/*
 * VIRTIO RNG Emulation via vhost-user
 *
 * Copyright (c) 2021 Mathieu Poirier <mathieu.poirier@linaro.org>
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

#define G_LOG_DOMAIN "vhost-user-rng"
#define G_LOG_USE_STRUCTURED 1

#include <glib.h>
#include <gio/gio.h>
#include <gio/gunixsocketaddress.h>
#include <glib-unix.h>
#include <glib/gstdio.h>
#include <pthread.h>
#include <signal.h>
#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <inttypes.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <time.h>
#include <unistd.h>
#include <endian.h>
#include <assert.h>

#include "qemu/cutils.h"
#include "subprojects/libvhost-user/libvhost-user-glib.h"
#include "subprojects/libvhost-user/libvhost-user.h"

#ifndef container_of
#define container_of(ptr, type, member) ({                      \
        const typeof(((type *) 0)->member) * __mptr = (ptr);     \
        (type *) ((char *) __mptr - offsetof(type, member)); })
#endif

typedef struct {
    VugDev dev;
    struct itimerspec ts;
    timer_t rate_limit_timer;
    pthread_mutex_t rng_mutex;
    pthread_cond_t rng_cond;
    int64_t quota_remaining;
    bool activate_timer;
    GMainLoop *loop;
} VuRNG;

static gboolean print_cap, verbose;
static gchar *source_path, *socket_path;
static gint source_fd, socket_fd = -1;

/* Defaults tailored on virtio-rng.c */
static uint32_t period_ms = 1 << 16;
static uint64_t max_bytes = INT64_MAX;

static void check_rate_limit(union sigval sv)
{
    VuRNG *rng = sv.sival_ptr;
    bool wakeup = false;

    pthread_mutex_lock(&rng->rng_mutex);
    /*
     * The timer has expired and the guest has used all available
     * entropy, which means function vu_rng_handle_request() is waiting
     * on us.  As such wake it up once we're done here.
     */
    if (rng->quota_remaining == 0) {
        wakeup = true;
    }

    /*
     * Reset the entropy available to the guest and tell function
     * vu_rng_handle_requests() to start the timer before using it.
     */
    rng->quota_remaining = max_bytes;
    rng->activate_timer = true;
    pthread_mutex_unlock(&rng->rng_mutex);

    if (wakeup) {
        pthread_cond_signal(&rng->rng_cond);
    }
}

static void setup_timer(VuRNG *rng)
{
    struct sigevent sev;
    int ret;

    memset(&rng->ts, 0, sizeof(struct itimerspec));
    rng->ts.it_value.tv_sec = period_ms / 1000;
    rng->ts.it_value.tv_nsec = (period_ms % 1000) * 1000000;

    /*
     * Call function check_rate_limit() as if it was the start of
     * a new thread when the timer expires.
     */
    sev.sigev_notify = SIGEV_THREAD;
    sev.sigev_notify_function = check_rate_limit;
    sev.sigev_value.sival_ptr = rng;
    /* Needs to be NULL if defaults attributes are to be used. */
    sev.sigev_notify_attributes = NULL;
    ret = timer_create(CLOCK_MONOTONIC, &sev, &rng->rate_limit_timer);
    if (ret < 0) {
        fprintf(stderr, "timer_create() failed\n");
    }

}


/* Virtio helpers */
static uint64_t rng_get_features(VuDev *dev)
{
    if (verbose) {
        g_info("%s: replying", __func__);
    }
    return 0;
}

static void rng_set_features(VuDev *dev, uint64_t features)
{
    if (verbose && features) {
        g_autoptr(GString) s = g_string_new("Requested un-handled feature");
        g_string_append_printf(s, " 0x%" PRIx64 "", features);
        g_info("%s: %s", __func__, s->str);
    }
}

static void vu_rng_handle_requests(VuDev *dev, int qidx)
{
    VuRNG *rng = container_of(dev, VuRNG, dev.parent);
    VuVirtq *vq = vu_get_queue(dev, qidx);
    VuVirtqElement *elem;
    size_t to_read;
    int len, ret;

    printf("vu_rng_handle_requests\n");

    for (;;) {
        /* Get element in the vhost virtqueue */
        elem = vu_queue_pop(dev, vq, sizeof(VuVirtqElement));
        if (!elem) {
            break;
        }

        printf("elem->in_sg[0].iov_base: 0x%lx\n", (uint64_t)elem->in_sg[0].iov_base);

        /* Get the amount of entropy to read from the vhost server */
        to_read = elem->in_sg[0].iov_len;

        pthread_mutex_lock(&rng->rng_mutex);

        /*
         * We have consumed all entropy available for this time slice.
         * Wait for the timer (check_rate_limit()) to tell us about the
         * start of a new time slice.
         */
        if (rng->quota_remaining == 0) {
            pthread_cond_wait(&rng->rng_cond, &rng->rng_mutex);
        }

        /* Start the timer if the last time slice has expired */
        if (rng->activate_timer == true) {
            rng->activate_timer = false;
            ret = timer_settime(rng->rate_limit_timer, 0, &rng->ts, NULL);
            if (ret < 0) {
                fprintf(stderr, "timer_settime() failed\n");
            }
        }

        /* Make sure we don't read more than it's available */
        if (rng->quota_remaining < to_read) {
            to_read = rng->quota_remaining;
        }

        len = read(source_fd, elem->in_sg[0].iov_base, to_read);

        /* Simply return 0 if an error occurs */
        if (len < 0) {
            len = 0;
        }

        rng->quota_remaining -= len;

        pthread_mutex_unlock(&rng->rng_mutex);

        vu_queue_push(dev, vq, elem, len);
        free(elem);
    }

    vu_queue_notify(dev, vq);
}

static void
vu_rng_queue_set_started(VuDev *dev, int qidx, bool started)
{
    VuVirtq *vq = vu_get_queue(dev, qidx);

    g_debug("queue started %d:%d\n", qidx, started);

    if (!qidx) {
        vu_set_queue_handler(dev, vq, started ? vu_rng_handle_requests : NULL);
    }
}

/*
 * Any messages not handled here are processed by the libvhost library
 * itself.
 */
static int rng_process_msg(VuDev *dev, VhostUserMsg *msg, int *do_reply)
{
    VuRNG *rng = container_of(dev, VuRNG, dev.parent);

    if (msg->request == VHOST_USER_NONE) {
        g_main_loop_quit(rng->loop);
        return 1;
    }

    return 0;
}

static const VuDevIface vuiface = {
    .set_features = rng_set_features,
    .get_features = rng_get_features,
    .queue_set_started = vu_rng_queue_set_started,
    .process_msg = rng_process_msg,
};

static gboolean hangup(gpointer user_data)
{
    GMainLoop *loop = (GMainLoop *) user_data;

    g_printerr("%s: caught hangup/quit signal, quitting", __func__);
    g_main_loop_quit(loop);
    return true;
}

static void panic(VuDev *dev, const char *msg)
{
    g_critical("%s\n", msg);
    exit(EXIT_FAILURE);
}

/* Print vhost-user.json backend program capabilities */
static void print_capabilities(void)
{
    printf("{\n");
    printf("  \"type\": \"RNG\"\n");
    printf("  \"filename\": [ RNG source ]\n");
    printf("}\n");
}

static GOptionEntry options[] = {
    { "socket-path", 's', 0, G_OPTION_ARG_FILENAME, &socket_path,
      "Location of vhost-user Unix domain socket, incompatible with --fd",
      "PATH" },
    { "fd", 'f', 0, G_OPTION_ARG_INT, &socket_fd,
      "Specify the backend file-descriptor, incompatible with --socket-path",
      "FD" },
    { "period", 'p', 0, G_OPTION_ARG_INT, &period_ms,
      "Time needed (in ms) to transfer a maximum amount of byte", NULL },
    { "max-bytes", 'm', 0, G_OPTION_ARG_INT64, &max_bytes,
      "Maximum amount of byte that can be transferred in a period", NULL },
    { "filename", 'n', 0, G_OPTION_ARG_FILENAME, &source_path,
      "RNG source, defaults to /dev/urandom", "PATH" },
    { "print-capabilities", 'c', 0, G_OPTION_ARG_NONE, &print_cap,
      "Output to stdout the backend capabilities in JSON format and exit",
      NULL},
    { "verbose", 'v', 0, G_OPTION_ARG_NONE, &verbose,
      "Be more verbose in output", NULL},
    { NULL }
};

int main(int argc, char *argv[])
{
    GError *error = NULL;
    GOptionContext *context;
    g_autoptr(GSocket) socket = NULL;
    char default_source[] = "/dev/urandom";
    char *source = default_source;
    VuRNG rng;

    context = g_option_context_new("vhost-user emulation of RNG device");
    g_option_context_add_main_entries(context, options, "vhost-user-rng");
    if (!g_option_context_parse(context, &argc, &argv, &error)) {
        g_printerr("option parsing failed: %s\n", error->message);
        exit(1);
    }

    if (print_cap) {
        print_capabilities();
        exit(0);
    }

    if (!socket_path && socket_fd < 0) {
        g_printerr("Please specify either --fd or --socket-path\n");
        exit(EXIT_FAILURE);
    }

    if (socket_path && socket_fd > 0) {
        g_printerr("Either --fd or --socket-path, not both\n");
        exit(EXIT_FAILURE);
    }

    if (max_bytes > INT64_MAX) {
        g_printerr("'max-bytes' parameter must be non-negative, "
                   "and less than 2^63\n");
        exit(EXIT_FAILURE);
    }

    if (period_ms <= 0) {
        g_printerr("'period' parameter expects a positive integer\n");
        exit(EXIT_FAILURE);
    }

    /*
     * Now create a vhost-user socket that we will receive messages
     * on. Once we have our handler set up we can enter the glib main
     * loop.
     */
    if (socket_path) {
        g_autoptr(GSocketAddress) addr = g_unix_socket_address_new(socket_path);
        g_autoptr(GSocket) bind_socket = g_socket_new(G_SOCKET_FAMILY_UNIX,
                                                      G_SOCKET_TYPE_STREAM,
                                                      G_SOCKET_PROTOCOL_DEFAULT,
                                                      &error);

        if (!g_socket_bind(bind_socket, addr, false, &error)) {
            g_printerr("Failed to bind to socket at %s (%s).\n",
                       socket_path, error->message);
            exit(EXIT_FAILURE);
        }
        if (!g_socket_listen(bind_socket, &error)) {
            g_printerr("Failed to listen on socket %s (%s).\n",
                       socket_path, error->message);
        }
        g_message("awaiting connection to %s", socket_path);
        socket = g_socket_accept(bind_socket, NULL, &error);
        if (!socket) {
            g_printerr("Failed to accept on socket %s (%s).\n",
                       socket_path, error->message);
        }
    } else {
        socket = g_socket_new_from_fd(socket_fd, &error);
        if (!socket) {
            g_printerr("Failed to connect to FD %d (%s).\n",
                       socket_fd, error->message);
            exit(EXIT_FAILURE);
        }
    }

    /* Overwrite default RNG source with what user provided, if any */
    if (source_path) {
        source = source_path;
    }

    source_fd = open(source, O_RDWR);
    if (source_fd < 0) {
        g_printerr("Failed to open RNG source %s\n", source);
        g_socket_close(socket, &error);
        unlink(socket_path);
        exit(EXIT_FAILURE);
    }

    /* catch exit signals */
    g_unix_signal_add(SIGHUP, hangup, rng.loop);
    g_unix_signal_add(SIGINT, hangup, rng.loop);

    /*
     * Create the main loop first so all the various sources can be
     * added. As well as catching signals we need to ensure vug_init
     * can add it's GSource watches.
     */
    rng.loop = g_main_loop_new(NULL, FALSE);

    if (!vug_init(&rng.dev, 1, g_socket_get_fd(socket),
                  panic, &vuiface)) {
        g_printerr("Failed to initialize libvhost-user-glib.\n");
        exit(EXIT_FAILURE);
    }

    rng.quota_remaining = max_bytes;
    rng.activate_timer = true;
    pthread_mutex_init(&rng.rng_mutex, NULL);
    pthread_cond_init(&rng.rng_cond, NULL);
    setup_timer(&rng);

    if (verbose) {
        g_info("period_ms: %d tv_sec: %ld tv_nsec: %lu\n",
               period_ms, rng.ts.it_value.tv_sec, rng.ts.it_value.tv_nsec);
    }

    g_message("entering main loop, awaiting messages");
    g_main_loop_run(rng.loop);
    g_message("finished main loop, cleaning up");

    g_main_loop_unref(rng.loop);
    vug_deinit(&rng.dev);
    timer_delete(rng.rate_limit_timer);
    close(source_fd);
    unlink(socket_path);
}