Converting pids into a new type ContextId

Keeping pid (and file descriptor, and scheme id, ...) as usize is a
footgun. Let's remove it.

kernel/context/context.rs

@@ -9,6 +9,10 @@ use context::memory::{Grant, Memory, SharedMemory, Tls};
 use syscall::data::Event;
 use sync::{WaitMap, WaitQueue};
 
+/// Unique identifier for a context (i.e. `pid`).
+use ::core::sync::atomic::AtomicUsize;
+int_like!(ContextId, AtomicContextId, usize, AtomicUsize);
+
 /// The status of a context - used for scheduling
 /// See syscall::process::waitpid and the sync module for examples of usage
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
@@ -22,9 +26,9 @@ pub enum Status {
 #[derive(Debug)]
 pub struct Context {
     /// The ID of this context
-    pub id: usize,
+    pub id: ContextId,
     /// The ID of the parent context
-    pub ppid: usize,
+    pub ppid: ContextId,
     /// The real user id
     pub ruid: u32,
     /// The real group id
@@ -42,7 +46,7 @@ pub struct Context {
     /// Context is halting parent
     pub vfork: bool,
     /// Context is being waited on
-    pub waitpid: Arc<WaitMap<usize, usize>>,
+    pub waitpid: Arc<WaitMap<ContextId, usize>>,
     /// Context should wake up at specified time
     pub wake: Option<(u64, u64)>,
     /// The architecture specific context
@@ -75,10 +79,10 @@ pub struct Context {
 
 impl Context {
     /// Create a new context
-    pub fn new(id: usize) -> Context {
+    pub fn new(id: ContextId) -> Context {
         Context {
             id: id,
-            ppid: 0,
+            ppid: ContextId::from(0),
             ruid: 0,
             rgid: 0,
             euid: 0,

kernel/context/event.rs

@@ -17,7 +17,7 @@ pub struct RegKey {
 
 #[derive(PartialEq, Eq, PartialOrd, Ord)]
 pub struct ProcessKey {
-    context_id: usize,
+    context_id: context::context::ContextId,
     fd: usize,
 }
 

kernel/context/list.rs

@@ -7,11 +7,11 @@ use spin::RwLock;
 
 use arch;
 use syscall::error::{Result, Error, EAGAIN};
-use super::context::Context;
+use super::context::{Context, ContextId};
 
 /// Context list type
 pub struct ContextList {
-    map: BTreeMap<usize, Arc<RwLock<Context>>>,
+    map: BTreeMap<ContextId, Arc<RwLock<Context>>>,
     next_id: usize
 }
 
@@ -25,7 +25,7 @@ impl ContextList {
     }
 
     /// Get the nth context.
-    pub fn get(&self, id: usize) -> Option<&Arc<RwLock<Context>>> {
+    pub fn get(&self, id: ContextId) -> Option<&Arc<RwLock<Context>>> {
         self.map.get(&id)
     }
 
@@ -34,7 +34,7 @@ impl ContextList {
         self.map.get(&super::CONTEXT_ID.load(Ordering::SeqCst))
     }
 
-    pub fn iter(&self) -> ::collections::btree_map::Iter<usize, Arc<RwLock<Context>>> {
+    pub fn iter(&self) -> ::collections::btree_map::Iter<ContextId, Arc<RwLock<Context>>> {
         self.map.iter()
     }
 
@@ -44,7 +44,7 @@ impl ContextList {
             self.next_id = 1;
         }
 
-        while self.map.contains_key(&self.next_id) {
+        while self.map.contains_key(&ContextId::from(self.next_id)) {
             self.next_id += 1;
         }
 
@@ -52,7 +52,7 @@ impl ContextList {
             return Err(Error::new(EAGAIN));
         }
 
-        let id = self.next_id;
+        let id = ContextId::from(self.next_id);
         self.next_id += 1;
 
         assert!(self.map.insert(id, Arc::new(RwLock::new(Context::new(id)))).is_none());
@@ -85,7 +85,7 @@ impl ContextList {
         Ok(context_lock)
     }
 
-    pub fn remove(&mut self, id: usize) -> Option<Arc<RwLock<Context>>> {
+    pub fn remove(&mut self, id: ContextId) -> Option<Arc<RwLock<Context>>> {
         self.map.remove(&id)
     }
 }

kernel/context/mod.rs

@@ -1,11 +1,12 @@
 //! Context management
 use alloc::boxed::Box;
-use core::sync::atomic::{AtomicUsize, ATOMIC_USIZE_INIT, Ordering};
+use core::sync::atomic::Ordering;
 use spin::{Once, RwLock, RwLockReadGuard, RwLockWriteGuard};
 
 pub use self::context::{Context, Status};
 pub use self::list::ContextList;
 pub use self::switch::switch;
+pub use context::context::ContextId;
 
 /// Context struct
 mod context;
@@ -35,7 +36,7 @@ pub const CONTEXT_MAX_FILES: usize = 65536;
 static CONTEXTS: Once<RwLock<ContextList>> = Once::new();
 
 #[thread_local]
-static CONTEXT_ID: AtomicUsize = ATOMIC_USIZE_INIT;
+static CONTEXT_ID: context::AtomicContextId = context::AtomicContextId::default();
 
 pub fn init() {
     let mut contexts = contexts_mut();
@@ -69,6 +70,6 @@ pub fn contexts_mut() -> RwLockWriteGuard<'static, ContextList> {
     CONTEXTS.call_once(init_contexts).write()
 }
 
-pub fn context_id() -> usize {
+pub fn context_id() -> context::ContextId {
     CONTEXT_ID.load(Ordering::SeqCst)
 }