6.3.3 FIFO Operations (original) (raw)

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I/O operations on a FIFO are essentially the same as for normal pipes, with once major exception. An ``open'' system call or library function should be used to physically open up a channel to the pipe. With half-duplex pipes, this is unnecessary, since the pipe resides in the kernel and not on a physical filesystem. In our examples, we will treat the pipe as a stream, opening it up with fopen(), and closing it with fclose().

Consider a simple server process:

/***************************************************************************** Excerpt from "Linux Programmer's Guide - Chapter 6" (C)opyright 1994-1995, Scott Burkett

MODULE: fifoserver.c *****************************************************************************/

#include <stdio.h> #include <stdlib.h> #include <sys/stat.h> #include <unistd.h>

#include <linux/stat.h>

#define FIFO_FILE "MYFIFO"

int main(void) { FILE *fp; char readbuf[80];

    /* Create the FIFO if it does not exist */
    umask(0);
    mknod(FIFO_FILE, S_IFIFO|0666, 0);

    while(1)
    {
            fp = fopen(FIFO_FILE, "r");
            fgets(readbuf, 80, fp);
            printf("Received string: %s\n", readbuf);
            fclose(fp);
    }

    return(0);

}

Since a FIFO blocks by default, run the server in the background after you compile it:

    $ fifoserver&

We will discuss a FIFO's blocking action in a moment. First, consider the following simple client frontend to our server:

/***************************************************************************** Excerpt from "Linux Programmer's Guide - Chapter 6" (C)opyright 1994-1995, Scott Burkett

MODULE: fifoclient.c *****************************************************************************/

#include <stdio.h> #include <stdlib.h>

#define FIFO_FILE "MYFIFO"

int main(int argc, char *argv[]) { FILE *fp;

    if ( argc != 2 ) {
            printf("USAGE: fifoclient [string]\n");
            exit(1);
    }

    if((fp = fopen(FIFO_FILE, "w")) == NULL) {
            perror("fopen");
            exit(1);
    }

    fputs(argv[1], fp);

    fclose(fp);
    return(0);

}

Converted on: Fri Mar 29 14:43:04 EST 1996