JFFS2: Use merge sort when parsing filesystem

When building the file system the existing code does an insertion into
a linked list. It attempts to speed this up by keeping a pointer to
where the last entry was inserted but it's still slow.

Now the nodes are just inserted into the list without searching
through for the correct place. This unsorted list is then sorted once
using mergesort after all the entries have been added to the list.
This speeds up the scanning of the flash file system considerably.

Signed-off-by: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>

1 files changed, 52 insertions, 0 deletions

diff --git a/fs/jffs2/mergesort.c b/fs/jffs2/mergesort.c
new file mode 100644
index 0000000000..6e633a1133
--- /dev/null
+++ b/fs/jffs2/mergesort.c
@@ -0,0 +1,52 @@
+/*
+ * This file is copyright 2001 Simon Tatham.
+ * Rewritten from original source 2006 by Dan Merillat for use in u-boot.
+ *
+ * Original code can be found at:
+ * http://www.chiark.greenend.org.uk/~sgtatham/algorithms/listsort.html
+ *
+ * SPDX-License-Identifier:	MIT
+ */
+
+#include <common.h>
+#include "jffs2_private.h"
+
+int sort_list(struct b_list *list)
+{
+	struct b_node *p, *q, *e, **tail;
+	int k, psize, qsize;
+
+	if (!list->listHead)
+		return 0;
+
+	for (k = 1; k < list->listCount; k *= 2) {
+		tail = &list->listHead;
+		for (p = q = list->listHead; p; p = q) {
+			/* step 'k' places from p; */
+			for (psize = 0; q && psize < k; psize++)
+				q = q->next;
+			qsize = k;
+
+			/* two lists, merge them. */
+			while (psize || (qsize && q)) {
+				/* merge the next element */
+				if (psize == 0 ||
+				    ((qsize && q) &&
+				     list->listCompare(p, q))) {
+					/* p is empty, or p > q, so q next */
+					e = q;
+					q = q->next;
+					qsize--;
+				} else {
+					e = p;
+					p = p->next;
+					psize--;
+				}
+				e->next = NULL; /* break accidental loops. */
+				*tail = e;
+				tail = &e->next;
+			}
+		}
+	}
+	return 0;
+}