sigaction struct on OS X

[w1ldptr]

I've been looking on signal-handling code in nix-rust to implement signal support in mio and it seems that sigaction struct definition for OS X is a bit off.

Relevant definition from 10.10:

/* union for signal handlers */
union __sigaction_u {
        void    (*__sa_handler)(int);
        void    (*__sa_sigaction)(int, struct __siginfo *,
                       void *);
};

/* Signal vector template for Kernel user boundary */
struct  __sigaction {
        union __sigaction_u __sigaction_u;  /* signal handler */
        void    (*sa_tramp)(void *, int, int, siginfo_t *, void *);
        sigset_t sa_mask;               /* signal mask to apply */
        int     sa_flags;               /* see signal options below */
};

/*                                                                                                                                                                              
 * Signal vector "template" used in sigaction call.                                                                                                                             
 */
struct  sigaction {
        union __sigaction_u __sigaction_u;  /* signal handler */
    sigset_t sa_mask;               /* signal mask to apply */
        int     sa_flags;               /* see signal options below */
};

struct definition from nix:

    #[cfg(any(target_os = "macos", target_os = "ios"))]
    #[repr(C)]
    #[allow(missing_copy_implementations)]
    pub struct sigaction {
        pub sa_handler: extern fn(libc::c_int),
        sa_tramp: *mut libc::c_void,
        pub sa_mask: sigset_t,
        pub sa_flags: SockFlag,
    }

So it seems that nix defines sigaction according to private kernel-user boundary OS X struct instead of public struct which actually used as param type to sigaction function.
Also I need the sa_sigaction(instead of sa_handler which is currently used in nix struct) handler to obtain siginfo_t structure and I'm struggling to define c-union in Rust. Any suggestions?

[vhbit]

@vbuslov there is no way to define unions in Rust, in case of data with the same size (like pointer to a function) workaround is to use mem::transmute.

[fiveop]

I have the same problem and was thinking of using one or two enums to encapsulate the differences between sa_handler, sa_sigaction as well as the difference between an actual function pointer and SIG_IGN and SIG_DFL. I'll work on a proposal.

[carllerche]

Great! Looking forward to it.

[fiveop]

#241 would solve the second part of the question. The first would be solved by using libc's raw structs instead of our own. See https://github.com/rust-lang-nursery/libc/blob/master/src/unix/bsd/apple/mod.rs .

[kamalmarhubi]

Filed #264 to track the first part. I'll start on the signal module which should let us close this.

[fiveop]

8f1d193 fixes the first part, which should resolve this issue.