Linux: Using Socketpair to pass descriptors between processes

1.socketpair

2.sendmsg/recvmsg

3.UNIX domain socket pass-through description word

Function: Create a loop duplex flow pipeline

Prototype:

int socketpair (int domain, int type, int protocol, int sv[2]);

Parameter domain: protocol family

Type: Socket type

Protocol: Protocol Type

SV: The returned socket pair

Return value: Successfully returned 0, failed to return-1

Full-duplex pipeline created through Sockpair to enable parent-child process communication

#include <stdio.h>#include<stdlib.h>#include<string.h>#include<unistd.h>#include<errno.h>#include<sys/types.h>#include<sys/socket.h>#include<netinet/inch.h>#include<arpa/inet.h>#defineErr_exit (M) Do{perror (M);    Exit (Exit_failure); } while(0)intMainintargcConst Char*argv[]) {    intsockfds[2]; intRET = socket (Pf_unix, Sock_stream,0, Sockfds); if(ret = =-1) Err_exit ("Sockpair");    pid_t pid; PID=Fork (); if(PID = =-1) Err_exit ("Fork"); if(PID >0)    {        intval =0; Close (sockfd[1]);  while(1)        {            ++Val; printf ("sending data:%d\n", Val); Write (sockfds[0], &val,sizeof(Val)); Read (sockfd[0], &val,sizeof(Val)); printf ("data received:%d\n", Val); Sleep (1); }    }Else if(PID = =0)    {        intVal; Close (sockfds[0]);  while(1) {Read (sockfds[1], &val,sizeof(Val)); ++Val; Write (sockfds[1], &val,sizeof(Val)); }    }    return 0; }

It is found that the value of Val is constantly increasing and is being passed on between parent and child processes;

Let's take a look at the more powerful sendmsg function

 ssize_t sendmsg (int  sockfd, const  Span style= "COLOR: #0000ff" >struct  msghdr *msg, int  flags); 

struct MSGHDR {
void *msg_name; /* Optional Address */
Socklen_t Msg_namelen; /* Size of Address */
struct Iovec *msg_iov; /* Scatter/gather Array */
size_t Msg_iovlen; /* # elements in Msg_iov */
void *msg_control; /* Ancillary data, see below */
size_t Msg_controllen; /* Ancillary Data buffer Len */
int msg_flags; /* Flags on received message */
};

Parameter explanation:

1.void *msg_name; /* Optional Address */
Socklen_t Msg_namelen;

These two parameters determine the address to send

2.        struct Iovec *msg_iov; /* Scatter/gather Array */

The data we want to send is stored in this structure.

struct Iovec {
void *iov_base; /* Starting address */This corresponds to buffer
size_t Iov_len; /* Number of bytes to transfer */buffer length
};

Structure above
++++++

This is a MSGHDR.

3. Secondary information when the next few data.

We implement pass descriptors through our own encapsulation sendmsg

Write a Send Yourself

Linux: Using Socketpair to pass descriptors between processes