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Re: [Xen-devel] [PATCH v6 01/12] xen: allow only sizeof(bool) variables for boolean_param()

On 09.03.2020 12:43, Julien Grall wrote:
> On 26/02/2020 12:46, Juergen Gross wrote:
>> @@ -46,7 +48,8 @@ extern const struct kernel_param __param_start[], 
>> __param_end[];
>>       __kparam __setup_##_var = \
>>           { .name = __setup_str_##_var, \
>>             .type = OPT_BOOL, \
>> -          .len = sizeof(_var), \
>> +          .len = sizeof(_var) + \
>> +                 BUILD_BUG_ON_ZERO(sizeof(_var) != sizeof(bool)), \
>  From my understanding, sizeof(bool) is not necessarily 1 (it can be 
> greater). While this is fine to use it in Xen, I think we want it to 
> always be one when exposed in the hypfs.

I don't think so: We want variable of type 'bool' to be updated
consistently (i.e. by a write to the full variable). Hence I
think sizeof(bool) is correct here. I can see though that the
hypercall interface then gains a dependency on the hypervisor's
representation of 'bool', but I think such ought to be taken
care of in the function carrying out the write, not in the
macro here.


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