fn get_si_fd()

in reverie-ptrace/src/timer.rs [625:671]

• 33 lines of code
• 1 McCabe index (conditional complexity)

fn get_si_fd(signal: &libc::siginfo_t) -> libc::c_int {
    // This almost certainly broken for anything other than linux (glibc?).
    //
    // The `libc` crate doesn't expose these fields properly, because the
    // current version was released before union support, and `siginfo_t` is a
    // messy enum/union, making this super fragile.
    //
    // `libc` has an accessor system in place, but only for a few particular
    // signal types as of right now. We could submit a PR for SIGPOLL/SIGIO, but
    // until then, this is copies the currently used accessor idea.

    #[repr(C)]
    #[derive(Copy, Clone)]
    struct sifields_sigpoll {
        si_band: libc::c_long,
        si_fd: libc::c_int,
    }
    #[repr(C)]
    union sifields {
        _align_pointer: *mut libc::c_void,
        sigpoll: sifields_sigpoll,
    }
    #[repr(C)]
    struct siginfo_f {
        _siginfo_base: [libc::c_int; 3],
        sifields: sifields,
        padding: [libc::c_int; 24],
    }

    // These compile to no-op or unconditional runtime panic, which is good,
    // because code not using timers continues to work.
    assert_eq!(
        core::mem::size_of::<siginfo_f>(),
        core::mem::size_of_val(signal),
    );
    assert_eq!(
        core::mem::align_of::<siginfo_f>(),
        core::mem::align_of_val(signal),
    );

    unsafe {
        (*(signal as *const _ as *const siginfo_f))
            .sifields
            .sigpoll
            .si_fd
    }
}