Date: Tue, 08 May 2007 12:48:20 -0700 From: Julian Elischer <julian@elischer.org> To: Hans Petter Selasky <hselasky@c2i.net> Cc: Giorgos Keramidas <keramida@freebsd.org>, freebsd-arch@freebsd.org Subject: Re: Missing LIST_PREV() ? Message-ID: <4640D404.6040204@elischer.org> In-Reply-To: <200705082100.51354.hselasky@c2i.net> References: <200705051617.34162.hselasky@c2i.net> <200705081128.25708.jhb@freebsd.org> <4640C52E.7010209@elischer.org> <200705082100.51354.hselasky@c2i.net>
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Hans Petter Selasky wrote: > On Tuesday 08 May 2007 20:45, Julian Elischer wrote: >> John Baldwin wrote: >>> On Monday 07 May 2007 04:25:18 pm Giorgos Keramidas wrote: >>>> with other compilers. >>> This can be fixed by passing the type as an argument which is what >>> TAILQ_PREV() does: >>> >>> #define TAILQ_PREV(elm, headname, field) \ >>> (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last)) >>> >>> I'm not sure how portable offsetof() would be though. In general if you >>> want this feature, you should just use a TAILQ though. TAILQ_ENTRY() is >>> the same size as a LIST_ENTRY(), it just adds one more pointer to the >>> HEAD structure. It is also specifically designed to make TAILQ_PREV() >>> work w/o needing the offsetof() hack. >> I agree with this.. that's why we have the different types. >> The suggested change in ingenious but I don't know how portable it is.. > > I suggested the following at hacker's: > > #define LIST_PREV(head,elm,field,type) \ > (((elm) == LIST_FIRST(head)) ? ((struct type *)0) : \ > ((struct type *)(((uint8_t *)((elm)->field.le_prev)) - \ > ((uint8_t *)&LIST_NEXT((struct type *)0,field))))) > > What do you think? > > --HPS > _______________________________________________ > freebsd-arch@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-arch > To unsubscribe, send any mail to "freebsd-arch-unsubscribe@freebsd.org" I think I'd rather use offsetof() with a #ifdef offsetof around it. and a comment saying that if you are using this you probably should be using a TAILQ. The question is "should we, just because we can?"
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