cleancache: Make cleancache_init use a pointer for the ops

Instead of using a backend_registered to determine whether a backend is
enabled.  This allows us to remove the backend_register check and just
do 'if (cleancache_ops)'

[v1: Rebase on top of b97c4b430b0a (ramster->zcache move]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Bob Liu <lliubbo@gmail.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Andor Daam <andor.daam@googlemail.com>
Cc: Dan Magenheimer <dan.magenheimer@oracle.com>
Cc: Florian Schmaus <fschmaus@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Stefan Hengelein <ilendir@googlemail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c
index 09c69c8..6bd4ebb 100644
--- a/drivers/staging/zcache/zcache-main.c
+++ b/drivers/staging/zcache/zcache-main.c
@@ -1576,9 +1576,9 @@
 	.init_fs = zcache_cleancache_init_fs
 };
 
-struct cleancache_ops zcache_cleancache_register_ops(void)
+struct cleancache_ops *zcache_cleancache_register_ops(void)
 {
-	struct cleancache_ops old_ops =
+	struct cleancache_ops *old_ops =
 		cleancache_register_ops(&zcache_cleancache_ops);
 
 	return old_ops;
@@ -1860,7 +1860,7 @@
 	}
 	zbud_init();
 	if (zcache_enabled && !disable_cleancache) {
-		struct cleancache_ops old_ops;
+		struct cleancache_ops *old_ops;
 
 		register_shrinker(&zcache_shrinker);
 		old_ops = zcache_cleancache_register_ops();
@@ -1870,7 +1870,7 @@
 		pr_info("%s: cleancache: ignorenonactive = %d\n",
 			namestr, !disable_cleancache_ignore_nonactive);
 #endif
-		if (old_ops.init_fs != NULL)
+		if (old_ops != NULL)
 			pr_warn("%s: cleancache_ops overridden\n", namestr);
 	}
 	if (zcache_enabled && !disable_frontswap) {
diff --git a/drivers/xen/tmem.c b/drivers/xen/tmem.c
index 7a01a5f..fd79eab0 100644
--- a/drivers/xen/tmem.c
+++ b/drivers/xen/tmem.c
@@ -236,7 +236,7 @@
 }
 __setup("nocleancache", no_cleancache);
 
-static struct cleancache_ops __initdata tmem_cleancache_ops = {
+static struct cleancache_ops tmem_cleancache_ops = {
 	.put_page = tmem_cleancache_put_page,
 	.get_page = tmem_cleancache_get_page,
 	.invalidate_page = tmem_cleancache_flush_page,
@@ -392,9 +392,9 @@
 	BUG_ON(sizeof(struct cleancache_filekey) != sizeof(struct tmem_oid));
 	if (tmem_enabled && use_cleancache) {
 		char *s = "";
-		struct cleancache_ops old_ops =
+		struct cleancache_ops *old_ops =
 			cleancache_register_ops(&tmem_cleancache_ops);
-		if (old_ops.init_fs != NULL)
+		if (old_ops)
 			s = " (WARNING: cleancache_ops overridden)";
 		printk(KERN_INFO "cleancache enabled, RAM provided by "
 				 "Xen Transcendent Memory%s\n", s);