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

syscall/src/scheme.rs

@@ -0,0 +1,29 @@
+use core::ops::{Deref, DerefMut};
+use core::{mem, slice};
+
+#[derive(Copy, Clone, Debug, Default)]
+#[repr(packed)]
+pub struct Packet {
+    pub id: usize,
+    pub a: usize,
+    pub b: usize,
+    pub c: usize,
+    pub d: usize
+}
+
+impl Deref for Packet {
+    type Target = [u8];
+    fn deref(&self) -> &[u8] {
+        unsafe {
+            slice::from_raw_parts(self as *const Packet as *const u8, mem::size_of::<Packet>()) as &[u8]
+        }
+    }
+}
+
+impl DerefMut for Packet {
+    fn deref_mut(&mut self) -> &mut [u8] {
+        unsafe {
+            slice::from_raw_parts_mut(self as *mut Packet as *mut u8, mem::size_of::<Packet>()) as &mut [u8]
+        }
+    }
+}