unistd: add {get,set}domainname

This implements `getdomainname(2)` and `setdomainname(2)`, which are
Linux-specific extensions. References:
 * http://man7.org/linux/man-pages/man2/getdomainname.2.html
 * http://man7.org/linux/man-pages/man2/setdomainname.2.html

Author: lucab

CHANGELOG.md

@@ -48,6 +48,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - Added the `from_raw()` method to `WaitStatus` for converting raw status values
   to `WaitStatus` independent of syscalls.
   ([#741](https://github.com/nix-rust/nix/pull/741))
+- Added `nix::unistd::{getdomainname, setdomainname}` on Linux.
+  ([#816](https://github.com/nix-rust/nix/pull/816))
 
 ### Changed
 - Use native `pipe2` on all BSD targets.  Users should notice no difference.

src/unistd.rs

@@ -756,6 +756,36 @@ pub fn gethostname<'a>(buffer: &'a mut [u8]) -> Result<&'a CStr> {
     })
 }
 
+/// Set the NIS domain name (see
+/// [setdomainname(2)](http://man7.org/linux/man-pages/man2/setdomainname.2.html)).
+#[cfg(target_os = "linux")]
+pub fn setdomainname<S: AsRef<OsStr>>(name: S) -> Result<()> {
+    let ptr = name.as_ref().as_bytes().as_ptr() as *const c_char;
+    let len = name.as_ref().len() as size_t;
+
+    let res = unsafe { libc::setdomainname(ptr, len) };
+    Errno::result(res).map(drop)
+}
+
+/// Get the domain name and store it in the provided buffer, returning a pointer
+/// the CStr in that buffer on success (see
+/// [getdomainname(2)](http://man7.org/linux/man-pages/man2/getdomainname.2.html)).
+///
+/// This function call attempts to get the NIS domain name for the running system
+/// and store it in a provided buffer.  The buffer will be populated with bytes up
+/// to the length of the provided slice including a NUL terminating byte.
+#[cfg(target_os = "linux")]
+pub fn getdomainname<'a>(buffer: &'a mut [u8]) -> Result<&'a CStr> {
+    let ptr = buffer.as_mut_ptr() as *mut c_char;
+    let len = buffer.len() as size_t;
+
+    let res = unsafe { libc::getdomainname(ptr, len) };
+    Errno::result(res).map(|_| {
+        buffer[len - 1] = 0; // ensure always null-terminated
+        unsafe { CStr::from_ptr(buffer.as_ptr() as *const c_char) }
+    })
+}
+
 /// Close a raw file descriptor
 ///
 /// Be aware that many Rust types implicitly close-on-drop, including

test/test_unistd.rs

@@ -404,3 +404,22 @@ fn test_pipe2() {
     let f1 = FdFlag::from_bits_truncate(fcntl(fd1, FcntlArg::F_GETFD).unwrap());
     assert!(f1.contains(FdFlag::FD_CLOEXEC));
 }
+
+#[test]
+fn test_gethostname() {
+    let mut buf = [0u8; 255];
+    let hn = gethostname(&mut buf);
+    assert!(hn.is_ok(), "Error: {:?}", hn.unwrap_err());
+    let hn_string = hn.unwrap().to_str();
+    assert!(hn_string.is_ok(), "Error: {:?}", hn_string.unwrap_err());
+}
+
+#[test]
+#[cfg(target_os = "linux")]
+fn test_getdomainname() {
+    let mut buf = [0u8; 64];
+    let dn = getdomainname(&mut buf);
+    assert!(dn.is_ok(), "Error: {:?}", dn.unwrap_err());
+    let dn_string = dn.unwrap().to_str();
+    assert!(dn_string.is_ok(), "Error: {:?}", dn_string.unwrap_err());
+}