Re: [Xen-devel] [PATCH 1/3] xen: sync the CMOS RTC as well as the Xen wallclock

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Oct 12, 2012 at 01:57:12PM +0100, David Vrabel wrote:
> From: David Vrabel <david.vrabel@xxxxxxxxxx>
> 
> If NTP is used in dom0 and it is synchronized to its clock source,
> then the kernel will periodically synchronize the Xen wallclock with
> the system time.  Updates to the Xen wallclock do not persist across
> reboots, so also synchronize the CMOS RTC (as on bare metal).
> 
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> ---
>  arch/x86/xen/time.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> index 0296a95..5e7f536 100644
> --- a/arch/x86/xen/time.c
> +++ b/arch/x86/xen/time.c
> @@ -14,6 +14,7 @@
>  #include <linux/kernel_stat.h>
>  #include <linux/math64.h>
>  #include <linux/gfp.h>
> +#include <linux/mc146818rtc.h>
>  
>  #include <asm/pvclock.h>
>  #include <asm/xen/hypervisor.h>
> @@ -208,6 +209,10 @@ static int xen_set_wallclock(unsigned long now)
>       if (!xen_initial_domain())
>               return -1;
>  
> +     /* Set the hardware RTC. */
> +     mach_set_rtc_mmss(now);

So how does this work? Is the hypervisor traping on the RTC CMOS clock?

> +
> +     /* Set the Xen wallclock. */
>       op.cmd = XENPF_settime;
>       op.u.settime.secs = now;
>       op.u.settime.nsecs = 0;
> -- 
> 1.7.2.5

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