/*
 * Copyright (c) 2022  Institute of Computing Technology, Chinese Academy
 *                     of Sciences
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 *
 * The license below extends only to copyright in the software and shall
 * not be construed as granting a license to any other intellectual
 * property including but not limited to intellectual property relating
 * to a hardware implementation of the functionality of the software
 * licensed hereunder.  You may use the software subject to the license
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 * Redistribution and use in source and binary forms, with or without
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 * met: redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer;
 * redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
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 * neither the name of the copyright holders nor the names of its
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 * this software without specific prior written permission.
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#include "dev/virtio/rng.hh"

#include <fcntl.h>
#include <unistd.h>

#include "debug/VIORng.hh"
#include "params/VirtIORng.hh"
#include "sim/system.hh"

namespace gem5
{

VirtIORng::VirtIORng(const Params &params)
    : VirtIODeviceBase(params, ID_RNG, 0, 0),
      qReq(params.system->physProxy, byteOrder, params.qSize,
           params.entropy_source, *this)
{
    registerQueue(qReq);
}

VirtIORng::~VirtIORng()
{
}

VirtIORng::RngQueue::RngQueue(PortProxy &proxy, ByteOrder bo,
    uint16_t size, const std::string &rng_file_path,
    VirtIORng &_parent)
    : VirtQueue(proxy, bo, size), parent(_parent), dist(0,255)
{
    rng_fd = open(rng_file_path.c_str(), O_RDONLY);
    if (rng_fd < 0) {
        DPRINTF(VIORng, "error when open entropy source: %s\n",
                rng_file_path.c_str());
    }
}

void
VirtIORng::readConfig(PacketPtr pkt, Addr cfgOffset)
{
    // There are no configuration for RNG device
    pkt->makeResponse();
}

void
VirtIORng::RngQueue::trySend()
{
    DPRINTF(VIORng, "try send\n");

    VirtDescriptor *d;
    while ((d = consumeDescriptor())) {
        DPRINTF(VIORng, "Got descriptor (len: %i)\n", d->size());
        size_t len = 0;
        while (len < d->size()) {
            uint8_t byte = 0;
            bool rng_read_success = false;
            if (rng_fd >= 0) {
                ssize_t result = read(rng_fd, &byte, sizeof(uint8_t));
                rng_read_success = (result > 0);
            }
            if (!rng_read_success) {
                // fallback to C++ std rng generator
                byte = dist(rd_device);
            }
            d->chainWrite(len, &byte, sizeof(uint8_t));
            ++len;
        }

        // Tell the guest that we are done with this descriptor.
        produceDescriptor(d, len);
        parent.kick();
    }
}

} // namespace gem5