Generic netlink编程入门
通过generic netlink可以实现内核和用户空间的通信，genetlink是通过family来管理的（哈希表），
genl_ctrl 是一个特殊的Family, 它是由Generic Netlink自己注册和实现，并用来查询Family列表、管理各个Family的添加、删除等事件的。用户空间先根据family name请求到相应的family ID，而后进行相互沟通。
static struct genl_family
genl_ctrl = {
.id = GENL_ID_CTRL,
.name = "nlctrl",
.version = 0x2,
.maxattr = CTRL_ATTR_MAX,
.netnsok = true,
};
static struct genl_ops genl_ctrl_ops = {
.cmd = CTRL_CMD_GETFAMILY,
.doit = ctrl_getfamily,
.dumpit = ctrl_dumpfamily,
.policy = ctrl_policy,
};
.id = GENL_ID_CTRL,
.name = "nlctrl",
.version = 0x2,
.maxattr = CTRL_ATTR_MAX,
.netnsok = true,
};
static struct genl_ops genl_ctrl_ops = {
.cmd = CTRL_CMD_GETFAMILY,
.doit = ctrl_getfamily,
.dumpit = ctrl_dumpfamily,
.policy = ctrl_policy,
};
static const struct nla_policy ctrl_policy[CTRL_ATTR_MAX+1] = {
[ CTRL_ATTR_FAMILY_ID] = { .type = NLA_U16 },
[CTRL_ATTR_FAMILY_NAME] = { .type = NLA_NUL_STRING, .len = L_NAMSIZ - 1 },
};
[ CTRL_ATTR_FAMILY_ID] = { .type = NLA_U16 },
[CTRL_ATTR_FAMILY_NAME] = { .type = NLA_NUL_STRING, .len = L_NAMSIZ - 1 },
};
genl_kern.c
#include
#include
#include
#include
/*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)
/*atribute policy就是定义各个属性的具体类型，参见net/netlink.h*/
static struct nla_policy doc_exmpl_genl_policy[DOC_EXMPL_A_MAX + 1] = {
[DOC_EXMPL_A_MSG] = {.type = NLA_NUL_STRING},
};
#define VERSION_NR 1
//generic netlink family 定义
static struct genl_family doc_exmpl_genl_family = {
.id = GENL_ID_GENERATE,
.hdrsize = 0,
.name = "CONTROL_EXMPL",
.version = VERSION_NR,
.maxattr = DOC_EXMPL_A_MAX,
};
/*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)
//echo command handler,接收一个msg并回复
int doc_exmpl_echo(struct sk_buff *skb2, struct genl_info *info){
struct nlattr *na;
struct sk_buff *skb;
int rc;
void *msg_hdr;
char *data;
if(info == NULL)
goto error;
//对于每个属性，genl_info的域attrs可以索引到具体结构，里面有payload
na = info->attrs[DOC_EXMPL_A_MSG];
if(na){
data = (char *)nla_data(na);
if(!data) printk("Receive data error!\n");
else printk("Recv:%s\n",data);
}else{
printk("No info->attrs %d\n",DOC_EXMPL_A_MSG);
}
skb = genlmsg_new(NLMSG_GOODSIZE,GFP_KERNEL);
if(!skb) goto error;
/*构建消息头，函数原型是
genlmsgput(struct sk_buff *,int pid,int seq_number,
struct genl_family *,int flags,u8 command_index);
*/
msg_hdr = genlmsg_put(skb,0,info->snd_seq+1,&doc_exmpl_genl_family,
0,DOC_EXMPL_C_ECHO);
if(msg_hdr == NULL){
rc = -ENOMEM;
goto error;
}
//填充具体的netlink attribute:DOC_EXMPL_A_MSG，这是实际要传的数据
rc = nla_put_string(skb,DOC_EXMPL_A_MSG,"Hello World from kernel space!");
if(rc != 0) goto error;
genlmsg_end(skb,msg_hdr);//消息构建完成
//单播发送给用户空间的某个进程
rc = genlmsg_unicast(genl_info_net(info),skb,info->snd_pid);
if(rc != 0){
printk("Unicast to process:%d failed!\n",info->snd_pid);
goto error;
}
return 0;
error:
printk("Error occured in doc_echo!\n");
return 0;
}
//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,
};
//内核入口，注册generic netlink family/operations
static int __init genKernel_init(void) {
int rc;
printk("Generic Netlink Example Module inserted.\n");
rc = genl_register_family(&doc_exmpl_genl_family);
if (rc != 0) {
goto failure;
}
rc = genl_register_ops(&doc_exmpl_genl_family,&doc_exmpl_genl_ops_echo);
if (rc != 0) {
printk("Register ops: %i\n",rc);
genl_unregister_family(&doc_exmpl_genl_family);
goto failure;
}
return 0;
failure:
printk("Error occured while inserting generic netlink example module\n");
return -1;
}
static void __exit genKernel_exit(void) {
int ret;
printk("Generic Netlink Example Module unloaded.\n");
ret = genl_unregister_ops(&doc_exmpl_genl_family,&doc_exmpl_genl_ops_echo);
if(ret != 0) {
printk("Unregister ops failed: %i\n",ret);
return;
}
ret = genl_unregister_family(&doc_exmpl_genl_family);
if(ret !=0) {
printk("Unregister family failed:%i\n",ret);
}
}
module_init(genKernel_init);
module_exit(genKernel_exit);
MODULE_LICENSE("GPL");
genl_user.c
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
//宏定义：根据generic netlink msg的具体构造定位
#define GENLMSG_DATA(glh) ((void *)(NLMSG_DATA(glh) + GENL_HDRLEN))
#define GENLMSG_PAYLOAD(glh) (NLMSG_PAYLOAD(glh, 0) - GENL_HDRLEN)
#define NLA_DATA(na) ((void *)((char*)(na) + NLA_HDRLEN))
#define MESSAGE_TO_KERNEL "Hello World from user space!"
int nl_fd;
struct sockaddr_nl nl_address;
int nl_family_id;
int len;
struct nlattr *nl_na;
struct { //
struct nlmsghdr n;
struct genlmsghdr g;
char buf[256];
} nl_request_msg, nl_response_msg;
int main(void) {
nl_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_GENERIC);
if (nl_fd < 0) {
perror("socket()");
return -1;
}
memset(&nl_address, 0, sizeof(nl_address));
nl_address.nl_family = AF_NETLINK;
nl_address.nl_groups = 0;
if (bind(nl_fd, (struct sockaddr *) &nl_address, sizeof(nl_address)) < 0) {
perror("bind()");
close(nl_fd);
return -1;
}
nl_request_msg.n.nlmsg_type = GENL_ID_CTRL;//这是内核中genl_ctl的id
nl_request_msg.n.nlmsg_flags = NLM_F_REQUEST;
nl_request_msg.n.nlmsg_seq = 0;
nl_request_msg.n.nlmsg_pid = getpid();
nl_request_msg.n.nlmsg_len = NLMSG_LENGTH(GENL_HDRLEN);
//Populate the payload's "family header" : which in our case is genlmsghdr
nl_request_msg.g.cmd = CTRL_CMD_GETFAMILY;
nl_request_msg.g.version = 0x1;
//Populate the payload's "netlink attributes"
nl_na = (struct nlattr *) GENLMSG_DATA(&nl_request_msg);//其实就相当于在nl_request_msg 的buf域中构造一个nla
nl_na->nla_type = CTRL_ATTR_FAMILY_NAME;
nl_na->nla_len = strlen("CONTROL_EXMPL") + 1 + NLA_HDRLEN;
strcpy(NLA_DATA(nl_na), "CONTROL_EXMPL"); //Family name length can be upto 16 chars including \0
nl_request_msg.n.nlmsg_len += NLMSG_ALIGN(nl_na->nla_len);
memset(&nl_address, 0, sizeof(nl_address));
nl_address.nl_family = AF_NETLINK;
len= sendto(nl_fd, (char *) &nl_request_msg, nl_request_msg.n.nlmsg_len,
0, (struct sockaddr *) &nl_address, sizeof(nl_address));
if (len != nl_request_msg.n.nlmsg_len) {
perror("sendto()");
close(nl_fd);
return -1;
}
len= recv(nl_fd, &nl_response_msg, sizeof(nl_response_msg), 0);
if (len < 0) {
perror("recv()");
return -1;
}
if (!NLMSG_OK((&nl_response_msg.n), len)) {
fprintf(stderr, "family ID request : invalid message\n");
return -1;
}
if (nl_response_msg.n.nlmsg_type == NLMSG_ERROR) { //error
fprintf(stderr, "family ID request : receive error\n");
return -1;
}
//解析出attribute中的family id
nl_na = (struct nlattr *) GENLMSG_DATA(&nl_response_msg);
nl_na = (struct nlattr *) ((char *) nl_na + NLA_ALIGN(nl_na->nla_len));
if (nl_na->nla_type == CTRL_ATTR_FAMILY_ID) {
nl_family_id = *(__u16 *) NLA_DATA(nl_na);//第一次通信就是为了得到需要的family ID
}
memset(&nl_request_msg, 0, sizeof(nl_request_msg));
memset(&nl_response_msg, 0, sizeof(nl_response_msg));
nl_request_msg.n.nlmsg_len = NLMSG_LENGTH(GENL_HDRLEN);
nl_request_msg.n.nlmsg_type = nl_family_id;
nl_request_msg.n.nlmsg_flags = NLM_F_REQUEST;
nl_request_msg.n.nlmsg_seq = 60;
nl_request_msg.n.nlmsg_pid = getpid();
nl_request_msg.g.cmd = 1; //corresponds to DOC_EXMPL_C_ECHO;
nl_na = (struct nlattr *) GENLMSG_DATA(&nl_request_msg);
nl_na->nla_type = 1; // corresponds to DOC_EXMPL_A_MSG
nl_na->nla_len = sizeof(MESSAGE_TO_KERNEL)+NLA_HDRLEN; //Message length
memcpy(NLA_DATA(nl_na), MESSAGE_TO_KERNEL, sizeof(MESSAGE_TO_KERNEL));
nl_request_msg.n.nlmsg_len += NLMSG_ALIGN(nl_na->nla_len);
memset(&nl_address, 0, sizeof(nl_address));
nl_address.nl_family = AF_NETLINK;
len = sendto(nl_fd, (char *) &nl_request_msg, nl_request_msg.n.nlmsg_len,
0, (struct sockaddr *) &nl_address, sizeof(nl_address));
if (len != nl_request_msg.n.nlmsg_len) {
perror("sendto()");
close(nl_fd);
return -1;
}
printf("Sent to kernel: %s\n",MESSAGE_TO_KERNEL);
len = recv(nl_fd, &nl_response_msg, sizeof(nl_response_msg), 0);
if (len < 0) {
perror("recv()");
return -1;
}
//异常处理
if (nl_response_msg.n.nlmsg_type == NLMSG_ERROR) { //Error
printf("Error while receiving reply from kernel: NACK Received\n");
close(nl_fd);
return -1;
}
if (len < 0) {
printf("Error while receiving reply from kernel\n");
close(nl_fd);
return -1;
}
if (!NLMSG_OK((&nl_response_msg.n), len)) {
printf("Error while receiving reply from kernel: Invalid Message\n");
close(nl_fd);
return -1;
}
//解析收到的来自内核的reply
len = GENLMSG_PAYLOAD(&nl_response_msg.n);
nl_na = (struct nlattr *) GENLMSG_DATA(&nl_response_msg);
printf("Kernel replied: %s\n",(char *)NLA_DATA(nl_na));
close(nl_fd);
return 0;
} 参考： 1. http://people.ee.ethz.ch/~arkeller/linux/multi/kernel_user_space_howto-3.html