c - mqueue 消息中传递结构

Question

我正在尝试读取 IP/RAW 套接字数据包及其参数(例如指向 IP 数据包的字符指针及其大小)，将其放入 WRONLY 模式下的 mqueue 中，并以 RDONLY 模式从队列中检索相同的参数。我正在使用消息(msg)的结构来发送和接收。发送消息时，两个参数都成功放入队列中，但在检索时它返回段错误。我的发送和接收文件如下:

mq_send.c

#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#include<sys/stat.h>
#include<sys/types.h>
#include<mqueue.h>
#include<errno.h>
#include<netinet/ip_icmp.h>   
#include<netinet/udp.h> 
#include<netinet/tcp.h>  
#include<netinet/ip.h>
#include<netinet/in.h>
#include<netinet/if_ether.h>
#include<net/ethernet.h>
#include<sys/socket.h>
#include<arpa/inet.h>
#include<sys/ioctl.h>
#include<sys/time.h>
#include<sys/types.h>
#include<unistd.h>
#include"external.h"

#define QUEUE_NAME  "/test_queue"
#define MAX_SIZE    71680

#define CHECK(x) \
    do { \
        if (!(x)) { \
            fprintf(stderr, "%s:%d: ", __func__, __LINE__); \
            perror(#x); \
            exit(-1); \
        } \
    } while (0) \


struct sockaddr_in source,dest;
int tcp=0,udp=0,icmp=0,others=0,igmp=0,total=0,i,j;

struct mymsg
{
    char buff[MAX_SIZE];
    int size;
};


int main(int argc, char **argv)
{
    mqd_t mq;
    struct mymsg m;
    struct mq_attr attr;
    //char buff[MAX_SIZE];
    unsigned char* buffer = (unsigned char*) malloc(sizeof(65536));
    int saddr_size,sock_raw;
    struct sockaddr saddr;
    int data_size;

    attr.mq_flags = 0;
    attr.mq_maxmsg = 10;
    attr.mq_msgsize = MAX_SIZE;
    attr.mq_curmsgs = 0;

    mq = mq_open(QUEUE_NAME, O_CREAT | O_WRONLY, 0644, &attr);
    CHECK((mqd_t)-1 != mq);

    memset(buffer, 0, MAX_SIZE);    

    sock_raw = socket( AF_PACKET , SOCK_RAW , htons(ETH_P_ALL)) ;
    if(sock_raw < 0)
    {
       perror("Socket Error\n");
       return 1;
    }
    saddr_size = sizeof saddr;
    data_size = recvfrom(sock_raw , buffer ,65536 , 0 , &saddr , (socklen_t*)&saddr_size);

    if(data_size <0 )
    {
       printf("Recvfrom error , failed to get packets\n");
       return 1;
    }

    memcpy(m.buff,buffer,65536);
    m.size=data_size;

    //char *a="hi";
    //CHECK(0 <= mq_send(mq, (char *)&a, MAX_SIZE, 0));
    CHECK(0 <= mq_send(mq, (char *)&m, MAX_SIZE, 0));

    printf("Packet msg:%s size:%d\n",buffer,data_size);
    printf("Sent msg:%s size:%d\n",m.buff,m.size);

    ProcessPacket(m.buff , m.size);

    CHECK((mqd_t)-1 != mq_close(mq));

    close(sock_raw);

    return 0;
}

mq_receive.c

#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#include<sys/stat.h>
#include<sys/types.h>
#include<mqueue.h>
#include<errno.h>
#include<netinet/ip_icmp.h>   
#include<netinet/udp.h> 
#include<netinet/tcp.h>  
#include<netinet/ip.h>
#include<netinet/in.h>
#include<netinet/if_ether.h>
#include<net/ethernet.h>
#include<sys/socket.h>
#include<arpa/inet.h>
#include<sys/ioctl.h>
#include<sys/time.h>
#include<sys/types.h>
#include<unistd.h>
#include"external.h"

#define QUEUE_NAME  "/test_queue"
#define MAX_SIZE    71680

#define CHECK(x) \
    do { \
        if (!(x)) { \
            fprintf(stderr, "%s:%d: ", __func__, __LINE__); \
            perror(#x); \
            exit(-1); \
        } \
    } while (0) \

struct sockaddr_in source,dest;
int tcp=0,udp=0,icmp=0,others=0,igmp=0,total=0,i,j;

typedef struct mymsg
{
    unsigned char *buff;
    int size;
}msg;

int main(int argc, char *argv[])
{
    mqd_t mq;
    msg *m=(msg *)malloc(sizeof(msg));
    m->buff=(unsigned char*) malloc(sizeof(MAX_SIZE));
    int data_size;

    mq = mq_open(QUEUE_NAME, O_RDONLY);
    CHECK((mqd_t)-1 != mq);

    memset(m->buff, 0, MAX_SIZE+1);

    ssize_t bytes_read;


    bytes_read = mq_receive(mq, (char *)m, MAX_SIZE, NULL);
    CHECK(bytes_read >= 0);
    printf("Received buff:%s size:%d\n", m->buff,m->size);
    //ProcessPacket(m.buff , data_size);

    /* cleanup */
    CHECK((mqd_t)-1 != mq_close(mq));
    CHECK((mqd_t)-1 != mq_unlink(QUEUE_NAME));

    return 0;
}

mqueue_send.c 的输出:

bcg@BCGA53:~/Desktop/mqueue$ sudo ./mq_sendPacket msg:�������M��� size:60Sent msg:�������M��� size:60

mq_receive.c 的输出:

bcg@BCGA53:~/Desktop/mqueue$ sudo ./mq_receiveSegmentation fault

Answer 1

unsigned char* buffer = (unsigned char*) malloc(sizeof(65536));

上面的代码分配可容纳 sizeof(65536) 字节的内存。问题是 sizeof(65536) 与 sizeof(int) 相同，通常是 4 或 8 个字节。

您应该使用这个:

unsigned char* buffer = (unsigned char*) malloc(sizeof(char[65536]));

或者这个

unsigned char* buffer = (unsigned char*) malloc(65536);

还有其他错误 - 例如，您在 mq_send() 中使用了 MAX_SIZE，而您应该使用 sizeof(m)。您的错误的根本原因是上面概述的问题。

事实上，这种分配是没有意义的(至少在上面提供的代码中)，因为您可以直接接收到消息结构 - 那么您就不会看到这个问题。