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 61dc3b2c834b..c72f4f3b912c 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 717e94811e4e..c0ff404c31b7 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 d15638529389..803647bc8400 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 09462adfbe33..2e69b9c30437 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 c38f6a0e30b1..47cd5fcad2c8 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 08469ec05850..d3f9c2c663c4 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 2049d179ccd5..a79b3cc09e94 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 fcbdcb3ae13e..bdebe83c3195 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);