sysvmq: Implement send and recv and refactor

Implement sending to and receiving from SysV IPC message queues. While
at it refactor the whole library. Write documentation for the sysvmq
library.

sysvmq/tests/main.rs

@@ -0,0 +1,68 @@
+use sysvmq::SysvMq;
+
+#[test]
+fn new_send_recv_delete() {
+    let mut mq = SysvMq::new(0).expect("could not create SysV message queue with key 0");
+    let msg = b"this is a test";
+    let mut buf = [0u8; 14];
+    mq.send(msg)
+        .expect("could not send message to SysV message queue");
+    mq.recv(&mut buf)
+        .expect("could not receive message from SysV message queue");
+    mq.delete().expect("could not destroy SysV message queue");
+    assert_eq!(msg, &buf);
+}
+
+#[test]
+fn separate_send_recv_clone() {
+    let mut sender = SysvMq::new(0).expect("could not create SysV message queue with key 0");
+    let mut receiver = sender.clone();
+    let msg = b"this is another test";
+    let mut buf = [0u8; 20];
+    sender
+        .send(msg)
+        .expect("could not send message to SysV message queue");
+    receiver
+        .recv(&mut buf)
+        .expect("could not receive message from SysV message queue");
+    sender
+        .delete()
+        .expect("could not destroy SysV message queue");
+    assert_eq!(msg, &buf);
+}
+
+#[test]
+fn separate_send_recv_open() {
+    let mut sender = SysvMq::new(0).expect("could not create SysV message queue with key 0");
+    let mut receiver = SysvMq::open(sender.key, sender.id)
+        .expect("could not create second handle to SysV message queue");
+    let msg = b"this is another test";
+    let mut buf = [0u8; 20];
+    sender
+        .send(msg)
+        .expect("could not send message to SysV message queue");
+    receiver
+        .recv(&mut buf)
+        .expect("could not receive message from SysV message queue");
+    sender
+        .delete()
+        .expect("could not destroy SysV message queue");
+    assert_eq!(msg, &buf);
+}
+
+#[test]
+fn change_mode() {
+    let mut mq = SysvMq::new(0).expect("could not create SysV message queue with key 0");
+    let init_stats = mq
+        .stat()
+        .expect("could not get stats from SysV message queue");
+    mq.mode(0o666)
+        .expect("could not set mode of SysV message queue");
+    let new_stats = mq
+        .stat()
+        .expect("could not get stats from SysV message queue");
+    mq.delete().expect("could not destroy SysV message queue");
+
+    assert_eq!(0o644, init_stats.msg_perm.mode);
+    assert_eq!(0o666, new_stats.msg_perm.mode);
+}