fifo_rdonly_bug.c

[詳解]

/*++
/* NAME
/*  fifo_rdonly_bug 1
/* SUMMARY
/*  fifo server test program
/* SYNOPSIS
/*  fifo_rdonly_bug
/* DESCRIPTION
/*  fifo_rdonly_bug creates a FIFO and opens it read only. It
/*  then opens the FIFO for writing, writes one byte, and closes
/*  the writing end. On Linux Redhat 4.2 and 5.0, and HP-UX 9.05
/*  and 10.20, select() will report that the FIFO remains readable
/*  even after multiple read operations.
/* DIAGNOSTICS
/*  Problems are reported to the standard error stream.
/* LICENSE
/* .ad
/* .fi
/*  The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*--*/

#include <sys_defs.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>

#define FIFO_PATH   "test-fifo"
#define TRIGGER_DELAY   5

#define perrorexit(s)   { perror(s); exit(1); }

static void cleanup(void)
{
    printf("Removing fifo %s...\n", FIFO_PATH);
    if (unlink(FIFO_PATH))
    perrorexit("unlink");
    printf("Done.\n");
}

static void perrorcleanup(char *str)
{
    perror(str);
    cleanup();
    exit(0);
}

static void readable_event(int fd)
{
    char    ch;
    static int count = 0;

    if (read(fd, &ch, 1) < 0) {
    perror("read");
    sleep(1);
    }
    if (count++ > 5) {
    printf("FIFO remains readable after multiple reads.\n");
    cleanup();
    exit(1);
    }
}

int     main(int unused_argc, char **unused_argv)
{
    struct timeval tv;
    fd_set  read_fds;
    fd_set  except_fds;
    int     fd;
    int     fd2;

    (void) unlink(FIFO_PATH);

    printf("Create fifo %s...\n", FIFO_PATH);
    if (mkfifo(FIFO_PATH, 0600) < 0)
    perrorexit("mkfifo");

    printf("Open fifo %s, read-only mode...\n", FIFO_PATH);
    if ((fd = open(FIFO_PATH, O_RDONLY | O_NONBLOCK, 0)) < 0)
    perrorcleanup("open");

    printf("Write one byte to the fifo, then close it...\n");
    if ((fd2 = open(FIFO_PATH, O_WRONLY, 0)) < 0)
    perrorcleanup("open fifo O_WRONLY");
    if (write(fd2, "", 1) < 1)
    perrorcleanup("write one byte to fifo");
    if (close(fd2) < 0)
    perrorcleanup("close fifo");

    printf("Selecting the fifo for readability...\n");

    for (;;) {
    FD_ZERO(&read_fds);
    FD_SET(fd, &read_fds);
    FD_ZERO(&except_fds);
    FD_SET(fd, &except_fds);
    tv.tv_sec = 1;
    tv.tv_usec = 0;

    switch (select(fd + 1, &read_fds, (fd_set *) 0, &except_fds, &tv)) {
    case -1:
        perrorexit("select");
    default:
        if (FD_ISSET(fd, &except_fds)) {
        printf("Exceptional fifo condition! You are not normal!\n");
        readable_event(fd);
        } else if (FD_ISSET(fd, &read_fds)) {
        printf("Readable fifo condition\n");
        readable_event(fd);
        }
        break;
    case 0:
        printf("The fifo is not readable. You're normal.\n");
        cleanup();
        exit(0);
        break;
    }
    }
}