Fix warnings on nightly regarding "extern" functions (#2585)

"extern" without an ABI is deprecated.  So we need to explicitly use
"extern C".

Author: asomers

src/sys/signal.rs

@@ -757,11 +757,11 @@ pub enum SigHandler {
     /// Request that the signal be ignored.
     SigIgn,
     /// Use the given signal-catching function, which takes in the signal.
-    Handler(extern fn(libc::c_int)),
+    Handler(extern "C" fn(libc::c_int)),
     /// Use the given signal-catching function, which takes in the signal, information about how
     /// the signal was generated, and a pointer to the threads `ucontext_t`.
     #[cfg(not(target_os = "redox"))]
-    SigAction(extern fn(libc::c_int, *mut libc::siginfo_t, *mut libc::c_void))
+    SigAction(extern "C" fn(libc::c_int, *mut libc::siginfo_t, *mut libc::c_void))
 }
 
 /// Action to take on receipt of a signal. Corresponds to `sigaction`.
@@ -790,9 +790,9 @@ impl SigAction {
                  (*p).sa_sigaction = match handler {
                     SigHandler::SigDfl => libc::SIG_DFL,
                     SigHandler::SigIgn => libc::SIG_IGN,
-                    SigHandler::Handler(f) => f as *const extern fn(libc::c_int) as usize,
+                    SigHandler::Handler(f) => f as *const extern "C" fn(libc::c_int) as usize,
                     #[cfg(not(target_os = "redox"))]
-                    SigHandler::SigAction(f) => f as *const extern fn(libc::c_int, *mut libc::siginfo_t, *mut libc::c_void) as usize,
+                    SigHandler::SigAction(f) => f as *const extern "C" fn(libc::c_int, *mut libc::siginfo_t, *mut libc::c_void) as usize,
                 };
             }
         }
@@ -852,9 +852,9 @@ impl SigAction {
                 //   ensured that it is correctly initialized.
                 unsafe{
                     *(&p as *const usize
-                         as *const extern fn(_, _, _))
+                         as *const extern "C" fn(_, _, _))
                 }
-                as extern fn(_, _, _)),
+                as extern "C" fn(_, _, _)),
             p => SigHandler::Handler(
                 // Safe for one of two reasons:
                 // * The SigHandler was created by SigHandler::new, in which
@@ -864,9 +864,9 @@ impl SigAction {
                 //   ensured that it is correctly initialized.
                 unsafe{
                     *(&p as *const usize
-                         as *const extern fn(libc::c_int))
+                         as *const extern "C" fn(libc::c_int))
                 }
-                as extern fn(libc::c_int)),
+                as extern "C" fn(libc::c_int)),
         }
     }
 
@@ -880,12 +880,12 @@ impl SigAction {
             p if self.flags().contains(SaFlags::SA_SIGINFO) =>
                 SigHandler::SigAction(
                     *(&p as *const usize
-                         as *const extern fn(_, _, _))
-                as extern fn(_, _, _)),
+                         as *const extern "C" fn(_, _, _))
+                as extern "C" fn(_, _, _)),
             p => SigHandler::Handler(
                     *(&p as *const usize
-                         as *const extern fn(libc::c_int))
-                as extern fn(libc::c_int)),
+                         as *const extern "C" fn(libc::c_int))
+                as extern "C" fn(libc::c_int)),
         }
         }
     }
@@ -947,7 +947,7 @@ pub unsafe fn sigaction(signal: Signal, sigaction: &SigAction) -> Result<SigActi
 /// # use nix::sys::signal::{self, Signal, SigHandler};
 /// static SIGNALED: AtomicBool = AtomicBool::new(false);
 ///
-/// extern fn handle_sigint(signal: libc::c_int) {
+/// extern "C" fn handle_sigint(signal: libc::c_int) {
 ///     let signal = Signal::try_from(signal).unwrap();
 ///     SIGNALED.store(signal == Signal::SIGINT, Ordering::Relaxed);
 /// }
@@ -984,7 +984,7 @@ pub unsafe fn signal(signal: Signal, handler: SigHandler) -> Result<SigHandler>
             libc::SIG_DFL => SigHandler::SigDfl,
             libc::SIG_IGN => SigHandler::SigIgn,
             p => SigHandler::Handler(
-                unsafe { *(&p as *const usize as *const extern fn(libc::c_int)) } as extern fn(libc::c_int)),
+                unsafe { *(&p as *const usize as *const extern "C" fn(libc::c_int)) } as extern "C" fn(libc::c_int)),
         }
     })
 }

src/sys/statfs.rs

@@ -25,18 +25,18 @@ pub type fsid_t = libc::fsid_t;
 cfg_if! {
     if #[cfg(any(linux_android, target_os = "fuchsia"))] {
         type type_of_statfs = libc::statfs64;
-        const LIBC_FSTATFS: unsafe extern fn
+        const LIBC_FSTATFS: unsafe extern "C" fn
             (fd: libc::c_int, buf: *mut type_of_statfs) -> libc::c_int
             = libc::fstatfs64;
-        const LIBC_STATFS: unsafe extern fn
+        const LIBC_STATFS: unsafe extern "C" fn
             (path: *const libc::c_char, buf: *mut type_of_statfs) -> libc::c_int
             = libc::statfs64;
     } else {
         type type_of_statfs = libc::statfs;
-        const LIBC_FSTATFS: unsafe extern fn
+        const LIBC_FSTATFS: unsafe extern "C" fn
             (fd: libc::c_int, buf: *mut type_of_statfs) -> libc::c_int
             = libc::fstatfs;
-        const LIBC_STATFS: unsafe extern fn
+        const LIBC_STATFS: unsafe extern "C" fn
             (path: *const libc::c_char, buf: *mut type_of_statfs) -> libc::c_int
             = libc::statfs;
     }