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我编写了接受数据（结构形式）并将某些数据（相同结构格式）传回给用户空间的内核模块。我可以成功接收来自用户的消息，但我得到分段错误，而我尝试tp解引用从内核收到的数据结构的一些成员。我正在使用netlink套接字API。在用户空间使用netlink从内核接收数据时出错
示例代码如下：
用户space.c
#define NETLINK_USER 27
#define MAX_PAYLOAD 10000 /* maximum payload size*/
struct sockaddr_nl src_addr, dest_addr;
struct nlmsghdr *nlh = NULL;
struct iovec iov;
int sock_fd;
struct msghdr msg;
Response *p;
Response *req;
test r1;
test r2;
int main()
{
char *data;
data = malloc(4096 * sizeof(char));;
data = "data from user";
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();
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;
dest_addr.nl_groups = 0;
nlh = (struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_PAYLOAD));
memset(nlh, 0, NLMSG_SPACE(MAX_PAYLOAD));
nlh->nlmsg_len = NLMSG_LENGTH(MAX_PAYLOAD);
nlh->nlmsg_pid = getpid();
nlh->nlmsg_flags = 0;
p = malloc(2*sizeof(Response));
p[0].index = 1;
p[0].dataSize = 2;
p[0].data = data;
p[0].test2 = 3;
p[0].test3 = 4;
p[0].test4 = 5;
r1.t = 10;
r1.ip_addr = malloc(50*sizeof(char));
r1.ip_addr = "192.168.10.2";
p[0].test = &r1;
/* Extra for testing */
p[1].index = 2;
p[1].dataSize = 3;
//strcpy(p[1].data , "Data2 from User");
p[1].data = data;
p[1].test2 = 4;
p[1].test3 = 5;
p[1].test4 = 6;
r2.t = 20;
r2.ip_addr = malloc(50*sizeof(char));
r2.ip_addr = "192.168.20.2";
p[1].test = &r2;
memcpy(NLMSG_DATA(nlh), (void *)p, 2 * sizeof(*p));
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("Sending message to kernel\n");
sendmsg(sock_fd,&msg,0);
printf("Waiting for message from kernel\n");
/* Read message from kernel */
//recvmsg(sock_fd, &msg, 0);
req = (Response*)NLMSG_DATA(nlh);
printf("Recieved from Kernel:\n");
printf("index %d\n", req[0].index);
printf("dataSize %d\n", req[0].dataSize);
printf("data: %s\n", req[0].data); <---Segmentation fault from here
printf("test2 %d\n", req[0].test2);
printf("test3 %d\n", req[0].test3);
printf("test4 %d\n", req[0].test4);
printf("contents of test structure are %d,%s\n",req[0].test->t,req[0].test->ip_addr); <-----Segmentation fault
close(sock_fd);
Kernel_module.c
#include <linux/module.h>
#include <net/sock.h>
#include <linux/netlink.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#define NETLINK_USER 27
struct sock *nl_sk = NULL;
typedef struct _Response Response;
typedef struct _test test;
struct _test{
int t;
char *ip_addr;
};
struct _Response
{
int index;
int dataSize;
char *data;
int test2;
int test3;
int test4;
test *test;
};
static void hello_nl_recv_msg(struct sk_buff *skb) {
struct nlmsghdr *nlh;
int pid;
struct sk_buff *skb_out;
int msg_size;
int res;
Response *req;
Response *req1;
test t;
t.t = 1;
t.ip_addr = kmalloc(50*sizeof(char), GFP_KERNEL);
t.ip_addr = "129.63.45.1";
req1 = (Response *)kmalloc_array(2, sizeof(Response), GFP_KERNEL);
char *data;
data = kmalloc(4096 * sizeof(char), GFP_KERNEL);
data = "data from kernel";
printk(KERN_INFO "Entering: %s\n", __FUNCTION__);
msg_size= 2 * sizeof(*req1);
req1[0].index = 100;
req1[0].dataSize = 100;
req1[0].data = data;
req1[0].test2 = 100;
req1[0].test3 = 100;
req1[0].test4 = 100;
req1[0].test = &t;
printk("Sending to Userspace:\n");
/*Second set of message*/
req1[1].index = 102;
req1[1].dataSize = 103;
//strcpy(req1[1].data , "Data from Kernel");
req1[1].data = data;
req1[1].test2 = 100;
req1[1].test3 = 100;
req1[1].test4 = 100;
req1[1].test = &t;
nlh=(struct nlmsghdr*)skb->data;
req = (Response *)NLMSG_DATA(nlh); <--message received from user-space
printk("Recieved from Userspace:\n");
printk("index %d\n", req[0].index);
printk("dataSize %d\n", req[0].dataSize);
printk("data: %s\n", req[0].data);
printk("test2 %d\n", req[0].test2);
printk("test3 %d\n", req[0].test3);
printk("test4 %d\n", req[0].test4);
printk("contents of test are %d, %s\n",req[0].test->t,req[0].test->ip_addr);
printk("Next set of data\n");
printk("Recieved from Userspace:\n");
printk("index %d\n", req[1].index);
printk("dataSize %d\n", req[1].dataSize);
printk("data: %s\n", req[1].data);
printk("test2 %d\n", req[1].test2);
printk("test3 %d\n", req[1].test3);
printk("test4 %d\n", req[1].test4);
printk("contents of test are %d, %s\n",req[1].test->t,req[1].test->ip_addr);
pid = nlh->nlmsg_pid; /*pid of sending process */
skb_out = nlmsg_new(10000,0);
if(!skb_out)
{
printk(KERN_ERR "Failed to allocate new skb\n");
return;
}
nlh=nlmsg_put(skb_out,0,0,NLMSG_DONE,10000,0);
NETLINK_CB(skb_out).dst_group = 0; /* not in mcast group */
/*End of second set*/
memcpy(NLMSG_DATA(nlh), req1, 2 * sizeof(*req1));
res=nlmsg_unicast(nl_sk,skb_out,pid);
if(res<0)
printk(KERN_INFO "Error while sending bak to user\n");
}
static int __init hello_init(void) {
printk("Entering: %s\n",__FUNCTION__);
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.\n");
return -10;
}
return 0;
}
static void __exit hello_exit(void) {
printk(KERN_INFO "exiting hello module\n");
netlink_kernel_release(nl_sk);
}
module_init(hello_init); module_exit(hello_exit);
MODULE_LICENSE("GPL");
}
global.h
#ifndef __GLOBAL_H
#define __GLOBAL_H
typedef struct _Response Response;
typedef struct _test test;
struct _test{
int t;
char *ip_addr;
};
struct _Response
{
int index;
int dataSize;
char *data;
int test2;
int test3;
int test4;
test *test;
};
#endif
基本上问题是与指针。如果我使用char数据[4096]而不是字符指针，我收到消息。但是，在解引用测试结构时，我会遇到分段错误。如何解决这个问题？
感谢