This is what getrandom(2) does, and using getrandom is the recommended path. However, if you use getrandom(2), and you are in early boot, such as by systemd's journald, and you are using it for some pointless HMAC mechanism with a randomly generated key for no specified security goal and no clearly articulated threat model, then you can end up hanging the boot, leading to the entropy deadlock situation I described.

So getrandom(2) will block until the pool is seeded, and all newly written application should use it, and existing applications should switch to it. But you still need to try to lazily generated random keys, and think very hard about whether you really need to generate cryptographic grade random numbers before the user logs in.