Auto merge of #386 - bugaevc:reboot, r=fiveop

Add reboot() support on Linux

This adds support for calling [reboot(2)](http://linux.die.net/man/2/reboot) on Linux (useful for implementing PID 1!).

* **Testing**: I can't imagine how this could be tested other than manually, which is what I did to ensure it works.
* **libc**: for some reason libc includes neither `reboot()` function, nor `RB_*` constants, so I had to hack-define them here. Should I open a bug/PR against the libc crate?
* **API**: I went with `reboot()` function for restarting, powering off, halting, etc. and an additional `set_cad_enabled()` function for enabling/disabling Ctrl-Alt-Delete, which still corresponds to `reboot()` C call, but has different semantics and return type. (But I'm open to suggestions here -- maybe it would be better to separate each action into its own function, i.e. `restart()`, `poweroff()`, `halt()`?)
* **Documentation**: I see most of the things in nix are undocumented, so I didn't document anything except for the `set_cad_enabled()` function, which obviously uses a non-standard name.
* **Portability**: I implemented the Linux version as I'm not familiar with anything else, but there surely are others (ex. [BSD](http://www.freebsd.org/cgi/man.cgi?reboot(2))). If I didn't mess up anything, the new code is only compiled on Linux/Android, so it should be straightforward to implement the other versions too.

src/sys/mod.rs

@@ -31,6 +31,9 @@ pub mod stat;
 #[cfg(any(target_os = "linux", target_os = "android"))]
 pub mod syscall;
 
+#[cfg(any(target_os = "linux"))]
+pub mod reboot;
+
 #[cfg(not(target_os = "ios"))]
 pub mod termios;
 

src/sys/reboot.rs

@@ -0,0 +1,43 @@
+//! Reboot/shutdown or enable/disable Ctrl-Alt-Delete.
+
+use {Errno, Error, Result};
+use libc;
+use void::Void;
+use std::mem::drop;
+
+/// How exactly should the system be rebooted.
+///
+/// See [`set_cad_enabled()`](fn.set_cad_enabled.html) for
+/// enabling/disabling Ctrl-Alt-Delete.
+#[repr(i32)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum RebootMode {
+    RB_HALT_SYSTEM = libc::RB_HALT_SYSTEM,
+    RB_KEXEC = libc::RB_KEXEC,
+    RB_POWER_OFF = libc::RB_POWER_OFF,
+    RB_AUTOBOOT = libc::RB_AUTOBOOT,
+    // we do not support Restart2,
+    RB_SW_SUSPEND = libc::RB_SW_SUSPEND,
+}
+
+pub fn reboot(how: RebootMode) -> Result<Void> {
+    unsafe {
+        libc::reboot(how as libc::c_int)
+    };
+    Err(Error::Sys(Errno::last()))
+}
+
+/// Enable or disable the reboot keystroke (Ctrl-Alt-Delete).
+///
+/// Corresponds to calling `reboot(RB_ENABLE_CAD)` or `reboot(RB_DISABLE_CAD)` in C.
+pub fn set_cad_enabled(enable: bool) -> Result<()> {
+    let cmd = if enable {
+        libc::RB_ENABLE_CAD
+    } else {
+        libc::RB_DISABLE_CAD
+    };
+    let res = unsafe {
+        libc::reboot(cmd)
+    };
+    Errno::result(res).map(drop)
+}