리눅스 멀티프로세스 소켓 프로그래밍에 대한 질문입니다

if (pid == 0)
		write_routine(sock,buf);
	else
		read_routine(sock,buf);

#include <sys/socket.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#define BUFSIZE 30
void error_handling(char *message);
void read_routine(int sock, char *buf);
void write_routine(int sock, char *buf);
 
int main(int argc, char **argv)
{
	int sock;
	pid_t pid;
	char buf[BUFSIZE];
	struct sockaddr_in serv_addr;
	if (argc != 3)
	{
		printf("Usage : ./%s [IP] [Port] \n",argv[0]);
		exit(1);
	}
 
	sock = socket(PF_INET,SOCK_STREAM,0);
	if (sock < 0)
		error_handling("socket() error");
 
	memset(&serv_addr,0,sizeof(serv_addr));
	serv_addr.sin_family = AF_INET;
	serv_addr.sin_addr.s_addr = inet_addr(argv[1]);
	serv_addr.sin_port = htons(atoi(argv[2]));
 
	if (connect(sock,(struct sockaddr*)&serv_addr,sizeof(serv_addr)) < 0)
		error_handling("connect() error");
	else
		printf("Connected....................\n");
 
	pid = fork();
	if (pid == 0)
		write_routine(sock,buf);
	else
		read_routine(sock,buf);
 
	close(sock);
	return 0;
}
 
void read_routine(int sock, char *buf)
{
	int recv_len;
	while (1)
	{
		recv_len = read(sock,buf,BUFSIZE-1);
		if (recv_len == 0)
			return;
		else
			printf("Message from server: ");
 
		while (recv_len == BUFSIZE-1)
		{
			printf("%s",buf);
			recv_len = read(sock,buf,BUFSIZE-1);
		}
		buf[recv_len-1] = 0;
		printf("%s\n",buf);
	}
}
 
void write_routine(int sock, char *buf)
{
	while (1)
	{
		fgets(buf,BUFSIZE-1,stdin);
		if (!strcmp(buf,"q\n") || !strcmp(buf,"Q\n"))
		{
			shutdown(sock,SHUT_WR);
			return;
		}
		write(sock,buf,strlen(buf));
	}
}
 
void error_handling(char *message)
{
	fputs(message,stderr);
	fputc('\n',stderr);
	exit(1);
}