Messages in this thread | | | Date | Thu, 06 Dec 2007 14:03:21 -0800 | From | Jeremy Fitzhardinge <> | Subject | Re: [PATCH 1/19] unify desc_struct |
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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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