Btrfs: shared seed device

This patch makes seed device possible to be shared by
multiple mounted file systems. The sharing is achieved
by cloning seed device's btrfs_fs_devices structure.
Thanks you,
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>

fs/btrfs/disk-io.c

@@ -1711,7 +1711,7 @@ struct btrfs_root *open_ctree(struct super_block *sb,
 	}
 
 	mutex_lock(&fs_info->chunk_mutex);
-	ret = btrfs_read_sys_array(tree_root, btrfs_super_bytenr(disk_super));
+	ret = btrfs_read_sys_array(tree_root);
 	mutex_unlock(&fs_info->chunk_mutex);
 	if (ret) {
 		printk("btrfs: failed to read the system array on %s\n",

fs/btrfs/extent-tree.c

@@ -218,7 +218,7 @@ static int cache_block_group(struct btrfs_root *root,
 	struct btrfs_key key;
 	struct extent_buffer *leaf;
 	int slot;
-	u64 last = block_group->key.objectid;
+	u64 last;
 
 	if (!block_group)
 		return 0;
@@ -239,7 +239,8 @@ static int cache_block_group(struct btrfs_root *root,
 	 * skip the locking here
 	 */
 	path->skip_locking = 1;
-	key.objectid = max_t(u64, last, BTRFS_SUPER_INFO_OFFSET);
+	last = max_t(u64, block_group->key.objectid, BTRFS_SUPER_INFO_OFFSET);
+	key.objectid = last;
 	key.offset = 0;
 	btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
 	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
@@ -5335,8 +5336,20 @@ static int noinline relocate_one_extent(struct btrfs_root *extent_root,
 			prev_block = block_start;
 		}
 
-		if (ref_path->owner_objectid >= BTRFS_FIRST_FREE_OBJECTID &&
-		    pass >= 2) {
+		btrfs_record_root_in_trans(found_root);
+		if (ref_path->owner_objectid >= BTRFS_FIRST_FREE_OBJECTID) {
+			/*
+			 * try to update data extent references while
+			 * keeping metadata shared between snapshots.
+			 */
+			if (pass == 1) {
+				ret = relocate_one_path(trans, found_root,
+						path, &first_key, ref_path,
+						group, reloc_inode);
+				if (ret < 0)
+					goto out;
+				continue;
+			}
 			/*
 			 * use fallback method to process the remaining
 			 * references.
@@ -5359,23 +5372,9 @@ static int noinline relocate_one_extent(struct btrfs_root *extent_root,
 						path, extent_key,
 						&first_key, ref_path,
 						new_extents, nr_extents);
-			if (ret < 0)
-				goto out;
-			continue;
-		}
-
-		btrfs_record_root_in_trans(found_root);
-		if (ref_path->owner_objectid < BTRFS_FIRST_FREE_OBJECTID) {
+		} else {
 			ret = relocate_tree_block(trans, found_root, path,
 						  &first_key, ref_path);
-		} else {
-			/*
-			 * try to update data extent references while
-			 * keeping metadata shared between snapshots.
-			 */
-			ret = relocate_one_path(trans, found_root, path,
-						&first_key, ref_path,
-						group, reloc_inode);
 		}
 		if (ret < 0)
 			goto out;

fs/btrfs/super.c

@@ -58,14 +58,15 @@ static struct super_operations btrfs_super_ops;
 static void btrfs_put_super (struct super_block * sb)
 {
 	struct btrfs_root *root = btrfs_sb(sb);
-	struct btrfs_fs_info *fs = root->fs_info;
 	int ret;
 
 	ret = close_ctree(root);
 	if (ret) {
 		printk("close ctree returns %d\n", ret);
 	}
-	btrfs_sysfs_del_super(fs);
+#if 0
+	btrfs_sysfs_del_super(root->fs_info);
+#endif
 	sb->s_fs_info = NULL;
 }
 
@@ -349,11 +350,12 @@ static int btrfs_fill_super(struct super_block * sb,
 		err = -ENOMEM;
 		goto fail_close;
 	}
-
+#if 0
 	/* this does the super kobj at the same time */
 	err = btrfs_sysfs_add_super(tree_root->fs_info);
 	if (err)
 		goto fail_close;
+#endif
 
 	sb->s_root = root_dentry;
 

fs/btrfs/volumes.c

@@ -47,7 +47,6 @@ static int init_first_rw_device(struct btrfs_trans_handle *trans,
 				struct btrfs_device *device);
 static int btrfs_relocate_sys_chunks(struct btrfs_root *root);
 
-
 #define map_lookup_size(n) (sizeof(struct map_lookup) + \
 			    (sizeof(struct btrfs_bio_stripe) * (n)))
 
@@ -74,34 +73,29 @@ static void unlock_chunks(struct btrfs_root *root)
 	mutex_unlock(&root->fs_info->chunk_mutex);
 }
 
+static void free_fs_devices(struct btrfs_fs_devices *fs_devices)
+{
+	struct btrfs_device *device;
+	WARN_ON(fs_devices->opened);
+	while (!list_empty(&fs_devices->devices)) {
+		device = list_entry(fs_devices->devices.next,
+				    struct btrfs_device, dev_list);
+		list_del(&device->dev_list);
+		kfree(device->name);
+		kfree(device);
+	}
+	kfree(fs_devices);
+}
+
 int btrfs_cleanup_fs_uuids(void)
 {
 	struct btrfs_fs_devices *fs_devices;
-	struct btrfs_device *dev;
 
 	while (!list_empty(&fs_uuids)) {
 		fs_devices = list_entry(fs_uuids.next,
 					struct btrfs_fs_devices, list);
 		list_del(&fs_devices->list);
-		while(!list_empty(&fs_devices->devices)) {
-			dev = list_entry(fs_devices->devices.next,
-					 struct btrfs_device, dev_list);
-			if (dev->bdev) {
-				close_bdev_exclusive(dev->bdev, dev->mode);
-				fs_devices->open_devices--;
-			}
-			fs_devices->num_devices--;
-			if (dev->writeable)
-				fs_devices->rw_devices--;
-			list_del(&dev->dev_list);
-			list_del(&dev->dev_alloc_list);
-			kfree(dev->name);
-			kfree(dev);
-		}
-		WARN_ON(fs_devices->num_devices);
-		WARN_ON(fs_devices->open_devices);
-		WARN_ON(fs_devices->rw_devices);
-		kfree(fs_devices);
+		free_fs_devices(fs_devices);
 	}
 	return 0;
 }
@@ -304,12 +298,55 @@ static noinline int device_list_add(const char *path,
 	return 0;
 }
 
+static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig)
+{
+	struct btrfs_fs_devices *fs_devices;
+	struct btrfs_device *device;
+	struct btrfs_device *orig_dev;
+
+	fs_devices = kzalloc(sizeof(*fs_devices), GFP_NOFS);
+	if (!fs_devices)
+		return ERR_PTR(-ENOMEM);
+
+	INIT_LIST_HEAD(&fs_devices->devices);
+	INIT_LIST_HEAD(&fs_devices->alloc_list);
+	INIT_LIST_HEAD(&fs_devices->list);
+	fs_devices->latest_devid = orig->latest_devid;
+	fs_devices->latest_trans = orig->latest_trans;
+	memcpy(fs_devices->fsid, orig->fsid, sizeof(fs_devices->fsid));
+
+	list_for_each_entry(orig_dev, &orig->devices, dev_list) {
+		device = kzalloc(sizeof(*device), GFP_NOFS);
+		if (!device)
+			goto error;
+
+		device->name = kstrdup(orig_dev->name, GFP_NOFS);
+		if (!device->name)
+			goto error;
+
+		device->devid = orig_dev->devid;
+		device->work.func = pending_bios_fn;
+		memcpy(device->uuid, orig_dev->uuid, sizeof(device->uuid));
+		device->barriers = 1;
+		spin_lock_init(&device->io_lock);
+		INIT_LIST_HEAD(&device->dev_list);
+		INIT_LIST_HEAD(&device->dev_alloc_list);
+
+		list_add(&device->dev_list, &fs_devices->devices);
+		device->fs_devices = fs_devices;
+		fs_devices->num_devices++;
+	}
+	return fs_devices;
+error:
+	free_fs_devices(fs_devices);
+	return ERR_PTR(-ENOMEM);
+}
+
 int btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices)
 {
 	struct list_head *tmp;
 	struct list_head *cur;
 	struct btrfs_device *device;
-	int seed_devices = 0;
 
 	mutex_lock(&uuid_mutex);
 again:
@@ -328,17 +365,14 @@ int btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices)
 			device->writeable = 0;
 			fs_devices->rw_devices--;
 		}
-		if (!seed_devices) {
 		list_del_init(&device->dev_list);
 		fs_devices->num_devices--;
 		kfree(device->name);
 		kfree(device);
 	}
-	}
 
 	if (fs_devices->seed) {
 		fs_devices = fs_devices->seed;
-		seed_devices = 1;
 		goto again;
 	}
 
@@ -348,10 +382,9 @@ int btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices)
 
 static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
 {
-	struct btrfs_fs_devices *seed_devices;
 	struct list_head *cur;
 	struct btrfs_device *device;
-again:
+
 	if (--fs_devices->opened > 0)
 		return 0;
 
@@ -370,30 +403,37 @@ static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
 		device->writeable = 0;
 		device->in_fs_metadata = 0;
 	}
+	WARN_ON(fs_devices->open_devices);
+	WARN_ON(fs_devices->rw_devices);
 	fs_devices->opened = 0;
 	fs_devices->seeding = 0;
-	fs_devices->sprouted = 0;
 
-	seed_devices = fs_devices->seed;
-	fs_devices->seed = NULL;
-	if (seed_devices) {
-		fs_devices = seed_devices;
-		goto again;
-	}
 	return 0;
 }
 
 int btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
 {
+	struct btrfs_fs_devices *seed_devices = NULL;
 	int ret;
 
 	mutex_lock(&uuid_mutex);
 	ret = __btrfs_close_devices(fs_devices);
+	if (!fs_devices->opened) {
+		seed_devices = fs_devices->seed;
+		fs_devices->seed = NULL;
+	}
 	mutex_unlock(&uuid_mutex);
+
+	while (seed_devices) {
+		fs_devices = seed_devices;
+		seed_devices = fs_devices->seed;
+		__btrfs_close_devices(fs_devices);
+		free_fs_devices(fs_devices);
+	}
 	return ret;
 }
 
-int __btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
+static int __btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 				fmode_t flags, void *holder)
 {
 	struct block_device *bdev;
@@ -490,12 +530,8 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 
 	mutex_lock(&uuid_mutex);
 	if (fs_devices->opened) {
-		if (fs_devices->sprouted) {
-			ret = -EBUSY;
-		} else {
 		fs_devices->opened++;
 		ret = 0;
-		}
 	} else {
 		ret = __btrfs_open_devices(fs_devices, flags, holder);
 	}
@@ -1043,12 +1079,8 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
 		goto error_brelse;
 
 	device->in_fs_metadata = 0;
-	if (device->fs_devices == root->fs_info->fs_devices) {
 	list_del_init(&device->dev_list);
-		root->fs_info->fs_devices->num_devices--;
-		if (device->bdev)
-			device->fs_devices->open_devices--;
-	}
+	device->fs_devices->num_devices--;
 
 	next_device = list_entry(root->fs_info->fs_devices->devices.next,
 				 struct btrfs_device, dev_list);
@@ -1057,20 +1089,15 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
 	if (device->bdev == root->fs_info->fs_devices->latest_bdev)
 		root->fs_info->fs_devices->latest_bdev = next_device->bdev;
 
-	num_devices = btrfs_super_num_devices(&root->fs_info->super_copy) - 1;
-	btrfs_set_super_num_devices(&root->fs_info->super_copy, num_devices);
-
-	if (device->fs_devices != root->fs_info->fs_devices) {
-		BUG_ON(device->writeable);
-		brelse(bh);
-		if (bdev)
-			close_bdev_exclusive(bdev, FMODE_READ);
-
 	if (device->bdev) {
 		close_bdev_exclusive(device->bdev, device->mode);
 		device->bdev = NULL;
 		device->fs_devices->open_devices--;
 	}
+
+	num_devices = btrfs_super_num_devices(&root->fs_info->super_copy) - 1;
+	btrfs_set_super_num_devices(&root->fs_info->super_copy, num_devices);
+
 	if (device->fs_devices->open_devices == 0) {
 		struct btrfs_fs_devices *fs_devices;
 		fs_devices = root->fs_info->fs_devices;
@@ -1082,9 +1109,7 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
 		fs_devices->seed = device->fs_devices->seed;
 		device->fs_devices->seed = NULL;
 		__btrfs_close_devices(device->fs_devices);
-		}
-		ret = 0;
-		goto out;
+		free_fs_devices(device->fs_devices);
 	}
 
 	/*
@@ -1099,20 +1124,10 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
 		set_buffer_dirty(bh);
 		sync_dirty_buffer(bh);
 	}
-	brelse(bh);
 
-	if (device->bdev) {
-		/* one close for the device struct or super_block */
-		close_bdev_exclusive(device->bdev, device->mode);
-	}
-	if (bdev) {
-		/* one close for us */
-		close_bdev_exclusive(bdev, FMODE_READ);
-	}
 	kfree(device->name);
 	kfree(device);
 	ret = 0;
-	goto out;
 
 error_brelse:
 	brelse(bh);
@@ -1133,34 +1148,41 @@ static int btrfs_prepare_sprout(struct btrfs_trans_handle *trans,
 {
 	struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
 	struct btrfs_fs_devices *old_devices;
+	struct btrfs_fs_devices *seed_devices;
 	struct btrfs_super_block *disk_super = &root->fs_info->super_copy;
 	struct btrfs_device *device;
 	u64 super_flags;
 
 	BUG_ON(!mutex_is_locked(&uuid_mutex));
-	if (!fs_devices->seeding || fs_devices->opened != 1)
+	if (!fs_devices->seeding)
 		return -EINVAL;
 
-	old_devices = kzalloc(sizeof(*fs_devices), GFP_NOFS);
-	if (!old_devices)
+	seed_devices = kzalloc(sizeof(*fs_devices), GFP_NOFS);
+	if (!seed_devices)
 		return -ENOMEM;
 
-	memcpy(old_devices, fs_devices, sizeof(*old_devices));
-	old_devices->opened = 1;
-	old_devices->sprouted = 1;
-	INIT_LIST_HEAD(&old_devices->devices);
-	INIT_LIST_HEAD(&old_devices->alloc_list);
-	list_splice_init(&fs_devices->devices, &old_devices->devices);
-	list_splice_init(&fs_devices->alloc_list, &old_devices->alloc_list);
-	list_for_each_entry(device, &old_devices->devices, dev_list) {
-		device->fs_devices = old_devices;
+	old_devices = clone_fs_devices(fs_devices);
+	if (IS_ERR(old_devices)) {
+		kfree(seed_devices);
+		return PTR_ERR(old_devices);
 	}
+
 	list_add(&old_devices->list, &fs_uuids);
 
+	memcpy(seed_devices, fs_devices, sizeof(*seed_devices));
+	seed_devices->opened = 1;
+	INIT_LIST_HEAD(&seed_devices->devices);
+	INIT_LIST_HEAD(&seed_devices->alloc_list);
+	list_splice_init(&fs_devices->devices, &seed_devices->devices);
+	list_splice_init(&fs_devices->alloc_list, &seed_devices->alloc_list);
+	list_for_each_entry(device, &seed_devices->devices, dev_list) {
+		device->fs_devices = seed_devices;
+	}
+
 	fs_devices->seeding = 0;
 	fs_devices->num_devices = 0;
 	fs_devices->open_devices = 0;
-	fs_devices->seed = old_devices;
+	fs_devices->seed = seed_devices;
 
 	generate_random_uuid(fs_devices->fsid);
 	memcpy(root->fs_info->fsid, fs_devices->fsid, BTRFS_FSID_SIZE);
@@ -2642,7 +2664,6 @@ int btrfs_unplug_page(struct btrfs_mapping_tree *map_tree,
 				 NULL, 0, page);
 }
 
-
 static void end_bio_multi_stripe(struct bio *bio, int err)
 {
 	struct btrfs_multi_bio *multi = bio->bi_private;
@@ -2840,6 +2861,7 @@ static struct btrfs_device *add_missing_dev(struct btrfs_root *root,
 	device->dev_root = root->fs_info->dev_root;
 	device->devid = devid;
 	device->work.func = pending_bios_fn;
+	device->fs_devices = fs_devices;
 	fs_devices->num_devices++;
 	spin_lock_init(&device->io_lock);
 	INIT_LIST_HEAD(&device->dev_alloc_list);
@@ -2980,8 +3002,10 @@ static int open_seed_devices(struct btrfs_root *root, u8 *fsid)
 		ret = -ENOENT;
 		goto out;
 	}
-	if (fs_devices->opened) {
-		ret = -EBUSY;
+
+	fs_devices = clone_fs_devices(fs_devices);
+	if (IS_ERR(fs_devices)) {
+		ret = PTR_ERR(fs_devices);
 		goto out;
 	}
 
@@ -2992,13 +3016,13 @@ static int open_seed_devices(struct btrfs_root *root, u8 *fsid)
 
 	if (!fs_devices->seeding) {
 		__btrfs_close_devices(fs_devices);
+		free_fs_devices(fs_devices);
 		ret = -EINVAL;
 		goto out;
 	}
 
 	fs_devices->seed = root->fs_info->fs_devices->seed;
 	root->fs_info->fs_devices->seed = fs_devices;
-	fs_devices->sprouted = 1;
 out:
 	mutex_unlock(&uuid_mutex);
 	return ret;
@@ -3011,7 +3035,6 @@ static int read_one_dev(struct btrfs_root *root,
 	struct btrfs_device *device;
 	u64 devid;
 	int ret;
-	int seed_devices = 0;
 	u8 fs_uuid[BTRFS_UUID_SIZE];
 	u8 dev_uuid[BTRFS_UUID_SIZE];
 
@@ -3025,14 +3048,13 @@ static int read_one_dev(struct btrfs_root *root,
 
 	if (memcmp(fs_uuid, root->fs_info->fsid, BTRFS_UUID_SIZE)) {
 		ret = open_seed_devices(root, fs_uuid);
-		if (ret)
+		if (ret && !btrfs_test_opt(root, DEGRADED))
 			return ret;
-		seed_devices = 1;
 	}
 
 	device = btrfs_find_device(root, devid, dev_uuid, fs_uuid);
 	if (!device || !device->bdev) {
-		if (!btrfs_test_opt(root, DEGRADED) || seed_devices)
+		if (!btrfs_test_opt(root, DEGRADED))
 			return -EIO;
 
 		if (!device) {
@@ -3074,7 +3096,7 @@ int btrfs_read_super_device(struct btrfs_root *root, struct extent_buffer *buf)
 	return read_one_dev(root, buf, dev_item);
 }
 
-int btrfs_read_sys_array(struct btrfs_root *root, u64 sb_bytenr)
+int btrfs_read_sys_array(struct btrfs_root *root)
 {
 	struct btrfs_super_block *super_copy = &root->fs_info->super_copy;
 	struct extent_buffer *sb;
@@ -3089,7 +3111,7 @@ int btrfs_read_sys_array(struct btrfs_root *root, u64 sb_bytenr)
 	u32 cur;
 	struct btrfs_key key;
 
-	sb = btrfs_find_create_tree_block(root, sb_bytenr,
+	sb = btrfs_find_create_tree_block(root, BTRFS_SUPER_INFO_OFFSET,
 					  BTRFS_SUPER_INFO_SIZE);
 	if (!sb)
 		return -ENOMEM;

fs/btrfs/volumes.h

@@ -93,7 +93,6 @@ struct btrfs_fs_devices {
 
 	struct btrfs_fs_devices *seed;
 	int seeding;
-	int sprouted;
 
 	int opened;
 };
@@ -127,7 +126,7 @@ int btrfs_map_block(struct btrfs_mapping_tree *map_tree, int rw,
 int btrfs_rmap_block(struct btrfs_mapping_tree *map_tree,
 		     u64 chunk_start, u64 physical, u64 devid,
 		     u64 **logical, int *naddrs, int *stripe_len);
-int btrfs_read_sys_array(struct btrfs_root *root, u64 sb_bytenr);
+int btrfs_read_sys_array(struct btrfs_root *root);
 int btrfs_read_chunk_tree(struct btrfs_root *root);
 int btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
 		      struct btrfs_root *extent_root, u64 type);