流程ID在Linux中是非负面的吗？

I am implementing a syscall that is called in user-space, lets say by foo. The syscall accesses foo's task_struct ( throught the global pointer current), prints it's name and pid, then goes on to foo's parent-process, foo's parent's parent etc. Prints all their names and pids up to and including the init process's.I am implementing a syscall that is called in u