Add dependency resolver for plugins.

This has been something I wanted to avoid, but then I stumbled so hard
on it myself I simply had to add it.  With this commit finit actually
comes of age -- it's now possible to do anything a modern init can --
only faster! :-)

Included in this commit is the OpenBSD version of sys/queue.h, which
unline all versions of the same file on Linux has the _FOREACH_SAFE
macros for iterating over a linked list.

The plugins are now in a TAILQ, loaded in alphabetic order and, unless
the dependency resolver says otherwise, added last in the queue.  So,
naming your plugins according to standard sysvinit rules: S01, S02,
etc. takes care of the most basic dependency resolution.  When that is
not sufficient, simply add a line ".depends = { "other_plugin",
"another_plugin" }," to your plugin_t definition.  Be careful though
for circular dependencies, we don't check for those.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Makefile

@@ -35,7 +35,7 @@ PKG         = $(NAME)-$(VERSION)
 DEV         = $(NAME)-dev
 ARCHIVE     = $(PKG).tar.xz
 EXEC        = finit reboot
-HEADERS     = plugin.h svc.h helpers.h
+HEADERS     = plugin.h svc.h helpers.h queue.h
 DISTFILES   = LICENSE README ChangeLog finit.conf services
 OBJS        = finit.o conf.o helpers.o sig.o svc.o plugin.o
 OBJS       += strlcpy.o

plugin.c

@@ -26,18 +26,22 @@
 #include <dirent.h>		/* readdir() et al */
 #include <poll.h>
 #include <string.h>
-#include <sys/queue.h>		/* BSD sys/queue.h API */
 
 #include "finit.h"
 #include "private.h"
 #include "helpers.h"
 #include "plugin.h"
+#include "queue.h"		/* BSD sys/queue.h API */
+#include "lite.h"
 
 #define is_io_plugin(p) ((p)->io.cb && (p)->io.fd >= 0)
 
-static size_t        num_fds = 0;
+static char         *plugpath = NULL; /* Set by first load. */
+static size_t        num_fds  = 0;
 static struct pollfd fds[MAX_NUM_FDS];
-static LIST_HEAD(, plugin) plugins = LIST_HEAD_INITIALIZER();
+static TAILQ_HEAD(, plugin) plugins = TAILQ_HEAD_INITIALIZER(plugins);
+
+static void check_plugin_depends(plugin_t *plugin);
 
 int plugin_register(plugin_t *plugin)
 {
@@ -57,6 +61,14 @@ int plugin_register(plugin_t *plugin)
 			plugin->name = (char *)info.dli_fname;
 	}
 
+	/* Already registered? */
+	if (plugin_find(plugin->name)) {
+		_d("... %s already loaded.", plugin->name);
+		return 0;
+	}
+
+	check_plugin_depends(plugin);
+
 	if (is_io_plugin(plugin)) {
 		if (num_fds + 1 >= MAX_NUM_FDS) {
 			num_fds = MAX_NUM_SVC;
@@ -88,14 +100,14 @@ int plugin_register(plugin_t *plugin)
 		return 1;
 	}
 
-	LIST_INSERT_HEAD(&plugins, plugin, link);
+	TAILQ_INSERT_TAIL(&plugins, plugin, link);
 
 	return 0;
 }
 
 int plugin_unregister(plugin_t *plugin)
 {
-	LIST_REMOVE(plugin, link);
+	TAILQ_REMOVE(&plugins, plugin, link);
 
 	if (plugin->svc.cb) {
 		svc_t *svc = svc_find(plugin->name);
@@ -111,12 +123,64 @@ int plugin_unregister(plugin_t *plugin)
 	return 0;
 }
 
+
+#define SEARCH_PLUGIN(str)						\
+	PLUGIN_ITERATOR(p, tmp) {					\
+		_d("Comparing %s against plugin %s", str, p->name);	\
+		if (!strcmp(p->name, str))				\
+			return p;					\
+	}
+
+/**
+ * plugin_find - Find a plugin by name
+ * @name: With or without path, or .so extension
+ *
+ * This function uses an opporunistic search for a suitable plugin and
+ * returns the first match.  Albeit with at least some measure of
+ * heuristics.
+ *
+ * First it checks for an exact match.  If no match is found and @name
+ * starts with a slash the search ends.  Otherwise a new search with the
+ * plugin path prepended to @name is made.  Also, if @name does not end
+ * with .so it too is added to @name before searching.
+ *
+ * Returns:
+ * On success the pointer to the matching &plugin_t is returned,
+ * otherwise %NULL is returned.
+ */
+plugin_t *plugin_find(char *name)
+{
+	plugin_t *p, *tmp;
+
+	if (!name) {
+		errno = EINVAL;
+		return NULL;
+	}
+
+	SEARCH_PLUGIN(name);
+
+	if (name[0] != '/') {
+		int noext;
+		char path[256];
+
+		noext = strcmp(name + strlen(name) - 3, ".so");
+		snprintf (path, sizeof(path), "%s%s%s%s", plugpath,
+			  fisslashdir(plugpath) ? "" : "/",
+			  name, noext ? ".so" : "");
+
+		SEARCH_PLUGIN(path);
+	}
+
+	errno = ENOENT;
+	return NULL;
+}
+
 /* Private daemon API *******************************************************/
 void plugin_run_hooks(hook_point_t no)
 {
-	plugin_t *p;
+	plugin_t *p, *tmp;
 
-	PLUGIN_ITERATOR(p) {
+	PLUGIN_ITERATOR(p, tmp) {
 		if (p->hook[no].cb) {
 			_d("Calling %s hook n:o %d from runloop...", basename(p->name), no);
 			p->hook[no].cb(p->hook[no].arg);
@@ -127,10 +191,10 @@ void plugin_run_hooks(hook_point_t no)
 /* Generic libev I/O callback, looks up correct plugin and calls its callback */
 static void generic_io_cb(int fd, int events)
 {
-	plugin_t *p;
+	plugin_t *p, *tmp;
 
 	/* Find matching plugin, pick first matching fd */
-	PLUGIN_ITERATOR(p) {
+	PLUGIN_ITERATOR(p, tmp) {
 		if (is_io_plugin(p) && p->io.fd == fd) {
 			_d("Calling I/O %s from runloop...", basename(p->name));
 			p->io.cb(p->io.arg, fd, events);
@@ -168,9 +232,9 @@ void plugin_monitor(void)
 static void init_plugins(void)
 {
 	int i = 0;
-	plugin_t *p;
+	plugin_t *p, *tmp;
 
-	PLUGIN_ITERATOR(p) {
+	PLUGIN_ITERATOR(p, tmp) {
 		if (is_io_plugin(p)) {
 			_d("Initializing plugin %s for I/O", basename(p->name));
 			fds[i].revents = 0;
@@ -180,6 +244,70 @@ static void init_plugins(void)
 	}
 }
 
+
+/**
+ * load_one - Load one plugin
+ * @path: Path to finit plugins, usually %PLUGIN_PATH
+ * @name: Name of plugin, optionally ending in ".so"
+ *
+ * Loads a plugin from @path/@name[.so].  Note, if ".so" is missing from
+ * the plugin @name it is added before attempting to load.
+ *
+ * It is up to the plugin itself ot register itself as a "ctor" with the
+ * %PLUGIN_INIT macro so that plugin_register() is called automatically.
+ *
+ * Returns:
+ * POSIX OK(0) on success, non-zero otherwise.
+ */
+static int load_one(char *path, char *name)
+{
+	int noext;
+	char plugin[256];
+	void *handle;
+
+	if (!path || !fisdir(path)) {
+		errno = EINVAL;
+		return 1;
+	}
+
+	noext = strcmp(name + strlen(name) - 3, ".so");
+	snprintf(plugin, sizeof(plugin), "%s/%s%s", path, name, noext ? ".so" : "");
+	_d("Loading plugin %s ...", basename(plugin));
+	handle = dlopen(plugin, RTLD_LAZY | RTLD_GLOBAL);
+	if (!handle) {
+		_d("Failed loading plugin %s: %s", plugin, dlerror());
+		return 1;
+	}
+
+	return 0;
+}
+
+/**
+ * check_plugin_depends - Check and load any plugins this one depends on.
+ * @plugin: Plugin with possible depends to check
+ *
+ * Very simple dependency resolver, should actually load the plugin of
+ * the correct .name, but currently loads a matching filename.
+ *
+ * Works, but only for now.  A better way might be to have a try_load()
+ * that actually loads all plugins and checks their &plugin_t for the
+ * correct .name.
+ */
+static void check_plugin_depends(plugin_t *plugin)
+{
+	int i;
+
+	for (i = 0; i < PLUGIN_DEP_MAX && plugin->depends[i]; i++) {
+		_d("Plugin %s depends on %s ...", plugin->name, plugin->depends[i]);
+		if (plugin_find(plugin->depends[i])) {
+			_d("OK plugin %s was already loaded.", plugin->depends[i]);
+			continue;
+		}
+
+		load_one(plugpath, plugin->depends[i]);
+	}
+}
+
 int plugin_load_all(char *path)
 {
 	int fail = 0;
@@ -190,27 +318,13 @@ int plugin_load_all(char *path)
 		_e("Failed, cannot open plugin directory %s: %s", path, strerror(errno));
 		return 1;
 	}
+	plugpath = path;
 
 	while ((entry = readdir(dp))) {
-		char *ext = entry->d_name + strlen(entry->d_name) - 3;
-
-		if (!strcmp(ext, ".so")) {
-			int result = 0;
-			void *handle;
-			char plugin[1024];
-
-			snprintf(plugin, sizeof(plugin), "%s/%s", path, entry->d_name);
-//			print_desc("   Loading plugin ", basename(plugin));
-			handle = dlopen(plugin, RTLD_LAZY | RTLD_GLOBAL);
-			if (!handle) {
-				_d("Failed loading plugin %s: %s", plugin, dlerror());
-				result = 1;
-			}
-			if (result)
-				fail++;
-
-//			print_result(result);
-		}
+//		print_desc("   Loading plugin ", basename(plugin));
+		if (load_one(path, entry->d_name))
+			fail++;
+//		print_result(result);
 	}
 
 	closedir(dp);

plugin.h

@@ -25,16 +25,17 @@
 #define FINIT_PLUGIN_H_
 
 #include <poll.h>
-#include <sys/queue.h>		/* BSD sys/queue.h API */
+#include "queue.h"		/* BSD sys/queue.h API */
 #include "svc.h"
 
+#define PLUGIN_DEP_MAX  10
 #define PLUGIN_IO_READ  POLLIN
 #define PLUGIN_IO_WRITE POLLOUT
 
 #define PLUGIN_INIT(x) static void __attribute__ ((constructor)) x(void)
 #define PLUGIN_EXIT(x) static void __attribute__ ((destructor))  x(void)
 
-#define PLUGIN_ITERATOR(x)  LIST_FOREACH(x, &plugins, link)
+#define PLUGIN_ITERATOR(x, tmp) TAILQ_FOREACH_SAFE(x, &plugins, link, tmp)
 
 /*
  * Predefined hook points for easier plugin debugging 
@@ -76,9 +77,9 @@ typedef enum {
  */
 typedef struct plugin {
 	/* BSD sys/queue.h linked list node. */
-	LIST_ENTRY(plugin) link;
+	TAILQ_ENTRY(plugin) link;
 
-	/* Plugin name, defaults to plugin path if unset.
+	/* Plugin name, defaults to basename of plugin path if unset.
 	 * NOTE: Must be same as @cmd for service plugins! */
 	char *name;
 
@@ -101,12 +102,17 @@ typedef struct plugin {
 		void  *arg;
 		void (*cb)(void *arg, int fd, int events);
 	} io;
+
+	char *depends[PLUGIN_DEP_MAX]; /* List of other .name's this depends on. */
 } plugin_t;
 
 /* Public plugin API */
 int plugin_register   (plugin_t *plugin);
 int plugin_unregister (plugin_t *plugin);
 
+/* Helper API */
+plugin_t *plugin_find (char *name);
+
 #endif	/* FINIT_PLUGIN_H_ */
 
 /**

plugins/bootmisc.c

@@ -85,6 +85,7 @@ static void setup(void *UNUSED(arg))
 }
 
 static plugin_t plugin = {
+	.name = "bootmisc",
 	.hook[HOOK_BASEFS_UP] = {
 		.cb  = setup
 	},

plugins/dbus.c

@@ -41,6 +41,7 @@ static plugin_t plugin = {
 	.hook[HOOK_NETWORK_UP] = {
 		.cb  = setup
 	},
+	.depends = { "bootmisc", },
 };
 
 PLUGIN_INIT(plugin_init)

plugins/resolvconf.c

@@ -68,6 +68,7 @@ static plugin_t plugin = {
 	.hook[HOOK_BASEFS_UP] = {
 		.cb  = setup
 	},
+	.depends = { "bootmisc", },
 };
 
 PLUGIN_INIT(plugin_init)

plugins/urandom.c

@@ -44,6 +44,7 @@ static plugin_t plugin = {
 	.hook[HOOK_BASEFS_UP] = {
 		.cb  = setup
 	},
+	.depends = { "bootmisc", }
 };
 
 PLUGIN_INIT(plugin_init)

plugins/x11-common.c

@@ -56,6 +56,7 @@ static plugin_t plugin = {
 	.hook[HOOK_NETWORK_UP] = {
 		.cb  = setup
 	},
+	.depends = { "bootmisc", }
 };
 
 PLUGIN_INIT(plugin_init)

queue.h

@@ -0,0 +1,568 @@
+/*	$OpenBSD: queue.h,v 1.36 2012/04/11 13:29:14 naddy Exp $	*/
+/*	$NetBSD: queue.h,v 1.11 1996/05/16 05:17:14 mycroft Exp $	*/
+
+/*
+ * Copyright (c) 1991, 1993
+ *	The Regents of the University of California.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ *	@(#)queue.h	8.5 (Berkeley) 8/20/94
+ */
+
+#ifndef	_SYS_QUEUE_H_
+#define	_SYS_QUEUE_H_
+
+/*
+ * This file defines five types of data structures: singly-linked lists, 
+ * lists, simple queues, tail queues, and circular queues.
+ *
+ *
+ * A singly-linked list is headed by a single forward pointer. The elements
+ * are singly linked for minimum space and pointer manipulation overhead at
+ * the expense of O(n) removal for arbitrary elements. New elements can be
+ * added to the list after an existing element or at the head of the list.
+ * Elements being removed from the head of the list should use the explicit
+ * macro for this purpose for optimum efficiency. A singly-linked list may
+ * only be traversed in the forward direction.  Singly-linked lists are ideal
+ * for applications with large datasets and few or no removals or for
+ * implementing a LIFO queue.
+ *
+ * A list is headed by a single forward pointer (or an array of forward
+ * pointers for a hash table header). The elements are doubly linked
+ * so that an arbitrary element can be removed without a need to
+ * traverse the list. New elements can be added to the list before
+ * or after an existing element or at the head of the list. A list
+ * may only be traversed in the forward direction.
+ *
+ * A simple queue is headed by a pair of pointers, one the head of the
+ * list and the other to the tail of the list. The elements are singly
+ * linked to save space, so elements can only be removed from the
+ * head of the list. New elements can be added to the list before or after
+ * an existing element, at the head of the list, or at the end of the
+ * list. A simple queue may only be traversed in the forward direction.
+ *
+ * A tail queue is headed by a pair of pointers, one to the head of the
+ * list and the other to the tail of the list. The elements are doubly
+ * linked so that an arbitrary element can be removed without a need to
+ * traverse the list. New elements can be added to the list before or
+ * after an existing element, at the head of the list, or at the end of
+ * the list. A tail queue may be traversed in either direction.
+ *
+ * A circle queue is headed by a pair of pointers, one to the head of the
+ * list and the other to the tail of the list. The elements are doubly
+ * linked so that an arbitrary element can be removed without a need to
+ * traverse the list. New elements can be added to the list before or after
+ * an existing element, at the head of the list, or at the end of the list.
+ * A circle queue may be traversed in either direction, but has a more
+ * complex end of list detection.
+ *
+ * For details on the use of these macros, see the queue(3) manual page.
+ */
+
+#if defined(QUEUE_MACRO_DEBUG) || (defined(_KERNEL) && defined(DIAGNOSTIC))
+#define _Q_INVALIDATE(a) (a) = ((void *)-1)
+#else
+#define _Q_INVALIDATE(a)
+#endif
+
+/*
+ * Singly-linked List definitions.
+ */
+#define SLIST_HEAD(name, type)						\
+struct name {								\
+	struct type *slh_first;	/* first element */			\
+}
+ 
+#define	SLIST_HEAD_INITIALIZER(head)					\
+	{ NULL }
+ 
+#define SLIST_ENTRY(type)						\
+struct {								\
+	struct type *sle_next;	/* next element */			\
+}
+ 
+/*
+ * Singly-linked List access methods.
+ */
+#define	SLIST_FIRST(head)	((head)->slh_first)
+#define	SLIST_END(head)		NULL
+#define	SLIST_EMPTY(head)	(SLIST_FIRST(head) == SLIST_END(head))
+#define	SLIST_NEXT(elm, field)	((elm)->field.sle_next)
+
+#define	SLIST_FOREACH(var, head, field)					\
+	for((var) = SLIST_FIRST(head);					\
+	    (var) != SLIST_END(head);					\
+	    (var) = SLIST_NEXT(var, field))
+
+#define	SLIST_FOREACH_SAFE(var, head, field, tvar)			\
+	for ((var) = SLIST_FIRST(head);				\
+	    (var) && ((tvar) = SLIST_NEXT(var, field), 1);		\
+	    (var) = (tvar))
+
+/*
+ * Singly-linked List functions.
+ */
+#define	SLIST_INIT(head) {						\
+	SLIST_FIRST(head) = SLIST_END(head);				\
+}
+
+#define	SLIST_INSERT_AFTER(slistelm, elm, field) do {			\
+	(elm)->field.sle_next = (slistelm)->field.sle_next;		\
+	(slistelm)->field.sle_next = (elm);				\
+} while (0)
+
+#define	SLIST_INSERT_HEAD(head, elm, field) do {			\
+	(elm)->field.sle_next = (head)->slh_first;			\
+	(head)->slh_first = (elm);					\
+} while (0)
+
+#define	SLIST_REMOVE_AFTER(elm, field) do {				\
+	(elm)->field.sle_next = (elm)->field.sle_next->field.sle_next;	\
+} while (0)
+
+#define	SLIST_REMOVE_HEAD(head, field) do {				\
+	(head)->slh_first = (head)->slh_first->field.sle_next;		\
+} while (0)
+
+#define SLIST_REMOVE(head, elm, type, field) do {			\
+	if ((head)->slh_first == (elm)) {				\
+		SLIST_REMOVE_HEAD((head), field);			\
+	} else {							\
+		struct type *curelm = (head)->slh_first;		\
+									\
+		while (curelm->field.sle_next != (elm))			\
+			curelm = curelm->field.sle_next;		\
+		curelm->field.sle_next =				\
+		    curelm->field.sle_next->field.sle_next;		\
+		_Q_INVALIDATE((elm)->field.sle_next);			\
+	}								\
+} while (0)
+
+/*
+ * List definitions.
+ */
+#define LIST_HEAD(name, type)						\
+struct name {								\
+	struct type *lh_first;	/* first element */			\
+}
+
+#define LIST_HEAD_INITIALIZER(head)					\
+	{ NULL }
+
+#define LIST_ENTRY(type)						\
+struct {								\
+	struct type *le_next;	/* next element */			\
+	struct type **le_prev;	/* address of previous next element */	\
+}
+
+/*
+ * List access methods
+ */
+#define	LIST_FIRST(head)		((head)->lh_first)
+#define	LIST_END(head)			NULL
+#define	LIST_EMPTY(head)		(LIST_FIRST(head) == LIST_END(head))
+#define	LIST_NEXT(elm, field)		((elm)->field.le_next)
+
+#define LIST_FOREACH(var, head, field)					\
+	for((var) = LIST_FIRST(head);					\
+	    (var)!= LIST_END(head);					\
+	    (var) = LIST_NEXT(var, field))
+
+#define	LIST_FOREACH_SAFE(var, head, field, tvar)			\
+	for ((var) = LIST_FIRST(head);				\
+	    (var) && ((tvar) = LIST_NEXT(var, field), 1);		\
+	    (var) = (tvar))
+
+/*
+ * List functions.
+ */
+#define	LIST_INIT(head) do {						\
+	LIST_FIRST(head) = LIST_END(head);				\
+} while (0)
+
+#define LIST_INSERT_AFTER(listelm, elm, field) do {			\
+	if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)	\
+		(listelm)->field.le_next->field.le_prev =		\
+		    &(elm)->field.le_next;				\
+	(listelm)->field.le_next = (elm);				\
+	(elm)->field.le_prev = &(listelm)->field.le_next;		\
+} while (0)
+
+#define	LIST_INSERT_BEFORE(listelm, elm, field) do {			\
+	(elm)->field.le_prev = (listelm)->field.le_prev;		\
+	(elm)->field.le_next = (listelm);				\
+	*(listelm)->field.le_prev = (elm);				\
+	(listelm)->field.le_prev = &(elm)->field.le_next;		\
+} while (0)
+
+#define LIST_INSERT_HEAD(head, elm, field) do {				\
+	if (((elm)->field.le_next = (head)->lh_first) != NULL)		\
+		(head)->lh_first->field.le_prev = &(elm)->field.le_next;\
+	(head)->lh_first = (elm);					\
+	(elm)->field.le_prev = &(head)->lh_first;			\
+} while (0)
+
+#define LIST_REMOVE(elm, field) do {					\
+	if ((elm)->field.le_next != NULL)				\
+		(elm)->field.le_next->field.le_prev =			\
+		    (elm)->field.le_prev;				\
+	*(elm)->field.le_prev = (elm)->field.le_next;			\
+	_Q_INVALIDATE((elm)->field.le_prev);				\
+	_Q_INVALIDATE((elm)->field.le_next);				\
+} while (0)
+
+#define LIST_REPLACE(elm, elm2, field) do {				\
+	if (((elm2)->field.le_next = (elm)->field.le_next) != NULL)	\
+		(elm2)->field.le_next->field.le_prev =			\
+		    &(elm2)->field.le_next;				\
+	(elm2)->field.le_prev = (elm)->field.le_prev;			\
+	*(elm2)->field.le_prev = (elm2);				\
+	_Q_INVALIDATE((elm)->field.le_prev);				\
+	_Q_INVALIDATE((elm)->field.le_next);				\
+} while (0)
+
+/*
+ * Simple queue definitions.
+ */
+#define SIMPLEQ_HEAD(name, type)					\
+struct name {								\
+	struct type *sqh_first;	/* first element */			\
+	struct type **sqh_last;	/* addr of last next element */		\
+}
+
+#define SIMPLEQ_HEAD_INITIALIZER(head)					\
+	{ NULL, &(head).sqh_first }
+
+#define SIMPLEQ_ENTRY(type)						\
+struct {								\
+	struct type *sqe_next;	/* next element */			\
+}
+
+/*
+ * Simple queue access methods.
+ */
+#define	SIMPLEQ_FIRST(head)	    ((head)->sqh_first)
+#define	SIMPLEQ_END(head)	    NULL
+#define	SIMPLEQ_EMPTY(head)	    (SIMPLEQ_FIRST(head) == SIMPLEQ_END(head))
+#define	SIMPLEQ_NEXT(elm, field)    ((elm)->field.sqe_next)
+
+#define SIMPLEQ_FOREACH(var, head, field)				\
+	for((var) = SIMPLEQ_FIRST(head);				\
+	    (var) != SIMPLEQ_END(head);					\
+	    (var) = SIMPLEQ_NEXT(var, field))
+
+#define	SIMPLEQ_FOREACH_SAFE(var, head, field, tvar)			\
+	for ((var) = SIMPLEQ_FIRST(head);				\
+	    (var) && ((tvar) = SIMPLEQ_NEXT(var, field), 1);		\
+	    (var) = (tvar))
+
+/*
+ * Simple queue functions.
+ */
+#define	SIMPLEQ_INIT(head) do {						\
+	(head)->sqh_first = NULL;					\
+	(head)->sqh_last = &(head)->sqh_first;				\
+} while (0)
+
+#define SIMPLEQ_INSERT_HEAD(head, elm, field) do {			\
+	if (((elm)->field.sqe_next = (head)->sqh_first) == NULL)	\
+		(head)->sqh_last = &(elm)->field.sqe_next;		\
+	(head)->sqh_first = (elm);					\
+} while (0)
+
+#define SIMPLEQ_INSERT_TAIL(head, elm, field) do {			\
+	(elm)->field.sqe_next = NULL;					\
+	*(head)->sqh_last = (elm);					\
+	(head)->sqh_last = &(elm)->field.sqe_next;			\
+} while (0)
+
+#define SIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do {		\
+	if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)\
+		(head)->sqh_last = &(elm)->field.sqe_next;		\
+	(listelm)->field.sqe_next = (elm);				\
+} while (0)
+
+#define SIMPLEQ_REMOVE_HEAD(head, field) do {			\
+	if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL) \
+		(head)->sqh_last = &(head)->sqh_first;			\
+} while (0)
+
+#define SIMPLEQ_REMOVE_AFTER(head, elm, field) do {			\
+	if (((elm)->field.sqe_next = (elm)->field.sqe_next->field.sqe_next) \
+	    == NULL)							\
+		(head)->sqh_last = &(elm)->field.sqe_next;		\
+} while (0)
+
+/*
+ * Tail queue definitions.
+ */
+#define TAILQ_HEAD(name, type)						\
+struct name {								\
+	struct type *tqh_first;	/* first element */			\
+	struct type **tqh_last;	/* addr of last next element */		\
+}
+
+#define TAILQ_HEAD_INITIALIZER(head)					\
+	{ NULL, &(head).tqh_first }
+
+#define TAILQ_ENTRY(type)						\
+struct {								\
+	struct type *tqe_next;	/* next element */			\
+	struct type **tqe_prev;	/* address of previous next element */	\
+}
+
+/* 
+ * tail queue access methods 
+ */
+#define	TAILQ_FIRST(head)		((head)->tqh_first)
+#define	TAILQ_END(head)			NULL
+#define	TAILQ_NEXT(elm, field)		((elm)->field.tqe_next)
+#define TAILQ_LAST(head, headname)					\
+	(*(((struct headname *)((head)->tqh_last))->tqh_last))
+/* XXX */
+#define TAILQ_PREV(elm, headname, field)				\
+	(*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
+#define	TAILQ_EMPTY(head)						\
+	(TAILQ_FIRST(head) == TAILQ_END(head))
+
+#define TAILQ_FOREACH(var, head, field)					\
+	for((var) = TAILQ_FIRST(head);					\
+	    (var) != TAILQ_END(head);					\
+	    (var) = TAILQ_NEXT(var, field))
+
+#define	TAILQ_FOREACH_SAFE(var, head, field, tvar)			\
+	for ((var) = TAILQ_FIRST(head);					\
+	    (var) != TAILQ_END(head) &&					\
+	    ((tvar) = TAILQ_NEXT(var, field), 1);			\
+	    (var) = (tvar))
+
+
+#define TAILQ_FOREACH_REVERSE(var, head, headname, field)		\
+	for((var) = TAILQ_LAST(head, headname);				\
+	    (var) != TAILQ_END(head);					\
+	    (var) = TAILQ_PREV(var, headname, field))
+
+#define	TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)	\
+	for ((var) = TAILQ_LAST(head, headname);			\
+	    (var) != TAILQ_END(head) &&					\
+	    ((tvar) = TAILQ_PREV(var, headname, field), 1);		\
+	    (var) = (tvar))
+
+/*
+ * Tail queue functions.
+ */
+#define	TAILQ_INIT(head) do {						\
+	(head)->tqh_first = NULL;					\
+	(head)->tqh_last = &(head)->tqh_first;				\
+} while (0)
+
+#define TAILQ_INSERT_HEAD(head, elm, field) do {			\
+	if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)	\
+		(head)->tqh_first->field.tqe_prev =			\
+		    &(elm)->field.tqe_next;				\
+	else								\
+		(head)->tqh_last = &(elm)->field.tqe_next;		\
+	(head)->tqh_first = (elm);					\
+	(elm)->field.tqe_prev = &(head)->tqh_first;			\
+} while (0)
+
+#define TAILQ_INSERT_TAIL(head, elm, field) do {			\
+	(elm)->field.tqe_next = NULL;					\
+	(elm)->field.tqe_prev = (head)->tqh_last;			\
+	*(head)->tqh_last = (elm);					\
+	(head)->tqh_last = &(elm)->field.tqe_next;			\
+} while (0)
+
+#define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {		\
+	if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\
+		(elm)->field.tqe_next->field.tqe_prev =			\
+		    &(elm)->field.tqe_next;				\
+	else								\
+		(head)->tqh_last = &(elm)->field.tqe_next;		\
+	(listelm)->field.tqe_next = (elm);				\
+	(elm)->field.tqe_prev = &(listelm)->field.tqe_next;		\
+} while (0)
+
+#define	TAILQ_INSERT_BEFORE(listelm, elm, field) do {			\
+	(elm)->field.tqe_prev = (listelm)->field.tqe_prev;		\
+	(elm)->field.tqe_next = (listelm);				\
+	*(listelm)->field.tqe_prev = (elm);				\
+	(listelm)->field.tqe_prev = &(elm)->field.tqe_next;		\
+} while (0)
+
+#define TAILQ_REMOVE(head, elm, field) do {				\
+	if (((elm)->field.tqe_next) != NULL)				\
+		(elm)->field.tqe_next->field.tqe_prev =			\
+		    (elm)->field.tqe_prev;				\
+	else								\
+		(head)->tqh_last = (elm)->field.tqe_prev;		\
+	*(elm)->field.tqe_prev = (elm)->field.tqe_next;			\
+	_Q_INVALIDATE((elm)->field.tqe_prev);				\
+	_Q_INVALIDATE((elm)->field.tqe_next);				\
+} while (0)
+
+#define TAILQ_REPLACE(head, elm, elm2, field) do {			\
+	if (((elm2)->field.tqe_next = (elm)->field.tqe_next) != NULL)	\
+		(elm2)->field.tqe_next->field.tqe_prev =		\
+		    &(elm2)->field.tqe_next;				\
+	else								\
+		(head)->tqh_last = &(elm2)->field.tqe_next;		\
+	(elm2)->field.tqe_prev = (elm)->field.tqe_prev;			\
+	*(elm2)->field.tqe_prev = (elm2);				\
+	_Q_INVALIDATE((elm)->field.tqe_prev);				\
+	_Q_INVALIDATE((elm)->field.tqe_next);				\
+} while (0)
+
+/*
+ * Circular queue definitions.
+ */
+#define CIRCLEQ_HEAD(name, type)					\
+struct name {								\
+	struct type *cqh_first;		/* first element */		\
+	struct type *cqh_last;		/* last element */		\
+}
+
+#define CIRCLEQ_HEAD_INITIALIZER(head)					\
+	{ CIRCLEQ_END(&head), CIRCLEQ_END(&head) }
+
+#define CIRCLEQ_ENTRY(type)						\
+struct {								\
+	struct type *cqe_next;		/* next element */		\
+	struct type *cqe_prev;		/* previous element */		\
+}
+
+/*
+ * Circular queue access methods 
+ */
+#define	CIRCLEQ_FIRST(head)		((head)->cqh_first)
+#define	CIRCLEQ_LAST(head)		((head)->cqh_last)
+#define	CIRCLEQ_END(head)		((void *)(head))
+#define	CIRCLEQ_NEXT(elm, field)	((elm)->field.cqe_next)
+#define	CIRCLEQ_PREV(elm, field)	((elm)->field.cqe_prev)
+#define	CIRCLEQ_EMPTY(head)						\
+	(CIRCLEQ_FIRST(head) == CIRCLEQ_END(head))
+
+#define CIRCLEQ_FOREACH(var, head, field)				\
+	for((var) = CIRCLEQ_FIRST(head);				\
+	    (var) != CIRCLEQ_END(head);					\
+	    (var) = CIRCLEQ_NEXT(var, field))
+
+#define	CIRCLEQ_FOREACH_SAFE(var, head, field, tvar)			\
+	for ((var) = CIRCLEQ_FIRST(head);				\
+	    (var) != CIRCLEQ_END(head) &&				\
+	    ((tvar) = CIRCLEQ_NEXT(var, field), 1);			\
+	    (var) = (tvar))
+
+#define CIRCLEQ_FOREACH_REVERSE(var, head, field)			\
+	for((var) = CIRCLEQ_LAST(head);					\
+	    (var) != CIRCLEQ_END(head);					\
+	    (var) = CIRCLEQ_PREV(var, field))
+
+#define	CIRCLEQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)	\
+	for ((var) = CIRCLEQ_LAST(head, headname);			\
+	    (var) != CIRCLEQ_END(head) && 				\
+	    ((tvar) = CIRCLEQ_PREV(var, headname, field), 1);		\
+	    (var) = (tvar))
+
+/*
+ * Circular queue functions.
+ */
+#define	CIRCLEQ_INIT(head) do {						\
+	(head)->cqh_first = CIRCLEQ_END(head);				\
+	(head)->cqh_last = CIRCLEQ_END(head);				\
+} while (0)
+
+#define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {		\
+	(elm)->field.cqe_next = (listelm)->field.cqe_next;		\
+	(elm)->field.cqe_prev = (listelm);				\
+	if ((listelm)->field.cqe_next == CIRCLEQ_END(head))		\
+		(head)->cqh_last = (elm);				\
+	else								\
+		(listelm)->field.cqe_next->field.cqe_prev = (elm);	\
+	(listelm)->field.cqe_next = (elm);				\
+} while (0)
+
+#define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {		\
+	(elm)->field.cqe_next = (listelm);				\
+	(elm)->field.cqe_prev = (listelm)->field.cqe_prev;		\
+	if ((listelm)->field.cqe_prev == CIRCLEQ_END(head))		\
+		(head)->cqh_first = (elm);				\
+	else								\
+		(listelm)->field.cqe_prev->field.cqe_next = (elm);	\
+	(listelm)->field.cqe_prev = (elm);				\
+} while (0)
+
+#define CIRCLEQ_INSERT_HEAD(head, elm, field) do {			\
+	(elm)->field.cqe_next = (head)->cqh_first;			\
+	(elm)->field.cqe_prev = CIRCLEQ_END(head);			\
+	if ((head)->cqh_last == CIRCLEQ_END(head))			\
+		(head)->cqh_last = (elm);				\
+	else								\
+		(head)->cqh_first->field.cqe_prev = (elm);		\
+	(head)->cqh_first = (elm);					\
+} while (0)
+
+#define CIRCLEQ_INSERT_TAIL(head, elm, field) do {			\
+	(elm)->field.cqe_next = CIRCLEQ_END(head);			\
+	(elm)->field.cqe_prev = (head)->cqh_last;			\
+	if ((head)->cqh_first == CIRCLEQ_END(head))			\
+		(head)->cqh_first = (elm);				\
+	else								\
+		(head)->cqh_last->field.cqe_next = (elm);		\
+	(head)->cqh_last = (elm);					\
+} while (0)
+
+#define	CIRCLEQ_REMOVE(head, elm, field) do {				\
+	if ((elm)->field.cqe_next == CIRCLEQ_END(head))			\
+		(head)->cqh_last = (elm)->field.cqe_prev;		\
+	else								\
+		(elm)->field.cqe_next->field.cqe_prev =			\
+		    (elm)->field.cqe_prev;				\
+	if ((elm)->field.cqe_prev == CIRCLEQ_END(head))			\
+		(head)->cqh_first = (elm)->field.cqe_next;		\
+	else								\
+		(elm)->field.cqe_prev->field.cqe_next =			\
+		    (elm)->field.cqe_next;				\
+	_Q_INVALIDATE((elm)->field.cqe_prev);				\
+	_Q_INVALIDATE((elm)->field.cqe_next);				\
+} while (0)
+
+#define CIRCLEQ_REPLACE(head, elm, elm2, field) do {			\
+	if (((elm2)->field.cqe_next = (elm)->field.cqe_next) ==		\
+	    CIRCLEQ_END(head))						\
+		(head).cqh_last = (elm2);				\
+	else								\
+		(elm2)->field.cqe_next->field.cqe_prev = (elm2);	\
+	if (((elm2)->field.cqe_prev = (elm)->field.cqe_prev) ==		\
+	    CIRCLEQ_END(head))						\
+		(head).cqh_first = (elm2);				\
+	else								\
+		(elm2)->field.cqe_prev->field.cqe_next = (elm2);	\
+	_Q_INVALIDATE((elm)->field.cqe_prev);				\
+	_Q_INVALIDATE((elm)->field.cqe_next);				\
+} while (0)
+
+#endif	/* !_SYS_QUEUE_H_ */