A way to get the global g state from the initialization of the RNG device.

[dinosaure]

Currently, with MirageOS, it's not possible to get the g state from the initialization (and be able to pass it to some others computations). It should be very nice for the initialize function to return the g state - and then, get it from the start function of an unikernel instead of an unit value. WDYT? The patch should be small but I think it breaks the API.

[hannesm]

I'm not sure I understand what you try to achieve here, sorry. Could you elaborate on the use case you have in mind?

[dinosaure]

So, I have an application (functorized over the Mirage_random.S given by mirage) which expects the g state to be able to generate something random from this state. So I need to pass it from whatever it comes from. In the MirageOS context, due to Mirage_random.S, the type g is completely abstract and I don't have any way to get/create it and use it. It would be nice to have this g state at the start function to pass it then to my application (and ensure a full control of how the application generate random stuffs).

More concretely, a SMTP submission service needs Random.g to generate a stamp needed for the SMTP authentication.

Of course, I can rely on the global state but I lost the ability to fully control the behavior of my application.

[hannesm]

hmm, I fail to understand your requirement. do you need to preserve the generator state for later (potentially a restart)?

Indeed, g is abstract and global. it also changes quickly over time (using rdrand/rdseed and lwt enter_hook). if you have the requirement to preserve g and re-generate the exact same random, my best bet would be to generate random data (with Mirage_crypto_rng.generate) and then construct your own generator (e.g. https://github.com/mirleft/ocaml-x509/blob/v0.14.1/lib/private_key.ml#L23-L26). Since g is abstract, you won't be able to dump and restore it.

In other applications (see the X509 code as well) I've just used an optonal g -- would that be an option for you as well?