#include <stdio.h>#include <stdlib.h>#include <string.h>#include <signal.h>#include <time.h>#include <sys/types.h>#include <sys/ipc.h>#include <sys/msg.h>#define KEYPATH "/root/chat"#define NAMESIZE 16#define MSGSIZE 128#define LEN sizeof(int)+sizeof(int)+NAMESIZE+MSGSIZE#define SERTYPE 1 #define NORMAL 0#define REGISTER 1#define UNREGISTER -1typedef struct node{    int id;    struct node  *next;}USR;struct msgbuf{    long mtype;    int subtype;    int id;    char nickname[NAMESIZE];    char mtext[MSGSIZE];}buf_in, buf_out;int msgid;USR *head;USR * myregister(USR *head, int id){   USR *p = (USR *)malloc(sizeof(USR));   p->id = id;   p->next = head->next;   head->next = p;   return head;} int unregister(USR *head, int id){   USR *p, *q;   p = head;   q = p->next;    while( (q->id != id) && (q->next != NULL) )   {      p = q;      q = q->next;   }   if ( q->id == id)    {       p->next = q->next;       free(q);       return 1;   }     return 0;}int broadcast(int msgid, USR *head, int mode){   USR *p;   p = head->next;   buf_out.subtype = mode;   while( p != NULL)   {       buf_out.mtype = p->id;      if ( msgsnd(msgid, &buf_out, LEN, 0) != 0 )      {         perror("server send message error");         exit(-1);      }      p = p->next;   }      return 1;}/*void signal_handler(){   read(pfd[0], buf_out.mtext, 20);    strcpy(buf_out.nickname, "from server...");   broadcast(msgid, head, NORMAL);}  */int main(){   int pid;   key_t key;   char command[20];   //signal(SIGUSR1, signal_handler);    if ( (key=ftok(KEYPATH, 'c')) == -1 )   {      printf("faile to locate %s\n", KEYPATH);      exit(-1);   }   msgid = msgget(key, IPC_CREAT|IPC_EXCL|0666);   if ( msgid == -1 )   {      perror("msgget");      exit(-1);   }/*   if ( pipe(pfd) < 0 )   {      msgctl(msgid, IPC_RMID, NULL);      perror("pipe...");      exit(-1);   }*/      if ( (pid = fork()) == -1 )   {      msgctl(msgid, IPC_RMID, NULL);      perror("fork");      exit(-1);   }   if ( pid == 0 )   {      while ( 1 )      {           printf("\n(server console):");          if ( fgets(command, 20, stdin) != NULL )         {             if ( strncmp(command, "quit", 4) == 0 )             {                 printf("The server is down...\n");                 kill(getppid(), SIGKILL);                 sleep(1);                 msgctl(msgid, IPC_RMID, NULL);                 exit(0);             }             else             {                 buf_out.mtype = SERTYPE;                 buf_out.subtype = NORMAL;                 strcpy(buf_out.nickname, "from server...");                 strcpy(buf_out.mtext, command);                 if ( msgsnd(msgid, &buf_out, LEN, 0) < 0 )                 {                    perror("msgsnd");                 }                 //write(pfd[1], command, 10);                 //kill(getppid(), SIGUSR1);             }         }      }   }   else   {      head = (USR *)malloc(sizeof(USR));      head->next = NULL;      while(1)      {         if ( msgrcv(msgid, &buf_in, LEN, 1, 0) == -1 )         {            perror("msgrcv");            exit(-1);         }         else         {               buf_out = buf_in;             switch(buf_in.subtype)             {                case UNREGISTER:                         unregister(head, buf_in.id);                         strcpy(buf_out.mtext, "has left...");                         broadcast(msgid, head, UNREGISTER);                                              break;                case  REGISTER:                         head = myregister(head, buf_in.id);                         strcpy(buf_out.mtext, "has joined in...");                         broadcast(msgid, head, REGISTER);                          break;                case  NORMAL:                          broadcast(msgid, head, NORMAL);                         break;             }          }    // end of if       }   } }