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Re: in which we present an ugly hack to make sys/queue.h CIRCLEQ work

On 2013-11-20 wrote:

i'm going to commit this soon, but if anyone has more useful hacks or
real fixes, please let me/these lists know and we'll consider them.

+ * If we ever choose to change the ABI of the CIRCLEQ macros, we could fix
+ * this by changing the

If changing the ABI (or for places where it doesn't matter), please consider gcq (in gcq.h, gcq(3)). Or use part of it (I think the *_TYPED macros are drop in replacements for CIRCLEQ). Also, slhchi is the only thing in the tree that uses it and while in theory some third party software could use it, I'd assume that in practice anyone who did would just copy it, so it wouldn't be a problem to alter the interface some if needed. Also, while I did test it at the time I haven't used it again yet so it is possible there are bugs lurking outside of what slhci uses.

I don't fully understand the strict aliasing rules, but the only thing that seems like it might cause trouble is gcq_head(), which is not used internally but provided to be able to treat any element as the head for iteration purposes (presumably because you don't have a designated head, so not CIRCLEQ usage). It casts a struct to a struct that contains only that struct and is used only to cast back. If that isn't safe, that function could just be removed and replaced with an explanation of why it isn't safe, however I expect it to be safe because it is never used except to cast to the inner type (the head only has a separate type to make it hard to accidently mess up the argument order).


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