lib: Introduce generic list_sort function

There are two copies of list_sort() in the tree already, one in the DRM
code, another in ubifs.  Now XFS needs this as well.  Create a generic
list_sort() function from the ubifs version and convert existing users
to it so we don't end up with yet another copy in the tree.

Signed-off-by: Dave Chinner <david@fromorbit.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Acked-by: Artem Bityutskiy <dedekind@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 95 deletions

diff --git a/fs/ubifs/gc.c b/fs/ubifs/gc.c
index 618c2701d3a7..e5a3d8e96bb7 100644
--- a/fs/ubifs/gc.c
+++ b/fs/ubifs/gc.c
@@ -54,6 +54,7 @@
  */
 
 #include <linux/pagemap.h>
+#include <linux/list_sort.h>
 #include "ubifs.h"
 
 /*
@@ -108,101 +109,6 @@ static int switch_gc_head(struct ubifs_info *c)
 }
 
 /**
- * list_sort - sort a list.
- * @priv: private data, passed to @cmp
- * @head: the list to sort
- * @cmp: the elements comparison function
- *
- * This function has been implemented by Mark J Roberts <mjr@znex.org>. It
- * implements "merge sort" which has O(nlog(n)) complexity. The list is sorted
- * in ascending order.
- *
- * The comparison function @cmp is supposed to return a negative value if @a is
- * than @b, and a positive value if @a is greater than @b. If @a and @b are
- * equivalent, then it does not matter what this function returns.
- */
-static void list_sort(void *priv, struct list_head *head,
-                      int (*cmp)(void *priv, struct list_head *a,
-                                 struct list_head *b))
-{
-        struct list_head *p, *q, *e, *list, *tail, *oldhead;
-        int insize, nmerges, psize, qsize, i;
-
-        if (list_empty(head))
-                return;
-
-        list = head->next;
-        list_del(head);
-        insize = 1;
-        for (;;) {
-                p = oldhead = list;
-                list = tail = NULL;
-                nmerges = 0;
-
-                while (p) {
-                        nmerges++;
-                        q = p;
-                        psize = 0;
-                        for (i = 0; i < insize; i++) {
-                                psize++;
-                                q = q->next == oldhead ? NULL : q->next;
-                                if (!q)
-                                        break;
-                        }
-
-                        qsize = insize;
-                        while (psize > 0 || (qsize > 0 && q)) {
-                                if (!psize) {
-                                        e = q;
-                                        q = q->next;
-                                        qsize--;
-                                        if (q == oldhead)
-                                                q = NULL;
-                                } else if (!qsize || !q) {
-                                        e = p;
-                                        p = p->next;
-                                        psize--;
-                                        if (p == oldhead)
-                                                p = NULL;
-                                } else if (cmp(priv, p, q) <= 0) {
-                                        e = p;
-                                        p = p->next;
-                                        psize--;
-                                        if (p == oldhead)
-                                                p = NULL;
-                                } else {
-                                        e = q;
-                                        q = q->next;
-                                        qsize--;
-                                        if (q == oldhead)
-                                                q = NULL;
-                                }
-                                if (tail)
-                                        tail->next = e;
-                                else
-                                        list = e;
-                                e->prev = tail;
-                                tail = e;
-                        }
-                        p = q;
-                }
-
-                tail->next = list;
-                list->prev = tail;
-
-                if (nmerges <= 1)
-                        break;
-
-                insize *= 2;
-        }
-
-        head->next = list;
-        head->prev = list->prev;
-        list->prev->next = head;
-        list->prev = head;
-}
-
-/**
  * data_nodes_cmp - compare 2 data nodes.
  * @priv: UBIFS file-system description object
  * @a: first data node