Problem with function signatures of getpriority and setpriority for gnu linux

[bvaisvil]

This issue is for version 0.2.70 compiling for x86_64-unknown-linux-gnu on 5.1.18-200.fc29.x86_64

The function signatures of getpriority and setpriority are defined as such:

    pub fn getpriority(which: ::__priority_which_t, who: ::id_t) -> ::c_int;
    pub fn setpriority(
        which: ::__priority_which_t,
        who: ::id_t,
        prio: ::c_int,
    ) -> ::c_int;

The issue is the first argument, which is defined as a __priority_which_t (a c_uint) however, the which constants (PRIO_PROCESS, etc) are defined as c_int.

So passing PRIO_PROCESS to either function results in a compiler error:

error[E0308]: mismatched types
 --> src/main.rs:6:34
  |
6 |         let result = getpriority(PRIO_PROCESS, pid);
  |                                  ^^^^^^^^^^^^ expected `u32`, found `i32`
  |
help: you can convert an `i32` to `u32` and panic if the converted value wouldn't fit
  |
6 |         let result = getpriority(PRIO_PROCESS.try_into().unwrap(), pid);
  |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Here's my code to reproduce the issue:

use libc::{getpriority, PRIO_PROCESS, id_t};

fn main() {
    let pid: id_t = 0;
    unsafe {
        let result = getpriority(PRIO_PROCESS, pid);
        println!("{}", result);
    }
}

Please let me know if there is anything else I can provide to help.

[JohnTitor]

We should define PRIO_PROCESS and other two constants as __priority_which_t since it's a c_enum in glibc like __rlimit_resource_t and related items.