Hook in list.h from Linux

Unfortunately in CCAN they made separation of list_head into list_head &
list_node (for better type safety I suppose), but that leads e.g. to
inablility to insert element in the middle of the list.

We take the code from util-linux.git (v2.25-165-g9138d6f)[1] which claims
LGPL license for it, with which we are fine.

[1] https://git.kernel.org/cgit/utils/util-linux/util-linux.git/tree/include/list.h?id=v2.25-165-g9138d6f

3rdparty/include/linux/list.h

+/* from util-linux.git v2.25-165-g9138d6f include/list.h */
+/*
+ * Copyright (C) 2008 Karel Zak <kzak@redhat.com>
+ * Copyright (C) 1999-2008 by Theodore Ts'o
+ *
+ * This file may be redistributed under the terms of the
+ * GNU Lesser General Public License.
+ *
+ * (based on list.h from e2fsprogs)
+ * Merge sort based on kernel's implementation.
+ */
+
+#ifndef UTIL_LINUX_LIST_H
+#define UTIL_LINUX_LIST_H
+
+/* TODO: use AC_C_INLINE */
+#ifdef __GNUC__
+#define _INLINE_ static __inline__
+#else                         /* For Watcom C */
+#define _INLINE_ static inline
+#endif
+
+/*
+ * Simple doubly linked list implementation.
+ *
+ * Some of the internal functions ("__xxx") are useful when
+ * manipulating whole lists rather than single entries, as
+ * sometimes we already know the next/prev entries and we can
+ * generate better code by using them directly rather than
+ * using the generic single-entry routines.
+ */
+
+struct list_head {
+	struct list_head *next, *prev;
+};
+
+#define LIST_HEAD_INIT(name) { &(name), &(name) }
+
+#define LIST_HEAD(name) \
+	struct list_head name = LIST_HEAD_INIT(name)
+
+#define INIT_LIST_HEAD(ptr) do { \
+	(ptr)->next = (ptr); (ptr)->prev = (ptr); \
+} while (0)
+
+/*
+ * Insert a new entry between two known consecutive entries.
+ *
+ * This is only for internal list manipulation where we know
+ * the prev/next entries already!
+ */
+_INLINE_ void __list_add(struct list_head * add,
+	struct list_head * prev,
+	struct list_head * next)
+{
+	next->prev = add;
+	add->next = next;
+	add->prev = prev;
+	prev->next = add;
+}
+
+/**
+ * list_add - add a new entry
+ * @add:	new entry to be added
+ * @head:	list head to add it after
+ *
+ * Insert a new entry after the specified head.
+ * This is good for implementing stacks.
+ */
+_INLINE_ void list_add(struct list_head *add, struct list_head *head)
+{
+	__list_add(add, head, head->next);
+}
+
+/**
+ * list_add_tail - add a new entry
+ * @add:	new entry to be added
+ * @head:	list head to add it before
+ *
+ * Insert a new entry before the specified head.
+ * This is useful for implementing queues.
+ */
+_INLINE_ void list_add_tail(struct list_head *add, struct list_head *head)
+{
+	__list_add(add, head->prev, head);
+}
+
+/*
+ * Delete a list entry by making the prev/next entries
+ * point to each other.
+ *
+ * This is only for internal list manipulation where we know
+ * the prev/next entries already!
+ */
+_INLINE_ void __list_del(struct list_head * prev,
+				  struct list_head * next)
+{
+	next->prev = prev;
+	prev->next = next;
+}
+
+/**
+ * list_del - deletes entry from list.
+ * @entry:	the element to delete from the list.
+ *
+ * list_empty() on @entry does not return true after this, @entry is
+ * in an undefined state.
+ */
+_INLINE_ void list_del(struct list_head *entry)
+{
+	__list_del(entry->prev, entry->next);
+}
+
+/**
+ * list_del_init - deletes entry from list and reinitialize it.
+ * @entry:	the element to delete from the list.
+ */
+_INLINE_ void list_del_init(struct list_head *entry)
+{
+	__list_del(entry->prev, entry->next);
+	INIT_LIST_HEAD(entry);
+}
+
+/**
+ * list_empty - tests whether a list is empty
+ * @head:	the list to test.
+ */
+_INLINE_ int list_empty(struct list_head *head)
+{
+	return head->next == head;
+}
+
+/**
+ * list_entry_is_last - tests whether is entry last in the list
+ * @entry:	the entry to test.
+ * @head:	the list to test.
+ */
+_INLINE_ int list_entry_is_last(struct list_head *entry, struct list_head *head)
+{
+	return head->prev == entry;
+}
+
+/**
+ * list_splice - join two lists
+ * @list:	the new list to add.
+ * @head:	the place to add it in the first list.
+ */
+_INLINE_ void list_splice(struct list_head *list, struct list_head *head)
+{
+	struct list_head *first = list->next;
+
+	if (first != list) {
+		struct list_head *last = list->prev;
+		struct list_head *at = head->next;
+
+		first->prev = head;
+		head->next = first;
+
+		last->next = at;
+		at->prev = last;
+	}
+}
+
+/**
+ * list_entry - get the struct for this entry
+ * @ptr:	the &struct list_head pointer.
+ * @type:	the type of the struct this is embedded in.
+ * @member:	the name of the list_struct within the struct.
+ */
+#define list_entry(ptr, type, member) ({              \
+	const typeof( ((type *)0)->member ) *__mptr = (ptr);   \
+	(type *)( (char *)__mptr - offsetof(type,member) );})
+
+
+#define list_first_entry(head, type, member) \
+	((head) && (head)->next != (head) ? list_entry((head)->next, type, member) : NULL)
+
+#define list_last_entry(head, type, member) \
+	((head) && (head)->prev != (head) ? list_entry((head)->prev, type, member) : NULL)
+
+/**
+ * list_for_each - iterate over elements in a list
+ * @pos:	the &struct list_head to use as a loop counter.
+ * @head:	the head for your list.
+ */
+#define list_for_each(pos, head) \
+	for (pos = (head)->next; pos != (head); pos = pos->next)
+
+/**
+ * list_for_each_backwardly - iterate over elements in a list in reverse
+ * @pos:	the &struct list_head to use as a loop counter.
+ * @head:	the head for your list.
+ */
+#define list_for_each_backwardly(pos, head) \
+	for (pos = (head)->prev; pos != (head); pos = pos->prev)
+
+/**
+ * list_for_each_safe - iterate over elements in a list, but don't dereference
+ *                      pos after the body is done (in case it is freed)
+ * @pos:	the &struct list_head to use as a loop counter.
+ * @pnext:	the &struct list_head to use as a pointer to the next item.
+ * @head:	the head for your list (not included in iteration).
+ */
+#define list_for_each_safe(pos, pnext, head) \
+	for (pos = (head)->next, pnext = pos->next; pos != (head); \
+	     pos = pnext, pnext = pos->next)
+
+#define MAX_LIST_LENGTH_BITS 20
+
+/*
+ * Returns a list organized in an intermediate format suited
+ * to chaining of merge() calls: null-terminated, no reserved or
+ * sentinel head node, "prev" links not maintained.
+ */
+_INLINE_ struct list_head *merge(int (*cmp)(struct list_head *a,
+					  struct list_head *b,
+					  void *data),
+			       void *data,
+			       struct list_head *a, struct list_head *b)
+{
+	struct list_head head, *tail = &head;
+
+	while (a && b) {
+		/* if equal, take 'a' -- important for sort stability */
+		if ((*cmp)(a, b, data) <= 0) {
+			tail->next = a;
+			a = a->next;
+		} else {
+			tail->next = b;
+			b = b->next;
+		}
+		tail = tail->next;
+	}
+	tail->next = a ? a : b;
+	return head.next;
+}
+
+/*
+ * Combine final list merge with restoration of standard doubly-linked
+ * list structure.  This approach duplicates code from merge(), but
+ * runs faster than the tidier alternatives of either a separate final
+ * prev-link restoration pass, or maintaining the prev links
+ * throughout.
+ */
+_INLINE_ void merge_and_restore_back_links(int (*cmp)(struct list_head *a,
+						    struct list_head *b,
+						    void *data),
+					 void *data,
+					 struct list_head *head,
+					 struct list_head *a, struct list_head *b)
+{
+	struct list_head *tail = head;
+
+	while (a && b) {
+		/* if equal, take 'a' -- important for sort stability */
+		if ((*cmp)(a, b, data) <= 0) {
+			tail->next = a;
+			a->prev = tail;
+			a = a->next;
+		} else {
+			tail->next = b;
+			b->prev = tail;
+			b = b->next;
+		}
+		tail = tail->next;
+	}
+	tail->next = a ? a : b;
+
+	do {
+		/*
+		 * In worst cases this loop may run many iterations.
+		 * Continue callbacks to the client even though no
+		 * element comparison is needed, so the client's cmp()
+		 * routine can invoke cond_resched() periodically.
+		 */
+		(*cmp)(tail->next, tail->next, data);
+
+		tail->next->prev = tail;
+		tail = tail->next;
+	} while (tail->next);
+
+	tail->next = head;
+	head->prev = tail;
+}
+
+
+/**
+ * list_sort - sort a list
+ * @head: the list to sort
+ * @cmp: the elements comparison function
+ *
+ * This function implements "merge sort", which has O(nlog(n))
+ * complexity.
+ *
+ * The comparison function @cmp must return a negative value if @a
+ * should sort before @b, and a positive value if @a should sort after
+ * @b. If @a and @b are equivalent, and their original relative
+ * ordering is to be preserved, @cmp must return 0.
+ */
+_INLINE_ void list_sort(struct list_head *head,
+			int (*cmp)(struct list_head *a,
+				   struct list_head *b,
+				   void *data),
+			void *data)
+{
+	struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
+							   -- last slot is a sentinel */
+	size_t lev;  /* index into part[] */
+	size_t max_lev = 0;
+	struct list_head *list;
+
+	if (list_empty(head))
+		return;
+
+	memset(part, 0, sizeof(part));
+
+	head->prev->next = NULL;
+	list = head->next;
+
+	while (list) {
+		struct list_head *cur = list;
+		list = list->next;
+		cur->next = NULL;
+
+		for (lev = 0; part[lev]; lev++) {
+			cur = merge(cmp, data, part[lev], cur);
+			part[lev] = NULL;
+		}
+		if (lev > max_lev) {
+			/* list passed to list_sort() too long for efficiency */
+			if (lev >= ARRAY_SIZE(part) - 1)
+				lev--;
+			max_lev = lev;
+		}
+		part[lev] = cur;
+	}
+
+	for (lev = 0; lev < max_lev; lev++)
+		if (part[lev])
+			list = merge(cmp, data, part[lev], list);
+
+	merge_and_restore_back_links(cmp, data, head, part[max_lev], list);
+}
+
+#undef _INLINE_
+
+#endif /* UTIL_LINUX_LIST_H */