Generic Netlink(genl)介绍与例子
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2024-03-23 13:24:28
...
一、Generic Netlink介绍
介绍Generic Netlink之前，不得不说Netlink。Netlink是一种灵活的并且健壮的通讯方式，可以用于kernel to user、user to kernel、kernel to kernel甚至user to user的通讯。Netlink的通道是通过Family来组织的，但随着使用越来越多，Family ID已经不够分配了，所以才有了Generic Netlink。
所以，Generic Netlink其实是对Netlink报文中的数据进行了再次封装。
二、genl架构
+---------------------+ +---------------------+
| (3) application "A" | | (3) application "B" |
+------+--------------+ +--------------+------+
| |
\ /
\ /
| |
+-------+--------------------------------+-------+
| : : | user-space
=====+ : (5) kernel socket API : +================
| : : | kernel-space
+--------+-------------------------------+-------+
| |
+-----+-------------------------------+----+
| (1) Netlink subsystem |
+---------------------+--------------------+
|
+---------------------+--------------------+
| (2) Generic Netlink bus |
+--+--------------------------+-------+----+
| | |
+-------+---------+ | |
| (4) controller | / \
+-----------------+ / \
| |
+------------------+--+ +--+------------------+
| (3) kernel user "X" | | (3) kernel user "Y" |
+---------------------+ +---------------------+ genl架构图，https://wiki.linuxfoundation.org/networking/generic_netlink_howto#architectural-overview
三、genl数据包结构
要理解genl的程序，必须先了解genl数据包的结构。数据包的结构如下图所示
genl机制的数据包分了4层，用户的实际数据封装在attribute里，一个或多个attribute可以被封装在用户自定义的一个family报文里，一个family报文又被封装在genlmsg里，最后genlmsg被封装在nlmsg里，总共4层。
四、流程说明
1. 对于从user to kernel的通讯，driver必须先向内核注册一个struct genl_family，并且注册一些cmd的处理函数。这些cmd是跟某个family关联起来的。注册family的时候我们可以让内核自动为这个family分配一个ID。每个family都有一个唯一的ID，其中ID号0x10是被内核的nlctrl family所使用。当注册成功以后，如果user program向某个family发送cmd，那么内核就会回调对应cmd的处理函数。对于user program，使用前，除了要创建一个socket并绑定地址以外，还需要先通过family的名字获取family的ID。获取方法，就是向nlctrl这个family查询。详细的方法可以看后面的例子。有了family的ID以后，才能向该family发送cmd。
2.对于从kernel to user的通讯，采用的是广播的形式，只要user program监听了，都能收到。但是同样的，user program在监听前，也必须先查询到family的ID。
五、示例
网上很多例子都不是很完整，这里贴一个完整的例子源码供参考。
例子1：user到kernel，user program通过发送一个命令到内核，内核相应的模块接收到命令以后，执行对应的回调函数
kernel端：
-
#include <net/netlink.h>
-
#include <net/genetlink.h>
-
#include <linux/version.h>
-
-
#define TEST_GENL_MSG_FROM_KERNEL "Hello from kernel space!!!"
-
-
/* handler
-
* message handling code goes here; return 0 on success, negative
-
* values on failure
-
*/
-
static int doc_exmpl_echo(struct sk_buff *skb, struct genl_info *info);
-
-
-
/* netlink attributes */
-
enum {
-
DOC_EXMPL_A_UNSPEC,
-
DOC_EXMPL_A_MSG,
-
__DOC_EXMPL_A_MAX,
-
};
-
#define DOC_EXMPL_A_MAX (__DOC_EXMPL_A_MAX - 1)
-
-
/* attribute policy */
-
static
struct nla_policy doc_exmpl_genl_policy[DOC_EXMPL_A_MAX + 1] = {
-
[DOC_EXMPL_A_MSG] = { .type = NLA_NUL_STRING },
-
};
-
-
/* commands 定义命令类型，用户空间以此来表明需要执行的命令 */
-
enum {
-
DOC_EXMPL_C_UNSPEC,
-
DOC_EXMPL_C_ECHO,
-
__DOC_EXMPL_C_MAX,
-
};
-
#define DOC_EXMPL_C_MAX (__DOC_EXMPL_C_MAX - 1)
-
-
/* family definition */
-
static
struct genl_family doc_exmpl_genl_family = {
-
.id = GENL_ID_GENERATE,
//这里不指定family ID，由内核进行分配
-
.hdrsize =
0,
//自定义的头部长度，参考genl数据包结构
-
.name =
"DOC_EXMPL",
//这里定义family的名称，user program需要根据这个名字来找到对应的family ID。
-
.version =
1,
-
.maxattr = DOC_EXMPL_A_MAX,
-
};
-
-
/* operation definition 将命令command echo和具体的handler对应起来 */
-
static
struct genl_ops doc_exmpl_genl_ops_echo = {
-
.cmd = DOC_EXMPL_C_ECHO,
-
.flags =
0,
-
.policy = doc_exmpl_genl_policy,
-
.doit = doc_exmpl_echo,
-
.dumpit =
NULL,
-
};
-
-
static
struct genl_multicast_group doc_exmpl_genl_mcgrp = {
-
.name =
"DOC_EXMPL_GRP",
-
};
-
-
static inline int genl_msg_prepare_usr_msg(u8 cmd, size_t size, pid_t pid, struct sk_buff **skbp)
-
{
-
struct sk_buff *skb;
-
-
/* create a new netlink msg */
-
skb = genlmsg_new(size, GFP_KERNEL);
-
if (skb ==
NULL) {
-
return -ENOMEM;
-
}
-
-
/* Add a new netlink message to an skb */
-
genlmsg_put(skb, pid,
0, &doc_exmpl_genl_family,
0, cmd);
-
-
*skbp = skb;
-
return
0;
-
}
-
-
static inline int genl_msg_mk_usr_msg(struct sk_buff *skb, int type, void *data, int len)
-
{
-
int rc;
-
-
/* add a netlink attribute to a socket buffer */
-
if ((rc = nla_put(skb, type, len, data)) !=
0) {
-
return rc;
-
}
-
return
0;
-
}
-
-
/**
-
* genl_msg_send_to_user - 通过generic netlink发送数据到netlink
-
*
-
* @data: 发送数据缓存
-
* @len: 数据长度 单位：byte
-
* @pid: 发送到的客户端pid
-
*
-
* return:
-
* 0: 成功
-
* -1: 失败
-
*/
-
int genl_msg_send_to_user(void *data, int len, pid_t pid)
-
{
-
struct sk_buff *skb;
-
size_t size;
-
void *head;
-
int rc;
-
-
size = nla_total_size(len);
/* total length of attribute including padding */
-
-
rc = genl_msg_prepare_usr_msg(DOC_EXMPL_C_ECHO, size, pid, &skb);
-
if (rc) {
-
return rc;
-
}
-
-
rc = genl_msg_mk_usr_msg(skb, DOC_EXMPL_A_MSG, data, len);
-
if (rc) {
-
kfree_skb(skb);
-
return rc;
-
}
-
-
head = genlmsg_data(nlmsg_data(nlmsg_hdr(skb)));
-
-
rc = genlmsg_end(skb, head);
-
if (rc <
0) {
-
kfree_skb(skb);
-
return rc;
-
}
-
-
rc = genlmsg_unicast(&init_net, skb, pid);
-
if (rc <
0) {
-
return rc;
-
}
-
-
return
0;
-
}
-
-
//echo command handler, 命令处理函数，当接收到user program发出的命令后，这个函数会被内核调用
-
static int doc_exmpl_echo(struct sk_buff *skb, struct genl_info *info)
-
{
-
/* message handling code goes here; return 0 on success, negative values on failure */
-
struct nlmsghdr *nlhdr;
-
struct genlmsghdr *genlhdr;
-
struct nlattr *nlh;
-
char *str;
-
int ret;
-
-
nlhdr = nlmsg_hdr(skb);
-
genlhdr = nlmsg_data(nlhdr);
-
nlh = genlmsg_data(genlhdr);
-
str = nla_data(nlh);
-
printk(
"doc_exmpl_echo get: %s\n", str);
-
-
ret = genl_msg_send_to_user(TEST_GENL_MSG_FROM_KERNEL,
-
strlen(TEST_GENL_MSG_FROM_KERNEL) +
1, nlhdr->nlmsg_pid);
-
-
return ret;
-
}
-
-
static int genetlink_init(void)
-
{
-
int rc;
-
-
/**
-
* 1. Registering A Family
-
* This function doesn't exist past linux 3.12
-
*/
-
rc = genl_register_family(&doc_exmpl_genl_family);
-
if (rc !=
0)
-
goto err_out1;
-
-
rc = genl_register_ops(&doc_exmpl_genl_family, &doc_exmpl_genl_ops_echo);
-
if (rc !=
0)
-
goto err_out2;
-
-
/*
-
* for multicast
-
*/
-
rc = genl_register_mc_group(&doc_exmpl_genl_family, &doc_exmpl_genl_mcgrp);
-
if (rc !=
0)
-
goto err_out3;
-
-
LOGC(
"doc_exmpl_genl_mcgrp.id=%d", doc_exmpl_genl_mcgrp.id);
-
LOGC(
"genetlink_init OK");
-
return
0;
-
-
err_out3:
-
genl_unregister_ops(&doc_exmpl_genl_family, &doc_exmpl_genl_ops_echo);
-
err_out2:
-
genl_unregister_family(&doc_exmpl_genl_family);
-
err_out1:
-
LOGC(
"Error occured while inserting generic netlink example module\n");
-
return rc;
-
}
-
-
static void genetlink_exit(void)
-
{
-
LOGC(
"Generic Netlink Example Module unloaded.");
-
-
genl_unregister_mc_group(&doc_exmpl_genl_family, &doc_exmpl_genl_mcgrp);
-
genl_unregister_ops(&doc_exmpl_genl_family, &doc_exmpl_genl_ops_echo);
-
genl_unregister_family(&doc_exmpl_genl_family);
-
}
-
user program
-
#include <stdio.h>
-
#include <stdlib.h>
-
#include <errno.h>
-
#include <unistd.h>
-
#include <poll.h>
-
#include <string.h>
-
#include <fcntl.h>
-
#include <sys/types.h>
-
#include <sys/stat.h>
-
#include <sys/socket.h>
-
#include <sys/types.h>
-
#include <signal.h>
-
-
#include <linux/genetlink.h>
-
-
#define GENLMSG_DATA(glh) ((void*)(((char*)glh) + GENL_HDRLEN))
-
#define NLA_DATA(nla) ((void *)((char*)(nla) + NLA_HDRLEN))
-
#define NLA_NEXT(nla,len) ((len) -= NLA_ALIGN((nla)->nla_len), \
-
(struct nlattr*)(((char*)(nla)) + NLA_ALIGN((nla)->nla_len)))
-
#define NLA_OK(nla,len) ((len) >= (int)sizeof(struct nlattr) && \
-
(nla)->nla_len >= sizeof(struct nlattr) && \
-
(nla)->nla_len <= (len))
-
-
//copy from kernel driver genl_ops's cmd
-
enum {
-
DOC_EXMPL_C_UNSPEC,
-
DOC_EXMPL_C_ECHO,
-
__DOC_EXMPL_C_MAX,
-
};
-
-
//copy from kernel driver netlink attribute
-
enum {
-
DOC_EXMPL_A_UNSPEC,
-
DOC_EXMPL_A_MSG,
-
__DOC_EXMPL_A_MAX,
-
};
-
-
-
#define MESSAGE_TO_KERNEL "Hello World from user space!"
-
-
-
-
/**
-
* nla_attr_size - length of attribute size, NOT including padding
-
* @param payload length of payload
-
* @return
-
*/
-
static inline int nla_attr_size(int payload)
-
{
-
return NLA_HDRLEN + payload;
-
}
-
-
/**
-
* nla_total_size - total length of attribute including padding
-
* @param payload length of payload, NOT including NLA_HDR
-
*/
-
static inline int nla_total_size(int payload)
-
{
-
return NLA_ALIGN(nla_attr_size(payload));
-
}
-
-
static int genlmsg_open(void)
-
{
-
int sockfd;
-
struct sockaddr_nl nladdr;
-
int ret;
-
-
sockfd = socket(AF_NETLINK, SOCK_RAW, NETLINK_GENERIC);
-
if (sockfd <
0)
-
{
-
LOGC(
"socket: %m");
-
return
-1;
-
}
-
-
memset(&nladdr,
0,
sizeof(nladdr));
-
nladdr.nl_family = AF_NETLINK;
-
nladdr.nl_pid = getpid();
-
nladdr.nl_groups =
0xffffffff;
//这个是mask值，如果family ID & nl_groups为0，
-
//则这个family的广播就接收不到，所以这里设为0xffffffff就可以接收所有的family消息
-
-
ret = bind(sockfd, (struct sockaddr *)&nladdr,
sizeof(nladdr));
-
if (ret <
0)
-
{
-
LOGC(
"bind: %m");
-
ret =
-1;
-
goto err_out;
-
}
-
-
return sockfd;
-
-
err_out:
-
close(sockfd);
-
return ret;
-
}
-
-
static void *genlmsg_alloc(int *size)
-
{
-
unsigned
char *buf;
-
int len;
-
-
/*
-
* attribute len
-
* attr len = (nla_hdr + pad) + (payload(user data) + pad)
-
*/
-
len = nla_total_size(*size);
-
/*
-
* family msg len,
-
* but actually we have NOT custom family header
-
* family msg len = family_hdr + payload(attribute)
-
*/
-
len +=
0;
-
/*
-
* generic netlink msg len
-
* genlmsg len = (genlhdr + pad) + payload(family msg)
-
*/
-
len += GENL_HDRLEN;
-
/*
-
* netlink msg len
-
* nlmsg len = (nlmsghdr + pad) + (payload(genlmsg) + pad)
-
*/
-
len = NLMSG_SPACE(len);
-
-
buf =
malloc(len);
-
if (!buf)
-
return
NULL;
-
-
memset(buf,
0, len);
-
*size = len;
-
-
return buf;
-
}
-
-
static void genlmsg_free(void *buf)
-
{
-
if (buf)
-
free(buf);
-
}
-
-
static int genlmsg_send(int sockfd, unsigned short nlmsg_type, unsigned int nlmsg_pid,
-
unsigned
char genl_cmd,
unsigned
char genl_version,
-
unsigned
short nla_type,
const
void *nla_data,
unsigned
int nla_len)
-
{
-
struct nlmsghdr *nlh;
//netlink message header
-
struct genlmsghdr *glh;
//generic netlink message header
-
struct nlattr *nla;
//netlink attribute header
-
-
struct sockaddr_nl nladdr;
-
unsigned
char *buf;
-
int len;
-
-
int count;
-
int ret;
-
-
if ((nlmsg_type ==
0) || (!nla_data) || (nla_len <=
0))
-
{
-
return
-1;
-
}
-
-
len = nla_len;
-
buf = genlmsg_alloc(&len);
-
if (!buf)
-
return
-1;
-
-
nlh = (struct nlmsghdr *)buf;
-
nlh->nlmsg_len = len;
-
nlh->nlmsg_type = nlmsg_type;
-
nlh->nlmsg_flags = NLM_F_REQUEST;
-
nlh->nlmsg_seq =
0;
-
nlh->nlmsg_pid = nlmsg_pid;
-
-
glh = (struct genlmsghdr *)NLMSG_DATA(nlh);
-
glh->cmd = genl_cmd;
-
glh->version = genl_version;
-
-
-
nla = (struct nlattr *)GENLMSG_DATA(glh);
-
nla->nla_type = nla_type;
-
nla->nla_len = nla_attr_size(nla_len);
-
memcpy(NLA_DATA(nla), nla_data, nla_len);
-
-
memset(&nladdr,
0,
sizeof(nladdr));
-
nladdr.nl_family = AF_NETLINK;
-
-
count =
0;
-
ret =
0;
-
do {
-
-
ret = sendto(sockfd, &buf[count], len - count,
0,
-
(struct sockaddr *)&nladdr,
sizeof(nladdr));
-
if (ret <
0)
-
{
-
if (errno != EAGAIN)
-
{
-
count =
-1;
-
goto out;
-
}
-
}
-
else
-
{
-
count += ret;
-
}
-
-
}
while (count < len);
-
-
-
out:
-
genlmsg_free(buf);
-
-
LOGC(
"send return %d", count);
-
return count;
-
}
-
-
/**
-
*
-
* @param sockfd generic netlink socket fd
-
* @param buf the 'buf' is including the struct nlmsghdr,
-
* struct genlmsghdr and struct nlattr
-
* @param len size of 'buf'
-
* @return >0 size of genlmsg
-
* <0 error occur
-
*/
-
static int genlmsg_recv(int sockfd, unsigned char *buf, unsigned int len)
-
{
-
struct sockaddr_nl nladdr;
-
struct msghdr msg;
-
struct iovec iov;
-
-
int ret;
-
-
nladdr.nl_family = AF_NETLINK;
-
nladdr.nl_pid = getpid();
-
nladdr.nl_groups =
0xffffffff;
-
-
iov.iov_base = buf;
-
iov.iov_len = len;
-
-
msg.msg_name = (
void *)&nladdr;
-
msg.msg_namelen =
sizeof(nladdr);
-
msg.msg_iov = &iov;
-
msg.msg_iovlen =
1;
-
msg.msg_control =
NULL;
-
msg.msg_controllen =
0;
-
msg.msg_flags =
0;
-
ret = recvmsg(sockfd, &msg,
0);
-
ret = ret >
0 ? ret :
-1;
-
LOGC(
"recv return %d", ret);
-
return ret;
-
}
-
-
static int genlmsg_dispatch(struct nlmsghdr *nlmsghdr, unsigned int nlh_len,
-
int nlmsg_type,
int nla_type,
unsigned
char *buf,
int *len)
-
{
-
struct nlmsghdr *nlh;
-
struct genlmsghdr *glh;
-
struct nlattr *nla;
-
int nla_len;
-
-
int l;
-
int i;
-
int ret =
-1;
-
-
if (!nlmsghdr || !buf || !len)
-
return
-1;
-
-
LOGC(
"nlmsg_type = %d", nlmsghdr->nlmsg_type);
-
if (nlmsg_type && (nlmsghdr->nlmsg_type != nlmsg_type))
-
return
-1;
-
-
//读取到的数据流里面，可能会包含多条nlmsg
-
for (nlh = nlmsghdr; NLMSG_OK(nlh, nlh_len); nlh = NLMSG_NEXT(nlh, nlh_len))
-
{
-
/* The end of multipart message. */
-
if (nlh->nlmsg_type == NLMSG_DONE)
-
{
-
LOGC(
"get NLMSG_DONE");
-
ret =
0;
-
break;
-
}
-
-
if (nlh->nlmsg_type == NLMSG_ERROR)
-
{
-
LOGC(
"get NLMSG_ERROR");
-
ret =
-1;
-
break;
-
}
-
-
glh = (struct genlmsghdr *)NLMSG_DATA(nlh);
-
nla = (struct nlattr *)GENLMSG_DATA(glh);
//the first attribute
-
nla_len = nlh->nlmsg_len - GENL_HDRLEN;
//len of attributes
-
for (i =
0; NLA_OK(nla, nla_len); nla = NLA_NEXT(nla, nla_len), ++i)
-
{
-
//一条nlmsg里面，可能会包含多个attr
-
LOGC(
"%d. nla->nla_type = %d", i, nla->nla_type);
-
/* Match the family ID, copy the data to user */
-
if (nla_type == nla->nla_type)
-
{
-
l = nla->nla_len - NLA_HDRLEN;
//attribute里的payload就是内核返回给用户的实际数据
-
*len = *len > l ? l : *len;
-
memcpy(buf, NLA_DATA(nla), *len);
-
ret =
0;
-
break;
-
}
-
}
-
}
-
-
return ret;
-
}
-
-
static int genlmsg_get_family_id(int sockfd, const char *family_name)
-
{
-
void *buf;
-
int len;
-
__u16 id;
-
int l;
-
int ret;
-
-
ret = genlmsg_send(sockfd, GENL_ID_CTRL,
0, CTRL_CMD_GETFAMILY,
1,
-
CTRL_ATTR_FAMILY_NAME, family_name,
strlen(family_name) +
1);
-
if (ret <
0)
-
return
-1;
-
-
len =
256;
-
buf = genlmsg_alloc(&len);
-
if (!buf)
-
return
-1;
-
-
len = genlmsg_recv(sockfd, buf, len);
-
if (len <
0)
-
return len;
-
-
id =
0;
-
l =
sizeof(id);
-
genlmsg_dispatch((struct nlmsghdr *)buf, len,
0, CTRL_ATTR_FAMILY_ID, (
unsigned
char *)&id, &l);
-
-
genlmsg_free(buf);
-
-
return id >
0 ? id :
-1;
-
}
-
-
static void genlmsg_close(int sockfd)
-
{
-
if (sockfd >=
0)
-
close(sockfd);
-
}
-
-
-
-
#define BUF_SIZE 256
-
static int test_netlink_unicast(void)
-
{
-
struct nlmsghdr *nlh = NULL;
-
int sockfd =
-1;
-
unsigned
char buf[BUF_SIZE];
-
int len;
-
int id;
-
pid_t pid;
-
int ret;
-
-
len = BUF_SIZE;
-
nlh = genlmsg_alloc(&len);
-
if (!nlh)
-
return
-1;
-
-
sockfd = genlmsg_open();
-
if (sockfd <
0)
-
return
-1;
-
-
id = genlmsg_get_family_id(sockfd,
"DOC_EXMPL");
//这里必须先通过family的名字获取到family ID，名字需要与驱动里的一致
-
LOGC(
"get family ID[%d]", id);
-
if (id <=
0)
-
{
-
ret =
-1;
-
goto out;
-
}
-
-
pid = getpid();
-
ret = genlmsg_send(sockfd, id, pid, DOC_EXMPL_C_ECHO,
1,
-
DOC_EXMPL_A_MSG, MESSAGE_TO_KERNEL,
strlen(MESSAGE_TO_KERNEL) +
1);
//向内核发送genl消息
-
if (ret <
0)
-
{
-
goto out;
-
}
-
-
ret = genlmsg_recv(sockfd, (
unsigned
char *)nlh, len);
//等待内核的回复
-
if (ret >
0)
-
{
-
memset(buf,
0,
sizeof(buf));
-
len =
sizeof(buf);
-
ret = genlmsg_dispatch(nlh, ret, id, DOC_EXMPL_A_MSG, buf, &len);
-
if (ret ==
0)
-
{
-
printf(
"get: %s\n", buf);
-
}
-
}
-
-
out:
-
genlmsg_close(sockfd);
-
genlmsg_free(nlh);
-
-
return ret;
-
}
-
-
-
int main(int argc, char *argv[])
-
{
-
/*
-
* test netlink unicast
-
*/
-
test_netlink_unicast();
-
-
return
0;
-
}
例子2：kernel到user，user program先创建一个socket并监听，内核发生某个事件以后，就可以发送一个广播，通知user program
kernel端：
-
#include <net/netlink.h>
-
#include <net/genetlink.h>
-
#include <linux/version.h>
-
-
-
#define TEST_GENL_FAMILY_NAME "my-test-family"
-
#define TEST_GENL_MCAST_GROUP_NAME "my-test-group"
-
#define TEST_GENL_MSG_FROM_KERNEL "Hello from kernel space!!!"
-
-
/* handler
-
* message handling code goes here; return 0 on success, negative
-
* values on failure
-
*/
-
static int doc_exmpl_echo(struct sk_buff *skb, struct genl_info *info);
-
-
-
-
/* netlink attributes 可以通过枚举索引找到对应的类型，用户空间应用程序要传递这样的信息 */
-
enum {
-
DOC_EXMPL_A_UNSPEC,
-
DOC_EXMPL_A_MSG,
-
__DOC_EXMPL_A_MAX,
-
};
-
#define DOC_EXMPL_A_MAX (__DOC_EXMPL_A_MAX - 1)
-
-
/* attribute policy */
-
static
struct nla_policy doc_exmpl_genl_policy[DOC_EXMPL_A_MAX + 1] = {
-
[DOC_EXMPL_A_MSG] = { .type = NLA_NUL_STRING },
-
};
-
-
/* commands 定义命令类型，用户空间以此来表明需要执行的命令 */
-
enum {
-
DOC_EXMPL_C_UNSPEC,
-
DOC_EXMPL_C_ECHO,
-
__DOC_EXMPL_C_MAX,
-
};
-
#define DOC_EXMPL_C_MAX (__DOC_EXMPL_C_MAX - 1)
-
-
#if LINUX_VERSION_CODE < KERNEL_VERSION(3,13,0)
-
-
/* family definition */
-
static
struct genl_family doc_exmpl_genl_family = {
-
.id = GENL_ID_GENERATE,
//request a new channel number, assigned by kernel, NOT driver specific
-
.hdrsize =
0,
-
.name =
"DOC_EXMPL",
-
.version =
1,
-
.maxattr = DOC_EXMPL_A_MAX,
-
};
-
-
/* operation definition 将命令command echo和具体的handler对应起来 */
-
static
struct genl_ops doc_exmpl_genl_ops_echo = {
-
.cmd = DOC_EXMPL_C_ECHO,
-
.flags =
0,
-
.policy = doc_exmpl_genl_policy,
-
.doit = doc_exmpl_echo,
-
.dumpit =
NULL,
-
};
-
-
static
struct genl_multicast_group doc_exmpl_genl_mcgrp = {
-
.name =
"DOC_EXMPL_GRP",
-
};
-
-
//需要在其他地方主动调用这个函数发送广播
-
static int test_netlink_send(void)
-
{
-
struct sk_buff *skb = NULL;
-
void *msg_header =
NULL;
-
int size;
-
int rc;
-
-
/* allocate memory */
-
size = nla_total_size(
strlen(TEST_GENL_MSG_FROM_KERNEL) +
1) + nla_total_size(
0);
-
-
skb = genlmsg_new(size, GFP_KERNEL);
-
if (!skb)
-
return -ENOMEM;
-
-
/* add the genetlink message header */
-
msg_header = genlmsg_put(skb,
0,
0,
-
&doc_exmpl_genl_family,
0, DOC_EXMPL_C_ECHO);
-
if (!msg_header)
-
{
-
rc = -ENOMEM;
-
goto err_out;
-
}
-
-
/* add a DOC_EXMPL_A_MSG attribute */
-
rc = nla_put_string(skb, DOC_EXMPL_A_MSG, TEST_GENL_MSG_FROM_KERNEL);
-
if (rc !=
0)
-
goto err_out;
-
-
/* finalize the message */
-
genlmsg_end(skb, msg_header);
-
-
//multicast is send a message to a logical group
-
rc = genlmsg_multicast(skb,
0, doc_exmpl_genl_mcgrp.id, GFP_KERNEL);
-
if (rc !=
0 && rc != -ESRCH)
-
{
-
/* if NO one is waitting the message in user space,
-
* genlmsg_multicast return -ESRCH
-
*/
-
LOGC(
"genlmsg_multicast to user failed, return %d", rc);
-
-
/*
-
* attention:
-
* If you NOT call genlmsg_unicast/genlmsg_multicast and error occurs,
-
* call nlmsg_free(skb).
-
* But if you call genlmsg_unicast/genlmsg_multicast, NO need to call
-
* nlmsg_free(skb). If NOT, kernel crash.
-
*/
-
return rc;
-
}
-
-
LOGC(
"genlmsg_multicast Success");
-
-
/*
-
* Attention:
-
* Should NOT call nlmsg_free(skb) here. If NOT, kernel crash!!!
-
*/
-
return
0;
-
-
err_out:
-
if (skb)
-
nlmsg_free(skb);
-
return rc;
-
}
-
-
-
static int genetlink_init(struct my_module_priv *ctx)
-
{
-
int rc;
-
-
/**
-
* 1. Registering A Family
-
* This function doesn't exist past linux 3.12
-
*/
-
rc = genl_register_family(&doc_exmpl_genl_family);
-
if (rc !=
0)
-
goto err_out1;
-
-
rc = genl_register_ops(&doc_exmpl_genl_family, &doc_exmpl_genl_ops_echo);
-
if (rc !=
0)
-
goto err_out2;
-
-
/*
-
* for multicast
-
*/
-
rc = genl_register_mc_group(&doc_exmpl_genl_family, &doc_exmpl_genl_mcgrp);
-
if (rc !=
0)
-
goto err_out3;
-
-
LOGC(
"doc_exmpl_genl_mcgrp.id=%d", doc_exmpl_genl_mcgrp.id);
-
LOGC(
"genetlink_init OK");
-
return
0;
-
-
err_out3:
-
genl_unregister_ops(&doc_exmpl_genl_family, &doc_exmpl_genl_ops_echo);
-
err_out2:
-
genl_unregister_family(&doc_exmpl_genl_family);
-
err_out1:
-
LOGC(
"Error occured while inserting generic netlink example module\n");
-
return rc;
-
}
-
-
static void genetlink_exit(struct my_module_priv *ctx)
-
{
-
LOGC(
"Generic Netlink Example Module unloaded.");
-
-
genl_unregister_mc_group(&doc_exmpl_genl_family, &doc_exmpl_genl_mcgrp);
-
genl_unregister_ops(&doc_exmpl_genl_family, &doc_exmpl_genl_ops_echo);
-
genl_unregister_family(&doc_exmpl_genl_family);
-
}
-
-
static
struct my_module_work g_my_module_work = {
-
.do_test_probe = genetlink_init,
-
.do_test_remove = genetlink_exit,
-
};
user program
-
#include <stdio.h>
-
#include <stdlib.h>
-
#include <errno.h>
-
#include <unistd.h>
-
#include <poll.h>
-
#include <string.h>
-
#include <fcntl.h>
-
#include <sys/types.h>
-
#include <sys/stat.h>
-
#include <sys/socket.h>
-
#include <sys/types.h>
-
#include <signal.h>
-
-
#include <linux/genetlink.h>
-
-
#define GENLMSG_DATA(glh) ((void*)(((char*)glh) + GENL_HDRLEN))
-
#define NLA_DATA(nla) ((void *)((char*)(nla) + NLA_HDRLEN))
-
#define NLA_NEXT(nla,len) ((len) -= NLA_ALIGN((nla)->nla_len), \
-
(struct nlattr*)(((char*)(nla)) + NLA_ALIGN((nla)->nla_len)))
-
#define NLA_OK(nla,len) ((len) >= (int)sizeof(struct nlattr) && \
-
(nla)->nla_len >= sizeof(struct nlattr) && \
-
(nla)->nla_len <= (len))
-
-
//copy from kernel driver genl_ops's cmd
-
enum {
-
DOC_EXMPL_C_UNSPEC,
-
DOC_EXMPL_C_ECHO,
-
__DOC_EXMPL_C_MAX,
-
};
-
-
//copy from kernel driver netlink attribute
-
enum {
-
DOC_EXMPL_A_UNSPEC,
-
DOC_EXMPL_A_MSG,
-
__DOC_EXMPL_A_MAX,
-
};
-
-
-
#define MESSAGE_TO_KERNEL "Hello World from user space!"
-
-
-
-
/**
-
* nla_attr_size - length of attribute size, NOT including padding
-
* @param payload length of payload
-
* @return
-
*/
-
static inline int nla_attr_size(int payload)
-
{
-
return NLA_HDRLEN + payload;
-
}
-
-
/**
-
* nla_total_size - total length of attribute including padding
-
* @param payload length of payload, NOT including NLA_HDR
-
*/
-
static inline int nla_total_size(int payload)
-
{
-
return NLA_ALIGN(nla_attr_size(payload));
-
}
-
-
static int genlmsg_open(void)
-
{
-
int sockfd;
-
struct sockaddr_nl nladdr;
-
int ret;
-
-
sockfd = socket(AF_NETLINK, SOCK_RAW, NETLINK_GENERIC);
-
if (sockfd <
0)
-
{
-
LOGC(
"socket: %m");
-
return
-1;
-
}
-
-
memset(&nladdr,
0,
sizeof(nladdr));
-
nladdr.nl_family = AF_NETLINK;
-
nladdr.nl_pid = getpid();
-
nladdr.nl_groups =
0xffffffff;
-
-
ret = bind(sockfd, (struct sockaddr *)&nladdr,
sizeof(nladdr));
-
if (ret <
0)
-
{
-
LOGC(
"bind: %m");
-
ret =
-1;
-
goto err_out;
-
}
-
-
return sockfd;
-
-
err_out:
-
close(sockfd);
-
return ret;
-
}
-
-
static void *genlmsg_alloc(int *size)
-
{
-
unsigned
char *buf;
-
int len;
-
-
/*
-
* attribute len
-
* attr len = (nla_hdr + pad) + (payload(user data) + pad)
-
*/
-
len = nla_total_size(*size);
-
/*
-
* family msg len,
-
* but actually we have NOT custom family header
-
* family msg len = family_hdr + payload(attribute)
-
*/
-
len +=
0;
-
/*
-
* generic netlink msg len
-
* genlmsg len = (genlhdr + pad) + payload(family msg)
-
*/
-
len += GENL_HDRLEN;
-
/*
-
* netlink msg len
-
* nlmsg len = (nlmsghdr + pad) + (payload(genlmsg) + pad)
-
*/
-
len = NLMSG_SPACE(len);
-
-
buf =
malloc(len);
-
if (!buf)
-
return
NULL;
-
-
memset(buf,
0, len);
-
*size = len;
-
-
return buf;
-
}
-
-
static void genlmsg_free(void *buf)
-
{
-
if (buf)
-
free(buf);
-
}
-
-
static int genlmsg_send(int sockfd, unsigned short nlmsg_type, unsigned int nlmsg_pid,
-
unsigned
char genl_cmd,
unsigned
char genl_version,
-
unsigned
short nla_type,
const
void *nla_data,
unsigned
int nla_len)
-
{
-
struct nlmsghdr *nlh;
//netlink message header
-
struct genlmsghdr *glh;
//generic netlink message header
-
struct nlattr *nla;
//netlink attribute header
-
-
struct sockaddr_nl nladdr;
-
unsigned
char *buf;
-
int len;
-
-
int count;
-
int ret;
-
-
if ((nlmsg_type ==
0) || (!nla_data) || (nla_len <=
0))
-
{
-
return
-1;
-
}
-
-
len = nla_len;
-
buf = genlmsg_alloc(&len);
-
if (!buf)
-
return
-1;
-
-
nlh = (struct nlmsghdr *)buf;
-
nlh->nlmsg_len = len;
-
nlh->nlmsg_type = nlmsg_type;
-
nlh->nlmsg_flags = NLM_F_REQUEST;
-
nlh->nlmsg_seq =
0;
-
nlh->nlmsg_pid = nlmsg_pid;
-
-
glh = (struct genlmsghdr *)NLMSG_DATA(nlh);
-
glh->cmd = genl_cmd;
-
glh->version = genl_version;
-
-
-
nla = (struct nlattr *)GENLMSG_DATA(glh);
-
nla->nla_type = nla_type;
-
nla->nla_len = nla_attr_size(nla_len);
-
memcpy(NLA_DATA(nla), nla_data, nla_len);
-
-
memset(&nladdr,
0,
sizeof(nladdr));
-
nladdr.nl_family = AF_NETLINK;
-
-
count =
0;
-
ret =
0;
-
do {
-
-
ret = sendto(sockfd, &buf[count], len - count,
0,
-
(struct sockaddr *)&nladdr,
sizeof(nladdr));
-
if (ret <
0)
-
{
-
if (errno != EAGAIN)
-
{
-
count =
-1;
-
goto out;
-
}
-
}
-
else
-
{
-
count += ret;
-
}
-
-
}
while (count < len);
-
-
-
out:
-
genlmsg_free(buf);
-
-
LOGC(
"send return %d", count);
-
return count;
-
}
-
-
/**
-
*
-
* @param sockfd generic netlink socket fd
-
* @param buf the 'buf' is including the struct nlmsghdr,
-
* struct genlmsghdr and struct nlattr
-
* @param len size of 'buf'
-
* @return >0 size of genlmsg
-
* <0 error occur
-
*/
-
static int genlmsg_recv(int sockfd, unsigned char *buf, unsigned int len)
-
{
-
struct sockaddr_nl nladdr;
-
struct msghdr msg;
-
struct iovec iov;
-
-
int ret;
-
-
nladdr.nl_family = AF_NETLINK;
-
nladdr.nl_pid = getpid();
-
nladdr.nl_groups =
0xffffffff;
-
-
iov.iov_base = buf;
-
iov.iov_len = len;
-
-
msg.msg_name = (
void *)&nladdr;
-
msg.msg_namelen =
sizeof(nladdr);
-
msg.msg_iov = &iov;
-
msg.msg_iovlen =
1;
-
msg.msg_control =
NULL;
-
msg.msg_controllen =
0;
-
msg.msg_flags =
0;
-
ret = recvmsg(sockfd, &msg,
0);
-
ret = ret >
0 ? ret :
-1;
-
LOGC(
"recv return %d", ret);
-
return ret;
-
}
-
-
static int genlmsg_dispatch(struct nlmsghdr *nlmsghdr, unsigned int nlh_len,
-
int nlmsg_type,
int nla_type,
unsigned
char *buf,
int *len)
-
{
-
struct nlmsghdr *nlh;
-
struct genlmsghdr *glh;
-
struct nlattr *nla;
-
int nla_len;
-
-
int l;
-
int i;
-
int ret =
-1;
-
-
if (!nlmsghdr || !buf || !len)
-
return
-1;
-
-
LOGC(
"nlmsg_type = %d", nlmsghdr->nlmsg_type);
-