1 files changed, 217 insertions, 0 deletions
diff --git a/lib/list_sort.c b/lib/list_sort.c
new file mode 100644
index 0000000..4b5cb79
--- /dev/null
+++ b/lib/list_sort.c
@@ -0,0 +1,217 @@
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/list_sort.h>
+#include <linux/slab.h>
+#include <linux/list.h>
+
+#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.
+ */
+static struct list_head *merge(void *priv,
+				int (*cmp)(void *priv, struct list_head *a,
+					struct list_head *b),
+				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)(priv, a, b) <= 0) {
+			tail->next = a;
+			a = a->next;
+		} else {
+			tail->next = b;
+			b = b->next;
+		}
+		tail = tail->next;
+	}
+	tail->next = 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.
+ */
+static void merge_and_restore_back_links(void *priv,
+				int (*cmp)(void *priv, struct list_head *a,
+					struct list_head *b),
+				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)(priv, a, b) <= 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 ? : 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)(priv, tail, tail);
+
+		tail->next->prev = tail;
+		tail = tail->next;
+	} while (tail->next);
+
+	tail->next = head;
+	head->prev = tail;
+}
+
+/**
+ * list_sort - sort a list
+ * @priv: private data, opaque to list_sort(), passed to @cmp
+ * @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.
+ */
+void list_sort(void *priv, struct list_head *head,
+		int (*cmp)(void *priv, struct list_head *a,
+			struct list_head *b))
+{
+	struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
+						-- last slot is a sentinel */
+	int lev;  /* index into part[] */
+	int 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(priv, cmp, part[lev], cur);
+			part[lev] = NULL;
+		}
+		if (lev > max_lev) {
+			if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
+				printk_once(KERN_DEBUG "list passed to"
+					" list_sort() too long for"
+					" efficiency\n");
+				lev--;
+			}
+			max_lev = lev;
+		}
+		part[lev] = cur;
+	}
+
+	for (lev = 0; lev < max_lev; lev++)
+		if (part[lev])
+			list = merge(priv, cmp, part[lev], list);
+
+	merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
+}
+EXPORT_SYMBOL(list_sort);
+
+#ifdef DEBUG_LIST_SORT
+struct debug_el {
+	struct list_head l_h;
+	int value;
+	unsigned serial;
+};
+
+static int cmp(void *priv, struct list_head *a, struct list_head *b)
+{
+	return container_of(a, struct debug_el, l_h)->value
+	     - container_of(b, struct debug_el, l_h)->value;
+}
+
+/*
+ * The pattern of set bits in the list length determines which cases
+ * are hit in list_sort().
+ */
+#define LIST_SORT_TEST_LENGTH (512+128+2) /* not including head */
+
+static int __init list_sort_test(void)
+{
+	int i, r = 1, count;
+	struct list_head *head = kmalloc(sizeof(*head), GFP_KERNEL);
+	struct list_head *cur;
+
+	printk(KERN_WARNING "testing list_sort()\n");
+
+	cur = head;
+	for (i = 0; i < LIST_SORT_TEST_LENGTH; i++) {
+		struct debug_el *el = kmalloc(sizeof(*el), GFP_KERNEL);
+		BUG_ON(!el);
+		 /* force some equivalencies */
+		el->value = (r = (r * 725861) % 6599) % (LIST_SORT_TEST_LENGTH/3);
+		el->serial = i;
+
+		el->l_h.prev = cur;
+		cur->next = &el->l_h;
+		cur = cur->next;
+	}
+	head->prev = cur;
+
+	list_sort(NULL, head, cmp);
+
+	count = 1;
+	for (cur = head->next; cur->next != head; cur = cur->next) {
+		struct debug_el *el = container_of(cur, struct debug_el, l_h);
+		int cmp_result = cmp(NULL, cur, cur->next);
+		if (cur->next->prev != cur) {
+			printk(KERN_EMERG "list_sort() returned "
+						"a corrupted list!\n");
+			return 1;
+		} else if (cmp_result > 0) {
+			printk(KERN_EMERG "list_sort() failed to sort!\n");
+			return 1;
+		} else if (cmp_result == 0 &&
+				el->serial >= container_of(cur->next,
+					struct debug_el, l_h)->serial) {
+			printk(KERN_EMERG "list_sort() failed to preserve order"
+						 " of equivalent elements!\n");
+			return 1;
+		}
+		kfree(cur->prev);
+		count++;
+	}
+	kfree(cur);
+	if (count != LIST_SORT_TEST_LENGTH) {
+		printk(KERN_EMERG "list_sort() returned list of"
+						"different length!\n");
+		return 1;
+	}
+	return 0;
+}
+module_init(list_sort_test);
+#endif