Kernel 6.5 added a few new pidfd functions: SCM_PIDFD and SO_PEERPIDFD. The idea behind them is the same as SCM_CREDENTIALS and SO_PEERCRED respectively. The only difference is that the PIDFD functions return not a plain, numerical PID but a file descriptor instead. A plain PID is small number of type pid_t that is incremented for each new process and wraps over when too many processes have been created. This PID is usually used to look up some information about the process via files in /proc...
