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Date: Tue, 08 May 2007 11:45:02 -0700
From: Julian Elischer <julian@elischer.org>
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To: John Baldwin <jhb@freebsd.org>
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Cc: Hans Petter Selasky <hselasky@c2i.net>,
	Giorgos Keramidas <keramida@freebsd.org>, freebsd-arch@freebsd.org
Subject: Re: Missing LIST_PREV() ?
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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..