Re: [PATCH v8 04/11] public: xen.h: add definitions for UUID handling

[Volodymyr Babchuk <volodymyr_babchuk@epam.com>]

Hello Jan,

On 10.10.17 19:12, Jan Beulich wrote:
>>>> On 10.10.17 at 17:52, <volodymyr_babchuk@epam.com> wrote:
>> --- a/xen/include/public/xen.h
>> +++ b/xen/include/public/xen.h
>> @@ -930,6 +930,39 @@ __DEFINE_XEN_GUEST_HANDLE(uint16, uint16_t);
>>   __DEFINE_XEN_GUEST_HANDLE(uint32, uint32_t);
>>   __DEFINE_XEN_GUEST_HANDLE(uint64, uint64_t);
>>   
>> +typedef struct
>> +{
> 
> Please put the opening brace on the previous line.
Will fix.

>> +    uint8_t a[16];
>> +} xen_uuid_t;
>> +
>> +/*
>> + * XEN_DEFINE_UUID(0x00112233, 0x4455, 0x6677, 0x8899,
>> + *                 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff)
>> + * will construct UUID 00112233-4455-6677-8899-aabbccddeeff presented as
>> + * {0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88,
>> + * 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff};
>> + *
>> + * NB: This is compatible with Linux kernel and with libuuid, but it is not
>> + * compatible with Microsoft, as they use mixed-endian encoding (some
>> + * components are little-endian, some are big-endian).
>> + */
>> +#define XEN_DEFINE_UUID_(a, b, c, d, e1, e2, e3, e4, e5, e6)            \
>> +    {{((a) >> 24) & 0xFF, ((a) >> 16) & 0xFF,                           \
>> +      ((a) >>  8) & 0xFF, ((a) >>  0) & 0xFF,                           \
>> +      ((b) >>  8) & 0xFF, ((b) >>  0) & 0xFF,                           \
>> +      ((c) >>  8) & 0xFF, ((c) >>  0) & 0xFF,                           \
>> +      ((d) >>  8) & 0xFF, ((d) >>  0) & 0xFF,                           \
>> +                e1, e2, e3, e4, e5, e6}}
>> +
>> +/* Compound literals are supported in C99 and later. */
>> +#if defined (__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
> 
> I didn't notice this earlier - why no check for __GNUC__?
I have seen pattern "#if defined (__STDC_VERSION__) && __STDC_VERSION__ 
 >= 199901" in various places in XEN, so I did it alike.
Also, I'm using C99 feature, not gcc-only one.

>> +#define XEN_DEFINE_UUID(a, b, c, d, e1, e2, e3, e4, e5, e6)             \
>> +    (xen_uuid_t)XEN_DEFINE_UUID_(a, b, c, d, e1, e2, e3, e4, e5, e6)
> 
> This being (generally) usable as expression, I think it needs
> parentheses, so e.g. XEN_DEFINE_UUID(...).a[n] becomes
> possible (whatever that may be good for).
Good point, thanks.

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