Stamp out transmute except in certain cases

[kamalmarhubi]

nix is currently a bit too liberal with mem::transmute, using it in situations where some casts would suffice. I'd like to reduce these to a minimum because transmute is a scarily big hammer.

[fiveop]

All occurences. We can discuss each case and tick them off.

git grep -n transmute | while read line; do echo -n $line |  sed -r 's/([a-z\/\.]+\:[0-9]+:).*/\1/g' | sed -r 's/([^\:]+)\:([^\:]+)\:/\- \[ \] https\:\/\/github\.com\/nix-rust\/nix\/blob\/9c6c71a9f5fa4a64d8e5c2996988a93ff5f724c8\/\1#L\2\n/g'; done

• nix/src/sched.rs

  Line 195 in 9c6c71a

  ffi::sched_setaffinity(pid as pid_t, mem::size_of::<CpuSet>() as size_t, mem::transmute(cpuset))

• nix/src/sched.rs

  Line 210 in 9c6c71a

  ffi::clone(mem::transmute(callback as extern "C" fn(*mut Box<::std::ops::FnMut() -> isize>) -> i32),

• nix/src/sys/quota.rs

  Line 116 in 9c6c71a

  quotactl(quota::QuotaCmd(quota::Q_GETQUOTA, which), Some(special), id, mem::transmute(dqblk))

• nix/src/sys/quota.rs

  Line 124 in 9c6c71a

  quotactl(quota::QuotaCmd(quota::Q_SETQUOTA, which), Some(special), id, mem::transmute(&mut dqblk_copy))

• nix/src/sys/signal.rs

  Line 155 in 9c6c71a

  true => Ok(unsafe { mem::transmute(signum) }),

• nix/src/sys/signal.rs

  Line 301 in 9c6c71a

  SigHandler::SigDfl => unsafe { mem::transmute(libc::SIG_DFL) },

• nix/src/sys/signal.rs

  Line 302 in 9c6c71a

  SigHandler::SigIgn => unsafe { mem::transmute(libc::SIG_IGN) },

• nix/src/sys/signal.rs

  Line 303 in 9c6c71a

  SigHandler::Handler(f) => unsafe { mem::transmute(f) },

• nix/src/sys/signal.rs

  Line 304 in 9c6c71a

  SigHandler::SigAction(f) => unsafe { mem::transmute(f) },

• nix/src/sys/signalfd.rs

  Line 107 in 9c6c71a

  Ok(SIGNALFD_SIGINFO_SIZE) => Ok(Some(unsafe { mem::transmute(buffer) })),

• nix/src/sys/socket/addr.rs

  Line 409 in 9c6c71a

  unsafe { mem::transmute(&self.0.sun_path[..self.1]) }

• nix/src/sys/socket/addr.rs

  Line 503 in 9c6c71a

  SockAddr::Inet(InetAddr::V4(ref addr)) => (mem::transmute(addr), mem::size_of::<libc::sockaddr_in>() as libc::socklen_t),

• nix/src/sys/socket/addr.rs

  Line 504 in 9c6c71a

  SockAddr::Inet(InetAddr::V6(ref addr)) => (mem::transmute(addr), mem::size_of::<libc::sockaddr_in6>() as libc::socklen_t),

• nix/src/sys/socket/addr.rs

  Line 505 in 9c6c71a

  SockAddr::Unix(UnixAddr(ref addr, len)) => (mem::transmute(addr), (len + mem::size_of::<libc::sa_family_t>()) as libc::socklen_t),

• nix/src/sys/socket/addr.rs

  Line 507 in 9c6c71a

  SockAddr::Netlink(NetlinkAddr(ref sa)) => (mem::transmute(sa), mem::size_of::<libc::sockaddr_nl>() as libc::socklen_t),

• nix/src/sys/socket/mod.rs

  Line 151 in 9c6c71a

  let cmsg: &cmsghdr = unsafe { mem::transmute(buf.as_ptr()) };

• nix/src/sys/socket/mod.rs

  Line 484 in 9c6c71a

  mem::transmute(&addr),

• nix/src/sys/socket/mod.rs

  Line 588 in 9c6c71a

  let ret = ffi::getpeername(fd, mem::transmute(&addr), &mut len);

• nix/src/sys/socket/mod.rs

  Line 604 in 9c6c71a

  let ret = ffi::getsockname(fd, mem::transmute(&addr), &mut len);

• nix/src/sys/socket/sockopt.rs

  Line 209 in 9c6c71a

  mem::transmute(&mut self.val)

• nix/src/sys/socket/sockopt.rs

  Line 213 in 9c6c71a

  mem::transmute(&mut self.len)

• nix/src/sys/socket/sockopt.rs

  Line 232 in 9c6c71a

  mem::transmute(self.ptr)

• nix/src/sys/socket/sockopt.rs

  Line 254 in 9c6c71a

  mem::transmute(&mut self.val)

• nix/src/sys/socket/sockopt.rs

  Line 258 in 9c6c71a

  mem::transmute(&mut self.len)

• nix/src/sys/socket/sockopt.rs

  Line 277 in 9c6c71a

  mem::transmute(&self.val)

• nix/src/sys/socket/sockopt.rs

  Line 299 in 9c6c71a

  mem::transmute(&mut self.val)

• nix/src/sys/socket/sockopt.rs

  Line 303 in 9c6c71a

  mem::transmute(&mut self.len)

• nix/src/sys/socket/sockopt.rs

  Line 322 in 9c6c71a

  mem::transmute(&self.val)

• nix/src/sys/socket/sockopt.rs

  Line 344 in 9c6c71a

  mem::transmute(&mut self.val)

• nix/src/sys/socket/sockopt.rs

  Line 348 in 9c6c71a

  mem::transmute(&mut self.len)

• nix/src/sys/socket/sockopt.rs

  Line 367 in 9c6c71a

  mem::transmute(&self.val)

• nix/src/ucontext.rs

  Line 32 in 9c6c71a

  unsafe { mem::transmute(&mut self.context.uc_sigmask) }

• nix/src/ucontext.rs

  Line 36 in 9c6c71a

  unsafe { mem::transmute(&self.context.uc_sigmask) }

• nix/test/sys/test_socket.rs

  Line 59 in 9c6c71a

  let expect: &'static [c_char] = unsafe { mem::transmute(&b"/foo/bar"[..]) };