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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.10.17 at 17:52, <volodymyr_babchuk@xxxxxxxx> 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.

> +    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__?

> +#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).

Jan


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