Re: [Qemu-devel] [PATCH v3]MC146818 RTC: coordinate guest clock base to destination host after migration

[Paolo Bonzini]

On 26/09/2016 10:42, address@hidden wrote:
> MC146818 RTC: coordinate guest clock base to destination host after migration
> 
> qemu tracks guest time based on vector [base_rtc, last_update], in which
> last_update stands for a monotonic tick which is actually uptime of the host.
> according to rtc implementation codes of recent releases and upstream, after
> migration, the time base vector [base_rtc, last_update] isn't updated to
> coordinate with the destionation host, ie. qemu doesnt update last_update to
> uptime of the destination host.
> what problem have we got because of this bug? after migration, guest time may
> jump back to several days ago, that will make some critical business 
> applications,
> such as lotus notes, malfunction.
> this patch is trying to fix the problem. first, when vmsave in progress, we 
> rtc_update_time to refresh time stamp in cmos array, then during vmrestore,
> we rtc_set_time to update qemu base_rtc and last_update variable according to 
> time
> stamp in cmos array.
> 
> Signed-off-by: Junlian Bell <address@hidden>
> ---
>  hw/timer/mc146818rtc.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/timer/mc146818rtc.c b/hw/timer/mc146818rtc.c
> index ea625f2..1e0ed14 100644
> --- a/hw/timer/mc146818rtc.c
> +++ b/hw/timer/mc146818rtc.c
> @@ -717,11 +717,19 @@ static void rtc_set_date_from_host(ISADevice *dev)
>      rtc_set_cmos(s, &tm);
>  }
>  
> +static void rtc_pre_save(void *opaque) 

This patch doesn't compile cleanly (rtc_pre_save is unused, which gives
a warning), and also doesn't pass scripts/checkpatch.pl.

Thanks,

Paolo

> +{
> +    RTCState *s = opaque;
> +
> +    rtc_update_time(s);
> +}
> +
>  static int rtc_post_load(void *opaque, int version_id)
>  {
>      RTCState *s = opaque;
>  
> -    if (version_id <= 2) {
> +    if (version_id <= 2 ||
> +            rtc_clock == QEMU_CLOCK_REALTIME){
>          rtc_set_time(s);
>          s->offset = 0;
>          check_update_timer(s);
> -- 
> 2.9.0.windows.1
>