sys::prctl: adding calls about core scheduling for isolation based on

[devnexen]

cookie.

What does this PR do

Checklist:

• I have read CONTRIBUTING.md
• I have written necessary tests and rustdoc comments
• A change log has been added if this PR modifies nix's API

[SteveLauC]

These APIs do not seem right? From the kernel commit message, they should look like this:

prctl(PR_SCHED_CORE, PR_SCHED_CORE_GET, tgtpid, pidtype, &cookie)
prctl(PR_SCHED_CORE, PR_SCHED_CORE_CREATE, tgtpid, pidtype, NULL)
prctl(PR_SCHED_CORE, PR_SCHED_CORE_SHARE_TO, tgtpid, pidtype, NULL)
prctl(PR_SCHED_CORE, PR_SCHED_CORE_SHARE_FROM, srcpid, pidtype, NULL)

The third argument should always be a process ID, and the fourth argument should be a kernel enum pid_type:

enum pid_type {
	PIDTYPE_PID,
	PIDTYPE_TGID,
	PIDTYPE_PGID,
	PIDTYPE_SID,
	PIDTYPE_MAX,
};

For the PR_SCHED_CORE_GET sub-command, the cookie should be of type unsigned long long according to the kernel doc:

userspace pointer to an unsigned long long for storing the cookie returned by PR_SCHED_CORE_GET command. Should be 0 for all other commands.

[SteveLauC]

I think we should:

1. Add pid_type to the libc crate
2. Expose the full APIs, e.g., for the PR_SCHED_CORE_GET sub-command, it should be something like:

pub fn sched_core_get(tgtpid: Pid, pid_type: PidType) -> Result<libc::c_ulonglong>;