spin_is_locked(&s->lock));
 
-    before = mktime(tm->tm_year, tm->tm_mon + 1, tm->tm_mday,
+    before = mktime(get_year(tm->tm_year), tm->tm_mon + 1, tm->tm_mday,
                    tm->tm_hour, tm->tm_min, tm->tm_sec);
     
     tm->tm_sec = from_bcd(s, s->hw.cmos_data[RTC_SECONDS]);
@@ -179,7 +181,7 @@ static void rtc_set_time(RTCState *s)
     tm->tm_mon = from_bcd(s, s->hw.cmos_data[RTC_MONTH]) - 1;
     tm->tm_year = from_bcd(s, s->hw.cmos_data[RTC_YEAR]) + 100;
 
-    after = mktime(tm->tm_year, tm->tm_mon + 1, tm->tm_mday,
+    after = mktime(get_year(tm->tm_year), tm->tm_mon + 1, tm->tm_mday,
                    tm->tm_hour, tm->tm_min, tm->tm_sec);
 
     /* We use the guest's setting of the RTC to define the local-time 
@@ -257,7 +259,7 @@ static void rtc_next_second(RTCState *s)
                 if ( (unsigned)tm->tm_wday >= 7 )
                     tm->tm_wday = 0;
                 days_in_month = get_days_in_month(tm->tm_mon, 
-                                                  tm->tm_year + 1900);
+                                                  get_year(tm->tm_year));
                 tm->tm_mday++;
                 if ( tm->tm_mday < 1 )
                 {

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