Add realtime scheduling calls to std.os.linux (issue #19671)

[curuvar]

Add the following system calls to std.os.linux:

• sched_setscheduler
• sched_getscheduler
• sched_setparam
• sched_getparam
• sched_get_priority_min
• sched_get_priority_max

Also add required sched_param structure and SCHED constant definitions:

• pub const sched_param
• pub const SCHED

[Rexicon226]

should this not be an enum, rather than a struct?

[curuvar]

The problem with it being an enum is that the RESET_ON_FORK is not an independent value, but a flag that is ORed with one of the other values.

[rohlem]

I think the recommended thing to do would be to make it a packed struct, something like this (untested):

pub const SCHED = packed struct(i32) {
  pub const Mode = enum(u3) {
    /// normal multi-user scheduling
    pub const OTHER = 0;
    /// FIFO realtime scheduling
    pub const FIFO = 1;
    /// Round-robin realtime scheduling
    pub const RR = 2;
    /// For "batch" style execution of processes
    pub const BATCH = 3;
    /// Low latency scheduling
    pub const ISO = 4;
    /// For running very low priority background jobs
    pub const IDLE = 5;
    /// Sporadic task model deadline scheduling
    pub const DEADLINE = 6;
  };
  mode: Mode, //bits [0, 2]
  _3: u27 = 0, //bits [3, 29]
  /// set to true to stop children from inheriting policies
  RESET_ON_FORK: bool = false, //bit 30
  _31: u1 = 0, //bit 31
}

[curuvar]

Thank you. I will update my code accordingly.