Cannot access the si_pid field from waitid() call.

[gatoWololo]

Hello!

I'm trying call waitid() from libc like:

let mut siginfo: libc::siginfo_t = unsafe { std::mem::zeroed() };
let ignored = 0;
libc::waitid(libc::P_ALL, ignored, &mut siginfo as *mut libc::siginfo_t , libc::WNOWAIT | libc::WEXITED | libc::WSTOPPED )

I use waitid() instead of waitpid() or wait() since I want the WNOWAIT flag. According to man 2 waitid:

Upon  successful  return,  waitid()  fills  in the following fields of the siginfo_t
       structure pointed to by infop:

       si_pid      The process ID of the child.

However, looking at the declaration of sigino_t for Rust libc, it seems there is no si_pid field available. I know this is related to how sigino_t is defined #716.

Currently I'm linking out to C to get the correct field. It's ugly but it works.

pid_t getPid(siginfo_t* infop) {
  return infop->si_pid;
}

I would like to transmute/cast the struct in Rust, but I have no idea what the si_pid-containing version of siginfo_t looks like.

[gnzlbg]

I think we should just add methods to siginfo in Rust that do the union access internally.

[joshtriplett]

I just ran into this myself. I need access to si_pid for use with libc::WNOHANG: when calling waitid with WNOHANG, you have to check if si_pid == 0 to tell if you have a process status or if waitid has returned immediately because there aren't any waitable processes.

Long-term, I'd love to have the fields defined, but short-term, I'd settle for a method that returns the appropriate field value.

[joshtriplett]

#1858 should fix this.

[JohnTitor]

I'm going to close this as fixed by #1858.