Re: [Qemu-devel] [PATCH v2 2/2] s390/kvm: make TOD setting failures fatal for migration

[Thomas Huth <thuth@redhat.com>]

On 04.10.2017 12:57, Christian Borntraeger wrote:
> From: "Collin L. Walling" <walling@linux.vnet.ibm.com>
> 
> If we fail to set a proper TOD clock on the target system,  this can
> already result in some problematic cases. We print several warn messages
> on source and target in that case.
> 
> If kvm fails to set a nonzero epoch index, then we must ultimately fail
> the migration as this will result in a giant time leap backwards. This
> patch lets the migration fail if we can not set the guest time on the
> target.
> 
> On failure the guest will resume normally on the original host machine.
> 
> Signed-off-by: Collin L. Walling <walling@linux.vnet.ibm.com>
> Reviewed-by: Eric Farman <farman@linux.vnet.ibm.com>
> Reviewed-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> [split failure change from epoch index change, minor fixups]
> ---
>  hw/s390x/s390-virtio-ccw.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index fafbc6d..b7adb93 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -213,13 +213,10 @@ static int gtod_load(QEMUFile *f, void *opaque, int version_id)
>  
>      r = s390_set_clock(&tod_high, &tod_low);
>      if (r) {
> -        warn_report("Unable to set guest clock for migration: %s",
> -                    strerror(-r));
> -        error_printf("Guest clock will not be restored "
> -                     "which could cause the guest to hang.");
> +        error_report("Unable to set KVM guest TOD clock: %s", strerror(-r));
>      }
>  
> -    return 0;
> +    return r;
>  }

Reviewed-by: Thomas Huth <thuth@redhat.com>

(and I wonder whether we should fail the S390_TOD_CLOCK_VALUE_MISSING
case with returning an error instead of 0, too?)