[kernel] Track capability reference counts

First pass at reference-counting capabilities.

src/kernel/objects/process.cpp

@@ -1,3 +1,5 @@
+#include <new>
+
 #include <util/no_construct.h>
 
 #include "assert.h"
@@ -119,28 +121,44 @@ process::thread_exited(thread *th)
 void
 process::add_handle(j6_handle_t handle)
 {
-    m_handles.add(handle);
+    capability *c = g_cap_table.retain(handle);
+    kassert(c, "Trying to add a non-existant handle to a process!");
+
+    if (c) {
+        util::scoped_lock lock {m_handles_lock};
+        m_handles.add(handle);
+    }
 }
 
 bool
-process::remove_handle(j6_handle_t id)
+process::remove_handle(j6_handle_t handle)
 {
-    return m_handles.remove(id);
+    util::scoped_lock lock {m_handles_lock};
+    bool removed = m_handles.remove(handle);
+    lock.release();
+
+    if (removed)
+        g_cap_table.release(handle);
+
+    return removed;
 }
 
 bool
-process::has_handle(j6_handle_t id)
+process::has_handle(j6_handle_t handle)
 {
-    return m_handles.contains(id);
+    util::scoped_lock lock {m_handles_lock};
+    return m_handles.contains(handle);
 }
 
 size_t
 process::list_handles(j6_handle_descriptor *handles, size_t len)
 {
+    util::scoped_lock lock {m_handles_lock};
+
     size_t count = 0;
     for (j6_handle_t handle : m_handles) {
 
-        capability *cap = g_cap_table.find(handle);
+        capability *cap = g_cap_table.find_without_retain(handle);
         kassert(cap, "Found process handle that wasn't in the cap table");
         if (!cap) continue;
 

src/kernel/objects/process.h

@@ -3,7 +3,6 @@
 /// Definition of process kobject types
 
 #include <j6/cap_flags.h>
-#include <util/map.h>
 #include <util/node_map.h>
 #include <util/vector.h>
 
@@ -114,6 +113,7 @@ private:
     util::vector<thread*> m_threads;
 
     util::node_set<j6_handle_t, j6_handle_invalid, heap_allocated> m_handles;
+    util::spinlock m_handles_lock;
 
     enum class state : uint8_t { running, exited };
     state m_state;