btrfs: allow idmapped rename inode op

Enable btrfs_rename() to handle idmapped mounts. This is just a matter
of passing down the mount's userns.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -9550,6 +9550,7 @@ static int btrfs_rename_exchange(struct inode *old_dir,
 
 static int btrfs_whiteout_for_rename(struct btrfs_trans_handle *trans,
 				     struct btrfs_root *root,
+				     struct user_namespace *mnt_userns,
 				     struct inode *dir,
 				     struct dentry *dentry)
 {
@@ -9562,7 +9563,7 @@ static int btrfs_whiteout_for_rename(struct btrfs_trans_handle *trans,
 	if (ret)
 		return ret;
 
-	inode = btrfs_new_inode(trans, root, &init_user_ns, dir,
+	inode = btrfs_new_inode(trans, root, mnt_userns, dir,
 				dentry->d_name.name,
 				dentry->d_name.len,
 				btrfs_ino(BTRFS_I(dir)),
@@ -9599,9 +9600,10 @@ static int btrfs_whiteout_for_rename(struct btrfs_trans_handle *trans,
 	return ret;
 }
 
-static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
-			   struct inode *new_dir, struct dentry *new_dentry,
-			   unsigned int flags)
+static int btrfs_rename(struct user_namespace *mnt_userns,
+			struct inode *old_dir, struct dentry *old_dentry,
+			struct inode *new_dir, struct dentry *new_dentry,
+			unsigned int flags)
 {
 	struct btrfs_fs_info *fs_info = btrfs_sb(old_dir->i_sb);
 	struct btrfs_trans_handle *trans;
@@ -9791,8 +9793,8 @@ static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 	}
 
 	if (flags & RENAME_WHITEOUT) {
-		ret = btrfs_whiteout_for_rename(trans, root, old_dir,
-						old_dentry);
+		ret = btrfs_whiteout_for_rename(trans, root, mnt_userns,
+						old_dir, old_dentry);
 
 		if (ret) {
 			btrfs_abort_transaction(trans, ret);
@@ -9842,7 +9844,8 @@ static int btrfs_rename2(struct user_namespace *mnt_userns, struct inode *old_di
 		return btrfs_rename_exchange(old_dir, old_dentry, new_dir,
 					  new_dentry);
 
-	return btrfs_rename(old_dir, old_dentry, new_dir, new_dentry, flags);
+	return btrfs_rename(mnt_userns, old_dir, old_dentry, new_dir,
+			    new_dentry, flags);
 }
 
 struct btrfs_delalloc_work {