vfs: mnt_drop_write_file()

new helper (wrapper around mnt_drop_write()) to be used in pair with
mnt_want_write_file().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/ext2/ioctl.c b/fs/ext2/ioctl.c
index 61a3f96..1089f76 100644
--- a/fs/ext2/ioctl.c
+++ b/fs/ext2/ioctl.c
@@ -83,7 +83,7 @@
 		inode->i_ctime = CURRENT_TIME_SEC;
 		mark_inode_dirty(inode);
 setflags_out:
-		mnt_drop_write(filp->f_path.mnt);
+		mnt_drop_write_file(filp);
 		return ret;
 	}
 	case EXT2_IOC_GETVERSION:
@@ -100,7 +100,7 @@
 			inode->i_ctime = CURRENT_TIME_SEC;
 			mark_inode_dirty(inode);
 		}
-		mnt_drop_write(filp->f_path.mnt);
+		mnt_drop_write_file(filp);
 		return ret;
 	case EXT2_IOC_GETRSVSZ:
 		if (test_opt(inode->i_sb, RESERVATION)
@@ -145,7 +145,7 @@
 			rsv->rsv_goal_size = rsv_window_size;
 		}
 		mutex_unlock(&ei->truncate_mutex);
-		mnt_drop_write(filp->f_path.mnt);
+		mnt_drop_write_file(filp);
 		return 0;
 	}
 	default: