Re: [Qemu-devel] [PATCH/s390-next 3/3] s390x/flic: migrate ais states

[Christian Borntraeger]

On 07/13/2017 04:49 PM, Dr. David Alan Gilbert wrote:
> * Halil Pasic (address@hidden) wrote:
>>
>>
>> On 07/13/2017 02:27 PM, Cornelia Huck wrote:
>>>> +static void kvm_flic_ais_pre_save(void *opaque)
>>>> +{
>>>> +    KVMS390FLICStateMigTmp *tmp = opaque;
>>>> +    KVMS390FLICState *flic = tmp->parent;
>>>> +    struct kvm_s390_ais_all ais;
>>>> +    struct kvm_device_attr attr = {
>>>> +        .group = KVM_DEV_FLIC_AISM_ALL,
>>>> +        .addr = (uint64_t)&ais,
>>>> +        .attr = sizeof(ais),
>>>> +    };
>>>> +
>>>> +    if (ioctl(flic->fd, KVM_GET_DEVICE_ATTR, &attr)) {
>>>> +        error_report("Failed to retrieve kvm flic ais states");
>>> There's not much else we can do in that case, is there?
>>>
>>
>> I think this is a very good question! The ioctl should not fail
>> under any circumstances, but if it does we have a problem.
>>
>> Carrying on happily (what we do now) means effectively discarding
>> ais state. In general just discarding state ain't a good idea.
>>
>> In particular it might be OK, but the patch should explain that!
>>
>> Regarding what could/should we do in such a case (instead
>> of discarding state and carrying on happily) I don't know, so
>> I tend to agree with you regarding 'not much else we can do'.
>>
>> Adding Dave and Juan. Maybe they can tell.
> 
> I keep meaning to make the pre_save give a return value for failure,
> but it hasn't currently got one.

Would you accept patches for that?

> 
> You could try something like:
> 
>   qemu_file_set_error(migrate_get_current()->to_dst_file, -EINVAL);
> 
>   I *think* the migration code should spot that before it finishes
> but it might carry on for a little while before it does.

I will keep this patch as is, since this is one of the "should not happen"
cases.