Add random number scheme, update userutils to use it

schemes/randd/Cargo.toml

@@ -0,0 +1,3 @@
+[package]
+name = "randd"
+version = "0.1.0"

schemes/randd/src/main.rs

@@ -0,0 +1,59 @@
+#![feature(asm)]
+
+extern crate syscall;
+
+use std::fs::File;
+use std::io::{Read, Write};
+use std::thread;
+
+use syscall::{Packet, Result, Scheme};
+
+//TODO: Use a CSPRNG, allow write of entropy
+struct RandScheme;
+
+impl Scheme for RandScheme {
+    fn open(&self, _path: &[u8], _flags: usize, _uid: u32, _gid: u32) -> Result<usize> {
+        Ok(0)
+    }
+
+    fn dup(&self, file: usize) -> Result<usize> {
+        Ok(file)
+    }
+
+    fn read(&self, _file: usize, buf: &mut [u8]) -> Result<usize> {
+        let mut i = 0;
+        for chunk in buf.chunks_mut(8) {
+            let mut rand: u64;
+            unsafe {
+                asm!("rdrand rax"
+                    : "={rax}"(rand)
+                    :
+                    :
+                    : "intel", "volatile");
+            }
+            for b in chunk.iter_mut() {
+                *b = rand as u8;
+                rand = rand >> 8;
+                i += 1;
+            }
+        }
+        Ok(i)
+    }
+
+    fn close(&self, _file: usize) -> Result<usize> {
+        Ok(0)
+    }
+}
+
+fn main(){
+    thread::spawn(move || {
+        let mut socket = File::create(":rand").expect("rand: failed to create rand scheme");
+        let scheme = RandScheme;
+        loop {
+            let mut packet = Packet::default();
+            socket.read(&mut packet).expect("rand: failed to read events from rand scheme");
+            scheme.handle(&mut packet);
+            socket.write(&packet).expect("rand: failed to write responses to rand scheme");
+        }
+    });
+}