sys/queue.h: add STAILQ_REVERSE

[kib]

Summary

The implementation of the traditional interview question about in-place reversing of the single-linked list.

[markj]

sys/sys/queue.h

567

Rather than forcing consumers to declare these variable, it'd be better IMO to pass the type name as parameter, and declare temp variables within the macro. This is consistent with how the *_SWAP macros work.

[kib]

Define locals in the macro.

[markj]

Looks ok to me, but there should be a queue.3 update too.

[kib]

Update manpage.

[olce]

I've also written a corresponding test, to be uploaded to a new revision.

sys/sys/queue.h

567–579

(head)->stqh_last = &STAILQ_FIRST(head); is wrong.

I'm also suggesting to break early if the stailq is empty, as this seems clearer and it alleviates the need to introduce a similar test when setting ->stqh_last.

[kib]

Do nothing for empty stailq.
Fix stqh_last.

[olce]

I'd also suggest removing _Var = STAILQ_LAST(head, type, field); and setting ->stqh_first to _Varp directly, as _Varp already contains the old last/new first element.

[kib]

Rely on _Varp to set head.