stat.rs

let mut stb = syscall::Stat;
if syscall::call::fstat(*dirp.fd, &stb).unwrap() < 0 {
   do_something();
}
/*|     if syscall::call::fstat(*dirp.fd, &stb).unwrap() < 0 {
    |                                       ^^^^ types differ in mutability
    |
    = note: expected type `&mut syscall::Stat`
               found type `&syscall::Stat`*/