Re: [PATCH 3/3] xen/privcmd: add IOCTL_PRIVCMD_SYNC_WALLCLOCK to sync Xen's wallclock

[Konrad Rzeszutek Wilk <konrad@kernel.org>]

On Fri, Oct 12, 2012 at 01:57:14PM +0100, David Vrabel wrote:
> From: David Vrabel <david.vrabel@citrix.com>
> 
> Add a new ioctl to synchronize Xen's wallclock with the current system
> time.
> 
> This may be used by the tools to ensure that newly created domains see
> the correct wallclock time if NTP is not used in dom0 or if domains
> are started before NTP has synchronized.

So... how does this work with NTPD? As in does ntpd _not_ update the
hwclock enough?


> 
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> ---
>  arch/x86/xen/time.c   |   25 ++++++++++++++++++-------
>  drivers/xen/privcmd.c |   12 ++++++++++++
>  include/xen/privcmd.h |    8 ++++++++
>  include/xen/xen-ops.h |    2 ++
>  4 files changed, 40 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> index 11770d0..d481ac9 100644
> --- a/arch/x86/xen/time.c
> +++ b/arch/x86/xen/time.c
> @@ -8,6 +8,7 @@
>   * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
>   */
>  #include <linux/kernel.h>
> +#include <linux/export.h>
>  #include <linux/interrupt.h>
>  #include <linux/clocksource.h>
>  #include <linux/clockchips.h>
> @@ -192,6 +193,19 @@ static void xen_read_wallclock(struct timespec *ts)
>  	put_cpu_var(xen_vcpu);
>  }
>  
> +int xen_write_wallclock(const struct timespec *ts)
> +{
> +	struct xen_platform_op op;
> +
> +	op.cmd = XENPF_settime;
> +	op.u.settime.secs = ts->tv_sec;
> +	op.u.settime.nsecs = ts->tv_nsec;
> +	op.u.settime.system_time = xen_clocksource_read();
> +
> +	return HYPERVISOR_dom0_op(&op);
> +}
> +EXPORT_SYMBOL_GPL(xen_write_wallclock);
> +
>  static unsigned long xen_get_wallclock(void)
>  {
>  	struct timespec ts;
> @@ -202,7 +216,7 @@ static unsigned long xen_get_wallclock(void)
>  
>  static int xen_set_wallclock(unsigned long now)
>  {
> -	struct xen_platform_op op;
> +	struct timespec ts;
>  	int rc;
>  
>  	/* do nothing for domU */
> @@ -218,12 +232,9 @@ static int xen_set_wallclock(unsigned long now)
>  	 * update_persistent_wallclock() is called ~500 ms after 'now'
>  	 * so add an extra 500 ms.
>  	 */
> -	op.cmd = XENPF_settime;
> -	op.u.settime.secs = now;
> -	op.u.settime.nsecs = NSEC_PER_SEC / 2;
> -	op.u.settime.system_time = xen_clocksource_read();
> -
> -	rc = HYPERVISOR_dom0_op(&op);
> +	ts.tv_sec = now;
> +	ts.tv_nsec = NSEC_PER_SEC / 2;
> +	rc = xen_write_wallclock(&ts);
>  	WARN(rc != 0, "XENPF_settime failed: now=%ld\n", now);
>  
>  	return rc;
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index ccee0f1..ed2caf3 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -338,6 +338,14 @@ out:
>  	return ret;
>  }
>  
> +static long privcmd_ioctl_sync_wallclock(void)
> +{
> +	struct timespec ts;
> +
> +	getnstimeofday(&ts);
> +	return xen_write_wallclock(&ts);
> +}
> +
>  static long privcmd_ioctl(struct file *file,
>  			  unsigned int cmd, unsigned long data)
>  {
> @@ -357,6 +365,10 @@ static long privcmd_ioctl(struct file *file,
>  		ret = privcmd_ioctl_mmap_batch(udata);
>  		break;
>  
> +	case IOCTL_PRIVCMD_SYNC_WALLCLOCK:
> +		ret = privcmd_ioctl_sync_wallclock();
> +		break;
> +
>  	default:
>  		ret = -EINVAL;
>  		break;
> diff --git a/include/xen/privcmd.h b/include/xen/privcmd.h
> index 17857fb..d17d087 100644
> --- a/include/xen/privcmd.h
> +++ b/include/xen/privcmd.h
> @@ -66,6 +66,12 @@ struct privcmd_mmapbatch {
>   * @cmd: IOCTL_PRIVCMD_HYPERCALL
>   * @arg: &privcmd_hypercall_t
>   * Return: Value returned from execution of the specified hypercall.
> + *
> + * @cmd: IOCTL_PRIVCMD_SYNC_WALLCLOCK
> + * @arg: Unused.
> + * Synchronizes the Xen wallclock with the current system time.
> + * Return: 0 on success, or -1 on error with errno set to EPERM or
> + * EACCES.
>   */
>  #define IOCTL_PRIVCMD_HYPERCALL					\
>  	_IOC(_IOC_NONE, 'P', 0, sizeof(struct privcmd_hypercall))
> @@ -73,5 +79,7 @@ struct privcmd_mmapbatch {
>  	_IOC(_IOC_NONE, 'P', 2, sizeof(struct privcmd_mmap))
>  #define IOCTL_PRIVCMD_MMAPBATCH					\
>  	_IOC(_IOC_NONE, 'P', 3, sizeof(struct privcmd_mmapbatch))
> +#define IOCTL_PRIVCMD_SYNC_WALLCLOCK				\
> +	_IOC(_IOC_NONE, 'P', 5, 0)
>  
>  #endif /* __LINUX_PUBLIC_PRIVCMD_H__ */
> diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
> index 6a198e4..eefed22 100644
> --- a/include/xen/xen-ops.h
> +++ b/include/xen/xen-ops.h
> @@ -29,4 +29,6 @@ int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
>  			       unsigned long mfn, int nr,
>  			       pgprot_t prot, unsigned domid);
>  
> +int xen_write_wallclock(const struct timespec *ts);
> +
>  #endif /* INCLUDE_XEN_OPS_H */
> -- 
> 1.7.2.5
> 
> 
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