Function mbedtls_hmac_drbg_set_entropy_len 

pub unsafe extern "C" fn mbedtls_hmac_drbg_set_entropy_len(
    ctx: *mut mbedtls_hmac_drbg_context,
    len: usize,
)

\brief This function sets the amount of entropy grabbed on each seed or reseed.

See the documentation of mbedtls_hmac_drbg_seed() for the default value.

\param ctx The HMAC_DRBG context. \param len The amount of entropy to grab, in bytes.