wrappers for ->i_mutex access

parallel to mutex_{lock,unlock,trylock,is_locked,lock_nested},
inode_foo(inode) being mutex_foo(&inode->i_mutex).

Please, use those for access to ->i_mutex; over the coming cycle
->i_mutex will become rwsem, with ->lookup() done with it held
only shared.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/nilfs2/ioctl.c

@@ -158,7 +158,7 @@ static int nilfs_ioctl_setflags(struct inode *inode, struct file *filp,
 
 	flags = nilfs_mask_flags(inode->i_mode, flags);
 
-	mutex_lock(&inode->i_mutex);
+	inode_lock(inode);
 
 	oldflags = NILFS_I(inode)->i_flags;
 
@@ -186,7 +186,7 @@ static int nilfs_ioctl_setflags(struct inode *inode, struct file *filp,
 	nilfs_mark_inode_dirty(inode);
 	ret = nilfs_transaction_commit(inode->i_sb);
 out:
-	mutex_unlock(&inode->i_mutex);
+	inode_unlock(inode);
 	mnt_drop_write_file(filp);
 	return ret;
 }