Re: [PATCH 01/12] xen: introduce xen_dom_flags

[Julien Grall <julien@xen.org>]

On 15/04/2020 10:12, Jan Beulich wrote:
> On 15.04.2020 03:02, Stefano Stabellini wrote:
>> We are passing an extra special boolean flag at domain creation to
>> specify whether we want to the domain to be privileged (i.e. dom0) or
>> not. Another flag will be introduced later in this series.
>>
>> Introduce a new struct xen_dom_flags and move the privileged flag to it.
>> Other flags will be added to struct xen_dom_flags.
> 
> I'm unsure whether introducing a 2nd structure is worth it here.
> We could as well define some internal-use-only flags for
> struct xen_domctl_createdomain's respective field.

+1.

> 
>> --- a/xen/arch/x86/domain.c
>> +++ b/xen/arch/x86/domain.c
>> @@ -529,7 +529,8 @@ static bool emulation_flags_ok(const struct domain *d, uint32_t emflags)
>>   }
>>   
>>   int arch_domain_create(struct domain *d,
>> -                       struct xen_domctl_createdomain *config)
>> +                       struct xen_domctl_createdomain *config,
>> +                       struct xen_dom_flags *flags)
> 
> const (also elsewhere)?
> 
>> --- a/xen/arch/x86/setup.c
>> +++ b/xen/arch/x86/setup.c
>> @@ -706,6 +706,7 @@ void __init noreturn __start_xen(unsigned long mbi_p)
>>           .max_maptrack_frames = -1,
>>       };
>>       const char *hypervisor_name;
>> +    struct xen_dom_flags flags = { !pv_shim };
> 
> Here and elsewhere please use field designators right away, even if
> there's only a single field now.
> 
>> @@ -363,7 +363,7 @@ struct domain *domain_create(domid_t domid,
>>       ASSERT(is_system_domain(d) ? config == NULL : config != NULL);
>>   
>>       /* Sort out our idea of is_control_domain(). */
>> -    d->is_privileged = is_priv;
>> +    d->is_privileged =  flags ? flags->is_priv : false;
> 
> Stray double blanks.
> 
>> --- a/xen/common/domctl.c
>> +++ b/xen/common/domctl.c
>> @@ -364,6 +364,7 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
>>       bool_t copyback = 0;
>>       struct xen_domctl curop, *op = &curop;
>>       struct domain *d;
>> +    struct xen_dom_flags flags ={ false };
> 
> Missing blank.
> 
>> --- a/xen/include/xen/domain.h
>> +++ b/xen/include/xen/domain.h
>> @@ -63,8 +63,13 @@ void arch_vcpu_destroy(struct vcpu *v);
>>   int map_vcpu_info(struct vcpu *v, unsigned long gfn, unsigned offset);
>>   void unmap_vcpu_info(struct vcpu *v);
>>   
>> +struct xen_dom_flags {
>> +    bool is_priv;
> 
> Use a single bit bitfield instead? May even want to consider passing
> this struct by value then.

This is an alternative if extending xen_domctl_createdomain is not a 
solution. The bitfield is easier to extend because we don't need to 
create a new field for each flag in struct domain.

Cheers,

-- 
Julien Grall