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数据交换 genlink, 使用nl库

3.x 内核

kernel

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#include <linux/module.h>
#include <net/netlink.h>
#include <net/genetlink.h>
#include <linux/version.h>

#define MSG_KER "Hello from kernel space!!!"

struct family_hdr {
	int ff;
};

struct data_hdr {
	int len;
	int kk;
	char str[0];
};

/* netlink attributes */
enum {
	DOC_EXMPL_A_UNSPEC,
	DOC_EXMPL_A_MSG,
	DOC_EXMPL_A_MSG2,
	__DOC_EXMPL_A_MAX,
};
#define DOC_EXMPL_A_MAX (__DOC_EXMPL_A_MAX - 1)

/* 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)

static int nl_pre_doit(struct genl_ops*  ops, struct sk_buff* skb, struct genl_info* info)
{
	return 0;
}
static void nl_post_doit(struct genl_ops*  ops, struct sk_buff* skb, struct genl_info* info)
{
	return;
}

/* family definition */
static struct genl_family nl_family = {
	.id = GENL_ID_GENERATE,   //这里不指定family ID，由内核进行分配
	.hdrsize = sizeof(struct family_hdr),             //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,
	.pre_doit  = nl_pre_doit,
	.post_doit = nl_post_doit,
};

static int rcv_handler(struct genl_info *info)
{
	struct nlattr *tb[DOC_EXMPL_A_MAX + 1] = {0};
	struct family_hdr *fhdr = (struct family_hdr *)info->userhdr;
	struct data_hdr *hdr;
	int rc, i;
	int rcvlen;

	//printk("kernel recv: %d %d %d %s\n", fhdr->ff, hdr->len, hdr->kk, hdr->str);
	//printk("gg %d\n", info->nlhdr->nlmsg_len - ((u64)info->userhdr - (u64)info->nlhdr) - sizeof(struct family_hdr));
	rc = nla_parse(tb, DOC_EXMPL_A_MAX,
			info->userhdr + sizeof(struct family_hdr),
			info->nlhdr->nlmsg_len - ((u64)info->userhdr - (u64)info->nlhdr) - sizeof(struct family_hdr),
			NULL);
	if (rc) {
		printk("nla_parse err\n");
		return -1;
	}

	for (i = 1; i <= DOC_EXMPL_A_MAX; i ++) {
		if (!tb[i])
			continue;
		rcvlen = nla_len(tb[i]);
		hdr = (struct data_hdr*)nla_data(tb[i]);
		printk("ker-rcv: %d %d %d %d rcvlen=%d %s\n", i, fhdr->ff, hdr->len, hdr->kk, rcvlen, hdr->str);
	}
	return 0;
}


static int snd_handler(struct genl_info *info)
{
	struct sk_buff *reply = NULL;
	char sss[123];
	struct family_hdr *snd_fhdr;
	struct data_hdr *snd_hdr = (struct data_hdr *)sss;
	int err;

	reply = genlmsg_new(NLMSG_ALIGN(sizeof(struct family_hdr)) + NLMSG_ALIGN(sizeof(struct data_hdr)) + nla_total_size(strlen(MSG_KER)), GFP_KERNEL);
	if (!reply) {
		printk("genlmsg_new err\n");
		return -1;
	}

	snd_fhdr = (struct family_hdr *)genlmsg_put(reply, info->snd_portid, info->snd_seq, &nl_family, 0, DOC_EXMPL_C_ECHO);
	snd_fhdr->ff = 222;
	snd_hdr->len = 321;
	snd_hdr->kk = 654;
	strcpy(snd_hdr->str, MSG_KER);
	err = nla_put(reply, DOC_EXMPL_A_MSG, sizeof(struct data_hdr) + strlen(snd_hdr->str), snd_hdr);
	if (err) {
		printk("nla_put err\n");
		genlmsg_cancel(reply, snd_fhdr);
		return -2;
	}

	snd_hdr->len = 987;
	snd_hdr->kk = 789;
	err = nla_put(reply, DOC_EXMPL_A_MSG2, sizeof(struct data_hdr) + strlen(snd_hdr->str), snd_hdr);
	if (err) {
		printk("nla_put err2\n");
		genlmsg_cancel(reply, snd_fhdr);
		return -2;
	}

	genlmsg_end(reply, snd_fhdr);

	err = genlmsg_reply(reply, info);
	if (err)
		printk("genlmsg_reply err\n");

	return 0;
}

static int nl_echo(struct sk_buff *skb, struct genl_info *info)
{
	rcv_handler(info);
	snd_handler(info);
	return 0;
}

static struct genl_ops nl_ops[] = {
	{
		.cmd  = DOC_EXMPL_C_ECHO,
		.doit = nl_echo,
		.flags    = GENL_ADMIN_PERM,
	},
};

int genetlink_init(void)
{
	return genl_register_family_with_ops(&nl_family, nl_ops, ARRAY_SIZE(nl_ops));
}

void genetlink_exit(void)
{
	genl_unregister_family(&nl_family);
	printk("Generic Netlink_nl Example Module unloaded.\n");
}

module_init(genetlink_init);
module_exit(genetlink_exit);
MODULE_LICENSE("GPL");
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obj-m += genlink_nl.o

KDIR := /usr/src/kernels/`uname -r`/

PWD := `pwd`

default:
	make -C $(KDIR) M=$(PWD) modules

clean:
	rm -rf *.ko *.o *.mod.c .*.cmd .tmp_versions Module.symvers modules.order

user

gcc user_nl.c -lnl

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// gcc user_nl.c -lnl
//
#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 <asm/types.h>

//#include <linux/genetlink.h>
#include <netlink/socket.h>
#include <netlink/genl/genl.h>
#include <netlink/genl/family.h>
#include <netlink/genl/ctrl.h>
#include <netlink/msg.h>

#define MESSAGE_TO_KERNEL   "Hello World from user space!!"

struct family_hdr {
	int ff;
};

struct data_hdr {
	int len;
	int kk;
	char str[0];
};

/* netlink attributes */
enum {
	DOC_EXMPL_A_UNSPEC,
	DOC_EXMPL_A_MSG,
	DOC_EXMPL_A_MSG2,
	__DOC_EXMPL_A_MAX,
};
#define DOC_EXMPL_A_MAX (__DOC_EXMPL_A_MAX - 1)

//copy from kernel driver genl_ops's cmd
enum {
	DOC_EXMPL_C_UNSPEC,
	DOC_EXMPL_C_ECHO,
	__DOC_EXMPL_C_MAX,
};
#define DOC_EXMPL_C_MAX (__DOC_EXMPL_C_MAX - 1)

static int error_handler(struct sockaddr_nl *nla, struct nlmsgerr *err, void *arg)
{
	int *ret = arg;
	fprintf(stderr, "error\n");
	*ret = err->error;
	return NL_STOP;
}

static int finish_handler(struct nl_msg *msg, void *arg)
{
	int *ret = arg;
	*ret = 0;
	fprintf(stderr, "finish\n");
	return NL_SKIP;
}

static int ack_handler(struct nl_msg *msg, void *arg)
{
	int *ret = arg;
	*ret = 0;
	fprintf(stderr, "ack\n");
	return NL_STOP;
}

static int reply_handler(struct nl_msg *msg, void *arg)
{
	struct nlattr *tb[DOC_EXMPL_A_MAX + 1] = {0};
	struct genlmsghdr *gnlh = nlmsg_data(nlmsg_hdr(msg));
	struct family_hdr *fhdr = genlmsg_attrdata(gnlh, 0);
	struct data_hdr *hdr;
	int rc, i;
	int rcvlen;

	rc = nla_parse(tb, DOC_EXMPL_A_MAX,
			genlmsg_attrdata(gnlh, sizeof(struct family_hdr)),
			genlmsg_attrlen(gnlh, sizeof(struct family_hdr)), NULL);
	if (rc) {
		printf("nla_parse err\n");
		return NL_STOP;
	}

	for (i = 1; i <= DOC_EXMPL_A_MAX; i ++) {
		rcvlen = nla_len(tb[i]);
		hdr = (struct data_hdr*)nla_data(tb[i]);
		printf("rcv: %d %d %d %d rcvlen=%d %s\n", i, fhdr->ff, hdr->len, hdr->kk, rcvlen, hdr->str);
	}
	return NL_OK;
}

static int test_genlink_nl(void)
{
	struct nl_handle *nlsk;
	int nlid, err, ret;

	struct nl_msg *msg = NULL;
	struct nl_cb *cb = NULL;

	char cbdata[123], sss[123];
	struct family_hdr *fhdr;
	struct data_hdr *hdr = (struct data_hdr *)sss;

	nlsk = nl_handle_alloc();
	if (!nlsk) {
		printf("nl_socket_alloc err\n");
		return -1;
	}

	nl_set_buffer_size(nlsk, 8192, 8192);

	if (genl_connect(nlsk)) {
		printf("genl_connect err\n");
		goto free_nlsk;
	}

	nlid = genl_ctrl_resolve(nlsk, "DOC_EXMPL");
	if (nlid < 0) {
		printf("genl_ctrl_resolve err\n");
		goto free_nlsk;
	}

	msg = nlmsg_alloc();
	if (!msg) {
		printf("nlmsg_alloc err\n");
		goto free_nlsk;
	}

	cb = nl_cb_alloc(NL_CB_DEFAULT);
	if (!cb) {
		printf("nl_cb_alloc err\n");
		goto free_msg;
	}
	nl_socket_set_cb(nlsk, cb);

	fhdr = (struct family_hdr *)genlmsg_put(msg, 0, 0, nlid, sizeof(struct family_hdr), 0, DOC_EXMPL_C_ECHO, 0);
	if (!fhdr) {
		printf("genlmsg_put err\n");
		goto free_cb;
	}
	fhdr->ff = 111;

	hdr->len = 123;
	hdr->kk = 456;
	strcpy(hdr->str, MESSAGE_TO_KERNEL);
	ret = nla_put(msg, DOC_EXMPL_A_MSG, sizeof(struct data_hdr)+strlen(MESSAGE_TO_KERNEL), hdr);
	if (ret < 0) {
		printf("nla_put err\n");
		goto free_cb;
	}

	hdr->len = 700;
	hdr->kk = 800;
	ret = nla_put(msg, DOC_EXMPL_A_MSG2, sizeof(struct data_hdr)+strlen(MESSAGE_TO_KERNEL), hdr);
	if (ret < 0) {
		printf("nla_put err2\n");
		goto free_cb;
	}

	ret = nl_send_auto_complete(nlsk, msg);
	if (ret < 0) {
		printf("nl_send_auto_complete err\n");
		goto free_cb;
	}

	err = 1;
	nl_cb_err(cb, NL_CB_CUSTOM, error_handler, &err);
	nl_cb_set(cb, NL_CB_FINISH, NL_CB_CUSTOM, finish_handler, &err);
	nl_cb_set(cb, NL_CB_ACK, NL_CB_CUSTOM, ack_handler, &err);
	nl_cb_set(cb, NL_CB_VALID, NL_CB_CUSTOM, reply_handler, &cbdata);

	ret = nl_recvmsgs(nlsk, cb);
	if (ret) {
		printf("nl_recvmsgs err\n");
	}

	return err;

free_cb:
	nl_cb_put(cb);
free_msg:
	nlmsg_free(msg);
free_nlsk:
	nl_handle_destroy(nlsk);
	return -2;
}

int main(int argc, char *argv[])
{
	return test_genlink_nl();
}

数据交换 genlink

3.x 内核

kernel

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#include <linux/module.h>
#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: nla_len=%d, nla_type=%d, %s\n", nlh->nla_len, nlh->nla_type, str);

	ret = genl_msg_send_to_user(TEST_GENL_MSG_FROM_KERNEL,
			strlen(TEST_GENL_MSG_FROM_KERNEL) + 1,  nlhdr->nlmsg_pid);

	return ret;
}

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;

	printk("doc_exmpl_genl_mcgrp.id=%d", doc_exmpl_genl_mcgrp.id);
	printk("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:
	printk("Error occured while inserting generic netlink example module\n");
	return rc;
}

void genetlink_exit(void)
{
	printk("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);
}

module_init(genetlink_init);
module_exit(genetlink_exit);
MODULE_LICENSE("GPL");
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obj-m += genlink.o

KDIR := /usr/src/kernels/`uname -r`/

PWD := `pwd`

default:
	make -C $(KDIR) M=$(PWD) modules

clean:
	rm -rf *.ko *.o *.mod.c .*.cmd .tmp_versions Module.symvers modules.order

user

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#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) {
		printf("socket: %m\n");
		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) {
		printf("bind: %m\n");
		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);

	printf("send len %d\n", 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;
	printf("recv len %d\n", 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;

	printf("nlmsg_type = %d\n", 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) {
			printf("get NLMSG_DONE\n");
			ret = 0;
			break;
		}

		if (nlh->nlmsg_type == NLMSG_ERROR) {
			printf("get NLMSG_ERROR\n");
			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
			printf("%d. nla->nla_type = %d\n", 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;
}


#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
	printf("get family ID[%d]\n", 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:
	close(sockfd);
	genlmsg_free(nlh);
	return ret;
}

int main(int argc, char *argv[])
{
	test_netlink_unicast();
	return 0;
}

数据交换 netlink

3.x 内核

kernel

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#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/sched.h>
#include <net/sock.h>
#include <net/netlink.h>

#define NETLINK_TEST 29

struct sock *nl_sk = NULL;

void nl_data_ready(struct sk_buff *__skb)
{
	struct sk_buff *skb;
	struct nlmsghdr *nlh;
	u32 pid;
	int rc;
	int len = NLMSG_SPACE(1200);
	char str[100];

	printk("net_link: data is ready to read.\n");
	skb = skb_get(__skb);

	if (skb->len >= NLMSG_SPACE(0)) {
		nlh = nlmsg_hdr(skb);
		printk("net_link: recv %s.\n", (char *)NLMSG_DATA(nlh));
		memcpy(str, NLMSG_DATA(nlh), sizeof(str));
		pid = nlh->nlmsg_pid; /*pid of sending process */
		printk("net_link: pid is %d\n", pid);
		kfree_skb(skb);

		skb = alloc_skb(len, GFP_ATOMIC);
		if (!skb) {
			printk(KERN_ERR "net_link: allocate failed.\n");
			return;
		}
		nlh = nlmsg_put(skb, 0, 0, 0, 1200, 0);
		NETLINK_CB(skb).portid = 0; /* from kernel */

		memcpy(NLMSG_DATA(nlh), str, sizeof(str));
		strcpy(NLMSG_DATA(nlh) + 10, " from kernel");
		printk("net_link: going to send.\n");
		rc = netlink_unicast(nl_sk, skb, pid, MSG_DONTWAIT);
		if (rc < 0) {
			printk(KERN_ERR "net_link: can not unicast skb (%d)\n", rc);
		}
		printk("net_link: send is ok.\n");
	}
	return;
}

static int test_netlink(void)
{
	struct netlink_kernel_cfg cfg = {
		.groups       = 0,
		.input        = nl_data_ready,
		.cb_mutex = NULL,
		.flags        = 0,
		.bind     = NULL,
	};
	nl_sk = netlink_kernel_create(&init_net, NETLINK_TEST, &cfg);

	if (!nl_sk) {
		printk(KERN_ERR "net_link: Cannot create netlink socket.\n");
		return -EIO;
	}
	printk("net_link: create socket ok.\n");
	return 0;
}

int netlink_init(void)
{
	test_netlink();
	return 0;
}

void netlink_exit(void)
{
	if (nl_sk != NULL) {
		sock_release(nl_sk->sk_socket);
	}
	printk("net_link: remove ok.\n");
}

module_init(netlink_init);
module_exit(netlink_exit);
MODULE_LICENSE("GPL");

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obj-m += netlink.o

KDIR := /usr/src/kernels/`uname -r`/

PWD := `pwd`

default:
	make -C $(KDIR) M=$(PWD) modules

clean:
	rm -rf *.ko *.o *.mod.c .*.cmd .tmp_versions Module.symvers modules.order

user

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#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <string.h>
#include <asm/types.h>
#include <linux/netlink.h>
#include <linux/socket.h>

#define NETLINK_TEST 29

#define MAX_PAYLOAD 1024 

struct sockaddr_nl src_addr, dest_addr;
struct nlmsghdr *nlh = NULL;
struct iovec iov;
int sock_fd;
struct msghdr msg;

int main(int argc, char* argv[])
{
	sock_fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_TEST);

	memset(&msg, 0, sizeof(msg));
	memset(&src_addr, 0, sizeof(src_addr));
	src_addr.nl_family = AF_NETLINK;
	src_addr.nl_pid = getpid(); 
	src_addr.nl_groups = 0; 
	bind(sock_fd, (struct sockaddr*)&src_addr, sizeof(src_addr));

	memset(&dest_addr, 0, sizeof(dest_addr));
	dest_addr.nl_family = AF_NETLINK;
	dest_addr.nl_pid = 0; 
	dest_addr.nl_groups = 0; 

	nlh = (struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_PAYLOAD));
	nlh->nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD);
	nlh->nlmsg_pid = getpid(); 
	nlh->nlmsg_flags = 0;
	strcpy(NLMSG_DATA(nlh), "Hello you!");

	iov.iov_base = (void *)nlh;
	iov.iov_len = nlh->nlmsg_len;
	msg.msg_name = (void *)&dest_addr;
	msg.msg_namelen = sizeof(dest_addr);
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;

	printf(" Sending message. ...\n");
	sendmsg(sock_fd, &msg, 0);

	memset(nlh, 0, NLMSG_SPACE(MAX_PAYLOAD));
	printf(" Waiting message. ...\n");
	recvmsg(sock_fd, &msg, 0);
	printf(" Received message payload: len=%d, data=%s\n", nlh->nlmsg_len, NLMSG_DATA(nlh));

	close(sock_fd);
	return 0;
}