linux下的netlink编程
本文来自：http://blog.chinaunix.net/uid-25120309-id-3359137.html
在 Linux 2.4 版以后版本的内核中，几乎全部的中断过程与用户态进程的通信都是使用 netlink 套接字实现的，同时还使用 netlink 实现了 ip queue 工具，但 ip queue 的使用有其局限性，不能自由地用于各种中断过程。内核的帮助文档和其他一些 Linux 相关文章都没有对 netlink 套接字在中断过程和用户空间通信的应用上作详细的说明，使得很多用户对此只有一个模糊的概念。
Unicast Communication between Kernel and Application
在下面的例子中,一个用户空间进程发送一个netlink消息给内核模块,内核模块应答一个消息给发送进程,这里是用户空间的代码:
#include < sys / socket.h >
#include < linux / netlink.h >
#define MAX_PAYLOAD 1024 /* maximum payload size*/
struct sockaddr_nl src_addr, dest_addr;
struct msghdr msg;
struct nlmsghdr * nlh = NULL;
struct iovec iov;
int sock_fd;
void main() {
sock_fd = socket(PF_NETLINK, SOCK_RAW,NETLINK_TEST);
memset( & src_addr, 0 , sizeof (src_addr));
src__addr.nl_family = AF_NETLINK;
src_addr.nl_pid = getpid(); /* self pid */
src_addr.nl_groups = 0 ; /* not in mcast groups */
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 ; /* For Linux Kernel */
dest_addr.nl_groups = 0 ; /* unicast */
nlh = ( struct nlmsghdr * )malloc(
NLMSG_SPACE(MAX_PAYLOAD));
/* Fill the netlink message header */
nlh -> nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD);
nlh -> nlmsg_pid = getpid(); /* self pid */
nlh -> nlmsg_flags = 0 ;
/* Fill in the netlink message payload */
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 ;
sendmsg(fd, & msg, 0 );
/* Read message from kernel */
memset(nlh, 0 , NLMSG_SPACE(MAX_PAYLOAD));
recvmsg(fd, & msg, 0 );
printf( " Received message payload: %s " ,
NLMSG_DATA(nlh));
/* Close Netlink Socket */
close(sock_fd);
}
这里是内核代码:
struct sock * nl_sk = NULL;
void nl_data_ready ( struct sock * sk, int len)
{
wake_up_interruptible(sk -> sleep);
}
void netlink_test() {
struct sk_buff * skb = NULL;
struct nlmsghdr * nlh = NULL;
int err;
u32 pid;
nl_sk = netlink_kernel_create(NETLINK_TEST,
nl_data_ready);
/* wait for message coming down from user-space */
skb = skb_recv_datagram(nl_sk, 0 , 0 , & err);
nlh = ( struct nlmsghdr * )skb -> data;
printk( " %s: received netlink message payload:%s " ,
__FUNCTION__, NLMSG_DATA(nlh));
pid = nlh -> nlmsg_pid; /* pid of sending process */
NETLINK_CB(skb).groups = 0 ; /* not in mcast group */
NETLINK_CB(skb).pid = 0 ; /* from kernel */
NETLINK_CB(skb).dst_pid = pid;
NETLINK_CB(skb).dst_groups = 0 ; /* unicast */
netlink_unicast(nl_sk, skb, pid, MSG_DONTWAIT);
sock_release(nl_sk -> socket);
}
在内核模块被加载到内核,当我们运行用户程序,我们将看到下面的信息:
Received message payload: Hello you!
然后用dmesg我们可以看到内核输出:
netlink_test: received netlink message payload:
Hello you!
Multicast Communication between Kernel and Applications
这个例子中,两个应用程序在监听同一个netlink广播组.内核模块发送一个netlink消息给这个广播组,所用的应用程序都收到它,如下是用户程序代码:
#include < sys / socket.h >
#include < linux / netlink.h >
#define MAX_PAYLOAD 1024 /* maximum payload size*/
struct sockaddr_nl src_addr, dest_addr;
struct nlmsghdr * nlh = NULL;
struct iovec iov;
int sock_fd;
void main() {
sock_fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_TEST);
memset( & src_addr, 0 , sizeof (local_addr));
src_addr.nl_family = AF_NETLINK;
src_addr.nl_pid = getpid(); /* self pid */
/* interested in group 1<<0 */
src_addr.nl_groups = 1 ;
bind(sock_fd, ( struct sockaddr * ) & src_addr,
sizeof (src_addr));
memset( & dest_addr, 0 , sizeof (dest_addr));
nlh = ( struct nlmsghdr * )malloc(
NLMSG_SPACE(MAX_PAYLOAD));
memset(nlh, 0 , NLMSG_SPACE(MAX_PAYLOAD));
iov.iov_base = ( void * )nlh;
iov.iov_len = NLMSG_SPACE(MAX_PAYLOAD);
msg.msg_name = ( void * ) & dest_addr;
msg.msg_namelen = sizeof (dest_addr);
msg.msg_iov = & iov;
msg.msg_iovlen = 1 ;
printf( " Waiting for message from kernel " );
/* Read message from kernel */
recvmsg(fd, & msg, 0 );
printf( " Received message payload: %s " ,
NLMSG_DATA(nlh));
close(sock_fd);
}
内核代码:
#define MAX_PAYLOAD 1024
struct sock * nl_sk = NULL;
void netlink_test() {
sturct sk_buff * skb = NULL;
struct nlmsghdr * nlh;
int err;
nl_sk = netlink_kernel_create(NETLINK_TEST,
nl_data_ready);
skb = alloc_skb(NLMSG_SPACE(MAX_PAYLOAD),GFP_KERNEL);
nlh = ( struct nlmsghdr * )skb -> data;
nlh -> nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD);
nlh -> nlmsg_pid = 0 ; /* from kernel */
nlh -> nlmsg_flags = 0 ;
strcpy(NLMSG_DATA(nlh), " Greeting from kernel! " );
/* sender is in group 1<<0 */
NETLINK_CB(skb).groups = 1 ;
NETLINK_CB(skb).pid = 0 ; /* from kernel */
NETLINK_CB(skb).dst_pid = 0 ; /* multicast */
/* to mcast group 1<<0 */
NETLINK_CB(skb).dst_groups = 1 ;
/* multicast the message to all listening processes */
netlink_broadcast(nl_sk, skb, 0 , 1 , GFP_KERNEL);
sock_release(nl_sk -> socket);
}
我们运行用户程序:
./nl_recv &
Waiting for message from kernel
./nl_recv &
Waiting for message from kernel
然后我们加载内核模块到内核空间,会看到如下信息::
Received message payload: Greeting from kernel!
Received message payload: Greeting from kernel!
以下是一个简单的测试内核事件的应用程序：
#define MAX_PAYLOAD 1024
struct sockaddr_nl src_addr, dest_addr;
char * KernelMsg = NULL;
struct iovec iov;
int sock_fd;
struct msghdr msg;
int msglen;
#define DEVICE_ADD "add"
#define DEVICE_REMOVE "remove"
#define DEVICE_NAME "event0"
#define DEVICE_NAMELEN 6
void * DeviceManagement( void * arg)
{
sock_fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_KOBJECT_UEVENT);
int msgle;
memset( & src_addr, 0 , sizeof (src_addr));
src_addr.nl_family = AF_NETLINK;
src_addr.nl_pid = pthread_self() << 16 | getpid();
src_addr.nl_groups = 1 ;
bind(sock_fd, ( struct sockaddr * ) & src_addr, sizeof (src_addr));
memset( & dest_addr, 0 , sizeof (dest_addr));
KernelMsg = ( struct nlmsghdr * )malloc(MAX_PAYLOAD);
memset(KernelMsg, 0 , MAX_PAYLOAD);
iov.iov_base = ( void * )KernelMsg;
iov.iov_len = MAX_PAYLOAD;
msg.msg_name = ( void * ) & dest_addr;
msg.msg_namelen = sizeof (dest_addr);
msg.msg_iov = & iov;
msg.msg_iovlen = 1 ;
while ( 1 ) {
// printf("Waiting for message from kernel ");
recvmsg(sock_fd, & msg, 0 );
// printf("Receved message payload: %s ", KernelMsg);
msglen = strlen(KernelMsg);
// printf("Device: %s ", KernelMsg+msglen-DEVICE_NAMELEN);
if ( ! strncmp(DEVICE_NAME, KernelMsg + msglen - DEVICE_NAMELEN, DEVICE_NAMELEN)) {
if ( ! strncmp(DEVICE_ADD, KernelMsg, strlen(DEVICE_ADD)))
{
printf( " Add event0 device " );
USBKeyboardReady = 1 ;
}
else if ( ! strncmp(DEVICE_REMOVE, KernelMsg, strlen(DEVICE_REMOVE))) {
printf( " Remove event0 device " );
USBKeyboardReady = 0 ;
}
}
}
close(sock_fd);
}
示例：一个用户进程发送数据到内核，然后通过内核发送给另一个用户进程。
内核进程：netlink-exam-kern.c
// kernel module: netlink-exam-kern.c
#ifndef __KERNEL__
#define __KERNEL__
#endif
#ifndef MODULE
#define MODULE
#endif
#include < linux / config.h >
#include < linux / module.h >
#include < linux / netlink.h >
#include < linux / sched.h >
#include < net / sock.h >
#include < linux / proc_fs.h >
#define BUF_SIZE 16384
#define NL 30
static struct sock * netlink_exam_sock;
static unsigned char buffer[BUF_SIZE];
static unsigned int buffer_tail = 0 ;
static int exit_flag = 0 ;
static DECLARE_COMPLETION(exit_completion);
static void recv_handler( struct sock * sk, int length)
{
wake_up(sk -> sk_sleep);
}
static int process_message_thread( void * data)
{
struct sk_buff * skb = NULL;
struct nlmsghdr * nlhdr = NULL;
int len;
DEFINE_WAIT(wait);
daemonize( " mynetlink " );
while (exit_flag == 0 ) {
prepare_to_wait(netlink_exam_sock -> sk_sleep, & wait, TASK_INTERRUPTIBLE);
schedule();
finish_wait(netlink_exam_sock -> sk_sleep, & wait);
while ((skb = skb_dequeue( & netlink_exam_sock -> sk_receive_queue))
!= NULL) {
nlhdr = ( struct nlmsghdr * )skb -> data;
if (nlhdr -> nlmsg_len < sizeof ( struct nlmsghdr)) {
printk( " Corrupt netlink message. " );
continue ;
}
len = nlhdr -> nlmsg_len - NLMSG_LENGTH( 0 );
if (len + buffer_tail > BUF_SIZE) {
printk( " netlink buffer is full. " );
}
else {
memcpy(buffer + buffer_tail, NLMSG_DATA(nlhdr), len);
buffer_tail += len;
}
nlhdr -> nlmsg_pid = 0 ;
nlhdr -> nlmsg_flags = 0 ;
NETLINK_CB(skb).pid = 0 ;
NETLINK_CB(skb).dst_pid = 0 ;
NETLINK_CB(skb).dst_group = 1 ;
netlink_broadcast(netlink_exam_sock, skb, 0 , 1 , GFP_KERNEL);
}
}
complete( & exit_completion);
return 0 ;
}
static int netlink_exam_readproc( char * page, char ** start, off_t off,
int count, int * eof, void * data)
{
int len;
if (off >= buffer_tail) {
* eof = 1 ;
return 0 ;
}
else {
len = count;
if (count > PAGE_SIZE) {
len = PAGE_SIZE;
}
if (len > buffer_tail - off) {
len = buffer_tail - off;
}
memcpy(page, buffer + off, len);
* start = page;
return len;
}
}
static int __init netlink_exam_init( void )
{
netlink_exam_sock = netlink_kernel_create(NL, 0 , recv_handler, THIS_MODULE);
if ( ! netlink_exam_sock) {
printk( " Fail to create netlink socket. " );
return 1 ;
}
kernel_thread(process_message_thread, NULL, CLONE_KERNEL);
create_proc_read_entry( " netlink_exam_buffer " , 0444 , NULL, netlink_exam_readproc, 0 );
return 0 ;
}
static void __exit netlink_exam_exit( void )
{
exit_flag = 1 ;
wake_up(netlink_exam_sock -> sk_sleep);
wait_for_completion( & exit_completion);
sock_release(netlink_exam_sock -> sk_socket);
}
module_init(netlink_exam_init);
module_exit(netlink_exam_exit);
MODULE_LICENSE( " GPL " );
编译成模块：
ifneq ($(KERNELRELEASE),)
debug - objs : = netlink - exam - kern.o
obj - m : = netlink - exam - kern1.o
CFLAGS += - w - Wimplicit - function - declaration
else
PWD : = $(shell pwd)
KVER ?= $(shell uname - r)
KDIR : = / lib / modules / $(KVER) / build
all:
$(MAKE) - C $(KDIR) M = $(PWD)
clean:
rm - rf . * .cmd * .o * .mod.c * .ko .tmp_versions
endif
用户发送进程：netlink-exam-user-send.c
// application sender: netlink-exam-user-send.c
#include < stdio.h >
#include < stdlib.h >
#include < unistd.h >
#include < string .h >
#include < sys / types.h >
#include < sys / socket.h >
#include < linux / netlink.h >
#define MAX_MSGSIZE 1024
int main( int argc, char * argv[])
{
FILE * fp;
struct sockaddr_nl saddr, daddr;
struct nlmsghdr * nlhdr = NULL;
struct msghdr msg;
struct iovec iov;
int sd;
char text_line[MAX_MSGSIZE];
int ret = - 1 ;
if (argc < 2 ) {
printf( " Usage: %s atextfilename " , argv[ 0 ]);
exit( 1 );
}
if ((fp = fopen(argv[ 1 ], " r " )) == NULL) {
printf( " File %s dosen't exist. " );
exit( 1 );
}
sd = socket(AF_NETLINK, SOCK_RAW, 30 );
memset( & saddr, 0 , sizeof (saddr));
memset( & daddr, 0 , sizeof (daddr));
saddr.nl_family = AF_NETLINK;
saddr.nl_pid = getpid();
saddr.nl_groups = 0 ;
bind(sd, ( struct sockaddr * ) & saddr, sizeof (saddr));
daddr.nl_family = AF_NETLINK;
daddr.nl_pid = 0 ;
daddr.nl_groups = 0 ;
nlhdr = ( struct nlmsghdr * )malloc(NLMSG_SPACE(MAX_MSGSIZE));
while (fgets(text_line, MAX_MSGSIZE, fp)) {
memcpy(NLMSG_DATA(nlhdr), text_line, strlen(text_line));
memset( & msg, 0 , sizeof ( struct msghdr));
nlhdr -> nlmsg_len = NLMSG_LENGTH(strlen(text_line));
nlhdr -> nlmsg_pid = getpid(); /* self pid */
nlhdr -> nlmsg_flags = 0 ;
iov.iov_base = ( void * )nlhdr;
iov.iov_len = nlhdr -> nlmsg_len;
msg.msg_name = ( void * ) & daddr;
msg.msg_namelen = sizeof (daddr);
msg.msg_iov = & iov;
msg.msg_iovlen = 1 ;
ret = sendmsg(sd, & msg, 0 );
if (ret == - 1 ) {
perror( " sendmsg error: " );
}
}
close(sd);
return 0 ;
}
用户接收进程：netlink-exam-user-recv.c
// application sender: netlink-exam-user-send.c
#include < stdio.h >
#include < stdlib.h >
#include < unistd.h >
#include < string .h >
#include < sys / types.h >
#include < sys / socket.h >
#include < linux / netlink.h >
#define MAX_MSGSIZE 1024
int main( int argc, char * argv[])
{
FILE * fp;
struct sockaddr_nl saddr, daddr;
struct nlmsghdr * nlhdr = NULL;
struct msghdr msg;
struct iovec iov;
int sd;
char text_line[MAX_MSGSIZE];
int ret = - 1 ;
if (argc < 2 ) {
printf( " Usage: %s atextfilename " , argv[ 0 ]);
exit( 1 );
}
if ((fp = fopen(argv[ 1 ], " r " )) == NULL) {
printf( " File %s dosen't exist. " );
exit( 1 );
}
sd = socket(AF_NETLINK, SOCK_RAW, 30 );
memset( & saddr, 0 , sizeof (saddr));
memset( & daddr, 0 , sizeof (daddr));
saddr.nl_family = AF_NETLINK;
saddr.nl_pid = getpid();
saddr.nl_groups = 0 ;
bind(sd, ( struct sockaddr * ) & saddr, sizeof (saddr));
daddr.nl_family = AF_NETLINK;
daddr.nl_pid = 0 ;
daddr.nl_groups = 0 ;
nlhdr = ( struct nlmsghdr * )malloc(NLMSG_SPACE(MAX_MSGSIZE));
while (fgets(text_line, MAX_MSGSIZE, fp)) {
memcpy(NLMSG_DATA(nlhdr), text_line, strlen(text_line));
memset( & msg, 0 , sizeof ( struct msghdr));
nlhdr -> nlmsg_len = NLMSG_LENGTH(strlen(text_line));
nlhdr -> nlmsg_pid = getpid(); /* self pid */
nlhdr -> nlmsg_flags = 0 ;
iov.iov_base = ( void * )nlhdr;
iov.iov_len = nlhdr -> nlmsg_len;
msg.msg_name = ( void * ) & daddr;
msg.msg_namelen = sizeof (daddr);
msg.msg_iov = & iov;
msg.msg_iovlen = 1 ;
ret = sendmsg(sd, & msg, 0 );
if (ret == - 1 ) {
perror( " sendmsg error: " );
}
}
close(sd);
return 0 ;
}
