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    SubjectRe: [PATCH 1/19] unify desc_struct
    Glauber de Oliveira Costa wrote:
    > On Dec 6, 2007 6:54 PM, Andi Kleen <ak@suse.de> wrote:
    >
    >>> +/*
    >>> + * FIXME: Acessing the desc_struct through its fields is more elegant,
    >>> + * and should be the one valid thing to do. However, a lot of open code
    >>> + * still touches the a and b acessors, and doing this allow us to do it
    >>> + * incrementally. We keep the signature as a struct, rather than an union,
    >>> + * so we can get rid of it transparently in the future -- glommer
    >>> + */
    >>> +#define raw_desc_struct struct { unsigned int a, b; }
    >>> +#define detailed_desc_struct \
    >>> + struct { \
    >>> + u16 limit0; \
    >>> + u16 base0; \
    >>> + unsigned base1 : 8, type : 4, s : 1, dpl : 2, p : 1; \
    >>> + unsigned limit : 4, avl : 1, l : 1, d : 1, g : 1, base2 :8;\
    >>> + }
    >>>
    >> The standard clean way to do this is with a anonymous union.
    >>
    > It is an anonymous union.
    >
    > However:
    >
    > * It's an union of structs
    > * I wished to keep the toplevel type as a struct
    > The alternative would be to write:
    >
    > struct desc_struct {
    > union {
    > struct { unsigned int a, b; };
    > struct {
    > u16 limit0;
    > u16 base0;
    > unsigned base1 : 8, type : 4, s : 1, dpl : 2, p : 1;
    > unsigned limit : 4, avl : 1, l : 1, d : 1, g : 1, base2 :8;
    > };
    > };
    > };
    >
    > Which is fine, it's all the same in the end. Just with more shift
    > rights, and more visual pollution.
    >

    No, that's much clearer. It's a pity that the anonymous struct/union
    syntax isn't general enough to allow:

    struct desc_packed {
    u16 limit0;
    u16 base0;
    unsigned base1 : 8, type : 4, s : 1, dpl : 2, p : 1;
    unsigned limit : 4, avl : 1, l : 1, d : 1, g : 1, base2 :8;
    };

    struct desc {
    struct desc_packed;
    };

    J


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