Update handling of errno

This commit copies the latest errno-handling code from libstd's
`src/libstd/sys/unix/os.rs`, which brings support for more platforms.
The code has to be copied because libstd doesn't export `errno`
(`std::sys` is private).

serial-unix/src/error.rs

@@ -20,12 +20,13 @@
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 use core;
+use libc;
 
 use std::ffi::CStr;
 use std::io;
 use std::str;
 
-use libc::{c_int, c_char, size_t};
+use libc::{c_int, c_char};
 
 pub fn last_os_error() -> core::Error {
     from_raw_os_error(errno())
@@ -50,66 +51,62 @@ pub fn from_raw_os_error(errno: i32) -> core::Error {
 
 const TMPBUF_SZ: usize = 128;
 
-pub fn errno() -> i32 {
-    #[cfg(any(target_os = "macos", target_os = "ios", target_os = "freebsd"))]
-    unsafe fn errno_location() -> *const c_int {
-        extern { fn __error() -> *const c_int; }
-        __error()
-    }
-
-    #[cfg(target_os = "bitrig")]
-    fn errno_location() -> *const c_int {
-        extern {
-            fn __errno() -> *const c_int;
-        }
-        unsafe {
-            __errno()
-        }
-    }
-
-    #[cfg(target_os = "dragonfly")]
-    unsafe fn errno_location() -> *const c_int {
-        extern { fn __dfly_error() -> *const c_int; }
-        __dfly_error()
-    }
-
-    #[cfg(target_os = "openbsd")]
-    unsafe fn errno_location() -> *const c_int {
-        extern { fn __errno() -> *const c_int; }
-        __errno()
-    }
-
-    #[cfg(any(target_os = "linux", target_os = "android"))]
-    unsafe fn errno_location() -> *const c_int {
-        extern { fn __errno_location() -> *const c_int; }
-        __errno_location()
-    }
+extern {
+    #[cfg(not(target_os = "dragonfly"))]
+    #[cfg_attr(any(target_os = "linux",
+                   target_os = "emscripten",
+                   target_os = "fuchsia",
+                   target_os = "l4re"),
+               link_name = "__errno_location")]
+    #[cfg_attr(any(target_os = "bitrig",
+                   target_os = "netbsd",
+                   target_os = "openbsd",
+                   target_os = "android",
+                   target_env = "newlib"),
+               link_name = "__errno")]
+    #[cfg_attr(target_os = "solaris", link_name = "___errno")]
+    #[cfg_attr(any(target_os = "macos",
+                   target_os = "ios",
+                   target_os = "freebsd"),
+               link_name = "__error")]
+    #[cfg_attr(target_os = "haiku", link_name = "_errnop")]
+    fn errno_location() -> *mut c_int;
+}
 
+#[cfg(not(target_os = "dragonfly"))]
+pub fn errno() -> i32 {
     unsafe {
         (*errno_location()) as i32
     }
 }
 
-pub fn error_string(errno: i32) -> String {
-    #[cfg(target_os = "linux")]
+#[cfg(target_os = "dragonfly")]
+pub fn errno() -> i32 {
     extern {
-        #[link_name = "__xpg_strerror_r"]
-        fn strerror_r(errnum: c_int, buf: *mut c_char, buflen: size_t) -> c_int;
+        #[thread_local]
+        static errno: c_int;
     }
-    #[cfg(not(target_os = "linux"))]
+
+    unsafe { errno as i32 }
+}
+
+pub fn error_string(errno: i32) -> String {
     extern {
-        fn strerror_r(errnum: c_int, buf: *mut c_char, buflen: size_t) -> c_int;
+        #[cfg_attr(any(target_os = "linux", target_env = "newlib"),
+                   link_name = "__xpg_strerror_r")]
+        fn strerror_r(errnum: c_int, buf: *mut c_char,
+                      buflen: libc::size_t) -> c_int;
     }
 
     let mut buf = [0 as c_char; TMPBUF_SZ];
 
     let p = buf.as_mut_ptr();
     unsafe {
-        if strerror_r(errno as c_int, p, buf.len() as size_t) < 0 {
+        if strerror_r(errno as c_int, p, buf.len()) < 0 {
             panic!("strerror_r failure");
         }
 
         let p = p as *const _;
-        str::from_utf8(CStr::from_ptr(p).to_bytes()).unwrap().to_string()
+        str::from_utf8(CStr::from_ptr(p).to_bytes()).unwrap().to_owned()
     }
 }