进程间通信-socketpair

最近在看libcontainer中nsexec.c的实现，看到init进程的parent与child、grandchild之间的双工通信使用了socketpair。socketpair的使用与fifo类似，在不具名的情况下可以实现父子进程间简单的信息交换。

系统调用

#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
int socketpair(int domain, int type, int protocol, int sv[2]);

使用示例

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <stdbool.h>
#include <sys/wait.h>

#define ERR_EXIT(msg)     \
    do{                  \
        perror(msg);     \
        exit(EXIT_FAILURE); \
    }while(0)        

enum sync_t {
    PARENT_ACK = 0x41,
    CHILD_ACK = 0x43,
};
int main(){
    int sv[2];
    if(socketpair(AF_LOCAL,SOCK_STREAM,0,sv) == -1){
        ERR_EXIT("open socket pair error.");
    }
    pid_t cpid;
    cpid = fork();
    if(cpid == -1){
        ERR_EXIT("fork child error.");
    }
    int syncfd;
    if(cpid == 0){
        syncfd = sv[1];
        if(close(sv[0] < 0))
            ERR_EXIT("child close useless fd error.");
        bool complete = false;
        while(!complete){
            enum sync_t s;
            read(syncfd,&s,sizeof(s));
            if(s == PARENT_ACK){
                s = CHILD_ACK;
                write(syncfd,&s,sizeof(s));
                complete = true;
            }
        }
        printf("child sync finish.\n");
        exit(EXIT_SUCCESS);
    }else{
       syncfd = sv[0];
       if(close(sv[1] < 0)){
            ERR_EXIT("parent close useless fd error.");
       }
       bool complete = false;
       enum sync_t s;
       s = PARENT_ACK;
       write(syncfd,&s,sizeof(s));
       while(!complete){
            enum sync_t s;
            read(syncfd,&s,sizeof(s));
            if(s == CHILD_ACK){
                complete = true;
            } 
       }
       printf("parent sync finish.\n");
       waitpid(cpid,NULL,0);       
    }

    exit(EXIT_SUCCESS);
}