/*
 * virtio_rng.h — Virtio 1.0 entropy source driver for StarKernel
 *
 * Real hardware/host entropy, uniformly across all three architectures.
 * Exists specifically because this kernel has no per-arch RNG that covers
 * all three ISAs: amd64 has RDRAND and riscv64 has the Zkr extension, but
 * QEMU's aarch64 CPU models (including "max") expose neither RNDR nor any
 * other RNG property (checked directly against QEMU 10.2.1, see
 * vm_uuid.h's identical finding). A paravirtualized virtio-rng device
 * sidesteps the per-ISA gap entirely: the host supplies the entropy, the
 * guest-side protocol is identical on all three arches.
 *
 * QEMU-only: there is no virtio-rng on real hardware (Milestone 8, bare-
 * metal boot). A real per-arch RNG driver is a separate, later problem.
 *
 * Only one virtio-rng device is supported.
 */

#ifndef STARKERNEL_VIRTIO_RNG_H
#define STARKERNEL_VIRTIO_RNG_H

#include <stddef.h>
#include <stdint.h>

/* virtio PCI vendor (shared with every virtio device) */
#define VIRTIO_RNG_PCI_VENDOR_ID 0x1AF4u
/* device IDs: virtio device id 4 (entropy source) */
#define VIRTIO_RNG_DEVICE_MODERN 0x1044u
#define VIRTIO_RNG_DEVICE_LEGACY 0x1005u

/*
 * virtio_rng_init — locate the virtio-rng device on the PCI bus and bring
 * the driver up. Call once, before the first virtio_rng_get_bytes() call.
 *
 * Returns  0 on success.
 * Returns -1 if no virtio-rng device was found on the PCI bus.
 * Returns -2 on driver initialisation failure (bad BAR, queue setup, etc.).
 */
int virtio_rng_init(void);

/*
 * virtio_rng_ready — 1 if virtio_rng_init() has already succeeded.
 */
int virtio_rng_ready(void);

/*
 * virtio_rng_get_bytes — fill buf with n bytes of real host-supplied
 * entropy, blocking (polling) until all n bytes are obtained. The device
 * may return fewer bytes than requested per request; this loops
 * internally until the buffer is full.
 *
 * Returns  0 on success (buf fully filled).
 * Returns -1 if virtio_rng_init() has not succeeded.
 * Returns -2 on a device/timeout error partway through.
 */
int virtio_rng_get_bytes(uint8_t *buf, size_t n);

#endif /* STARKERNEL_VIRTIO_RNG_H */