UBUNTU: SAUCE: (no-up) bcache: decouple emitting a cached_dev CHANGE uevent

BugLink: http://bugs.launchpad.net/bugs/1729145

- decouple emitting a cached_dev CHANGE uevent which includes dev.uuid
  and dev.label from bch_cached_dev_run() which only happens when a
  bcacheX device is bound to the actual backing block device (bcache0 -> vdb)

- update bch_cached_dev_run() to invoke bch_cached_dev_emit_change() as
  needed; no functional code path changes here

- Modify register_bcache to detect a re-registering of a bcache
  cached_dev, and in that case call bcache_cached_dev_emit_change() to
Signed-off-by: Ryan Harper <ryan.harper@canonical.com>
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/md/bcache/bcache.h

@@ -906,6 +906,7 @@ int bch_flash_dev_create(struct cache_set *c, uint64_t size);
 
 int bch_cached_dev_attach(struct cached_dev *, struct cache_set *);
 void bch_cached_dev_detach(struct cached_dev *);
+void bch_cached_dev_emit_change(struct cached_dev *);
 void bch_cached_dev_run(struct cached_dev *);
 void bcache_device_stop(struct bcache_device *);
 

drivers/md/bcache/super.c

@@ -834,7 +834,7 @@ static void calc_cached_dev_sectors(struct cache_set *c)
 	c->cached_dev_sectors = sectors;
 }
 
-void bch_cached_dev_run(struct cached_dev *dc)
+void bch_cached_dev_emit_change(struct cached_dev *dc)
 {
 	struct bcache_device *d = &dc->disk;
 	char buf[SB_LABEL_SIZE + 1];
@@ -849,9 +849,18 @@ void bch_cached_dev_run(struct cached_dev *dc)
 	buf[SB_LABEL_SIZE] = '\0';
 	env[2] = kasprintf(GFP_KERNEL, "CACHED_LABEL=%s", buf);
 
+	/* won't show up in the uevent file, use udevadm monitor -e instead
+	 * only class / kset properties are persistent */
+	kobject_uevent_env(&disk_to_dev(d->disk)->kobj, KOBJ_CHANGE, env);
+	kfree(env[1]);
+	kfree(env[2]);
+
+}
+
+void bch_cached_dev_run(struct cached_dev *dc)
+{
+	struct bcache_device *d = &dc->disk;
 	if (atomic_xchg(&dc->running, 1)) {
-		kfree(env[1]);
-		kfree(env[2]);
 		return;
 	}
 
@@ -867,11 +876,9 @@ void bch_cached_dev_run(struct cached_dev *dc)
 
 	add_disk(d->disk);
 	bd_link_disk_holder(dc->bdev, dc->disk.disk);
-	/* won't show up in the uevent file, use udevadm monitor -e instead
-	 * only class / kset properties are persistent */
-	kobject_uevent_env(&disk_to_dev(d->disk)->kobj, KOBJ_CHANGE, env);
-	kfree(env[1]);
-	kfree(env[2]);
+
+	/* emit change event */
+	bch_cached_dev_emit_change(dc);
 
 	if (sysfs_create_link(&d->kobj, &disk_to_dev(d->disk)->kobj, "dev") ||
 	    sysfs_create_link(&disk_to_dev(d->disk)->kobj, &d->kobj, "bcache"))
@@ -1916,6 +1923,21 @@ static bool bch_is_open_backing(struct block_device *bdev) {
 	return false;
 }
 
+static struct cached_dev *bch_find_cached_dev(struct block_device *bdev) {
+	struct cache_set *c, *tc;
+	struct cached_dev *dc, *t;
+
+	list_for_each_entry_safe(c, tc, &bch_cache_sets, list)
+		list_for_each_entry_safe(dc, t, &c->cached_devs, list)
+			if (dc->bdev == bdev)
+				return dc;
+	list_for_each_entry_safe(dc, t, &uncached_devices, list)
+		if (dc->bdev == bdev)
+			return dc;
+
+	return NULL;
+}
+
 static bool bch_is_open_cache(struct block_device *bdev) {
 	struct cache_set *c, *tc;
 	struct cache *ca;
@@ -1941,6 +1963,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 	struct cache_sb *sb = NULL;
 	struct block_device *bdev = NULL;
 	struct page *sb_page = NULL;
+	struct cached_dev *dc = NULL;
 
 	if (!try_module_get(THIS_MODULE))
 		return -EBUSY;
@@ -1957,10 +1980,20 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 		if (bdev == ERR_PTR(-EBUSY)) {
 			bdev = lookup_bdev(strim(path), 0);
 			mutex_lock(&bch_register_lock);
-			if (!IS_ERR(bdev) && bch_is_open(bdev))
+			if (!IS_ERR(bdev) && bch_is_open(bdev)) {
 				err = "device already registered";
-			else
+				/* emit CHANGE event for backing devices to export
+				 * CACHED_{UUID/LABEL} values to udev */
+				if (bch_is_open_backing(bdev)) {
+					dc = bch_find_cached_dev(bdev);
+					if (dc) {
+						bch_cached_dev_emit_change(dc);
+						err = "device already registered (emitting change event)";
+					}
+				}
+			} else {
 				err = "device busy";
+            }
 			mutex_unlock(&bch_register_lock);
 			if (!IS_ERR(bdev))
 				bdput(bdev);