Implement user schemes. Example in pcid. Currently deadlocks in UserInner

drivers/pcid/src/main.rs

@@ -2,8 +2,10 @@
 
 extern crate syscall;
 
+use std::fs::File;
+use std::io::{Read, Write};
 use std::thread;
-use syscall::iopl;
+use syscall::{iopl, Packet};
 
 use pci::{Pci, PciBar, PciClass};
 
@@ -75,5 +77,17 @@ fn main() {
         unsafe { iopl(3).unwrap() };
 
         enumerate_pci();
+
+        let mut scheme = File::create(":pci").expect("pcid: failed to create pci scheme");
+        loop {
+            let mut packet = Packet::default();
+            scheme.read(&mut packet).expect("pcid: failed to read events from pci scheme");
+
+            println!("{:?}", packet);
+
+            packet.a = 0;
+
+            scheme.write(&packet).expect("pcid: failed to write responses to pci scheme");
+        }
     });
 }