md/raid5: factor out code for changing size of stripe cache.

Separate the actual 'change' code from the sysfs interface
so that it can eventually be called internally.
Signed-off-by: NNeilBrown <neilb@suse.de>

drivers/md/raid5.c

@@ -4566,23 +4566,15 @@ raid5_show_stripe_cache_size(mddev_t *mddev, char *page)
 		return 0;
 }
 
-static ssize_t
-raid5_store_stripe_cache_size(mddev_t *mddev, const char *page, size_t len)
+int
+raid5_set_cache_size(mddev_t *mddev, int size)
 {
 	raid5_conf_t *conf = mddev->private;
-	unsigned long new;
 	int err;
 
-	if (len >= PAGE_SIZE)
+	if (size <= 16 || size > 32768)
 		return -EINVAL;
-	if (!conf)
-		return -ENODEV;
-
-	if (strict_strtoul(page, 10, &new))
-		return -EINVAL;
-	if (new <= 16 || new > 32768)
-		return -EINVAL;
-	while (new < conf->max_nr_stripes) {
+	while (size < conf->max_nr_stripes) {
 		if (drop_one_stripe(conf))
 			conf->max_nr_stripes--;
 		else
@@ -4591,11 +4583,32 @@ raid5_store_stripe_cache_size(mddev_t *mddev, const char *page, size_t len)
 	err = md_allow_write(mddev);
 	if (err)
 		return err;
-	while (new > conf->max_nr_stripes) {
+	while (size > conf->max_nr_stripes) {
 		if (grow_one_stripe(conf))
 			conf->max_nr_stripes++;
 		else break;
 	}
+	return 0;
+}
+EXPORT_SYMBOL(raid5_set_cache_size);
+
+static ssize_t
+raid5_store_stripe_cache_size(mddev_t *mddev, const char *page, size_t len)
+{
+	raid5_conf_t *conf = mddev->private;
+	unsigned long new;
+	int err;
+
+	if (len >= PAGE_SIZE)
+		return -EINVAL;
+	if (!conf)
+		return -ENODEV;
+
+	if (strict_strtoul(page, 10, &new))
+		return -EINVAL;
+	err = raid5_set_cache_size(mddev, new);
+	if (err)
+		return err;
 	return len;
 }
 

drivers/md/raid5.h

@@ -497,4 +497,5 @@ static inline int algorithm_is_DDF(int layout)
 {
 	return layout >= 8 && layout <= 10;
 }
+extern int raid5_set_cache_size(mddev_t *mddev, int size);
 #endif