Re: [Xen-devel] [PATCH v2 12/12] xen/domain: Allocate d->vcpu[] in domain_create()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 15/08/18 16:18, Jan Beulich wrote:
>
>>>> --- a/xen/common/domctl.c
>>>> +++ b/xen/common/domctl.c
>>>> @@ -554,16 +554,9 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) 
>>>> u_domctl)
>>>>  
>>>>          ret = -EINVAL;
>>>>          if ( (d == current->domain) || /* no domain_pause() */
>>>> -             (max > domain_max_vcpus(d)) )
>>>> +             (max != d->max_vcpus) )   /* max_vcpus set up in 
>>>> createdomain */
>>>>              break;
>>>>  
>>>> -        /* Until Xenoprof can dynamically grow its vcpu-s array... */
>>>> -        if ( d->xenoprof )
>>>> -        {
>>>> -            ret = -EAGAIN;
>>>> -            break;
>>>> -        }
>>>> -
>>>>          /* Needed, for example, to ensure writable p.t. state is synced. 
>>>> */
>>>>          domain_pause(d);
>>>>  
>>>> @@ -581,38 +574,8 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) 
>>>> u_domctl)
>>>>              }
>>>>          }
>>>>  
>>>> -        /* We cannot reduce maximum VCPUs. */
>>>> -        ret = -EINVAL;
>>>> -        if ( (max < d->max_vcpus) && (d->vcpu[max] != NULL) 
>>>> )xc_domain_max_vcpus
>>>> -            goto maxvcpu_out;
>>>> -
>>>> -        /*
>>>> -         * For now don't allow increasing the vcpu count from a non-zero
>>>> -         * value: This code and all readers of d->vcpu would otherwise 
>>>> need
>>>> -         * to be converted to use RCU, but at present there's no tools 
>>>> side
>>>> -         * code path that would issue such a request.
>>>> -         */
>>>> -        ret = -EBUSY;
>>>> -        if ( (d->max_vcpus > 0) && (max > d->max_vcpus) )
>>>> -            goto maxvcpu_out;
>>>> -
>>>>          ret = -ENOMEM;
>>>>          online = cpupool_domain_cpumask(d);
>>>> -        if ( max > d->max_vcpus )
>>>> -        {
>>>> -            struct vcpu **vcpus;
>>>> -
>>>> -            BUG_ON(d->vcpu != NULL);
>>>> -            BUG_ON(d->max_vcpus != 0);
>>>> -
>>>> -            if ( (vcpus = xzalloc_array(struct vcpu *, max)) == NULL )
>>>> -                goto maxvcpu_out;
>>>> -
>>>> -            /* Install vcpu array /then/ update max_vcpus. */
>>>> -            d->vcpu = vcpus;
>>>> -            smp_wmb();
>>>> -            d->max_vcpus = max;
>>>> -        }
>>>>  
>>>>          for ( i = 0; i < max; i++ )
>>>>          {
>>> With all of this dropped, I think the domctl should be renamed. By
>>> dropping its "max" input at the same time, there would then also
>>> no longer be a need to check that the value matches what was
>>> stored during domain creation.
>> I'm still looking to eventually delete the hypercall, but we need to be
>> able to clean up all domain/vcpu allocations without calling
>> complete_domain_destroy, or rearrange the entry logic so
>> complete_domain_destroy() can be reused for a domain which isn't
>> currently in the domlist.
>>
>> Unfortunately, I think this is going to be fairly complicated, I think.
> Especially when we expect this to take some time, I think it would
> be quite helpful for the domctl to actually say what it does until
> then, rather than retaining its current (then misleading) name.

Renaming the domctl means renaming xc_domain_max_vcpus(), and the
python/ocaml stubs, the latter of which does have external users.

In this case, leaving things unchanged is the least disruptive course of
action.

~Andrew

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