Free unused compartments, so they don't leak

Following review feedback from Andrei, Laurie. Thanks both!

example_allocators/compartment_alloc/compartment_alloc.c

@@ -97,3 +97,32 @@ void *__capability malloc_compartment(size_t len, void *__capability compartment
 
     return allocated;
 }
+
+/*
+ * Unmaps the compartment identified by the `compartment_id` argument,
+ * effectively freeing it.
+ *
+ * Note that this is a naive implementation for demo purposes. The capabilities
+ * previously returned by `malloc_compartment` now point to de-allocated memory.
+ */
+void free_compartment(void *__capability compartment_id) {
+    int munmap_rc;
+    int i;
+
+    // Search for a compartment with the given identifier
+    for (i = 0; i < maxCompartments && compartments[i].identifier != compartment_id; i++)
+    {
+    }
+    if (i == maxCompartments)
+    {
+        perror("Given an ID for a non-existent compartment");
+        exit(1);
+    }
+
+    munmap_rc = munmap(compartments[i].buffer, compartments[i].max_allocated);
+    if (munmap_rc != 0) {
+        perror("Attempted to deallocate a compartment, but munmap errored");
+        exit(1);
+    }
+
+}

example_allocators/compartment_alloc/compartment_alloc.h

@@ -11,3 +11,4 @@ typedef struct _heap_compartment
 
 void *__capability init_compartment(size_t size_in_bytes, void *__capability dc);
 void *__capability malloc_compartment(size_t len, void *__capability component_id);
+void free_compartment(void *__capability compartment_id);

example_allocators/compartment_alloc/main.c

@@ -26,7 +26,13 @@ int main()
            "read-only.\n\tWe allocated 256 bytes.\n");
     pp_cap(c2_allocated_memory);
 
-    printf("\nCompleted successfully.\n");
 
+    // Clean up compartments
+    free_compartment(compartment1);
+    free_compartment(compartment2);
+
+    printf("\nFreed compartments.\n");
+
+    printf("\nCompleted successfully.\n");
     return 0;
 }