This tree is not created by mkfs.btrfs. Therefore when a filesystem
is mounted writable and the UUID tree does not exist, this tree is
created if required. The tree is also added to the fs_info structure
and initialized, but this commit does not yet read or write UUID tree
elements.

Signed-off-by: Stefan Behrens <sbehr...@giantdisaster.de>
---
 fs/btrfs/ctree.h       |  1 +
 fs/btrfs/disk-io.c     | 34 ++++++++++++++++++++++++++++++++++
 fs/btrfs/extent-tree.c |  3 +++
 fs/btrfs/volumes.c     | 26 ++++++++++++++++++++++++++
 fs/btrfs/volumes.h     |  1 +
 5 files changed, 65 insertions(+)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index ef7aa16..4f3328a 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1293,6 +1293,7 @@ struct btrfs_fs_info {
        struct btrfs_root *fs_root;
        struct btrfs_root *csum_root;
        struct btrfs_root *quota_root;
+       struct btrfs_root *uuid_root;
 
        /* the log root tree is a directory of all the other log roots */
        struct btrfs_root *log_root_tree;
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 3c2886c..1db446a 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1580,6 +1580,9 @@ struct btrfs_root *btrfs_read_fs_root_no_name(struct 
btrfs_fs_info *fs_info,
        if (location->objectid == BTRFS_QUOTA_TREE_OBJECTID)
                return fs_info->quota_root ? fs_info->quota_root :
                                             ERR_PTR(-ENOENT);
+       if (location->objectid == BTRFS_UUID_TREE_OBJECTID)
+               return fs_info->uuid_root ? fs_info->uuid_root :
+                                           ERR_PTR(-ENOENT);
 again:
        root = btrfs_lookup_fs_root(fs_info, location->objectid);
        if (root)
@@ -2037,6 +2040,12 @@ static void free_root_pointers(struct btrfs_fs_info 
*info, int chunk_root)
                info->quota_root->node = NULL;
                info->quota_root->commit_root = NULL;
        }
+       if (info->uuid_root) {
+               free_extent_buffer(info->uuid_root->node);
+               free_extent_buffer(info->uuid_root->commit_root);
+               info->uuid_root->node = NULL;
+               info->uuid_root->commit_root = NULL;
+       }
        if (chunk_root) {
                free_extent_buffer(info->chunk_root->node);
                free_extent_buffer(info->chunk_root->commit_root);
@@ -2097,11 +2106,13 @@ int open_ctree(struct super_block *sb,
        struct btrfs_root *chunk_root;
        struct btrfs_root *dev_root;
        struct btrfs_root *quota_root;
+       struct btrfs_root *uuid_root;
        struct btrfs_root *log_tree_root;
        int ret;
        int err = -EINVAL;
        int num_backups_tried = 0;
        int backup_index = 0;
+       bool create_uuid_tree = false;
 
        tree_root = fs_info->tree_root = btrfs_alloc_root(fs_info);
        chunk_root = fs_info->chunk_root = btrfs_alloc_root(fs_info);
@@ -2695,6 +2706,18 @@ retry_root_backup:
                fs_info->quota_root = quota_root;
        }
 
+       location.objectid = BTRFS_UUID_TREE_OBJECTID;
+       uuid_root = btrfs_read_tree_root(tree_root, &location);
+       if (IS_ERR(uuid_root)) {
+               ret = PTR_ERR(uuid_root);
+               if (ret != -ENOENT)
+                       goto recovery_tree_root;
+               create_uuid_tree = true;
+       } else {
+               uuid_root->track_dirty = 1;
+               fs_info->uuid_root = uuid_root;
+       }
+
        fs_info->generation = generation;
        fs_info->last_trans_committed = generation;
 
@@ -2881,6 +2904,17 @@ retry_root_backup:
 
        btrfs_qgroup_rescan_resume(fs_info);
 
+       if (create_uuid_tree) {
+               pr_info("btrfs: creating UUID tree\n");
+               ret = btrfs_create_uuid_tree(fs_info);
+               if (ret) {
+                       pr_warn("btrfs: failed to create the UUID tree %d\n",
+                               ret);
+                       close_ctree(tree_root);
+                       return ret;
+               }
+       }
+
        return 0;
 
 fail_qgroup:
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 6d5c5f7..1c4694a 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4308,6 +4308,9 @@ static struct btrfs_block_rsv *get_block_rsv(
        if (root == root->fs_info->csum_root && trans->adding_csums)
                block_rsv = trans->block_rsv;
 
+       if (root == root->fs_info->uuid_root)
+               block_rsv = trans->block_rsv;
+
        if (!block_rsv)
                block_rsv = root->block_rsv;
 
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index c58bf19..d4c7955 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3411,6 +3411,32 @@ int btrfs_cancel_balance(struct btrfs_fs_info *fs_info)
        return 0;
 }
 
+int btrfs_create_uuid_tree(struct btrfs_fs_info *fs_info)
+{
+       struct btrfs_trans_handle *trans;
+       struct btrfs_root *tree_root = fs_info->tree_root;
+       struct btrfs_root *uuid_root;
+
+       /*
+        * 1 - root node
+        * 1 - root item
+        */
+       trans = btrfs_start_transaction(tree_root, 2);
+       if (IS_ERR(trans))
+               return PTR_ERR(trans);
+
+       uuid_root = btrfs_create_tree(trans, fs_info,
+                                     BTRFS_UUID_TREE_OBJECTID);
+       if (IS_ERR(uuid_root)) {
+               btrfs_abort_transaction(trans, tree_root,
+                                       PTR_ERR(uuid_root));
+               return PTR_ERR(uuid_root);
+       }
+
+       fs_info->uuid_root = uuid_root;
+
+       return btrfs_commit_transaction(trans, tree_root);
+}
 /*
  * shrinking a device means finding all of the device extents past
  * the new size, and then following the back refs to the chunks.
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 857acd3..c3fcd60 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -315,6 +315,7 @@ int btrfs_resume_balance_async(struct btrfs_fs_info 
*fs_info);
 int btrfs_recover_balance(struct btrfs_fs_info *fs_info);
 int btrfs_pause_balance(struct btrfs_fs_info *fs_info);
 int btrfs_cancel_balance(struct btrfs_fs_info *fs_info);
+int btrfs_create_uuid_tree(struct btrfs_fs_info *fs_info);
 int btrfs_chunk_readonly(struct btrfs_root *root, u64 chunk_offset);
 int find_free_dev_extent(struct btrfs_device *device, u64 num_bytes,
                         u64 *start, u64 *max_avail);
-- 
1.8.3

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