Task: add an alloc_fd() function

kernel/include/thread/Task.h

@@ -46,6 +46,8 @@ struct Task
     Descriptor files[TASK_MAX_FDS];
 
     AddressSpace address_space;
+
+    int alloc_fd();
 };
 
 void set_context_from_task(Task& task, Context* ctx);

kernel/src/thread/Task.cpp

@@ -26,4 +26,17 @@ void task_restore_floating(Task& task)
 bool Task::is_user_task()
 {
     return user_task;
+}
+
+int Task::alloc_fd()
+{
+    int fd;
+    for (fd = 0; fd < TASK_MAX_FDS; fd++)
+    {
+        if (!files[fd].is_open()) break;
+    }
+
+    if (fd == TASK_MAX_FDS) { return -1; }
+
+    return fd;
 }