dm-multipath: ps-refcount.patch
Fixes the refcounting on the path-selectors. And, exports the
register/unregister functions.

From: Mike Christie <mikenc@us.ibm.com>

--- diff/drivers/md/dm-path-selector.c	2004-09-21 16:37:08.000000000 +0100
+++ source/drivers/md/dm-path-selector.c	2004-09-21 16:37:14.000000000 +0100
@@ -14,12 +14,14 @@
 #include <linux/slab.h>
 
 struct ps_internal {
-	struct path_selector_type pt;
+	struct path_selector_type pst;
 
 	struct list_head list;
 	long use;
 };
 
+#define pst_to_psi(__pst) container_of((__pst), struct ps_internal, pst)
+
 static LIST_HEAD(_path_selectors);
 static DECLARE_MUTEX(_lock);
 
@@ -28,8 +30,8 @@
 	struct ps_internal *li;
 
 	list_for_each_entry (li, &_path_selectors, list) {
-		if (!strcmp(name, li->pt.name))
-			return &li->pt;
+		if (!strcmp(name, li->pst.name))
+			return &li->pst;
 	}
 
 	return NULL;
@@ -37,32 +39,42 @@
 
 struct path_selector_type *dm_get_path_selector(const char *name)
 {
-	struct path_selector_type *lb;
+	struct path_selector_type *pst;
 
 	if (!name)
 		return NULL;
 
 	down(&_lock);
-	lb = __find_path_selector_type(name);
-	if (lb) {
-		struct ps_internal *li = (struct ps_internal *) lb;
-		li->use++;
+	pst = __find_path_selector_type(name);
+	if (pst) {
+		struct ps_internal *psi = pst_to_psi(pst);
+
+		if (psi->use == 0 && !try_module_get(pst->module))
+			psi = NULL;
+		else
+			psi->use++;
 	}
 	up(&_lock);
 
-	return lb;
+	return pst;
 }
 
-void dm_put_path_selector(struct path_selector_type *l)
+void dm_put_path_selector(struct path_selector_type *pst)
 {
-	struct ps_internal *li = (struct ps_internal *) l;
+	struct ps_internal *psi;
 
 	down(&_lock);
-	if (--li->use < 0)
+	pst = __find_path_selector_type(pst->name);
+	if (!pst)
+		return;
+
+	psi = pst_to_psi(pst);
+	if (--psi->use == 0)
+		module_put(psi->pst.module);
+
+	if (psi->use < 0)
 		BUG();
 	up(&_lock);
-
-	return;
 }
 
 static struct ps_internal *_alloc_path_selector(struct path_selector_type *pt)
@@ -71,7 +83,7 @@
 
 	if (psi) {
 		memset(psi, 0, sizeof(*psi));
-		memcpy(psi, pt, sizeof(*pt));
+		memcpy(&psi->pst, pt, sizeof(*pt));
 	}
 
 	return psi;
@@ -97,17 +109,20 @@
 	return r;
 }
 
+EXPORT_SYMBOL(dm_register_path_selector);
+
 int dm_unregister_path_selector(struct path_selector_type *pst)
 {
 	struct ps_internal *psi;
 
 	down(&_lock);
-	psi = (struct ps_internal *) __find_path_selector_type(pst->name);
-	if (!psi) {
+	pst = __find_path_selector_type(pst->name);
+	if (!pst) {
 		up(&_lock);
 		return -EINVAL;
 	}
 
+	psi = pst_to_psi(pst);
 	if (psi->use) {
 		up(&_lock);
 		return -ETXTBSY;
@@ -121,6 +136,8 @@
 	return 0;
 }
 
+EXPORT_SYMBOL(dm_unregister_path_selector);
+
 /*-----------------------------------------------------------------
  * Path handling code, paths are held in lists
  *---------------------------------------------------------------*/
@@ -274,6 +291,7 @@
 
 static struct path_selector_type rr_ps = {
 	.name = "round-robin",
+	.module = THIS_MODULE,
 	.table_args = 0,
 	.info_args = 0,
 	.ctr = rr_ctr,
--- diff/drivers/md/dm-path-selector.h	2004-09-21 16:37:08.000000000 +0100
+++ source/drivers/md/dm-path-selector.h	2004-09-21 16:37:14.000000000 +0100
@@ -69,6 +69,8 @@
 /* Information about a path selector type */
 struct path_selector_type {
 	char *name;
+	struct module *module;
+
 	unsigned int table_args;
 	unsigned int info_args;
 	ps_ctr_fn ctr;