如何使用 netlink 套接字与内核模块通信?

另外请不要告诉我看内核代码.我已经在做，但需要很多时间，而且我所剩的不多.更新:经过大量试验和错误，我有以下代码从用户程序向内核发送消息，但从内核到用户程序的消息，即使用 netlink_unicast() 不起作用.它不仅不工作，呼叫挂起系统，然后我必须重新启动机器.有人可以看看并告诉我我在做什么错.netlink_unicast() 调用在以下代码中进行了注释.内核到用户程序消息应该取消注释.用户程序#include #include #define NETLINK_USER 31#define MAX_PAYLOAD 1024/* 最大有效载荷大小*/结构 sockaddr_nl src_addr, dest_addr;结构 nlmsghdr *nlh = NULL;结构 iovec iov;int sock_fd;struct msghdr msg;无效主(){sock_fd=socket(PF_NETLINK, SOCK_RAW, NETLINK_USER);如果(袜子_fdnlmsg_len = NLMSG_SPACE(MAX_PAYLOAD);nlh->nlmsg_pid = getpid();nlh->nlmsg_flags = 0;strcpy(NLMSG_DATA(nlh)，你好")；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("向内核发送消息");sendmsg(sock_fd,&msg,0);printf("正在等待来自内核的消息");/* 从内核读取消息 */recvmsg(sock_fd, &msg, 0);printf("接收到的消息负载:%s",NLMSG_DATA(nlh));关闭(袜子_fd)；}内核代码#include #include #include #include #include #include #include #include #include #define NETLINK_USER 31结构袜 *nl_sk = NULL;静态无效 hello_nl_recv_msg(struct sk_buff *skb){结构 nlmsghdr *nlh;int pid;printk(KERN_INFO "输入:%s", __FUNCTION__);nlh=(struct nlmsghdr*)skb->数据；printk(KERN_INFO "Netlink 收到 msg 负载:%s",(char*)NLMSG_DATA(nlh));pid = nlh->nlmsg_pid;/*发送进程的pid */NETLINK_CB(skb).dst_group = 0;/* 不在 mcast 组中 */NETLINK_CB(skb).pid = 0;/* 从内核 *///NETLINK_CB(skb).groups = 0;/* 不在 mcast 组中 *///NETLINK_CB(skb).dst_pid = pid;printk("即将发送 msg bak:");//netlink_unicast(nl_sk,skb,pid,MSG_DONTWAIT);}静态 int __init hello_init(void){printk("输入:%s",__FUNCTION__);nl_sk=netlink_kernel_create(&init_net, NETLINK_USER, 0,hello_nl_recv_msg, NULL, THIS_MODULE);如果(！nl_sk){printk(KERN_ALERT "创建套接字时出错.");返回-10；}返回0；}静态无效 __exit hello_exit(void){printk(KERN_INFO "退出 hello 模块");netlink_kernel_release(nl_sk);}模块初始化(hello_init)；模块退出(你好退出)； 解决方案 在阅读内核源代码后，我终于设法让 netlink 套接字为我工作.下面是一个 Netlink 套接字基础的例子，即打开一个 netlink 套接字，读取和写入它，然后关闭它.内核模块#include #include #include #include #define NETLINK_USER 31结构袜 *nl_sk = NULL;静态无效 hello_nl_recv_msg(struct sk_buff *skb){结构 nlmsghdr *nlh;int pid;结构 sk_buff *skb_out;int msg_size;char *msg = "来自内核的你好";内部资源；printk(KERN_INFO "输入:%s", __FUNCTION__);msg_size = strlen(msg);nlh = (struct nlmsghdr *)skb->数据；printk(KERN_INFO "Netlink 收到 msg 负载:%s", (char *)nlmsg_data(nlh));pid = nlh->nlmsg_pid;/*发送进程的pid */skb_out = nlmsg_new(msg_size, 0);如果(！skb_out){printk(KERN_ERR "无法分配新的 skb");返回;}nlh = nlmsg_put(skb_out, 0, 0, NLMSG_DONE, msg_size, 0);NETLINK_CB(skb_out).dst_group = 0;/* 不在 mcast 组中 */strncpy(nlmsg_data(nlh), msg, msg_size);res = nlmsg_unicast(nl_sk, skb_out, pid);如果 (res 用户程序#include #include #include #include #include #include #define NETLINK_USER 31#define MAX_PAYLOAD 1024/* 最大有效载荷大小*/结构 sockaddr_nl src_addr, dest_addr;结构 nlmsghdr *nlh = NULL;结构 iovec iov;int sock_fd;struct msghdr msg;int main(){sock_fd = 套接字(PF_NETLINK，SOCK_RAW，NETLINK_USER)；如果 (sock_fd nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD);nlh->nlmsg_pid = getpid();nlh->nlmsg_flags = 0;strcpy(NLMSG_DATA(nlh)，你好")；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("向内核发送消息");sendmsg(sock_fd, &msg, 0);printf("正在等待来自内核的消息");/* 从内核读取消息 */recvmsg(sock_fd, &msg, 0);printf("接收到的消息负载:%s", NLMSG_DATA(nlh));关闭(袜子_fd)；}关于魔法常量NETLINK_USER 31的相关线程:内核空间中可以有超过 32 个 netlink 套接字吗?I am trying to write a linux kernel module that communicates with user process using netlink. I am using netlink because the user program I want to communicate to communicates only using sockets and I cant change that to add ioctl() or anything.Problem is that I cant figure out how to do that. I have googled but all examples I found are for old like this one and no longer valid for current kernel versions. I have also looked at this SO question but the sample here uses libnl for socket operations but I want to stick to standard socket functions (defined by sys/socket.h). So can some one plz guide me here to some tutorial or guide or some thing that can help me understand the interface and usage of netlink. I would highly appreciate a working example, nothing fancy, just a very basic example of how to establish a connection from a socket in user program to a socket in kernel and then send data from user process to kernel and receive back from kernel.Also please do not tell me to look at kernel code. I am already doing it but it will take a lot of time and I dont have lot of it left.Update:After lot of trial and error I have following code which sends message from user program to kernel but the message from kernel to user program i.e using netlink_unicast() is not working. Its not only not working, the call hangs the systems and then I have to restart the machine. Can some one plz take a look and tell me what wrong I am doing. The netlink_unicast() call is commented in the following code. It should be uncommented for kernel to user program message.User Program#include <sys/socket.h>#include <linux/netlink.h>#define NETLINK_USER 31#define MAX_PAYLOAD 1024 /* maximum payload size*/struct sockaddr_nl src_addr, dest_addr;struct nlmsghdr *nlh = NULL;struct iovec iov;int sock_fd;struct msghdr msg;void main(){ sock_fd=socket(PF_NETLINK, SOCK_RAW, NETLINK_USER); if(sock_fd<0) return -1; memset(&src_addr, 0, sizeof(src_addr)); src_addr.nl_family = AF_NETLINK; src_addr.nl_pid = getpid(); /* self pid */ /* interested in group 1<<0 */ bind(sock_fd, (struct sockaddr*)&src_addr, sizeof(src_addr)); memset(&dest_addr, 0, sizeof(dest_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)); memset(nlh, 0, NLMSG_SPACE(MAX_PAYLOAD)); nlh->nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD); nlh->nlmsg_pid = getpid(); nlh->nlmsg_flags = 0; strcpy(NLMSG_DATA(nlh), "Hello"); 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 to kernel"); sendmsg(sock_fd,&msg,0); printf("Waiting for message from kernel"); /* Read message from kernel */ recvmsg(sock_fd, &msg, 0); printf(" Received message payload: %s", NLMSG_DATA(nlh)); close(sock_fd);}Kernel Code#include <linux/module.h>#include <linux/kernel.h>#include <linux/init.h>#include <net/sock.h>#include <linux/socket.h>#include <linux/net.h>#include <asm/types.h>#include <linux/netlink.h>#include <linux/skbuff.h>#define NETLINK_USER 31struct sock *nl_sk = NULL;static void hello_nl_recv_msg(struct sk_buff *skb){ struct nlmsghdr *nlh; int pid; printk(KERN_INFO "Entering: %s", __FUNCTION__); nlh=(struct nlmsghdr*)skb->data; printk(KERN_INFO "Netlink received msg payload: %s", (char*)NLMSG_DATA(nlh)); pid = nlh->nlmsg_pid; /*pid of sending process */ NETLINK_CB(skb).dst_group = 0; /* not in mcast group */ NETLINK_CB(skb).pid = 0; /* from kernel */ //NETLINK_CB(skb).groups = 0; /* not in mcast group */ //NETLINK_CB(skb).dst_pid = pid; printk("About to send msg bak:"); //netlink_unicast(nl_sk,skb,pid,MSG_DONTWAIT);}static int __init hello_init(void){ printk("Entering: %s",__FUNCTION__); nl_sk=netlink_kernel_create(&init_net, NETLINK_USER, 0, hello_nl_recv_msg, NULL, THIS_MODULE); if(!nl_sk) { printk(KERN_ALERT "Error creating socket."); return -10; } return 0;}static void __exit hello_exit(void){ printk(KERN_INFO "exiting hello module"); netlink_kernel_release(nl_sk);}module_init(hello_init);module_exit(hello_exit); 解决方案 After reading kernel source I finally managed to make netlink sockets work for me. Below is an example of Netlink socket basics i.e opening a netlink socket, reading and writing to it and closing it.Kernel Module#include <linux/module.h>#include <net/sock.h>#include <linux/netlink.h>#include <linux/skbuff.h>#define NETLINK_USER 31struct sock *nl_sk = NULL;static void hello_nl_recv_msg(struct sk_buff *skb){ struct nlmsghdr *nlh; int pid; struct sk_buff *skb_out; int msg_size; char *msg = "Hello from kernel"; int res; printk(KERN_INFO "Entering: %s", __FUNCTION__); msg_size = strlen(msg); nlh = (struct nlmsghdr *)skb->data; printk(KERN_INFO "Netlink received msg payload:%s", (char *)nlmsg_data(nlh)); pid = nlh->nlmsg_pid; /*pid of sending process */ skb_out = nlmsg_new(msg_size, 0); if (!skb_out) { printk(KERN_ERR "Failed to allocate new skb"); return; } nlh = nlmsg_put(skb_out, 0, 0, NLMSG_DONE, msg_size, 0); NETLINK_CB(skb_out).dst_group = 0; /* not in mcast group */ strncpy(nlmsg_data(nlh), msg, msg_size); res = nlmsg_unicast(nl_sk, skb_out, pid); if (res < 0) printk(KERN_INFO "Error while sending bak to user");}static int __init hello_init(void){ printk("Entering: %s", __FUNCTION__); //nl_sk = netlink_kernel_create(&init_net, NETLINK_USER, 0, hello_nl_recv_msg, NULL, THIS_MODULE); struct netlink_kernel_cfg cfg = { .input = hello_nl_recv_msg, }; nl_sk = netlink_kernel_create(&init_net, NETLINK_USER, &cfg); if (!nl_sk) { printk(KERN_ALERT "Error creating socket."); return -10; } return 0;}static void __exit hello_exit(void){ printk(KERN_INFO "exiting hello module"); netlink_kernel_release(nl_sk);}module_init(hello_init); module_exit(hello_exit);MODULE_LICENSE("GPL");User Program#include <linux/netlink.h>#include <stdio.h>#include <stdlib.h>#include <string.h>#include <sys/socket.h>#include <unistd.h>#define NETLINK_USER 31#define MAX_PAYLOAD 1024 /* maximum payload size*/struct sockaddr_nl src_addr, dest_addr;struct nlmsghdr *nlh = NULL;struct iovec iov;int sock_fd;struct msghdr msg;int main(){ sock_fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_USER); if (sock_fd < 0) return -1; memset(&src_addr, 0, sizeof(src_addr)); src_addr.nl_family = AF_NETLINK; src_addr.nl_pid = getpid(); /* self pid */ 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)); memset(nlh, 0, NLMSG_SPACE(MAX_PAYLOAD)); nlh->nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD); nlh->nlmsg_pid = getpid(); nlh->nlmsg_flags = 0; strcpy(NLMSG_DATA(nlh), "Hello"); 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 to kernel"); sendmsg(sock_fd, &msg, 0); printf("Waiting for message from kernel"); /* Read message from kernel */ recvmsg(sock_fd, &msg, 0); printf("Received message payload: %s", NLMSG_DATA(nlh)); close(sock_fd);}Related thread about the magic constant NETLINK_USER 31: Can I have more than 32 netlink sockets in kernelspace? 这篇关于如何使用 netlink 套接字与内核模块通信?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！