Re: Pipes Again -- a simple test case

[Houder <houder@xs4all.nl>]

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On 2016-01-04 09:52, Marco Atzeri wrote:
> On 04/01/2016 09:03, Houder wrote:
>> Hi Corinna,
>> 
>> I have been looking for an STC to show why cmp fails on Cygwin (and to
>> show the
>> difference between Cygwin and Linux).
>> 
>> The STC below creates a pipe (pipe() is used), followed by calls to
>> fstat() and
>> stat() for both the read end and the write end of the pipe.
>> 
>> (I also tested with popen()/pclose(): same result)
>> 
>> Regards,
>> Henri
>> 
>> Btw, I am using W7 prof.; Cygwin-32 and Cygwin-64; 2.3.1 and 2.4.0
>> 
>> =====
>> 
>> The code for the STC is basically as follows:
> 
> in general a STC should be complete and attached as file.
> 
> I know where you took errExit and displayStatInfo, but
> it is anyway a extra effort time consuming for the others.

Yup ... find it attached to this post ... (I hope).

(I was busy "compiling" everyting in one file :-)

Regards,
Henri

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/*************************************************************************\
*                  Copyright (C) Michael Kerrisk, 2014.                   *
*                                                                         *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU Affero General Public License as published   *
* by the Free Software Foundation, either version 3 or (at your option)   *
* any later version. This program is distributed without any warranty.    *
* See the file COPYING.agpl-v3 for details.                               *
\*************************************************************************/

/* Listing 15-1 */

/* t_stat.c -- heavily modified
 - using fstat: minor: 198/7 ... i-node: both (mostly) zero <==== my guess is that Cygwin is "in error"
 - using  stat: minor: 199 ... i-node: numbers are different from one another (and non-zero)
*/
#define _BSD_SOURCE     /* Get major() and minor() from <sys/types.h> */
#include <sys/types.h>
#include <sys/stat.h>
#include <time.h>
//#include "file_perms.h"
//#include "tlpi_hdr.h"

#include <stdio.h>      /* Standard I/O functions */
#include <stdlib.h>     /* Prototypes of commonly used library functions,
                           plus EXIT_SUCCESS and EXIT_FAILURE constants */
#include <unistd.h>     /* Prototypes for many system calls */
#include <errno.h>      /* Declares errno and defines error constants */
#include <string.h>     /* Commonly used string-handling functions */

#include <stdarg.h>

#ifdef TRUE
#undef TRUE
#endif

#ifdef FALSE
#undef FALSE
#endif

typedef enum { FALSE, TRUE } Boolean;

static char *ename[] = {
    /*   0 */ "", 
    /*   1 */ "EPERM", "ENOENT", "ESRCH", "EINTR", "EIO", "ENXIO", 
    /*   7 */ "E2BIG", "ENOEXEC", "EBADF", "ECHILD", 
    /*  11 */ "EAGAIN/EWOULDBLOCK", "ENOMEM", "EACCES", "EFAULT", 
    /*  15 */ "ENOTBLK", "EBUSY", "EEXIST", "EXDEV", "ENODEV", 
    /*  20 */ "ENOTDIR", "EISDIR", "EINVAL", "ENFILE", "EMFILE", 
    /*  25 */ "ENOTTY", "ETXTBSY", "EFBIG", "ENOSPC", "ESPIPE", 
    /*  30 */ "EROFS", "EMLINK", "EPIPE", "EDOM", "ERANGE", "ENOMSG", 
    /*  36 */ "EIDRM", "ECHRNG", "EL2NSYNC", "EL3HLT", "EL3RST", 
    /*  41 */ "ELNRNG", "EUNATCH", "ENOCSI", "EL2HLT", "EDEADLK", 
    /*  46 */ "ENOLCK", "", "", "", "EBADE", "EBADR", "EXFULL", 
    /*  53 */ "ENOANO", "EBADRQC", "EBADSLT", "EDEADLOCK", "EBFONT", 
    /*  58 */ "", "", "ENOSTR", "ENODATA", "ETIME", "ENOSR", "ENONET", 
    /*  65 */ "ENOPKG", "EREMOTE", "ENOLINK", "EADV", "ESRMNT", 
    /*  70 */ "ECOMM", "EPROTO", "", "", "EMULTIHOP", "ELBIN", 
    /*  76 */ "EDOTDOT", "EBADMSG", "", "EFTYPE", "ENOTUNIQ", "EBADFD", 
    /*  82 */ "EREMCHG", "ELIBACC", "ELIBBAD", "ELIBSCN", "ELIBMAX", 
    /*  87 */ "ELIBEXEC", "ENOSYS", "ENMFILE", "ENOTEMPTY", 
    /*  91 */ "ENAMETOOLONG", "ELOOP", "", "", "EOPNOTSUPP", 
    /*  96 */ "EPFNOSUPPORT", "", "", "", "", "", "", "", "ECONNRESET", 
    /* 105 */ "ENOBUFS", "EAFNOSUPPORT", "EPROTOTYPE", "ENOTSOCK", 
    /* 109 */ "ENOPROTOOPT", "ESHUTDOWN", "ECONNREFUSED", "EADDRINUSE", 
    /* 113 */ "ECONNABORTED", "ENETUNREACH", "ENETDOWN", "ETIMEDOUT", 
    /* 117 */ "EHOSTDOWN", "EHOSTUNREACH", "EINPROGRESS", "EALREADY", 
    /* 121 */ "EDESTADDRREQ", "EMSGSIZE", "EPROTONOSUPPORT", 
    /* 124 */ "ESOCKTNOSUPPORT", "EADDRNOTAVAIL", "ENETRESET", 
    /* 127 */ "EISCONN", "ENOTCONN", "ETOOMANYREFS", "EPROCLIM", 
    /* 131 */ "EUSERS", "EDQUOT", "ESTALE", "ENOTSUP", "ENOMEDIUM", 
    /* 136 */ "ENOSHARE", "ECASECLASH", "EILSEQ", "EOVERFLOW", 
    /* 140 */ "ECANCELED", "ENOTRECOVERABLE", "EOWNERDEAD", "ESTRPIPE"
};

#define MAX_ENAME 143

static void
displayStatInfo(const struct stat *sb)
{
    printf("File type:                ");

    switch (sb->st_mode & S_IFMT) {
    case S_IFREG:  printf("regular file\n");            break;
    case S_IFDIR:  printf("directory\n");               break;
    case S_IFCHR:  printf("character device\n");        break;
    case S_IFBLK:  printf("block device\n");            break;
    case S_IFLNK:  printf("symbolic (soft) link\n");    break;
    case S_IFIFO:  printf("FIFO or pipe\n");            break;
    case S_IFSOCK: printf("socket\n");                  break;
    default:       printf("unknown file type?\n");      break;
    }

    printf("Device containing i-node: (%lx)   major=%lu   minor=%lu\n",
                (long) sb->st_dev, (long) major(sb->st_dev), (long) minor(sb->st_dev));

    printf("I-node number:            %llx - decimal: %llu\n", sb->st_ino, sb->st_ino);

    if (S_ISCHR(sb->st_mode) || S_ISBLK(sb->st_mode))
        printf(" **** Device number (st_rdev):  major=%ld; minor=%ld\n",
                (long) major(sb->st_rdev), (long) minor(sb->st_rdev));

    printf("File size:                %lld bytes\n", (long long) sb->st_size);
}

void errExit(const char *format, ...);

int
main(int argc, char *argv[])
{
    struct stat sb[2];
    int pfd[2];

    pid_t pid = getpid();
    if (pipe(pfd) != 0)
        errExit("pipe");

    for (int f = 0; f < 2; f++)
    {
        char symlnk[64];

        if (sprintf(symlnk, "/proc/%d/fd/%d", pid, pfd[0 + f]) <= 0)
            errExit("sprintf");
        !f ? printf("... %s (symbolic link to the  read end of the pipe)\n", symlnk)
           : printf("... %s (symbolic link to the write end of the pipe)\n", symlnk);

        printf("... using  stat()\n");
        if (stat(symlnk, sb) != 0)
            errExit("stat");
        displayStatInfo(sb);

        printf("... using fstat()\n");
        if ( fstat(pfd[0 + f], sb + 1) != 0 )
            errExit("fstat");
        displayStatInfo(sb + 1);
    }
    exit(EXIT_SUCCESS);
}

static void
terminate(Boolean useExit3)
{
    char *s;

    /* Dump core if EF_DUMPCORE environment variable is defined and
       is a nonempty string; otherwise call exit(3) or _exit(2),
       depending on the value of 'useExit3'. */

    s = getenv("EF_DUMPCORE");

    if (s != NULL && *s != '\0')
        abort();
    else if (useExit3)
        exit(EXIT_FAILURE);
    else
        _exit(EXIT_FAILURE);
}

static void
outputError(Boolean useErr, int err, Boolean flushStdout,
        const char *format, va_list ap)
{
#define BUF_SIZE 500
    char buf[BUF_SIZE], userMsg[BUF_SIZE], errText[BUF_SIZE];

    vsnprintf(userMsg, BUF_SIZE, format, ap);

    if (useErr)
        snprintf(errText, BUF_SIZE, " [%s %s]",
                (err > 0 && err <= MAX_ENAME) ?
                ename[err] : "?UNKNOWN?", strerror(err));
    else
        snprintf(errText, BUF_SIZE, ":");

    snprintf(buf, BUF_SIZE, "ERROR%s %s\n", errText, userMsg);

    if (flushStdout)
        fflush(stdout);       /* Flush any pending stdout */
    fputs(buf, stderr);
    fflush(stderr);           /* In case stderr is not line-buffered */
}

void
errExit(const char *format, ...)
{
    va_list argList;

    va_start(argList, format);
    outputError(TRUE, errno, TRUE, format, argList);
    va_end(argList);

    terminate(TRUE);
}

//=====

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