src/ncsi_util.cpp

#include "ncsi_util.hpp"

#include <errno.h>
#include <fcntl.h>
#include <linux/mctp.h>
#include <linux/ncsi.h>
#include <netlink/genl/ctrl.h>
#include <netlink/genl/genl.h>
#include <netlink/netlink.h>
#include <unistd.h>

#include <iostream>
#include <memory>
#include <optional>
#include <span>
#include <sstream>
#include <system_error>
#include <vector>

namespace phosphor
{
namespace network
{
namespace ncsi
{

static const char* mctp_iid_path = "/run/ncsi-mctp-iids";

NCSICommand::NCSICommand(uint8_t opcode, uint8_t package,
                         std::optional<uint8_t> channel,
                         std::span<unsigned char> payload) :
    opcode(opcode), package(package), channel(channel)
{
    this->payload.assign(payload.begin(), payload.end());
}

uint8_t NCSICommand::getChannel()
{
    return channel.value_or(CHANNEL_ID_NONE);
}

using CallBack = int (*)(struct nl_msg* msg, void* arg);

namespace internal
{

struct NCSIPacketHeader
{
    uint8_t MCID;
    uint8_t revision;
    uint8_t reserved;
    uint8_t id;
    uint8_t type;
    uint8_t channel;
    uint16_t length;
    uint32_t rsvd[2];
};

struct NCSIResponsePayload
{
    uint16_t response;
    uint16_t reason;
};

class NetlinkCommand
{
  public:
    NetlinkCommand() = delete;
    ~NetlinkCommand() = default;
    NetlinkCommand(const NetlinkCommand&) = delete;
    NetlinkCommand& operator=(const NetlinkCommand&) = delete;
    NetlinkCommand(NetlinkCommand&&) = default;
    NetlinkCommand& operator=(NetlinkCommand&&) = default;
    NetlinkCommand(
        int ncsiCmd, int operation = DEFAULT_VALUE,
        std::span<const unsigned char> p = std::span<const unsigned char>()) :
        ncsi_cmd(ncsiCmd), operation(operation), payload(p)
    {}

    int ncsi_cmd;
    int operation;
    std::span<const unsigned char> payload;
};

using nlMsgPtr = std::unique_ptr<nl_msg, decltype(&::nlmsg_free)>;
using nlSocketPtr = std::unique_ptr<nl_sock, decltype(&::nl_socket_free)>;

struct infoCallBackContext
{
    InterfaceInfo* info;
};

CallBack infoCallBack = [](struct nl_msg* msg, void* arg) {
    if (arg == nullptr)
    {
        std::cerr << "Internal error: invalid info callback context"
                  << std::endl;
        return -1;
    }

    struct infoCallBackContext* info = (struct infoCallBackContext*)arg;
    using namespace phosphor::network::ncsi;
    auto nlh = nlmsg_hdr(msg);

    struct nlattr* tb[NCSI_ATTR_MAX + 1] = {nullptr};
    struct nla_policy ncsiPolicy[NCSI_ATTR_MAX + 1] = {
        {NLA_UNSPEC, 0, 0}, {NLA_U32, 0, 0}, {NLA_NESTED, 0, 0},
        {NLA_U32, 0, 0},    {NLA_U32, 0, 0},
    };

    struct nlattr* packagetb[NCSI_PKG_ATTR_MAX + 1] = {nullptr};
    struct nla_policy packagePolicy[NCSI_PKG_ATTR_MAX + 1] = {
        {NLA_UNSPEC, 0, 0}, {NLA_NESTED, 0, 0}, {NLA_U32, 0, 0},
        {NLA_FLAG, 0, 0},   {NLA_NESTED, 0, 0},
    };

    struct nlattr* channeltb[NCSI_CHANNEL_ATTR_MAX + 1] = {nullptr};
    struct nla_policy channelPolicy[NCSI_CHANNEL_ATTR_MAX + 1] = {
        {NLA_UNSPEC, 0, 0}, {NLA_NESTED, 0, 0}, {NLA_U32, 0, 0},
        {NLA_FLAG, 0, 0},   {NLA_NESTED, 0, 0}, {NLA_UNSPEC, 0, 0},
    };

    auto ret = genlmsg_parse(nlh, 0, tb, NCSI_ATTR_MAX, ncsiPolicy);
    if (!tb[NCSI_ATTR_PACKAGE_LIST])
    {
        std::cerr << "No Packages" << std::endl;
        return -1;
    }

    auto attrTgt = static_cast<nlattr*>(nla_data(tb[NCSI_ATTR_PACKAGE_LIST]));
    if (!attrTgt)
    {
        std::cerr << "Package list attribute is null" << std::endl;
        return -1;
    }

    auto rem = nla_len(tb[NCSI_ATTR_PACKAGE_LIST]);
    nla_for_each_nested(attrTgt, tb[NCSI_ATTR_PACKAGE_LIST], rem)
    {
        ret = nla_parse_nested(packagetb, NCSI_PKG_ATTR_MAX, attrTgt,
                               packagePolicy);
        if (ret < 0)
        {
            std::cerr << "Failed to parse package nested" << std::endl;
            return -1;
        }

        PackageInfo pkg;

        if (packagetb[NCSI_PKG_ATTR_ID])
        {
            auto attrID = nla_get_u32(packagetb[NCSI_PKG_ATTR_ID]);
            pkg.id = attrID;
        }
        else
        {
            std::cout << "Package with no id" << std::endl;
        }

        if (packagetb[NCSI_PKG_ATTR_FORCED])
        {
            pkg.forced = true;
        }

        auto channelListTarget = static_cast<nlattr*>(
            nla_data(packagetb[NCSI_PKG_ATTR_CHANNEL_LIST]));

        auto channelrem = nla_len(packagetb[NCSI_PKG_ATTR_CHANNEL_LIST]);
        nla_for_each_nested(channelListTarget,
                            packagetb[NCSI_PKG_ATTR_CHANNEL_LIST], channelrem)
        {
            ret = nla_parse_nested(channeltb, NCSI_CHANNEL_ATTR_MAX,
                                   channelListTarget, channelPolicy);
            if (ret < 0)
            {
                std::cerr << "Failed to parse channel nested" << std::endl;
                continue;
            }

            ChannelInfo chan{};

            if (channeltb[NCSI_CHANNEL_ATTR_ID])
            {
                chan.id = nla_get_u32(channeltb[NCSI_CHANNEL_ATTR_ID]);
                chan.active = !!channeltb[NCSI_CHANNEL_ATTR_ACTIVE];
                chan.forced = !!channeltb[NCSI_CHANNEL_ATTR_FORCED];
            }
            else
            {
                std::cout << "Channel with no ID" << std::endl;
                continue;
            }

            if (channeltb[NCSI_CHANNEL_ATTR_VERSION_MAJOR])
            {
                chan.version_major =
                    nla_get_u32(channeltb[NCSI_CHANNEL_ATTR_VERSION_MAJOR]);
            }
            if (channeltb[NCSI_CHANNEL_ATTR_VERSION_MINOR])
            {
                chan.version_minor =
                    nla_get_u32(channeltb[NCSI_CHANNEL_ATTR_VERSION_MINOR]);
            }
            if (channeltb[NCSI_CHANNEL_ATTR_VERSION_STR])
            {
                chan.version =
                    nla_get_string(channeltb[NCSI_CHANNEL_ATTR_VERSION_STR]);
            }
            if (channeltb[NCSI_CHANNEL_ATTR_LINK_STATE])
            {
                chan.link_state =
                    nla_get_u32(channeltb[NCSI_CHANNEL_ATTR_LINK_STATE]);
            }
            if (channeltb[NCSI_CHANNEL_ATTR_VLAN_LIST])
            {
                auto vids = channeltb[NCSI_CHANNEL_ATTR_VLAN_LIST];
                auto vid = static_cast<nlattr*>(nla_data(vids));
                auto len = nla_len(vids);
                while (nla_ok(vid, len))
                {
                    auto id = nla_get_u16(vid);
                    chan.vlan_ids.push_back(id);
                    vid = nla_next(vid, &len);
                }
            }
            pkg.channels.push_back(chan);
        }

        info->info->packages.push_back(pkg);
    }
    return static_cast<int>(NL_STOP);
};

struct sendCallBackContext
{
    NCSIResponse resp;
};

CallBack sendCallBack = [](struct nl_msg* msg, void* arg) {
    using namespace phosphor::network::ncsi;
    auto nlh = nlmsg_hdr(msg);
    struct nlattr* tb[NCSI_ATTR_MAX + 1] = {nullptr};
    static struct nla_policy ncsiPolicy[NCSI_ATTR_MAX + 1] = {
        {NLA_UNSPEC, 0, 0}, {NLA_U32, 0, 0}, {NLA_NESTED, 0, 0},
        {NLA_U32, 0, 0},    {NLA_U32, 0, 0}, {NLA_BINARY, 0, 0},
        {NLA_FLAG, 0, 0},   {NLA_U32, 0, 0}, {NLA_U32, 0, 0},
    };

    if (arg == nullptr)
    {
        std::cerr << "Internal error: invalid send callback context"
                  << std::endl;
        return -1;
    }

    struct sendCallBackContext* ctx = (struct sendCallBackContext*)arg;

    auto ret = genlmsg_parse(nlh, 0, tb, NCSI_ATTR_MAX, ncsiPolicy);
    if (ret)
    {
        std::cerr << "Failed to parse message" << std::endl;
        return ret;
    }

    if (tb[NCSI_ATTR_DATA] == nullptr)
    {
        std::cerr << "Response: No data" << std::endl;
        return -1;
    }

    size_t data_len = nla_len(tb[NCSI_ATTR_DATA]);
    unsigned char* data = (unsigned char*)nla_data(tb[NCSI_ATTR_DATA]);

    ctx->resp.full_payload.assign(data, data + data_len);

    int rc = ctx->resp.parseFullPayload();
    if (rc)
    {
        return -1;
    }

    return static_cast<int>(NL_STOP);
};

int applyCmd(NetlinkInterface& interface, const NetlinkCommand& cmd,
             int package = DEFAULT_VALUE, int channel = DEFAULT_VALUE,
             int flags = NONE, CallBack function = nullptr, void* arg = nullptr)
{
    nlSocketPtr socket(nl_socket_alloc(), &::nl_socket_free);
    if (socket == nullptr)
    {
        std::cerr << "Unable to allocate memory for the socket" << std::endl;
        return -ENOMEM;
    }

    nl_socket_disable_auto_ack(socket.get());

    auto ret = genl_connect(socket.get());
    if (ret < 0)
    {
        std::cerr << "Failed to open the socket , RC : " << ret << std::endl;
        return ret;
    }

    auto driverID = genl_ctrl_resolve(socket.get(), "NCSI");
    if (driverID < 0)
    {
        std::cerr << "Failed to resolve, RC : " << ret << std::endl;
        return driverID;
    }

    nlMsgPtr msg(nlmsg_alloc(), &::nlmsg_free);
    if (msg == nullptr)
    {
        std::cerr << "Unable to allocate memory for the message" << std::endl;
        return -ENOMEM;
    }

    auto msgHdr = genlmsg_put(msg.get(), NL_AUTO_PORT, NL_AUTO_SEQ, driverID, 0,
                              flags, cmd.ncsi_cmd, 0);
    if (!msgHdr)
    {
        std::cerr << "Unable to add the netlink headers , COMMAND : "
                  << cmd.ncsi_cmd << std::endl;
        return -ENOMEM;
    }

    if (package != DEFAULT_VALUE)
    {
        ret = nla_put_u32(msg.get(), ncsi_nl_attrs::NCSI_ATTR_PACKAGE_ID,
                          package);
        if (ret < 0)
        {
            std::cerr << "Failed to set the attribute , RC : " << ret
                      << " PACKAGE " << package << std::endl;
            return ret;
        }
    }

    if (channel != DEFAULT_VALUE)
    {
        ret = nla_put_u32(msg.get(), ncsi_nl_attrs::NCSI_ATTR_CHANNEL_ID,
                          channel);
        if (ret < 0)
        {
            std::cerr << "Failed to set the attribute , RC : " << ret
                      << " CHANNEL : " << channel << std::endl;
            return ret;
        }
    }

    ret = nla_put_u32(msg.get(), ncsi_nl_attrs::NCSI_ATTR_IFINDEX,
                      interface.ifindex);
    if (ret < 0)
    {
        std::cerr << "Failed to set the attribute , RC : " << ret
                  << " INTERFACE : " << interface.ifindex << std::endl;
        return ret;
    }

    if ((cmd.ncsi_cmd == ncsi_nl_commands::NCSI_CMD_SET_PACKAGE_MASK) ||
        (cmd.ncsi_cmd == ncsi_nl_commands::NCSI_CMD_SET_CHANNEL_MASK))
    {
        if (cmd.payload.size() != sizeof(unsigned int))
        {
            std::cerr << "Package/Channel mask must be 32-bits" << std::endl;
            return -EINVAL;
        }
        int maskAttr =
            cmd.ncsi_cmd == ncsi_nl_commands::NCSI_CMD_SET_PACKAGE_MASK
                ? NCSI_ATTR_PACKAGE_MASK
                : NCSI_ATTR_CHANNEL_MASK;
        ret = nla_put_u32(
            msg.get(), maskAttr,
            *(reinterpret_cast<const unsigned int*>(cmd.payload.data())));
        if (ret < 0)
        {
            std::cerr << "Failed to set the mask attribute, RC : " << ret
                      << std::endl;
            return ret;
        }
    }
    else if (cmd.ncsi_cmd == ncsi_nl_commands::NCSI_CMD_SEND_CMD)
    {
        std::vector<unsigned char> pl(
            sizeof(NCSIPacketHeader) + cmd.payload.size());
        NCSIPacketHeader* hdr = reinterpret_cast<NCSIPacketHeader*>(pl.data());

        std::copy(cmd.payload.begin(), cmd.payload.end(),
                  pl.begin() + sizeof(NCSIPacketHeader));

        hdr->type = cmd.operation;
        hdr->length = htons(cmd.payload.size());

        ret = nla_put(msg.get(), ncsi_nl_attrs::NCSI_ATTR_DATA, pl.size(),
                      pl.data());
        if (ret < 0)
        {
            std::cerr << "Failed to set the data attribute, RC : " << ret
                      << std::endl;
            return ret;
        }

        nl_socket_disable_seq_check(socket.get());
    }

    // Add a callback function to the socket
    enum nl_cb_kind cb_kind = function ? NL_CB_CUSTOM : NL_CB_DEFAULT;
    nl_socket_modify_cb(socket.get(), NL_CB_VALID, cb_kind, function, arg);

    ret = nl_send_auto(socket.get(), msg.get());
    if (ret < 0)
    {
        std::cerr << "Failed to send the message , RC : " << ret << std::endl;
        return ret;
    }

    ret = nl_recvmsgs_default(socket.get());
    if (ret < 0)
    {
        std::cerr << "Failed to receive the message , RC : " << ret
                  << std::endl;
        return ret;
    }

    return 0;
}

} // namespace internal

std::string to_string(Interface& interface)
{
    return interface.toString();
}

NetlinkInterface::NetlinkInterface(int ifindex) : ifindex(ifindex) {}

std::string NetlinkInterface::toString()
{
    return std::to_string(ifindex);
}

std::optional<NCSIResponse> NetlinkInterface::sendCommand(NCSICommand& cmd)
{
    std::cout << "Send Command, CHANNEL : " << std::hex << (int)cmd.getChannel()
              << " , PACKAGE : " << (int)cmd.package << " , INTERFACE: " << this
              << std::dec << std::endl;

    internal::sendCallBackContext ctx{};

    internal::NetlinkCommand nl_cmd(ncsi_nl_commands::NCSI_CMD_SEND_CMD,
                                    cmd.opcode, cmd.payload);

    int rc = internal::applyCmd(*this, nl_cmd, cmd.package, cmd.getChannel(),
                                NONE, internal::sendCallBack, &ctx);

    if (rc < 0)
    {
        return {};
    }

    return ctx.resp;
}

int NetlinkInterface::setChannel(int package, int channel)
{
    std::cout << "Set CHANNEL : " << std::hex << channel << " , PACKAGE : "
              << package << " , INTERFACE : " << this << std::dec << std::endl;

    internal::NetlinkCommand cmd(ncsi_nl_commands::NCSI_CMD_SET_INTERFACE);

    return internal::applyCmd(*this, cmd, package, channel);
}

int NetlinkInterface::clearInterface()
{
    std::cout << "ClearInterface , INTERFACE : " << this << std::endl;

    internal::NetlinkCommand cmd(ncsi_nl_commands::NCSI_CMD_CLEAR_INTERFACE);
    return internal::applyCmd(*this, cmd);
}

std::optional<InterfaceInfo> NetlinkInterface::getInfo(int package)
{
    int rc, flags = package == DEFAULT_VALUE ? NLM_F_DUMP : NONE;
    InterfaceInfo info;

    std::cout << "Get Info , PACKAGE : " << std::hex << package
              << " , INTERFACE: " << this << std::dec << std::endl;

    struct internal::infoCallBackContext ctx = {
        .info = &info,
    };

    internal::NetlinkCommand cmd(ncsi_nl_commands::NCSI_CMD_PKG_INFO);

    rc = internal::applyCmd(*this, cmd, package, DEFAULT_VALUE, flags,
                            internal::infoCallBack, &ctx);

    if (rc < 0)
    {
        return {};
    }

    return info;
}

int NetlinkInterface::setPackageMask(unsigned int mask)
{
    std::cout << "Set Package Mask , INTERFACE: " << this
              << " MASK: " << std::hex << mask << std::dec << std::endl;
    auto payload = std::span<const unsigned char>(
        reinterpret_cast<const unsigned char*>(&mask),
        reinterpret_cast<const unsigned char*>(&mask) + sizeof(decltype(mask)));

    internal::NetlinkCommand cmd(ncsi_nl_commands::NCSI_CMD_SET_PACKAGE_MASK, 0,
                                 payload);
    return internal::applyCmd(*this, cmd);
}

int NetlinkInterface::setChannelMask(int package, unsigned int mask)
{
    std::cout << "Set Channel Mask , INTERFACE: " << this
              << " , PACKAGE : " << std::hex << package << " MASK: " << mask
              << std::dec << std::endl;
    auto payload = std::span<const unsigned char>(
        reinterpret_cast<const unsigned char*>(&mask),
        reinterpret_cast<const unsigned char*>(&mask) + sizeof(decltype(mask)));

    internal::NetlinkCommand cmd(ncsi_nl_commands::NCSI_CMD_SET_CHANNEL_MASK, 0,
                                 payload);
    return internal::applyCmd(*this, cmd);
}

int NCSIResponse::parseFullPayload()
{
    if (this->full_payload.size() < sizeof(internal::NCSIPacketHeader) +
                                        sizeof(internal::NCSIResponsePayload))
    {
        std::cerr << "Response: Not enough data for a response message"
                  << std::endl;
        return -1;
    }

    internal::NCSIPacketHeader* respHeader =
        reinterpret_cast<decltype(respHeader)>(this->full_payload.data());

    unsigned int payloadLen = ntohs(respHeader->length & htons(0x0fff));
    /* we have determined that the payload size is larger than *respHeader,
     * so cannot underflow here */
    if (payloadLen > this->full_payload.size() - sizeof(*respHeader))
    {
        std::cerr << "Invalid header length " << payloadLen << " (vs "
                  << (this->full_payload.size() - sizeof(*respHeader))
                  << ") in response" << std::endl;
        return -1;
    }

    this->opcode = respHeader->type;
    this->payload =
        std::span(this->full_payload.begin() + sizeof(*respHeader), payloadLen);

    internal::NCSIResponsePayload* respPayload =
        reinterpret_cast<decltype(respPayload)>(this->payload.data());
    this->response = ntohs(respPayload->response);
    this->reason = ntohs(respPayload->reason);

    return 0;
}

static const uint8_t MCTP_TYPE_NCSI = 2;

struct NCSIResponsePayload
{
    uint16_t response;
    uint16_t reason;
};

std::optional<NCSIResponse> MCTPInterface::sendCommand(NCSICommand& cmd)
{
    static constexpr uint8_t mcid = 0; /* no need to distinguish controllers */
    static constexpr size_t maxRespLen = 16384;
    size_t payloadLen, padLen;
    ssize_t wlen, rlen;

    payloadLen = cmd.payload.size();

    auto tmp = allocateIID();
    if (!tmp.has_value())
    {
        return {};
    }
    uint8_t iid = *tmp;

    internal::NCSIPacketHeader cmdHeader{};
    cmdHeader.MCID = mcid;
    cmdHeader.revision = 1;
    cmdHeader.id = iid;
    cmdHeader.type = cmd.opcode;
    cmdHeader.channel = (uint8_t)(cmd.package << 5 | cmd.getChannel());
    cmdHeader.length = htons(payloadLen);

    struct iovec iov[3];
    iov[0].iov_base = &cmdHeader;
    iov[0].iov_len = sizeof(cmdHeader);
    iov[1].iov_base = cmd.payload.data();
    iov[1].iov_len = payloadLen;

    /* the checksum must appear on a 4-byte boundary */
    padLen = 4 - (payloadLen & 0x3);
    if (padLen == 4)
    {
        padLen = 0;
    }
    uint8_t crc32buf[8] = {};
    /* todo: set csum; zeros currently indicate no checksum present */
    uint32_t crc32 = 0;

    memcpy(crc32buf + padLen, &crc32, sizeof(crc32));
    padLen += sizeof(crc32);

    iov[2].iov_base = crc32buf;
    iov[2].iov_len = padLen;

    struct sockaddr_mctp addr = {};
    addr.smctp_family = AF_MCTP;
    addr.smctp_network = net;
    addr.smctp_addr.s_addr = eid;
    addr.smctp_tag = MCTP_TAG_OWNER;
    addr.smctp_type = MCTP_TYPE_NCSI;

    struct msghdr msg = {};
    msg.msg_name = &addr;
    msg.msg_namelen = sizeof(addr);
    msg.msg_iov = iov;
    msg.msg_iovlen = 3;

    wlen = sendmsg(sd, &msg, 0);
    if (wlen < 0)
    {
        std::stringstream ss;
        std::cout << "Failed to send MCTP message, ERRNO: " << -errno
                  << std::endl;

        return {};
    }
    else if ((size_t)wlen != sizeof(cmdHeader) + payloadLen + padLen)
    {
        std::cout << "Short write sending MCTP message, LEN: " << wlen
                  << std::endl;
        return {};
    }

    internal::NCSIPacketHeader* respHeader;
    NCSIResponsePayload* respPayload = nullptr;
    NCSIResponse resp{};

    resp.full_payload.resize(maxRespLen);
    iov[0].iov_len = resp.full_payload.size();
    iov[0].iov_base = resp.full_payload.data();

    msg.msg_name = &addr;
    msg.msg_namelen = sizeof(addr);
    msg.msg_iov = iov;
    msg.msg_iovlen = 1;

    /* we have set SO_RCVTIMEO, so this won't block forever... */
    rlen = recvmsg(sd, &msg, MSG_TRUNC);
    if (rlen < 0)
    {
        std::cerr << "Failed to read MCTP response, ERRNO: " << -rlen
                  << std::endl;
        return {};
    }
    else if ((size_t)rlen < sizeof(*respHeader) + sizeof(*respPayload))
    {
        std::cerr << "Short read receiving MCTP message, LEN: " << rlen
                  << std::endl;
        return {};
    }
    else if ((size_t)rlen > maxRespLen)
    {
        std::cerr << "MCTP response is too large, LEN: " << rlen << std::endl;
        return {};
    }

    resp.full_payload.resize(rlen);

    respHeader =
        reinterpret_cast<decltype(respHeader)>(resp.full_payload.data());

    /* header validation */
    if (respHeader->MCID != mcid)
    {
        std::cerr << "Invalid MCID " << std::hex << (int)respHeader->MCID
                  << std::dec << " in response" << std::endl;
        return {};
    }

    if (respHeader->id != iid)
    {
        std::cerr << "Invalid IID " << std::hex << (int)respHeader->id
                  << std::dec << " in response" << std::endl;
        return {};
    }

    if (respHeader->type != (cmd.opcode | 0x80))
    {
        std::cerr << "Invalid opcode " << std::hex << (int)respHeader->type
                  << std::dec << " in response" << std::endl;
        return {};
    }

    int rc = resp.parseFullPayload();
    if (rc)
    {
        return {};
    }

    return resp;
}

std::string MCTPInterface::toString()
{
    return std::to_string(net) + "," + std::to_string(eid);
}

MCTPInterface::MCTPInterface(int net, uint8_t eid) : net(net), eid(eid)
{
    static const struct timeval receiveTimeout = {
        .tv_sec = 1,
        .tv_usec = 0,
    };

    int _sd = socket(AF_MCTP, SOCK_DGRAM, 0);
    if (_sd < 0)
    {
        throw std::system_error(errno, std::system_category(),
                                "Can't create MCTP socket");
    }

    int rc = setsockopt(_sd, SOL_SOCKET, SO_RCVTIMEO, &receiveTimeout,
                        sizeof(receiveTimeout));
    if (rc != 0)
    {
        throw std::system_error(errno, std::system_category(),
                                "Can't set socket receive timemout");
    }

    sd = _sd;
}

MCTPInterface::~MCTPInterface()
{
    close(sd);
}

/* Small fd wrapper to provide RAII semantics, closing the IID file descriptor
 * when we go out of scope.
 */
struct IidFd
{
    int fd;
    IidFd(int _fd) : fd(_fd) {};
    ~IidFd()
    {
        close(fd);
    };
};

std::optional<uint8_t> MCTPInterface::allocateIID()
{
    int fd = open(mctp_iid_path, O_RDWR | O_CREAT, 0600);
    if (fd < 0)
    {
        std::cerr << "Error opening IID database " << mctp_iid_path << ": "
                  << strerror(errno) << std::endl;
        return {};
    }

    IidFd iidFd(fd);

    /* lock while we read/modity/write; the lock will be short-lived, so
     * we keep it simple and lock the entire file range
     */
    struct flock flock = {
        .l_type = F_WRLCK,
        .l_whence = SEEK_SET,
        .l_start = 0,
        .l_len = 0,
        .l_pid = 0,
    };

    int rc = fcntl(iidFd.fd, F_OFD_SETLKW, &flock);
    if (rc)
    {
        std::cerr << "Error locking IID database " << mctp_iid_path << ": "
                  << strerror(errno) << std::endl;
        return {};
    }

    /* An EOF (rc == 0) would indicate that we don't yet have an entry for that
     * eid, which we handle as iid = 0.
     */
    uint8_t iid = 0;
    rc = pread(iidFd.fd, &iid, sizeof(iid), eid);
    if (rc < 0)
    {
        std::cerr << "Error reading IID database " << mctp_iid_path << ": "
                  << strerror(errno) << std::endl;
        return {};
    }

    /* DSP0222 defines valid IIDs in the range [1, 0xff], so manually wrap */
    if (iid == 0xff)
    {
        iid = 1;
    }
    else
    {
        iid++;
    }

    rc = pwrite(iidFd.fd, &iid, sizeof(iid), eid);
    if (rc != sizeof(iid))
    {
        std::cerr << "Error writing IID database " << mctp_iid_path << ": "
                  << strerror(errno) << std::endl;
        return {};
    }

    return iid;
}

} // namespace ncsi
} // namespace network
} // namespace phosphor