Re: [Xen-devel] [PATCH] xen: add macro for defining variable length array in public headers

[Jan Beulich <jbeulich@xxxxxxxx>]

On 30.08.2019 17:30, Juergen Gross wrote:
> On 30.08.19 17:22, Jan Beulich wrote:
>> On 30.08.2019 16:29, Juergen Gross wrote:
>>> On 30.08.19 16:21, Jan Beulich wrote:
>>>> On 30.08.2019 10:32, Juergen Gross wrote:
>>>>> --- a/xen/include/public/xen.h
>>>>> +++ b/xen/include/public/xen.h
>>>>> @@ -53,6 +53,15 @@ DEFINE_XEN_GUEST_HANDLE(uint64_t);
>>>>>    DEFINE_XEN_GUEST_HANDLE(xen_pfn_t);
>>>>>    DEFINE_XEN_GUEST_HANDLE(xen_ulong_t);
>>>>>    
>>>>> +/* Define a variable length array (depends on compiler). */
>>>>> +#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
>>>>> +#define __XEN_VARLEN_ARRAY_SIZE
>>>>> +#elif defined(__GNUC__)
>>>>> +#define __XEN_VARLEN_ARRAY_SIZE  0
>>>>> +#else
>>>>> +#define __XEN_VARLEN_ARRAY_SIZE  1 /* variable size */
>>>>> +#endif
>>>>
>>>> To be in line with the intentions, the C90 standard, and io/ring.h
>>>> I'd suggest to use FLEX instead of VARLEN. Furthermore, especially
>>>> in a public header, two double leading underscores need to go away.
>>>>
>>>> And then, with FLEX in the name, SIZE isn't really appropriate
>>>> anymore. Therefore I see three possible names: XEN_FLEXIBLE_ARRAY,
>>>> XEN_FLEX_ARRAY_DIMENSION (possibly just _DIM at its end), or
>>>> XEN_FLEX_ARRAY_DESIGNATOR.
>>>
>>> Okay to the "FLEX" part, but the "XEN_" prefix is not working due to
>>> compat header generation (that will result in COMPAT_ prefix in the
>>> compat headers).
>>>
>>> So any other ideas for a sensible prefix?
>>
>> Hmm, ugly. Perhaps all lower case then? Or have
> 
> xen_ and Xen_ are being converted, too.

For Xen_ I agree, but for xen_ I only see

 [ r"(struct|union|enum)\s+(xen_?)?(\w)", r"\1 compat_\3" ],

and

 [ r"(^|[^\w])xen_?(\w*)_compat_t([^\w]|$$)", r"\1compat_\2_t\3" ],

, neither of which should match your #define. But perhaps I'm
missing something.

Jan

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