get_entropy
OSSL_CORE_MAKE_FUNC(size_t, get_entropy, (const OSSL_CORE_HANDLE *handle, unsigned char **pout, int entropy, size_t min_len, size_t max_len))
(void *vctx, OSSL_INOUT_CALLBACK *get_entropy,
entropylen = get_entropy(drbg, &entropy, min_entropy,
entropylen = get_entropy(drbg, &entropy, drbg->strength,