Netlink 解析

Netlink 协议格式文档

基本结构

Netlink 消息由消息头和消息体组成:

struct nlmsghdr {
    __u32 nlmsg_len;    /* Length of message including header */
    __u16 nlmsg_type;   /* Message content */
    __u16 nlmsg_flags;  /* Additional flags */
    __u32 nlmsg_seq;    /* Sequence number */
    __u32 nlmsg_pid;    /* Sending process port ID */
};

消息头 (nlmsghdr)

nlmsg_len: 整个消息长度，包括头部
nlmsg_type: 消息类型 (如: NLMSG_NOOP, NLMSG_ERROR, NLMSG_DONE)
nlmsg_flags: 控制标志 (如: NLM_F_REQUEST, NLM_F_MULTI)
nlmsg_seq: 序列号用于追踪消息
nlmsg_pid: 发送进程的端口ID

属性格式 (nlattr)

消息体通常包含多个属性:

struct nlattr {
    __u16 nla_len;      /* Length of attribute including header */
    __u16 nla_type;     /* Type of attribute */
    /* Attribute payload follows */
};

消息类型

常见消息类型:

RTM_NEWLINK: 创建/修改网络接口
RTM_DELLINK: 删除网络接口
RTM_GETLINK: 查询网络接口
RTM_NEWADDR: 添加IP地址
RTM_DELADDR: 删除IP地址

协议家族

NETLINK_ROUTE: 网络路由和接口
NETLINK_FIREWALL: 防火墙相关
NETLINK_NFLOG: Netfilter日志
NETLINK_GENERIC: 通用协议

错误处理

错误消息格式:

struct nlmsgerr {
    int error;         /* Negative errno or 0 for acknowledgements */
    struct nlmsghdr msg; /* Original message header */
};

示例消息

获取网络接口列表的请求示例:

struct {
    struct nlmsghdr nh;
    struct ifinfomsg ifi;
} req = {
    .nh = {
        .nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg)),
        .nlmsg_type = RTM_GETLINK,
        .nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP,
        .nlmsg_seq = 1,
    },
    .ifi = {
        .ifi_family = AF_PACKET,
    },