Btrfs: superblock duplication

This patch implements superblock duplication. Superblocks
are stored at offset 16K, 64M and 256G on every devices.
Spaces used by superblocks are preserved by the allocator,
which uses a reverse mapping function to find the logical
addresses that correspond to superblocks. Thank you,

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>

8 files changed, 279 insertions, 119 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 61dc3b2..c72f4f3 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1595,8 +1595,7 @@ struct btrfs_root *open_ctree(struct super_block *sb,
 		     fs_info, BTRFS_ROOT_TREE_OBJECTID);
 
 
-	bh = __bread(fs_devices->latest_bdev,
-		     BTRFS_SUPER_INFO_OFFSET / 4096, 4096);
+	bh = btrfs_read_dev_super(fs_devices->latest_bdev);
 	if (!bh)
 		goto fail_iput;
 
@@ -1710,7 +1709,7 @@ struct btrfs_root *open_ctree(struct super_block *sb,
 	}
 
 	mutex_lock(&fs_info->chunk_mutex);
-	ret = btrfs_read_sys_array(tree_root);
+	ret = btrfs_read_sys_array(tree_root, btrfs_super_bytenr(disk_super));
 	mutex_unlock(&fs_info->chunk_mutex);
 	if (ret) {
 		printk("btrfs: failed to read the system array on %s\n",
@@ -1905,19 +1904,147 @@ static void btrfs_end_buffer_write_sync(struct buffer_head *bh, int uptodate)
 	put_bh(bh);
 }
 
-static int write_all_supers(struct btrfs_root *root)
+struct buffer_head *btrfs_read_dev_super(struct block_device *bdev)
+{
+	struct buffer_head *bh;
+	struct buffer_head *latest = NULL;
+	struct btrfs_super_block *super;
+	int i;
+	u64 transid = 0;
+	u64 bytenr;
+
+	/* we would like to check all the supers, but that would make
+	 * a btrfs mount succeed after a mkfs from a different FS.
+	 * So, we need to add a special mount option to scan for
+	 * later supers, using BTRFS_SUPER_MIRROR_MAX instead
+	 */
+	for (i = 0; i < 1; i++) {
+		bytenr = btrfs_sb_offset(i);
+		if (bytenr + 4096 >= i_size_read(bdev->bd_inode))
+			break;
+		bh = __bread(bdev, bytenr / 4096, 4096);
+		if (!bh)
+			continue;
+
+		super = (struct btrfs_super_block *)bh->b_data;
+		if (btrfs_super_bytenr(super) != bytenr ||
+		    strncmp((char *)(&super->magic), BTRFS_MAGIC,
+			    sizeof(super->magic))) {
+			brelse(bh);
+			continue;
+		}
+
+		if (!latest || btrfs_super_generation(super) > transid) {
+			brelse(latest);
+			latest = bh;
+			transid = btrfs_super_generation(super);
+		} else {
+			brelse(bh);
+		}
+	}
+	return latest;
+}
+
+static int write_dev_supers(struct btrfs_device *device,
+			    struct btrfs_super_block *sb,
+			    int do_barriers, int wait, int max_mirrors)
+{
+	struct buffer_head *bh;
+	int i;
+	int ret;
+	int errors = 0;
+	u32 crc;
+	u64 bytenr;
+	int last_barrier = 0;
+
+	if (max_mirrors == 0)
+		max_mirrors = BTRFS_SUPER_MIRROR_MAX;
+
+	/* make sure only the last submit_bh does a barrier */
+	if (do_barriers) {
+		for (i = 0; i < max_mirrors; i++) {
+			bytenr = btrfs_sb_offset(i);
+			if (bytenr + BTRFS_SUPER_INFO_SIZE >=
+			    device->total_bytes)
+				break;
+			last_barrier = i;
+		}
+	}
+
+	for (i = 0; i < max_mirrors; i++) {
+		bytenr = btrfs_sb_offset(i);
+		if (bytenr + BTRFS_SUPER_INFO_SIZE >= device->total_bytes)
+			break;
+
+		if (wait) {
+			bh = __find_get_block(device->bdev, bytenr / 4096,
+					      BTRFS_SUPER_INFO_SIZE);
+			BUG_ON(!bh);
+			brelse(bh);
+			wait_on_buffer(bh);
+			if (buffer_uptodate(bh)) {
+				brelse(bh);
+				continue;
+			}
+		} else {
+			btrfs_set_super_bytenr(sb, bytenr);
+
+			crc = ~(u32)0;
+			crc = btrfs_csum_data(NULL, (char *)sb +
+					      BTRFS_CSUM_SIZE, crc,
+					      BTRFS_SUPER_INFO_SIZE -
+					      BTRFS_CSUM_SIZE);
+			btrfs_csum_final(crc, sb->csum);
+
+			bh = __getblk(device->bdev, bytenr / 4096,
+				      BTRFS_SUPER_INFO_SIZE);
+			memcpy(bh->b_data, sb, BTRFS_SUPER_INFO_SIZE);
+
+			set_buffer_uptodate(bh);
+			get_bh(bh);
+			lock_buffer(bh);
+			bh->b_end_io = btrfs_end_buffer_write_sync;
+		}
+
+		if (i == last_barrier && do_barriers && device->barriers) {
+			ret = submit_bh(WRITE_BARRIER, bh);
+			if (ret == -EOPNOTSUPP) {
+				printk("btrfs: disabling barriers on dev %s\n",
+				       device->name);
+				set_buffer_uptodate(bh);
+				device->barriers = 0;
+				get_bh(bh);
+				lock_buffer(bh);
+				ret = submit_bh(WRITE, bh);
+			}
+		} else {
+			ret = submit_bh(WRITE, bh);
+		}
+
+		if (!ret && wait) {
+			wait_on_buffer(bh);
+			if (!buffer_uptodate(bh))
+				errors++;
+		} else if (ret) {
+			errors++;
+		}
+		if (wait)
+			brelse(bh);
+	}
+	return errors < i ? 0 : -1;
+}
+
+int write_all_supers(struct btrfs_root *root, int max_mirrors)
 {
 	struct list_head *cur;
 	struct list_head *head = &root->fs_info->fs_devices->devices;
 	struct btrfs_device *dev;
 	struct btrfs_super_block *sb;
 	struct btrfs_dev_item *dev_item;
-	struct buffer_head *bh;
 	int ret;
 	int do_barriers;
 	int max_errors;
 	int total_errors = 0;
-	u32 crc;
 	u64 flags;
 
 	max_errors = btrfs_super_num_devices(&root->fs_info->super_copy) - 1;
@@ -1944,40 +2071,11 @@ static int write_all_supers(struct btrfs_root *root)
 		btrfs_set_stack_device_sector_size(dev_item, dev->sector_size);
 		memcpy(dev_item->uuid, dev->uuid, BTRFS_UUID_SIZE);
 		memcpy(dev_item->fsid, dev->fs_devices->fsid, BTRFS_UUID_SIZE);
+
 		flags = btrfs_super_flags(sb);
 		btrfs_set_super_flags(sb, flags | BTRFS_HEADER_FLAG_WRITTEN);
 
-
-		crc = ~(u32)0;
-		crc = btrfs_csum_data(root, (char *)sb + BTRFS_CSUM_SIZE, crc,
-				      BTRFS_SUPER_INFO_SIZE - BTRFS_CSUM_SIZE);
-		btrfs_csum_final(crc, sb->csum);
-
-		bh = __getblk(dev->bdev, BTRFS_SUPER_INFO_OFFSET / 4096,
-			      BTRFS_SUPER_INFO_SIZE);
-
-		memcpy(bh->b_data, sb, BTRFS_SUPER_INFO_SIZE);
-		dev->pending_io = bh;
-
-		get_bh(bh);
-		set_buffer_uptodate(bh);
-		lock_buffer(bh);
-		bh->b_end_io = btrfs_end_buffer_write_sync;
-
-		if (do_barriers && dev->barriers) {
-			ret = submit_bh(WRITE_BARRIER, bh);
-			if (ret == -EOPNOTSUPP) {
-				printk("btrfs: disabling barriers on dev %s\n",
-				       dev->name);
-				set_buffer_uptodate(bh);
-				dev->barriers = 0;
-				get_bh(bh);
-				lock_buffer(bh);
-				ret = submit_bh(WRITE, bh);
-			}
-		} else {
-			ret = submit_bh(WRITE, bh);
-		}
+		ret = write_dev_supers(dev, sb, do_barriers, 0, max_mirrors);
 		if (ret)
 			total_errors++;
 	}
@@ -1985,8 +2083,8 @@ static int write_all_supers(struct btrfs_root *root)
 		printk("btrfs: %d errors while writing supers\n", total_errors);
 		BUG();
 	}
-	total_errors = 0;
 
+	total_errors = 0;
 	list_for_each(cur, head) {
 		dev = list_entry(cur, struct btrfs_device, dev_list);
 		if (!dev->bdev)
@@ -1994,29 +2092,9 @@ static int write_all_supers(struct btrfs_root *root)
 		if (!dev->in_fs_metadata || !dev->writeable)
 			continue;
 
-		BUG_ON(!dev->pending_io);
-		bh = dev->pending_io;
-		wait_on_buffer(bh);
-		if (!buffer_uptodate(dev->pending_io)) {
-			if (do_barriers && dev->barriers) {
-				printk("btrfs: disabling barriers on dev %s\n",
-				       dev->name);
-				set_buffer_uptodate(bh);
-				get_bh(bh);
-				lock_buffer(bh);
-				dev->barriers = 0;
-				ret = submit_bh(WRITE, bh);
-				BUG_ON(ret);
-				wait_on_buffer(bh);
-				if (!buffer_uptodate(bh))
-					total_errors++;
-			} else {
-				total_errors++;
-			}
-
-		}
-		dev->pending_io = NULL;
-		brelse(bh);
+		ret = write_dev_supers(dev, sb, do_barriers, 1, max_mirrors);
+		if (ret)
+			total_errors++;
 	}
 	if (total_errors > max_errors) {
 		printk("btrfs: %d errors while writing supers\n", total_errors);
@@ -2025,12 +2103,12 @@ static int write_all_supers(struct btrfs_root *root)
 	return 0;
 }
 
-int write_ctree_super(struct btrfs_trans_handle *trans, struct btrfs_root
-		      *root)
+int write_ctree_super(struct btrfs_trans_handle *trans,
+		      struct btrfs_root *root, int max_mirrors)
 {
 	int ret;
 
-	ret = write_all_supers(root);
+	ret = write_all_supers(root, max_mirrors);
 	return ret;
 }
 
@@ -2116,7 +2194,7 @@ int btrfs_commit_super(struct btrfs_root *root)
 	ret = btrfs_write_and_wait_transaction(NULL, root);
 	BUG_ON(ret);
 
-	ret = write_ctree_super(NULL, root);
+	ret = write_ctree_super(NULL, root, 0);
 	return ret;
 }
 
diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index 717e948..c0ff404 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -19,8 +19,20 @@
 #ifndef __DISKIO__
 #define __DISKIO__
 
-#define BTRFS_SUPER_INFO_OFFSET (16 * 1024)
+#define BTRFS_SUPER_INFO_OFFSET (64 * 1024)
 #define BTRFS_SUPER_INFO_SIZE 4096
+
+#define BTRFS_SUPER_MIRROR_MAX	 3
+#define BTRFS_SUPER_MIRROR_SHIFT 12
+
+static inline u64 btrfs_sb_offset(int mirror)
+{
+	u64 start = 16 * 1024;
+	if (mirror)
+		return start << (BTRFS_SUPER_MIRROR_SHIFT * mirror);
+	return BTRFS_SUPER_INFO_OFFSET;
+}
+
 struct btrfs_device;
 struct btrfs_fs_devices;
 
@@ -37,7 +49,8 @@ struct btrfs_root *open_ctree(struct super_block *sb,
 			      char *options);
 int close_ctree(struct btrfs_root *root);
 int write_ctree_super(struct btrfs_trans_handle *trans,
-		      struct btrfs_root *root);
+		      struct btrfs_root *root, int max_mirrors);
+struct buffer_head *btrfs_read_dev_super(struct block_device *bdev);
 int btrfs_commit_super(struct btrfs_root *root);
 struct extent_buffer *btrfs_find_tree_block(struct btrfs_root *root,
 					    u64 bytenr, u32 blocksize);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index d156385..803647b 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -189,6 +189,29 @@ static int add_new_free_space(struct btrfs_block_group_cache *block_group,
 	return 0;
 }
 
+static int remove_sb_from_cache(struct btrfs_root *root,
+				struct btrfs_block_group_cache *cache)
+{
+	u64 bytenr;
+	u64 *logical;
+	int stripe_len;
+	int i, nr, ret;
+
+	for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
+		bytenr = btrfs_sb_offset(i);
+		ret = btrfs_rmap_block(&root->fs_info->mapping_tree,
+				       cache->key.objectid, bytenr, 0,
+				       &logical, &nr, &stripe_len);
+		BUG_ON(ret);
+		while (nr--) {
+			btrfs_remove_free_space(cache, logical[nr],
+						stripe_len);
+		}
+		kfree(logical);
+	}
+	return 0;
+}
+
 static int cache_block_group(struct btrfs_root *root,
 			     struct btrfs_block_group_cache *block_group)
 {
@@ -197,9 +220,7 @@ static int cache_block_group(struct btrfs_root *root,
 	struct btrfs_key key;
 	struct extent_buffer *leaf;
 	int slot;
-	u64 last = 0;
-	u64 first_free;
-	int found = 0;
+	u64 last = block_group->key.objectid;
 
 	if (!block_group)
 		return 0;
@@ -220,23 +241,13 @@ static int cache_block_group(struct btrfs_root *root,
 	 * skip the locking here
 	 */
 	path->skip_locking = 1;
-	first_free = max_t(u64, block_group->key.objectid,
-			   BTRFS_SUPER_INFO_OFFSET + BTRFS_SUPER_INFO_SIZE);
-	key.objectid = block_group->key.objectid;
+	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);
 	if (ret < 0)
 		goto err;
-	ret = btrfs_previous_item(root, path, 0, BTRFS_EXTENT_ITEM_KEY);
-	if (ret < 0)
-		goto err;
-	if (ret == 0) {
-		leaf = path->nodes[0];
-		btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
-		if (key.objectid + key.offset > first_free)
-			first_free = key.objectid + key.offset;
-	}
+
 	while(1) {
 		leaf = path->nodes[0];
 		slot = path->slots[0];
@@ -258,11 +269,6 @@ static int cache_block_group(struct btrfs_root *root,
 			break;
 
 		if (btrfs_key_type(&key) == BTRFS_EXTENT_ITEM_KEY) {
-			if (!found) {
-				last = first_free;
-				found = 1;
-			}
-
 			add_new_free_space(block_group, root->fs_info, last,
 					   key.objectid);
 
@@ -272,13 +278,11 @@ next:
 		path->slots[0]++;
 	}
 
-	if (!found)
-		last = first_free;
-
 	add_new_free_space(block_group, root->fs_info, last,
 			   block_group->key.objectid +
 			   block_group->key.offset);
 
+	remove_sb_from_cache(root, block_group);
 	block_group->cached = 1;
 	ret = 0;
 err:
@@ -1974,10 +1978,8 @@ static int update_block_group(struct btrfs_trans_handle *trans,
 		if (alloc) {
 			old_val += num_bytes;
 			cache->space_info->bytes_used += num_bytes;
-			if (cache->ro) {
+			if (cache->ro)
 				cache->space_info->bytes_readonly -= num_bytes;
-				WARN_ON(1);
-			}
 			btrfs_set_block_group_used(&cache->item, old_val);
 			spin_unlock(&cache->lock);
 			spin_unlock(&cache->space_info->lock);
diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 09462ad..2e69b9c 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -290,7 +290,6 @@ __btrfs_remove_free_space(struct btrfs_block_group_cache *block_group,
 			ret = -EINVAL;
 			goto out;
 		}
-
 		unlink_free_space(block_group, info);
 
 		if (info->bytes == bytes) {
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index c38f6a0..47cd5fc 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1038,7 +1038,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 	mutex_unlock(&root->fs_info->trans_mutex);
 	ret = btrfs_write_and_wait_transaction(trans, root);
 	BUG_ON(ret);
-	write_ctree_super(trans, root);
+	write_ctree_super(trans, root, 0);
 
 	/*
 	 * the super is written, we can safely allow the tree-loggers
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 08469ec0..d3f9c2c 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -1996,7 +1996,7 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
 	btrfs_set_super_log_root_level(&root->fs_info->super_for_commit,
 		       btrfs_header_level(log->fs_info->log_root_tree->node));
 
-	write_ctree_super(trans, log->fs_info->tree_root);
+	write_ctree_super(trans, log->fs_info->tree_root, 2);
 	log->fs_info->tree_log_transid++;
 	log->fs_info->tree_log_batch = 0;
 	atomic_set(&log->fs_info->tree_log_commit, 0);
@@ -2006,7 +2006,6 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
 out:
 	mutex_unlock(&log->fs_info->tree_log_mutex);
 	return 0;
-
 }
 
 /* * free all the extents used by the tree log.  This should be called
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 2049d17..a79b3cc 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -423,15 +423,11 @@ int __btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 		}
 		set_blocksize(bdev, 4096);
 
-		bh = __bread(bdev, BTRFS_SUPER_INFO_OFFSET / 4096, 4096);
+		bh = btrfs_read_dev_super(bdev);
 		if (!bh)
 			goto error_close;
 
 		disk_super = (struct btrfs_super_block *)bh->b_data;
-		if (strncmp((char *)(&disk_super->magic), BTRFS_MAGIC,
-		    sizeof(disk_super->magic)))
-			goto error_brelse;
-
 		devid = le64_to_cpu(disk_super->dev_item.devid);
 		if (devid != device->devid)
 			goto error_brelse;
@@ -529,17 +525,12 @@ int btrfs_scan_one_device(const char *path, fmode_t flags, void *holder,
 	ret = set_blocksize(bdev, 4096);
 	if (ret)
 		goto error_close;
-	bh = __bread(bdev, BTRFS_SUPER_INFO_OFFSET / 4096, 4096);
+	bh = btrfs_read_dev_super(bdev);
 	if (!bh) {
 		ret = -EIO;
 		goto error_close;
 	}
 	disk_super = (struct btrfs_super_block *)bh->b_data;
-	if (strncmp((char *)(&disk_super->magic), BTRFS_MAGIC,
-	    sizeof(disk_super->magic))) {
-		ret = -EINVAL;
-		goto error_brelse;
-	}
 	devid = le64_to_cpu(disk_super->dev_item.devid);
 	transid = btrfs_super_generation(disk_super);
 	if (disk_super->label[0])
@@ -553,7 +544,6 @@ int btrfs_scan_one_device(const char *path, fmode_t flags, void *holder,
 	printk("devid %Lu transid %Lu %s\n", devid, transid, path);
 	ret = device_list_add(path, disk_super, devid, fs_devices_ret);
 
-error_brelse:
 	brelse(bh);
 error_close:
 	close_bdev_exclusive(bdev, flags);
@@ -1016,17 +1006,12 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
 		}
 
 		set_blocksize(bdev, 4096);
-		bh = __bread(bdev, BTRFS_SUPER_INFO_OFFSET / 4096, 4096);
+		bh = btrfs_read_dev_super(bdev);
 		if (!bh) {
 			ret = -EIO;
 			goto error_close;
 		}
 		disk_super = (struct btrfs_super_block *)bh->b_data;
-		if (strncmp((char *)(&disk_super->magic), BTRFS_MAGIC,
-			    sizeof(disk_super->magic))) {
-			ret = -ENOENT;
-			goto error_brelse;
-		}
 		devid = le64_to_cpu(disk_super->dev_item.devid);
 		dev_uuid = disk_super->dev_item.uuid;
 		device = btrfs_find_device(root, devid, dev_uuid,
@@ -2563,6 +2548,88 @@ int btrfs_map_block(struct btrfs_mapping_tree *map_tree, int rw,
 				 mirror_num, NULL);
 }
 
+int btrfs_rmap_block(struct btrfs_mapping_tree *map_tree,
+		     u64 chunk_start, u64 physical, u64 devid,
+		     u64 **logical, int *naddrs, int *stripe_len)
+{
+	struct extent_map_tree *em_tree = &map_tree->map_tree;
+	struct extent_map *em;
+	struct map_lookup *map;
+	u64 *buf;
+	u64 bytenr;
+	u64 length;
+	u64 stripe_nr;
+	int i, j, nr = 0;
+
+	spin_lock(&em_tree->lock);
+	em = lookup_extent_mapping(em_tree, chunk_start, 1);
+	spin_unlock(&em_tree->lock);
+
+	BUG_ON(!em || em->start != chunk_start);
+	map = (struct map_lookup *)em->bdev;
+
+	length = em->len;
+	if (map->type & BTRFS_BLOCK_GROUP_RAID10)
+		do_div(length, map->num_stripes / map->sub_stripes);
+	else if (map->type & BTRFS_BLOCK_GROUP_RAID0)
+		do_div(length, map->num_stripes);
+
+	buf = kzalloc(sizeof(u64) * map->num_stripes, GFP_NOFS);
+	BUG_ON(!buf);
+
+	for (i = 0; i < map->num_stripes; i++) {
+		if (devid && map->stripes[i].dev->devid != devid)
+			continue;
+		if (map->stripes[i].physical > physical ||
+		    map->stripes[i].physical + length <= physical)
+			continue;
+
+		stripe_nr = physical - map->stripes[i].physical;
+		do_div(stripe_nr, map->stripe_len);
+
+		if (map->type & BTRFS_BLOCK_GROUP_RAID10) {
+			stripe_nr = stripe_nr * map->num_stripes + i;
+			do_div(stripe_nr, map->sub_stripes);
+		} else if (map->type & BTRFS_BLOCK_GROUP_RAID0) {
+			stripe_nr = stripe_nr * map->num_stripes + i;
+		}
+		bytenr = chunk_start + stripe_nr * map->stripe_len;
+		for (j = 0; j < nr; j++) {
+			if (buf[j] == bytenr)
+				break;
+		}
+		if (j == nr)
+			buf[nr++] = bytenr;
+	}
+
+	for (i = 0; i > nr; i++) {
+		struct btrfs_multi_bio *multi;
+		struct btrfs_bio_stripe *stripe;
+		int ret;
+
+		length = 1;
+		ret = btrfs_map_block(map_tree, WRITE, buf[i],
+				      &length, &multi, 0);
+		BUG_ON(ret);
+
+		stripe = multi->stripes;
+		for (j = 0; j < multi->num_stripes; j++) {
+			if (stripe->physical >= physical &&
+			    physical < stripe->physical + length)
+				break;
+		}
+		BUG_ON(j >= multi->num_stripes);
+		kfree(multi);
+	}
+
+	*logical = buf;
+	*naddrs = nr;
+	*stripe_len = map->stripe_len;
+
+	free_extent_map(em);
+	return 0;
+}
+
 int btrfs_unplug_page(struct btrfs_mapping_tree *map_tree,
 		      u64 logical, struct page *page)
 {
@@ -3003,7 +3070,7 @@ 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)
+int btrfs_read_sys_array(struct btrfs_root *root, u64 sb_bytenr)
 {
 	struct btrfs_super_block *super_copy = &root->fs_info->super_copy;
 	struct extent_buffer *sb;
@@ -3018,7 +3085,7 @@ int btrfs_read_sys_array(struct btrfs_root *root)
 	u32 cur;
 	struct btrfs_key key;
 
-	sb = btrfs_find_create_tree_block(root, BTRFS_SUPER_INFO_OFFSET,
+	sb = btrfs_find_create_tree_block(root, sb_bytenr,
 					  BTRFS_SUPER_INFO_SIZE);
 	if (!sb)
 		return -ENOMEM;
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index fcbdcb3..bdebe83 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -28,7 +28,6 @@ struct btrfs_device {
 	struct list_head dev_alloc_list;
 	struct btrfs_fs_devices *fs_devices;
 	struct btrfs_root *dev_root;
-	struct buffer_head *pending_io;
 	struct bio *pending_bios;
 	struct bio *pending_bio_tail;
 	int running_pending;
@@ -125,7 +124,10 @@ int btrfs_alloc_dev_extent(struct btrfs_trans_handle *trans,
 int btrfs_map_block(struct btrfs_mapping_tree *map_tree, int rw,
 		    u64 logical, u64 *length,
 		    struct btrfs_multi_bio **multi_ret, int mirror_num);
-int btrfs_read_sys_array(struct btrfs_root *root);
+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_chunk_tree(struct btrfs_root *root);
 int btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
 		      struct btrfs_root *extent_root, u64 type);