layout: post
title: netlink通信机制-用户层
date: 2018-08-01 04:40:10
categories:
kernel
tags: kernel
内核层与用户层通信方式的话有很多种，比如procfs、sysfs、syscall、seq_file、netlink等几种吧。
IBM社区有篇文章作了更详细的介绍。
用户空间与内核空间数据交换的方式
最常用的算是netlink。
用户层
首先创建描述符
int skfd = socket(AF_NETLINK, SOCK_RAW, NETLINK_TEST);
初始化一个sockaddr_nl结构，与网络描述符绑定
sockaddr_nl 结构
struct sockaddr_nl {
__kernel_sa_family_t nl_family; /* AF_NETLINK （跟AF_INET对应）*/
unsigned short nl_pad; /* zero */
__u32 nl_pid; /* port ID （通信端口号）*/
__u32 nl_groups; /* multicast groups mask */
};
struct sockaddr_nl nladdr;
/*init netlink socket */
nladdr.nl_family = AF_NETLINK; /* AF_NETLINK or PE_NETLINK */
nladdr.nl_pad = 0; /* not use */
nladdr.nl_pid = 0; /* 传送到内核 */
nladdr.nl_groups = 0; /* 单播*/
/* bing 绑定netlink socket 与socket */
bind(skfd, (struct sockaddr *)&nladdr, sizeof(struct sockaddr_nl))
组装需要发送的消息msghdr结构
struct msghdr msg;
memset(&msg, 0, sizeof(msg));
msg.msg_name = (void *)&(nladdr);
msg.msg_namelen = sizeof(nladdr);
#define MAX_MSGSIZE 1024
char buffer[] = "hello kernel!!!";
/* netlink 消息头 */
struct nlmsghdr *nlhdr;
nlhdr = (struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_MSGSIZE));
strcpy(NLMSG_DATA(nlhdr),buffer);
nlhdr->nlmsg_len = NLMSG_LENGTH(strlen(buffer));
nlhdr->nlmsg_pid = getpid(); /* self pid */
nlhdr->nlmsg_flags = 0;
struct iovec iov;
iov.iov_base = (void *)nlhdr;
iov.iov_len = nlhdr->nlmsg_len;
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
上段代码总的来说分两大块。
- msg.msg_name 目的地址信息
- msg.msg_iov 源地址信息+源地址数据
等价于以下代码
iov.iov_base = nlhdr = (struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_MSGSIZE));
结构如下图:
netlink.png
结构体说明
struct msghdr {
void *msg_name; /* optional address */
socklen_t msg_namelen; /* size of address */
struct iovec *msg_iov; /* scatter/gather array */
size_t msg_iovlen; /* # elements in msg_iov */
void *msg_control; /* ancillary data, see below */
size_t msg_controllen; /* ancillary data buffer len */
int msg_flags; /* flags on received message */
};
/* msg_name： 数据的目的地址，网络包指向sockaddr_in, netlink则指向sockaddr_nl;
msg_namelen: msg_name 所代表的地址长度
msg_iov: 指向的是缓冲区数组
msg_iovlen: 缓冲区数组长度
msg_control: 辅助数据，控制信息(发送任何的控制信息)
msg_controllen: 辅助信息长度
msg_flags: 消息标识
*/
struct iovec { /* Scatter/gather array items */
void *iov_base; /* Starting address */
size_t iov_len; /* Number of bytes to transfer */
};
/* iov_base: iov_base指向数据包缓冲区，即参数buff，iov_len是buff的长度。msghdr中允许一次传递多个buff，
以数组的形式组织在 msg_iov中，msg_iovlen就记录数组的长度 （即有多少个buff）
*/
/* struct nlmsghd 是netlink消息头*/
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 */
};
发送消息到内核
sendmsg(skfd, &msg, 0);
接收来自内核的消息
sendmsg(skfd, &msg, 0);
代码
/**
* @file: ktest.c
* @brief: kernel example
* @author: lflish
* @date: 2018-8-1
* @email: [email protected]
**/
#include
#include
#include
#include
#include
#include
/* /usr/include/linux/netlink.h */
#include
#define NETLINK_TEST 30
int main()
{
/* 建立socket */
int skfd = socket(AF_NETLINK, SOCK_RAW, NETLINK_TEST);
if(skfd == -1){
perror("create socket error\n");
return -1;
}
/* netlink socket */
struct sockaddr_nl nladdr;
/*init netlink socket */
nladdr.nl_family = AF_NETLINK; /* AF_NETLINK or PE_NETLINK */
nladdr.nl_pad = 0; /* not use */
nladdr.nl_pid = 0; /* 传送到内核 */
nladdr.nl_groups = 0; /* 单播*/
/* bing 绑定netlink socket 与socket */
if( 0 != bind(skfd, (struct sockaddr *)&nladdr, sizeof(struct sockaddr_nl))){
perror("bind() error\n");
close(skfd);
return -1;
}
/* 构造msg消息*/
struct msghdr msg;
memset(&msg, 0, sizeof(msg));
msg.msg_name = (void *)&(nladdr);
msg.msg_namelen = sizeof(nladdr);
#define MAX_MSGSIZE 1024
char buffer[] = "hello kernel!!!";
/* netlink 消息头 */
struct nlmsghdr *nlhdr;
nlhdr = (struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_MSGSIZE));
strcpy(NLMSG_DATA(nlhdr),buffer);
nlhdr->nlmsg_len = NLMSG_LENGTH(strlen(buffer));
nlhdr->nlmsg_pid = getpid(); /* self pid */
nlhdr->nlmsg_flags = 0;
struct iovec iov;
iov.iov_base = (void *)nlhdr;
iov.iov_len = nlhdr->nlmsg_len;
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
sendmsg(skfd, &msg, 0);
/* recv */
//memset((char *)NLMSG_DATA(nlhdr), 0, 1024);
recvmsg(skfd, &msg, 0);
printf("kernel: %s\n", NLMSG_DATA(nlhdr));
//printf("kernel: %s\n", nlmsg_data(nlhdr));
close(skfd);
free(nlhdr);
return 0;
}
以上是用户层的通信模型
git实例源码
参考文档
结构、宏等说明实例 https://www.cnblogs.com/wenqiang/p/6306727.html
rfc3549 https://tools.ietf.org/html/rfc3549
这哥们的不错，但是是低版本内核 http://blog.chinaunix.net/uid-23069658-id-3405954.html
https://wenku.baidu.com/view/4d6af81da417866fb84a8eb5.html