Thread: UNIX mkfifo fails on a different files

Hello, I am trying to complete a finite IPC machine. For some unknown reason to me, mkfifo never succeeds. My first few atempts, it does after that it always return a non-zero value (which by the papers is fail).

Code:

struct msg* msg_generate(const char* mess);


int     open_read_from(struct msg* m);
int     open_write_to(struct msg* m);




static int eXec()
{
    struct msg* pm = msg_generate("hello IPC world!!!");


    int fdr = open_read_from(pm->fifo_files.fifo_read);
    int fdw = open_write_to(pm->fifo_files.fifo_write);


    // stick here
    for(;;) {
        // send messages and read them back...
        char rbuff[sizeof(struct msg)]= {0};
        char wbuff[sizeof(struct msg)] = {0};


        if (read(fdr, rbuff, sizeof(struct msg)) > 0) {
            printf("Read...\n");
            struct msg* p = (struct msg*) rbuff;
            printf("[message: %s][came from %d][ret: %d]\n",
                   p->message, p->pid, p->result);


        }


        while (fgets(wbuff, sizeof(struct msg), stdin) != -1) {
            if (write(fdw, wbuff, sizeof(struct msg)) == -1) {
                perror("Could not write to fifo...");
            }
        }
    }
    return 0; // or err code
}




int main(int argc, char** argv)
{


    return eXec();
}


int open_read_from(struct msg *m)
{
    int flags = (S_IFIFO | 0666);
    if(mkfifo(m->fifo_files.fifo_read, flags)!=0) {
        return -1;
    }
    return open(m->fifo_files.fifo_read, O_RDONLY|O_NONBLOCK);


}




int open_write_to(struct msg *m)
{


    int flags = (S_IFIFO | 0666);
    if(mkfifo(m->fifo_files.fifo_write, flags)!=0){
        return -1;
    }
    return open(m->fifo_files.fifo_write, O_WRONLY|O_NONBLOCK);


}




struct msg* msg_generate(const char* mess)
{
    if (!mess) {
        return 0;
    }
    static struct msg single;
    static int rcnt = 0;
    static int wcnt = 0;
    strcpy(single.message, mess);
    pid_t cp = getpid();


    sprintf(single.fifo_files.fifo_read, "/tmp/%dr%d", cp, rcnt++);
    sprintf(single.fifo_files.fifo_write, "/tmp/%dw%d", cp, wcnt++);


    single.pid = cp;
    single.result = 0; // ok for now
    return &single;


}

I am debugging my both functions for read and write, they both return -1 to me. Any info?

The fifo files you create don't magically disappear after your program ends. They are still in the file system. Look under /tmp for them and they'll all be there. If the file already exists, mkfifo will fail. Delete them. You should probably have your program remove them before it terminates.

BTW, the second parameter to mkfifo is not called "flags", it's called "mode" and doesn't take the S_IFIFO flag!