Added comments to process

risc_v/ch6/src/process.rs

@@ -12,7 +12,7 @@ use alloc::collections::linked_list::LinkedList;
 // We will have this list OWN the process. So, anytime we want
 // the process, we will consult the process list.
 static mut PROCESS_LIST: LinkedList<Process> = LinkedList::new();
-static mut CURRENT_0: u16 = 0;
+static mut CURRENT: [u16; 2] = [0; 2];
 
 /// We will eventually move this function out of here, but its
 /// job is just to take a slot in the process list.
@@ -27,23 +27,40 @@ fn init_process() {
 /// Add a process given a function address and then
 /// push it onto the LinkedList. Uses Process::new_default
 /// to create a new stack, etc.
-pub fn add_process_default(proc: fn()) {
+pub fn add_process_default(pr: fn()) {
     unsafe {
-        let p = Process::new_default(proc);
+        let p = Process::new_default(pr);
         PROCESS_LIST.push_back(p);
     }
 }
 
+// This should only be called once, and its job is to create
+// the init process. Right now, this process is in the kernel,
+// but later, it should call the shell.
 pub fn init() {
     add_process_default(init_process);
     unsafe {
         let p = PROCESS_LIST.back();
         if let Some(pd) = p {
-            CURRENT_0 = pd.pid;
+            // Put the initial process on the first CPU.
+            CURRENT[0] = pd.pid;
         }
     }
 }
 
+// Our process must be able to sleep, wait, or run.
+// Running - means that when the scheduler finds this process, it can run it.
+// Sleeping - means that the process is waiting on a certain amount of time.
+// Waiting - means that the process is waiting on I/O
+// Dead - We should never get here, but we can flag a process as Dead and clean
+//        it out of the list later.
+pub enum ProcessState {
+    Running,
+    Sleeping,
+    Waiting,
+    Dead
+}
+
 // Let's represent this in C ABI. We do this
 // because we need to access some of the fields
 // in assembly. Rust gets to choose how it orders
@@ -55,11 +72,16 @@ pub struct Process {
     stack: *mut u8,
     program_counter: usize,
     pid: u16,
+    state: ProcessState,
     data: ProcessData,
 }
 
 impl Process {
     pub fn new_default(func: fn()) -> Self {
+        // This probably shouldn't go here, but we need to calculate
+        // a new PID. For now, this just takes the bottom of the list
+        // and adds one to the PID. We assume that we're sorting the
+        // list in increasing PID order.
         let pd;
         unsafe {
             let plb = PROCESS_LIST.back();
@@ -67,21 +89,30 @@ impl Process {
                 pd = p.pid + 1;
             }
             else {
+                // If the list is empty, we allocate pid 1.
                 pd = 1
             }
         } 
+        // Now that we have a PID, let's create a new process.
+        // We set the process as waiting so that whomever called us
+        // can wake it up themselves. This allows us to take our time
+        // and allocate the process.
         Process {
             frame: TrapFrame::zero(),
             stack: alloc(1),
             program_counter: func as usize,
             pid: pd,
+            state: ProcessState::Waiting,
             data: ProcessData::zero()
         }
     }
 }
 
+// Since we're storing ownership of a Process in the linked list,
+// we can cause it to deallocate automatically when it is removed.
 impl Drop for Process {
     fn drop(&mut self) {
+        // We allocate the stack as a page.
         dealloc(self.stack);
     }
 }
@@ -93,6 +124,9 @@ pub struct ProcessData {
     cwd_path: [u8; 128],
 }
 
+// This is private data that we can query with system calls.
+// If we want to implement CFQ (completely fair queuing), which
+// is a per-process block queuing algorithm, we can put that here.
 impl ProcessData {
     pub fn zero() -> Self {
         ProcessData {