From owner-freebsd-hackers  Mon May 11 15:23:07 1998
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Date: 11 May 1998 22:22:31 -0000
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From: Julian Assange <proff@iq.org>
To: gibbs@FreeBSD.ORG
cc: hackers@FreeBSD.ORG
cc: dyson@FreeBSD.ORG
cc: mrg@eterna.com.au
Subject: more queue.h brokenness
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X-Loop: FreeBSD.ORG


I notice someone (gibbs?) has updated sys/queue.h

Unfortunately, because of the manner in which tqe_prev, and tqh_last
are calculated, TAILQ_LAST and TAILQ_PREV need to be redefined like so:

#define TAILQ_LAST(head) ((*((head)->tqh_last))? (*((head)->tqh_last)): TAILQ_FIRST(head))
#define TAILQ_PREV(head, elm, field) (((elm) == TAILQ_FIRST(head))?NULL: *((elm)->field.tqe_prev))

this is a hack-like solution; the alternative is to do away with the
double indirection of tqh_last and tqe_prev, which would be annoying.

the other queue.h types (where defined) also have this problem.

TAILQ_PREV is only used in vm/vm_object.c, which, presumably, is why
no-one has noticed the problem before (and why I've cc'd dyson).

Cheers,
Julian.

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