Btrfs: change how subvolumes are organized

btrfs allows subvolumes and snapshots anywhere in the directory tree.
If we snapshot a subvolume that contains a link to other subvolume
called subvolA, subvolA can be accessed through both the original
subvolume and the snapshot. This is similar to creating hard link to
directory, and has the very similar problems.

The aim of this patch is enforcing there is only one access point to
each subvolume. Only the first directory entry (the one added when
the subvolume/snapshot was created) is treated as valid access point.
The first directory entry is distinguished by checking root forward
reference. If the corresponding root forward reference is missing,
we know the entry is not the first one.

This patch also adds snapshot/subvolume rename support, the code
allows rename subvolume link across subvolumes.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 262 insertions, 106 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 9e81f3184f24..6036b36789cc 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2373,6 +2373,69 @@ static int btrfs_unlink(struct inode *dir, struct dentry *dentry)
         return ret;
 }
 
+int btrfs_unlink_subvol(struct btrfs_trans_handle *trans,
+                        struct btrfs_root *root,
+                        struct inode *dir, u64 objectid,
+                        const char *name, int name_len)
+{
+        struct btrfs_path *path;
+        struct extent_buffer *leaf;
+        struct btrfs_dir_item *di;
+        struct btrfs_key key;
+        u64 index;
+        int ret;
+
+        path = btrfs_alloc_path();
+        if (!path)
+                return -ENOMEM;
+
+        di = btrfs_lookup_dir_item(trans, root, path, dir->i_ino,
+                                   name, name_len, -1);
+        BUG_ON(!di || IS_ERR(di));
+
+        leaf = path->nodes[0];
+        btrfs_dir_item_key_to_cpu(leaf, di, &key);
+        WARN_ON(key.type != BTRFS_ROOT_ITEM_KEY || key.objectid != objectid);
+        ret = btrfs_delete_one_dir_name(trans, root, path, di);
+        BUG_ON(ret);
+        btrfs_release_path(root, path);
+
+        ret = btrfs_del_root_ref(trans, root->fs_info->tree_root,
+                                 objectid, root->root_key.objectid,
+                                 dir->i_ino, &index, name, name_len);
+        if (ret < 0) {
+                BUG_ON(ret != -ENOENT);
+                di = btrfs_search_dir_index_item(root, path, dir->i_ino,
+                                                 name, name_len);
+                BUG_ON(!di || IS_ERR(di));
+
+                leaf = path->nodes[0];
+                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
+                btrfs_release_path(root, path);
+                index = key.offset;
+        }
+
+        di = btrfs_lookup_dir_index_item(trans, root, path, dir->i_ino,
+                                         index, name, name_len, -1);
+        BUG_ON(!di || IS_ERR(di));
+
+        leaf = path->nodes[0];
+        btrfs_dir_item_key_to_cpu(leaf, di, &key);
+        WARN_ON(key.type != BTRFS_ROOT_ITEM_KEY || key.objectid != objectid);
+        ret = btrfs_delete_one_dir_name(trans, root, path, di);
+        BUG_ON(ret);
+        btrfs_release_path(root, path);
+
+        btrfs_i_size_write(dir, dir->i_size - name_len * 2);
+        dir->i_mtime = dir->i_ctime = CURRENT_TIME;
+        ret = btrfs_update_inode(trans, root, dir);
+        BUG_ON(ret);
+        dir->i_sb->s_dirt = 1;
+
+        btrfs_free_path(path);
+        return 0;
+}
+
 static int btrfs_rmdir(struct inode *dir, struct dentry *dentry)
 {
         struct inode *inode = dentry->d_inode;
@@ -2382,29 +2445,31 @@ static int btrfs_rmdir(struct inode *dir, struct dentry *dentry)
         struct btrfs_trans_handle *trans;
         unsigned long nr = 0;
 
-        /*
-         * the FIRST_FREE_OBJECTID check makes sure we don't try to rmdir
-         * the root of a subvolume or snapshot
-         */
         if (inode->i_size > BTRFS_EMPTY_DIR_SIZE ||
-            inode->i_ino == BTRFS_FIRST_FREE_OBJECTID) {
+            inode->i_ino == BTRFS_FIRST_FREE_OBJECTID)
                 return -ENOTEMPTY;
-        }
 
         trans = btrfs_start_transaction(root, 1);
         btrfs_set_trans_block_group(trans, dir);
 
+        if (unlikely(inode->i_ino == BTRFS_EMPTY_SUBVOL_DIR_OBJECTID)) {
+                err = btrfs_unlink_subvol(trans, root, dir,
+                                          BTRFS_I(inode)->location.objectid,
+                                          dentry->d_name.name,
+                                          dentry->d_name.len);
+                goto out;
+        }
+
         err = btrfs_orphan_add(trans, inode);
         if (err)
-                goto fail_trans;
+                goto out;
 
         /* now the directory is empty */
         err = btrfs_unlink_inode(trans, root, dir, dentry->d_inode,
                                  dentry->d_name.name, dentry->d_name.len);
         if (!err)
                 btrfs_i_size_write(inode, 0);
-
-fail_trans:
+out:
         nr = trans->blocks_used;
         ret = btrfs_end_transaction_throttle(trans, root);
         btrfs_btree_balance_dirty(root, nr);
@@ -3091,29 +3156,67 @@ out_err:
  * is kind of like crossing a mount point.
  */
 static int fixup_tree_root_location(struct btrfs_root *root,
-                             struct btrfs_key *location,
-                             struct btrfs_root **sub_root,
-                             struct dentry *dentry)
+                                    struct inode *dir,
+                                    struct dentry *dentry,
+                                    struct btrfs_key *location,
+                                    struct btrfs_root **sub_root)
 {
-        struct btrfs_root_item *ri;
+        struct btrfs_path *path;
+        struct btrfs_root *new_root;
+        struct btrfs_root_ref *ref;
+        struct extent_buffer *leaf;
+        int ret;
+        int err = 0;
 
-        if (btrfs_key_type(location) != BTRFS_ROOT_ITEM_KEY)
-                return 0;
-        if (location->objectid == BTRFS_ROOT_TREE_OBJECTID)
-                return 0;
+        path = btrfs_alloc_path();
+        if (!path) {
+                err = -ENOMEM;
+                goto out;
+        }
 
-        *sub_root = btrfs_read_fs_root(root->fs_info, location,
-                                        dentry->d_name.name,
-                                        dentry->d_name.len);
-        if (IS_ERR(*sub_root))
-                return PTR_ERR(*sub_root);
+        err = -ENOENT;
+        ret = btrfs_find_root_ref(root->fs_info->tree_root, path,
+                                  BTRFS_I(dir)->root->root_key.objectid,
+                                  location->objectid);
+        if (ret) {
+                if (ret < 0)
+                        err = ret;
+                goto out;
+        }
 
-        ri = &(*sub_root)->root_item;
-        location->objectid = btrfs_root_dirid(ri);
-        btrfs_set_key_type(location, BTRFS_INODE_ITEM_KEY);
-        location->offset = 0;
+        leaf = path->nodes[0];
+        ref = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_root_ref);
+        if (btrfs_root_ref_dirid(leaf, ref) != dir->i_ino ||
+            btrfs_root_ref_name_len(leaf, ref) != dentry->d_name.len)
+                goto out;
 
-        return 0;
+        ret = memcmp_extent_buffer(leaf, dentry->d_name.name,
+                                   (unsigned long)(ref + 1),
+                                   dentry->d_name.len);
+        if (ret)
+                goto out;
+
+        btrfs_release_path(root->fs_info->tree_root, path);
+
+        new_root = btrfs_read_fs_root_no_name(root->fs_info, location);
+        if (IS_ERR(new_root)) {
+                err = PTR_ERR(new_root);
+                goto out;
+        }
+
+        if (btrfs_root_refs(&new_root->root_item) == 0) {
+                err = -ENOENT;
+                goto out;
+        }
+
+        *sub_root = new_root;
+        location->objectid = btrfs_root_dirid(&new_root->root_item);
+        location->type = BTRFS_INODE_ITEM_KEY;
+        location->offset = 0;
+        err = 0;
+out:
+        btrfs_free_path(path);
+        return err;
 }
 
 static void inode_tree_add(struct inode *inode)
@@ -3246,11 +3349,34 @@ struct inode *btrfs_iget(struct super_block *s, struct btrfs_key *location,
         return inode;
 }
 
+static struct inode *new_simple_dir(struct super_block *s,
+                                    struct btrfs_key *key,
+                                    struct btrfs_root *root)
+{
+        struct inode *inode = new_inode(s);
+
+        if (!inode)
+                return ERR_PTR(-ENOMEM);
+
+        init_btrfs_i(inode);
+
+        BTRFS_I(inode)->root = root;
+        memcpy(&BTRFS_I(inode)->location, key, sizeof(*key));
+        BTRFS_I(inode)->dummy_inode = 1;
+
+        inode->i_ino = BTRFS_EMPTY_SUBVOL_DIR_OBJECTID;
+        inode->i_op = &simple_dir_inode_operations;
+        inode->i_fop = &simple_dir_operations;
+        inode->i_mode = S_IFDIR | S_IRUGO | S_IWUSR | S_IXUGO;
+        inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
+
+        return inode;
+}
+
 struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
 {
         struct inode *inode;
-        struct btrfs_inode *bi = BTRFS_I(dir);
-        struct btrfs_root *root = bi->root;
+        struct btrfs_root *root = BTRFS_I(dir)->root;
         struct btrfs_root *sub_root = root;
         struct btrfs_key location;
         int ret;
@@ -3263,17 +3389,25 @@ struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
         if (ret < 0)
                 return ERR_PTR(ret);
 
-        inode = NULL;
-        if (location.objectid) {
-                ret = fixup_tree_root_location(root, &location, &sub_root,
-                                                dentry);
-                if (ret < 0)
-                        return ERR_PTR(ret);
-                if (ret > 0)
-                        return ERR_PTR(-ENOENT);
+        if (location.objectid == 0)
+                return NULL;
+
+        if (location.type == BTRFS_INODE_ITEM_KEY) {
+                inode = btrfs_iget(dir->i_sb, &location, root);
+                return inode;
+        }
+
+        BUG_ON(location.type != BTRFS_ROOT_ITEM_KEY);
+
+        ret = fixup_tree_root_location(root, dir, dentry,
+                                       &location, &sub_root);
+        if (ret < 0) {
+                if (ret != -ENOENT)
+                        inode = ERR_PTR(ret);
+                else
+                        inode = new_simple_dir(dir->i_sb, &location, sub_root);
+        } else {
                 inode = btrfs_iget(dir->i_sb, &location, sub_root);
-                if (IS_ERR(inode))
-                        return ERR_CAST(inode);
         }
         return inode;
 }
@@ -3283,9 +3417,6 @@ static struct dentry *btrfs_lookup(struct inode *dir, struct dentry *dentry,
 {
         struct inode *inode;
 
-        if (dentry->d_name.len > BTRFS_NAME_LEN)
-                return ERR_PTR(-ENAMETOOLONG);
-
         inode = btrfs_lookup_dentry(dir, dentry);
         if (IS_ERR(inode))
                 return ERR_CAST(inode);
@@ -3691,26 +3822,35 @@ int btrfs_add_link(struct btrfs_trans_handle *trans,
                    struct inode *parent_inode, struct inode *inode,
                    const char *name, int name_len, int add_backref, u64 index)
 {
-        int ret;
+        int ret = 0;
         struct btrfs_key key;
         struct btrfs_root *root = BTRFS_I(parent_inode)->root;
 
-        key.objectid = inode->i_ino;
-        btrfs_set_key_type(&key, BTRFS_INODE_ITEM_KEY);
-        key.offset = 0;
+        if (unlikely(inode->i_ino == BTRFS_FIRST_FREE_OBJECTID)) {
+                memcpy(&key, &BTRFS_I(inode)->root->root_key, sizeof(key));
+        } else {
+                key.objectid = inode->i_ino;
+                btrfs_set_key_type(&key, BTRFS_INODE_ITEM_KEY);
+                key.offset = 0;
+        }
+
+        if (unlikely(inode->i_ino == BTRFS_FIRST_FREE_OBJECTID)) {
+                ret = btrfs_add_root_ref(trans, root->fs_info->tree_root,
+                                         key.objectid, root->root_key.objectid,
+                                         parent_inode->i_ino,
+                                         index, name, name_len);
+        } else if (add_backref) {
+                ret = btrfs_insert_inode_ref(trans, root,
+                                             name, name_len, inode->i_ino,
+                                             parent_inode->i_ino, index);
+        }
 
-        ret = btrfs_insert_dir_item(trans, root, name, name_len,
-                                    parent_inode->i_ino,
-                                    &key, btrfs_inode_type(inode),
-                                    index);
         if (ret == 0) {
-                if (add_backref) {
-                        ret = btrfs_insert_inode_ref(trans, root,
-                                                     name, name_len,
-                                                     inode->i_ino,
-                                                     parent_inode->i_ino,
-                                                     index);
-                }
+                ret = btrfs_insert_dir_item(trans, root, name, name_len,
+                                            parent_inode->i_ino, &key,
+                                            btrfs_inode_type(inode), index);
+                BUG_ON(ret);
+
                 btrfs_i_size_write(parent_inode, parent_inode->i_size +
                                    name_len * 2);
                 parent_inode->i_mtime = parent_inode->i_ctime = CURRENT_TIME;
@@ -4800,31 +4940,29 @@ static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 {
         struct btrfs_trans_handle *trans;
         struct btrfs_root *root = BTRFS_I(old_dir)->root;
+        struct btrfs_root *dest = BTRFS_I(new_dir)->root;
         struct inode *new_inode = new_dentry->d_inode;
         struct inode *old_inode = old_dentry->d_inode;
         struct timespec ctime = CURRENT_TIME;
         u64 index = 0;
+        u64 root_objectid;
         int ret;
 
-        /* we're not allowed to rename between subvolumes */
-        if (BTRFS_I(old_inode)->root->root_key.objectid !=
-            BTRFS_I(new_dir)->root->root_key.objectid)
+        /* we only allow rename subvolume link between subvolumes */
+        if (old_inode->i_ino != BTRFS_FIRST_FREE_OBJECTID && root != dest)
                 return -EXDEV;
 
-        if (S_ISDIR(old_inode->i_mode) && new_inode &&
-            new_inode->i_size > BTRFS_EMPTY_DIR_SIZE) {
+        if (old_inode->i_ino == BTRFS_EMPTY_SUBVOL_DIR_OBJECTID ||
+            (new_inode && new_inode->i_ino == BTRFS_FIRST_FREE_OBJECTID))
                 return -ENOTEMPTY;
-        }
 
-        /* to rename a snapshot or subvolume, we need to juggle the
-         * backrefs.  This isn't coded yet
-         */
-        if (old_inode->i_ino == BTRFS_FIRST_FREE_OBJECTID)
-                return -EXDEV;
+        if (S_ISDIR(old_inode->i_mode) && new_inode &&
+            new_inode->i_size > BTRFS_EMPTY_DIR_SIZE)
+                return -ENOTEMPTY;
 
         ret = btrfs_check_metadata_free_space(root);
         if (ret)
-                goto out_unlock;
+                return ret;
 
         /*
          * we're using rename to replace one file with another.
@@ -4837,6 +4975,9 @@ static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 
         trans = btrfs_start_transaction(root, 1);
 
+        if (dest != root)
+                btrfs_record_root_in_trans(trans, dest);
+
         /*
          * make sure the inode gets flushed if it is replacing
          * something.
@@ -4846,18 +4987,22 @@ static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
                 btrfs_add_ordered_operation(trans, root, old_inode);
         }
 
-        /*
-         * this is an ugly little race, but the rename is required to make
-         * sure that if we crash, the inode is either at the old name
-         * or the new one.  pinning the log transaction lets us make sure
-         * we don't allow a log commit to come in after we unlink the
-         * name but before we add the new name back in.
-         */
-        btrfs_pin_log_trans(root);
+        if (old_inode->i_ino == BTRFS_FIRST_FREE_OBJECTID) {
+                /* force full log commit if subvolume involved. */
+                root->fs_info->last_trans_log_full_commit = trans->transid;
+        } else {
+                /*
+                 * this is an ugly little race, but the rename is required
+                 * to make sure that if we crash, the inode is either at the
+                 * old name or the new one.  pinning the log transaction lets
+                 * us make sure we don't allow a log commit to come in after
+                 * we unlink the name but before we add the new name back in.
+                 */
+                btrfs_pin_log_trans(root);
+        }
 
         btrfs_set_trans_block_group(trans, new_dir);
 
-        btrfs_inc_nlink(old_dentry->d_inode);
         old_dir->i_ctime = old_dir->i_mtime = ctime;
         new_dir->i_ctime = new_dir->i_mtime = ctime;
         old_inode->i_ctime = ctime;
@@ -4865,47 +5010,58 @@ static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
         if (old_dentry->d_parent != new_dentry->d_parent)
                 btrfs_record_unlink_dir(trans, old_dir, old_inode, 1);
 
-        ret = btrfs_unlink_inode(trans, root, old_dir, old_dentry->d_inode,
-                                 old_dentry->d_name.name,
-                                 old_dentry->d_name.len);
-        if (ret)
-                goto out_fail;
+        if (unlikely(old_inode->i_ino == BTRFS_FIRST_FREE_OBJECTID)) {
+                root_objectid = BTRFS_I(old_inode)->root->root_key.objectid;
+                ret = btrfs_unlink_subvol(trans, root, old_dir, root_objectid,
+                                        old_dentry->d_name.name,
+                                        old_dentry->d_name.len);
+        } else {
+                btrfs_inc_nlink(old_dentry->d_inode);
+                ret = btrfs_unlink_inode(trans, root, old_dir,
+                                         old_dentry->d_inode,
+                                         old_dentry->d_name.name,
+                                         old_dentry->d_name.len);
+        }
+        BUG_ON(ret);
 
         if (new_inode) {
                 new_inode->i_ctime = CURRENT_TIME;
-                ret = btrfs_unlink_inode(trans, root, new_dir,
-                                         new_dentry->d_inode,
-                                         new_dentry->d_name.name,
-                                         new_dentry->d_name.len);
-                if (ret)
-                        goto out_fail;
+                if (unlikely(new_inode->i_ino ==
+                             BTRFS_EMPTY_SUBVOL_DIR_OBJECTID)) {
+                        root_objectid = BTRFS_I(new_inode)->location.objectid;
+                        ret = btrfs_unlink_subvol(trans, dest, new_dir,
+                                                root_objectid,
+                                                new_dentry->d_name.name,
+                                                new_dentry->d_name.len);
+                        BUG_ON(new_inode->i_nlink == 0);
+                } else {
+                        ret = btrfs_unlink_inode(trans, dest, new_dir,
+                                                 new_dentry->d_inode,
+                                                 new_dentry->d_name.name,
+                                                 new_dentry->d_name.len);
+                }
+                BUG_ON(ret);
                 if (new_inode->i_nlink == 0) {
                         ret = btrfs_orphan_add(trans, new_dentry->d_inode);
-                        if (ret)
-                                goto out_fail;
+                        BUG_ON(ret);
                 }
-
         }
         ret = btrfs_set_inode_index(new_dir, &index);
-        if (ret)
-                goto out_fail;
+        BUG_ON(ret);
 
-        ret = btrfs_add_link(trans, new_dentry->d_parent->d_inode,
-                             old_inode, new_dentry->d_name.name,
+        ret = btrfs_add_link(trans, new_dir, old_inode,
+                             new_dentry->d_name.name,
                              new_dentry->d_name.len, 1, index);
-        if (ret)
-                goto out_fail;
+        BUG_ON(ret);
 
-        btrfs_log_new_name(trans, old_inode, old_dir,
-                                       new_dentry->d_parent);
-out_fail:
+        if (old_inode->i_ino != BTRFS_FIRST_FREE_OBJECTID) {
+                btrfs_log_new_name(trans, old_inode, old_dir,
+                                   new_dentry->d_parent);
+                btrfs_end_log_trans(root);
+        }
 
-        /* this btrfs_end_log_trans just allows the current
-         * log-sub transaction to complete
-         */
-        btrfs_end_log_trans(root);
         btrfs_end_transaction_throttle(trans, root);
-out_unlock:
+
         return ret;
 }