Missing LIST_PREV() ?

[John Baldwin]

On Tuesday 08 May 2007 03:00:51 pm 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?

Just use a TAILQ, that's what it is there for.

-- 
John Baldwin