用户空间具体是如何处理dpif_upcall ?（3）执行flow_miss_op->dpif_op,与内核沟通

     阶段三：调用datapath interface具体实现类（这里是dpif_linux_class）的operate方法进行批量处理，后面如果有剩余项的话再分别调用/put/del/execute。将对应的参数通过nla发送到内核（内核来真正的执行操作）然后接收回应来更新统计信息。流程图如下：

---

-------------lib/dpif.c

void   dpif_operate(struct dpif *dpif, struct dpif_op **ops, size_t n_ops)
{
    size_t i;

    if (dpif->dpif_class->operate) {
         dpif->dpif_class->operate(dpif, ops, n_ops);
          //这里呼叫具体datapa-interface-class的operate函数；这里应该是看dpif_linux_class->dpif_linux_operate；
        for (i = 0; i < n_ops; i++) {
            struct dpif_op *op = ops[i];

            switch (op->type) {
            case DPIF_OP_FLOW_PUT:
                log_flow_put_message(dpif, &op->u.flow_put, op->error);
                break;

            case DPIF_OP_FLOW_DEL:
                log_flow_del_message(dpif, &op->u.flow_del, op->error);
                break;

            case DPIF_OP_EXECUTE:
                log_execute_message(dpif, &op->u.execute, op->error);
                break;
            }
        }
        return;
    }
     //接下来完成上面operate没有处理完的flow_miss_op，思路一样；
    for (i = 0; i < n_ops; i++) {
        struct dpif_op *op = ops[i];

        switch (op->type) {
        case DPIF_OP_FLOW_PUT:
            op->error =  dpif_flow_put__(dpif, &op->u.flow_put);
            break;

        case DPIF_OP_FLOW_DEL:
            op->error =  dpif_flow_del__(dpif, &op->u.flow_del);
            break;

        case DPIF_OP_EXECUTE:
            op->error = dpif_execute__(dpif, &op->u.execute);
            break;

        default:
            NOT_REACHED();
        }
    }
}

---

这里牵扯到的数据结构有：

struct  flow_miss_op {
    struct dpif_op dpif_op;
    struct subfacet *subfacet;  /* Subfacet  */
    void *garbage;              /* Pointer to pass to free(), NULL if none. */
    uint64_t stub[1024 / 8];    /* Temporary buffer. */
};

struct  dpif_op {
    enum dpif_op_type type;
    int error;
    union {
        struct dpif_flow_put flow_put;
        struct dpif_flow_del flow_del;
         struct dpif_execute execute;
    } u;
};

enum  dpif_op_type {
    DPIF_OP_FLOW_PUT = 1,
    DPIF_OP_FLOW_DEL,
    DPIF_OP_EXECUTE,
};

struct  dpif_execute {
    const struct nlattr *key;       /* Partial flow key (only for metadata). */
    size_t key_len;                 /* Length of 'key' in bytes. */
     const struct nlattr *actions;   /* Actions to execute on packet. */
    size_t actions_len;             /* Length of 'actions' in bytes. */
    const struct ofpbuf *packet;    /* Packet to execute. */
};

struct  dpif_flow_put {
    /* Input. */
    enum dpif_flow_put_flags flags; /* DPIF_FP_*. */
     const struct nlattr *key;       /* Flow to put. */
    size_t key_len;                 /* Length of 'key' in bytes. */
    const struct nlattr *actions;   /* Actions to perform on flow. */
    size_t actions_len;             /* Length of 'actions' in bytes. */

    /* Output. */
    struct dpif_flow_stats *stats;  /* Optional flow statistics. */
};

enum dpif_flow_put_flags {
    DPIF_FP_CREATE = 1 << 0,    /* Allow creating a new flow. */
    DPIF_FP_MODIFY = 1 << 1,    /* Allow modifying an existing flow. */
    DPIF_FP_ZERO_STATS = 1 << 2 /* Zero the stats of an existing flow. */
};

---

------------lib/dpif-linux.c

static void  dpif_linux_operate(struct dpif *dpif, struct dpif_op **ops, size_t n_ops)
{
    while (n_ops > 0) {
        size_t chunk = MIN(n_ops, MAX_OPS);
         dpif_linux_operate__(dpif, ops, chunk);
        ops += chunk;    //防止n_ops太大，要分批量处理（MAX_OPS=50）；
        n_ops -= chunk;
    }
}

static void  dpif_linux_operate__(struct dpif *dpif_, struct dpif_op **ops, size_t n_ops)
{
    struct dpif_linux *dpif = dpif_linux_cast(dpif_);

    struct op_auxdata {
        struct  nl_transaction txn;

        struct ofpbuf request;
        uint64_t request_stub[1024 / 8];  // ？？

        struct ofpbuf reply;
        uint64_t reply_stub[1024 / 8];
    } auxes[MAX_OPS];

    struct nl_transaction *txnsp[MAX_OPS];
    size_t i;

    assert(n_ops <= MAX_OPS);
    for (i = 0; i < n_ops; i++) {
        struct op_auxdata *aux = &auxes[i];
        struct dpif_op *op = ops[i];
        struct dpif_flow_put *put;
        struct dpif_flow_del *del;
        struct dpif_execute *execute;
        struct dpif_linux_flow flow;

        ofpbuf_use_stub(&aux->request, aux->request_stub, sizeof aux->request_stub);
        aux->txn.request = &aux->request;

        ofpbuf_use_stub(&aux->reply, aux->reply_stub, sizeof aux->reply_stub);
        aux->txn.reply = NULL;

        switch (op->type) {
        case DPIF_OP_FLOW_PUT:
            put = &op->u.flow_put;
             dpif_linux_init_flow_put(dpif_, put, &flow);
            if (put->stats) {
                flow.nlmsg_flags |= NLM_F_ECHO; //
                aux->txn.reply = &aux->reply;
            }
             dpif_linux_flow_to_ofpbuf(&flow, &aux->request);

               //这里会把&op->u.flow_put中dpif_flow_put 里面的key和action等信息，包装成nla的形式到&aux->request中；
            break;

        case DPIF_OP_FLOW_DEL:
            del = &op->u.flow_del;
            dpif_linux_init_flow_del(dpif_, del, &flow);
            if (del->stats) {
                flow.nlmsg_flags |= NLM_F_ECHO;
                aux->txn.reply = &aux->reply;
            }
            dpif_linux_flow_to_ofpbuf(&flow, &aux->request);
            break;

        case DPIF_OP_EXECUTE:
            execute = &op->u.execute;
            dpif_linux_encode_execute(dpif->dp_ifindex, execute,&aux->request);
            break;

        default:
            NOT_REACHED();
        }
    }

    for (i = 0; i < n_ops; i++) {
        txnsp[i] = &auxes[i].txn;
    }
     nl_sock_transact_multiple(genl_sock, txnsp, n_ops);

    for (i = 0; i < n_ops; i++) {
        struct op_auxdata *aux = &auxes[i];
        struct nl_transaction *txn = &auxes[i].txn;
        struct dpif_op *op = ops[i];
        struct dpif_flow_put *put;
        struct dpif_flow_del *del;

        op->error = txn->error;

        switch (op->type) {
        case DPIF_OP_FLOW_PUT:
            put = &op->u.flow_put;
            if (put->stats) {
                if (!op->error) {
                    struct dpif_linux_flow reply;
                    //将来自内核的reply：nla解析到dpif_linux_flow 结构体，继而用其中的状态统计信息完善dpif_flow_put ->stats字段中；

                    op->error =  dpif_linux_flow_from_ofpbuf(&reply,txn->reply);
                    if (!op->error) {
                        dpif_linux_flow_get_stats(&reply, put->stats);
                    }
                }

                if (op->error) {
                    memset(put->stats, 0, sizeof *put->stats);
                }
            }
            break;

        case DPIF_OP_FLOW_DEL:
            del = &op->u.flow_del;
            if (del->stats) {
                if (!op->error) {
                    struct dpif_linux_flow reply;

                    op->error =  dpif_linux_flow_from_ofpbuf(&reply,txn->reply);
                    if (!op->error) {
                        dpif_linux_flow_get_stats(&reply, del->stats);
                    }
                }

                if (op->error) {
                    memset(del->stats, 0, sizeof *del->stats);
                }
            }
            break;

        case DPIF_OP_EXECUTE:  //底层执行了就行；
            break;

        default:
            NOT_REACHED();
        }

        ofpbuf_uninit(&aux->request);
        ofpbuf_uninit(&aux->reply);
    }
}

---

/* Datapath interface for the openvswitch Linux kernel module. */
struct  dpif_linux {
    struct dpif dpif;
    int dp_ifindex;

    /* Upcall messages. */
    struct dpif_channel channels[N_CHANNELS];
    uint32_t ready_mask;        /* 1-bit for each sock with unread messages. */
     int epoll_fd;               /* epoll fd that includes channel socks. */
    long long int next_scale;   /* Next time to scale down the sketches. */

    /* Change notification. */
    struct sset changed_ports;  /* Ports that have changed. */
    struct nln_notifier *port_notifier;
    bool change_error;

    /* Port number allocation. */
    uint16_t alloc_port_no;
};

---

--------------lib/netlink-socket.h

nl_transaction 表征的是用户空间和内核空间通信的一次抽象

/* Batching transactions. */
struct  nl_transaction {
    /* Filled in by client. */
    struct ofpbuf *request;     /* Request to send. */

    struct ofpbuf *reply;       /* Reply (empty if reply was an error code). */

     //客户必须要初始化reply，NULL：如果不会在意响应；否则就该指向已分配的内存空间，至少要能容纳nlmsg header；
    int error;                  /* Positive errno value, 0 if no error. */
};

---

---------------lib/dpif-linux.c

struct  dpif_linux_flow {
    /* Generic Netlink header. */
    uint8_t cmd;

    /* struct ovs_header. */
    unsigned int nlmsg_flags;
    int dp_ifindex;

    /* Attributes.
     *
     * The 'stats' member points to 64-bit data that might only be aligned on
     * 32-bit boundaries, so get_unaligned_u64() should be used to access its
     * values.
     *
     * If 'actions' is nonnull then OVS_FLOW_ATTR_ACTIONS will be included in
     * the Netlink version of the command, even if actions_len is zero. */
    const struct nlattr *key;           /* OVS_FLOW_ATTR_KEY. */
    size_t key_len;
    const struct nlattr *actions;       /* OVS_FLOW_ATTR_ACTIONS. */
    size_t actions_len;
    const struct ovs_flow_stats *stats; /* OVS_FLOW_ATTR_STATS. */
    const uint8_t *tcp_flags;           /* OVS_FLOW_ATTR_TCP_FLAGS. */
    const ovs_32aligned_u64 *used;      /* OVS_FLOW_ATTR_USED. */
    bool clear;                         /* OVS_FLOW_ATTR_CLEAR. */
};

---

static void  dpif_linux_init_flow_put (struct dpif *dpif_, const struct dpif_flow_put *put, struct dpif_linux_flow *request)
{
    static struct nlattr dummy_action;

    struct dpif_linux *dpif = dpif_linux_cast(dpif_);

    dpif_linux_flow_init(request);
    request->cmd = (put->flags & DPIF_FP_CREATE ? OVS_FLOW_CMD_NEW : OVS_FLOW_CMD_SET);
    request->dp_ifindex = dpif->dp_ifindex;
    request->key = put->key;
    request->key_len = put->key_len;
    /* Ensure that OVS_FLOW_ATTR_ACTIONS will always be included. */
    request->actions = put->actions ? put->actions : &dummy_action;
    request->actions_len = put->actions_len;
    if (put->flags & DPIF_FP_ZERO_STATS) {
        request->clear = true;
    }
    request->nlmsg_flags = put->flags & DPIF_FP_MODIFY ? 0 : NLM_F_CREATE;
}

---

     填充缓冲区ofbuf：ovsheader+nla（其中ovsheader中有dp_ifindex，nla包括key和action）；

static void   dpif_linux_flow_to_ofpbuf(const struct dpif_linux_flow *flow, struct ofpbuf *buf)
{
    struct ovs_header *ovs_header;

    nl_msg_put_genlmsghdr(buf, 0, ovs_flow_family,NLM_F_REQUEST | flow->nlmsg_flags,
                                              flow->cmd, OVS_FLOW_VERSION);

    ovs_header = ofpbuf_put_uninit(buf, sizeof *ovs_header);
    ovs_header->dp_ifindex = flow->dp_ifindex;

    if (flow->key_len) {
        nl_msg_put_unspec(buf, OVS_FLOW_ATTR_KEY, flow->key, flow->key_len);
    }

    if (flow->actions || flow->actions_len) {
        nl_msg_put_unspec(buf, OVS_FLOW_ATTR_ACTIONS, flow->actions, flow->actions_len);
    }

    /* We never need to send these to the kernel. */
    assert(!flow->stats);
    assert(!flow->tcp_flags);
    assert(!flow->used);

    if (flow->clear) {
        nl_msg_put_flag(buf, OVS_FLOW_ATTR_CLEAR);
    }
}

---

---------------lib/netlink-socket.c

通过netlink socket将nl_transaction中的request发送到内核层，并且接收回应到reply中，在发送每个消息之前，该函数会根据定长每个请求中的nlmsg_len来适应ofpbuf的大小，设置nlmsg_pid，初始化nlmsg_seq。（纯粹的netlink是不可靠的传输协议）， 最终这个函数执行成功返回后，**transactions里面含有来自内核的响应信息。

void  nl_sock_transact_multiple(struct nl_sock *sock,struct nl_transaction **transactions, size_t n)
{
    int max_batch_count;
    int error;

    if (!n) {
        return;
    }

    error = nl_sock_cow__(sock);
    if (error) {
        nl_sock_record_errors__(transactions, n, error);
        return;
    }

    /* In theory, every request could have a 64 kB reply.  But the default and
     * maximum socket rcvbuf size with typical Dom0 memory sizes both tend to
     * be a bit below 128 kB, so that would only allow a single message in a
     * "batch".  So we assume that replies average (at most) 4 kB, which allows
     * a good deal of batching.
     *
     * In practice, most of the requests that we batch either have no reply at
     * all or a brief reply. */
    max_batch_count = MAX(sock->rcvbuf / 4096, 1);
    max_batch_count = MIN(max_batch_count, max_iovs);

    while (n > 0) {
        size_t count, bytes;
        size_t done;

        /* Batch up to 'max_batch_count' transactions.  But cap it at about a
         * page of requests total because big skbuffs are expensive to
         * allocate in the kernel.  */
#if defined(PAGESIZE)
        enum { MAX_BATCH_BYTES = MAX(1, PAGESIZE - 512) };
#else
        enum { MAX_BATCH_BYTES = 4096 - 512 };
#endif
        bytes = transactions[0]->request->size;
        for (count = 1; count < n && count < max_batch_count; count++) {
            if (bytes + transactions[count]->request->size > MAX_BATCH_BYTES) {
                break;
            }
            bytes += transactions[count]->request->size;
        }

        error =  nl_sock_transact_multiple__(sock, transactions, count, &done);
        transactions += done;
        n -= done;

        if (error == ENOBUFS) {
            VLOG_DBG_RL(&rl, "receive buffer overflow, resending request");
        } else if (error) {
            VLOG_ERR_RL(&rl, "transaction error (%s)", strerror(error));
            nl_sock_record_errors__(transactions, n, error);
        }
    }
}

---

static int  nl_sock_transact_multiple__(struct nl_sock *sock,struct nl_transaction **transactions, size_t n,size_t *done)
{
    uint64_t tmp_reply_stub[1024 / 8];
    struct nl_transaction tmp_txn;
    struct ofpbuf tmp_reply;

    uint32_t base_seq;
    struct iovec iovs[MAX_IOVS];
    struct msghdr msg;
    int error;
    int i;

    base_seq = nl_sock_allocate_seq(sock, n);
    *done = 0;
    for (i = 0; i < n; i++) {
        struct nl_transaction *txn = transactions[i];
        struct nlmsghdr *nlmsg = nl_msg_nlmsghdr(txn->request);

        nlmsg->nlmsg_len = txn->request->size;
        nlmsg->nlmsg_seq = base_seq + i;
        nlmsg->nlmsg_pid = sock->pid;

        iovs[i].iov_base = txn->request->data;
        iovs[i].iov_len = txn->request->size;
    }

    memset(&msg, 0, sizeof msg);
    msg.msg_iov = iovs;
    msg.msg_iovlen = n;
    do {
        error =  sendmsg(sock->fd, &msg, 0) < 0 ? errno : 0;
    } while (error == EINTR);

    for (i = 0; i < n; i++) {
        struct nl_transaction *txn = transactions[i];

        log_nlmsg(__func__, error, txn->request->data, txn->request->size,sock->protocol);
    }
    if (!error) {
        COVERAGE_ADD(netlink_sent, n);
    }

    if (error) {
        return error;
    }

    ofpbuf_use_stub(&tmp_reply, tmp_reply_stub, sizeof tmp_reply_stub);
    tmp_txn.request = NULL;
    tmp_txn.reply = &tmp_reply;
    tmp_txn.error = 0;
    while (n > 0) {
        struct nl_transaction *buf_txn, *txn;
        uint32_t seq;

        /* Find a transaction whose buffer we can use for receiving a reply.
         * If no such transaction is left, use tmp_txn. */
        buf_txn = &tmp_txn;
        for (i = 0; i < n; i++) {
            if (transactions[i]->reply) {
                buf_txn = transactions[i];
                break;
            }
        }

        /* Receive a reply. */
        error =  nl_sock_recv__(sock, buf_txn->reply, false);
        if (error) {
            if (error == EAGAIN) {
                nl_sock_record_errors__(transactions, n, 0);
                *done += n;
                error = 0;
            }
            break;
        }

        /* Match the reply up with a transaction. */
        seq = nl_msg_nlmsghdr(buf_txn->reply)->nlmsg_seq;
        if (seq < base_seq || seq >= base_seq + n) {
            VLOG_DBG_RL(&rl, "ignoring unexpected seq %#"PRIx32, seq);
            continue;
        }
        i = seq - base_seq;
        txn = transactions[i];

        /* Fill in the results for 'txn'. */
        if (nl_msg_nlmsgerr(buf_txn->reply, &txn->error)) {
            if (txn->reply) {
                ofpbuf_clear(txn->reply);
            }
            if (txn->error) {
                VLOG_DBG_RL(&rl, "received NAK error=%d (%s)", error, strerror(txn->error));
            }
        } else {
            txn->error = 0;
            if (txn->reply && txn != buf_txn) {
                /* Swap buffers. */
                struct ofpbuf *reply = buf_txn->reply;
                buf_txn->reply = txn->reply;
                 txn->reply = reply;
            }
        }

        /* Fill in the results for transactions before 'txn'.  (We have to do
         * this after the results for 'txn' itself because of the buffer swap
         * above.) */
        nl_sock_record_errors__(transactions, i, 0);

        /* Advance. */
        *done += i + 1;
        transactions += i + 1;
        n -= i + 1;
        base_seq += i + 1;
    }
    ofpbuf_uninit(&tmp_reply);

    return error;
}

---

static int  nl_sock_recv__(struct nl_sock *sock, struct ofpbuf *buf, bool wait)
{
    /* We can't accurately predict the size of the data to be received.  The
     * caller is supposed to have allocated enough space in 'buf' to handle the
     * "typical" case.  To handle exceptions, we make available enough space in
     * 'tail' to allow Netlink messages to be up to 64 kB long (a reasonable
     * figure since that's the maximum length of a Netlink attribute). */
    struct nlmsghdr *nlmsghdr;
    uint8_t tail[65536];
    struct iovec iov[2];
    struct msghdr msg;
    ssize_t retval;

    assert(buf->allocated >= sizeof *nlmsghdr);
    ofpbuf_clear(buf);

    iov[0].iov_base = buf->base;
    iov[0].iov_len = buf->allocated;
    iov[1].iov_base = tail;
    iov[1].iov_len = sizeof tail;

    memset(&msg, 0, sizeof msg);
    msg.msg_iov = iov;
    msg.msg_iovlen = 2;

    do {
        retval =  recvmsg(sock->fd, &msg, wait ? 0 : MSG_DONTWAIT);
    } while (retval < 0 && errno == EINTR);

    if (retval < 0) {
        int error = errno;
        if (error == ENOBUFS) {
            /* Socket receive buffer overflow dropped one or more messages that
             * the kernel tried to send to us. */
            COVERAGE_INC(netlink_overflow);
        }
        return error;
    }

    if (msg.msg_flags & MSG_TRUNC) {
        VLOG_ERR_RL(&rl, "truncated message (longer than %zu bytes)",
                    sizeof tail);
        return E2BIG;
    }

    nlmsghdr = buf->data;
    if (retval < sizeof *nlmsghdr
        || nlmsghdr->nlmsg_len < sizeof *nlmsghdr
        || nlmsghdr->nlmsg_len > retval) {
        VLOG_ERR_RL(&rl, "received invalid nlmsg (%zd bytes < %zu)",
                    retval, sizeof *nlmsghdr);
        return EPROTO;
    }

    if (STRESS(netlink_overflow)) {
        return ENOBUFS;
    }

    buf->size = MIN(retval, buf->allocated);
    if (retval > buf->allocated) {
        COVERAGE_INC(netlink_recv_jumbo);
        ofpbuf_put(buf, tail, retval - buf->allocated);
    }

    log_nlmsg(__func__, 0, buf->data, buf->size, sock->protocol);
    COVERAGE_INC(netlink_received);

    return 0;
}

---

     将缓存中的内容按照ovs_flow_policy策略解析到dpif_linux_flow 中，该结构体中有字段指向ofpbuf，所以当调用者在使用这个flow的时候，不能释放这个缓存。

static int  dpif_linux_flow_from_ofpbuf(struct dpif_linux_flow *flow, const struct ofpbuf *buf)
{
    static const struct nl_policy ovs_flow_policy[] = {
        [OVS_FLOW_ATTR_KEY] = { .type = NL_A_NESTED },
        [OVS_FLOW_ATTR_ACTIONS] = { .type = NL_A_NESTED, .optional = true },
        [OVS_FLOW_ATTR_STATS] = { NL_POLICY_FOR(struct ovs_flow_stats), .optional = true },
        [OVS_FLOW_ATTR_TCP_FLAGS] = { .type = NL_A_U8, .optional = true },
        [OVS_FLOW_ATTR_USED] = { .type = NL_A_U64, .optional = true },
        /* The kernel never uses OVS_FLOW_ATTR_CLEAR. */
    };

    struct nlattr *a[ARRAY_SIZE(ovs_flow_policy)];
    struct ovs_header *ovs_header;
    struct nlmsghdr *nlmsg;
    struct genlmsghdr *genl;
    struct ofpbuf b;

    dpif_linux_flow_init(flow);

    ofpbuf_use_const(&b, buf->data, buf->size);
    nlmsg = ofpbuf_try_pull(&b, sizeof *nlmsg);
    genl = ofpbuf_try_pull(&b, sizeof *genl);
    ovs_header = ofpbuf_try_pull(&b, sizeof *ovs_header);
    if (!nlmsg || !genl || !ovs_header
        || nlmsg->nlmsg_type != ovs_flow_family
        || !nl_policy_parse(&b, 0, ovs_flow_policy, a,
                            ARRAY_SIZE(ovs_flow_policy))) {
        return EINVAL;
    }

     flow->nlmsg_flags = nlmsg->nlmsg_flags;
    flow->dp_ifindex = ovs_header->dp_ifindex;
    flow->key = nl_attr_get(a[OVS_FLOW_ATTR_KEY]);
    flow->key_len = nl_attr_get_size(a[OVS_FLOW_ATTR_KEY]);
    if (a[OVS_FLOW_ATTR_ACTIONS]) {
        flow->actions = nl_attr_get(a[OVS_FLOW_ATTR_ACTIONS]);
        flow->actions_len = nl_attr_get_size(a[OVS_FLOW_ATTR_ACTIONS]);
    }
    if (a[OVS_FLOW_ATTR_STATS]) {
        flow->stats = nl_attr_get(a[OVS_FLOW_ATTR_STATS]);
    }
    if (a[OVS_FLOW_ATTR_TCP_FLAGS]) {
        flow->tcp_flags = nl_attr_get(a[OVS_FLOW_ATTR_TCP_FLAGS]);
    }
    if (a[OVS_FLOW_ATTR_USED]) {
        flow->used = nl_attr_get(a[OVS_FLOW_ATTR_USED]);
    }
    return 0;
}

---

static int  dpif_flow_put__(struct dpif *dpif, const struct dpif_flow_put *put)
{
    int error;

    COVERAGE_INC(dpif_flow_put);
    assert(!(put->flags & ~(DPIF_FP_CREATE | DPIF_FP_MODIFY | DPIF_FP_ZERO_STATS)));

     error = dpif->dpif_class->flow_put(dpif, put);
    if (error && put->stats) {
        memset(put->stats, 0, sizeof *put->stats);
    }
    log_flow_put_message(dpif, put, error);
    return error;
}

static int  dpif_linux_flow_put(struct dpif *dpif_, const struct dpif_flow_put *put)
{
    struct dpif_linux_flow request, reply;
    struct ofpbuf *buf;
    int error;

    dpif_linux_init_flow_put(dpif_, put, &request);
    error =  dpif_linux_flow_transact(&request, put->stats ? &reply : NULL, put->stats ? &buf : NULL);
    if (!error && put->stats) {
        dpif_linux_flow_get_stats(&reply, put->stats);
        ofpbuf_delete(buf);
    }
    return error;
}

/* Executes 'request' in the kernel datapath.  If the command fails, returns a
* positive errno value.  Otherwise, if 'reply' and 'bufp' are null, returns 0
* without doing anything else.  If 'reply' and 'bufp' are nonnull, then the
* result of the command is expected to be a flow also, which is decoded and
* stored in '*reply' and '*bufp'.  The caller must free '*bufp' when the reply
* is no longer needed ('reply' will contain pointers into '*bufp'). */
static int  dpif_linux_flow_transact(struct dpif_linux_flow *request, struct dpif_linux_flow *reply, struct ofpbuf **bufp)
{
    struct ofpbuf *request_buf;
    int error;

    assert((reply != NULL) == (bufp != NULL));

    if (reply) {
        request->nlmsg_flags |= NLM_F_ECHO;
    }

    request_buf = ofpbuf_new(1024);
    dpif_linux_flow_to_ofpbuf(request, request_buf);
    error =  nl_sock_transact(genl_sock, request_buf, bufp);
    ofpbuf_delete(request_buf);

    if (reply) {
        if (!error) {
            error = dpif_linux_flow_from_ofpbuf(reply, *bufp);
        }
        if (error) {
            dpif_linux_flow_init(reply);
            ofpbuf_delete(*bufp);
            *bufp = NULL;
        }
    }
    return error;
}

---

static int  dpif_linux_flow_del(struct dpif *dpif_, const struct dpif_flow_del *del)
{
    struct dpif_linux_flow request, reply;
    struct ofpbuf *buf;
    int error;

    dpif_linux_init_flow_del(dpif_, del, &request);
    error = dpif_linux_flow_transact(&request,  del->stats ? &reply : NULL, del->stats ? &buf : NULL);
    if (!error && del->stats) {
        dpif_linux_flow_get_stats(&reply, del->stats);
        ofpbuf_delete(buf);
    }
    return error;
}

---

static int  dpif_linux_execute(struct dpif *dpif_, const struct dpif_execute *execute)
{
    struct dpif_linux *dpif = dpif_linux_cast(dpif_);

    return dpif_linux_execute__(dpif->dp_ifindex, execute);
}

static int  dpif_linux_execute__(int dp_ifindex, const struct dpif_execute *execute)
{
    uint64_t request_stub[1024 / 8];
    struct ofpbuf request;
    int error;

    ofpbuf_use_stub(&request, request_stub, sizeof request_stub);
     dpif_linux_encode_execute(dp_ifindex, execute, &request);
    error =  nl_sock_transact(genl_sock, &request, NULL);
    ofpbuf_uninit(&request);

    return error;
}

static void  dpif_linux_encode_execute(int dp_ifindex, const struct dpif_execute *d_exec,struct ofpbuf *buf)
{
    struct ovs_header *k_exec;

    ofpbuf_prealloc_tailroom(buf, (64    + d_exec->packet->size + d_exec->key_len  + d_exec->actions_len));

    nl_msg_put_genlmsghdr(buf, 0, ovs_packet_family, NLM_F_REQUEST,  OVS_PACKET_CMD_EXECUTE, OVS_PACKET_VERSION);

    k_exec = ofpbuf_put_uninit(buf, sizeof *k_exec);
    k_exec->dp_ifindex = dp_ifindex;

    nl_msg_put_unspec(buf, OVS_PACKET_ATTR_PACKET,d_exec->packet->data, d_exec->packet->size);
    nl_msg_put_unspec(buf, OVS_PACKET_ATTR_KEY, d_exec->key, d_exec->key_len);
    nl_msg_put_unspec(buf, OVS_PACKET_ATTR_ACTIONS, d_exec->actions, d_exec->actions_len);
}

---