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Bug#287824: marked as done (libc6: fseek() fails and returns -1 without setting errno)



Your message dated Wed, 26 Jan 2005 23:01:28 +0900
with message-id <81acqwp9vr.wl@omega.webmasters.gr.jp>
and subject line Bug#287824: libc6: fseek() fails and returns -1 without setting errno
has caused the attached Bug report to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

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From: Johan Walles <walles@mailblocks.com>
To: Debian Bug Tracking System <submit@bugs.debian.org>
Subject: libc6: fseek() fails and returns -1 without setting errno
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Date: Thu, 30 Dec 2004 12:42:18 +0100
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Package: libc6
Version: 2.3.2.ds1-18
Severity: normal


The output of the following program is:
"
johan@foo:~/src/test$ ./a.out
fseek: Unknown error 12345
"

Since I set errno to 12345 before making the (failing) fseek() call,
fseek() itself apparently fails without setting errno.

Here's the strace output between opening the file and failing:
"
open("/proc/self/mem", O_RDONLY)        = 3
fstat64(3, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7fe8000
_llseek(3, 18446744072635807744, [3526037055030344891], SEEK_SET) = -1073743872
dup(2)                                  = 4
fcntl64(4, F_GETFL)                     = 0x2 (flags O_RDWR)
fstat64(4, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 5), ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7fe7000
_llseek(4, 0, 0xbffff768, SEEK_CUR)     = -1 ESPIPE (Illegal seek)
write(4, "fseek: Unknown error 12345\n", 27fseek: Unknown error 12345
) = 27
"

And the program itself:

"
/* The point of this program is to try to access one of its own local
 * variables by reading it from /proc/self/mem. */

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

int main(int argc, char *argv[])
{
  int variable = 42;
  int readvalue = 0;
  FILE *mem = fopen("/proc/self/mem", "r");
  
  errno = 12345;
  if (fseek(mem, (size_t)&variable, SEEK_SET) != 0) {
    perror("fseek");
    exit(EXIT_FAILURE);
  }
  
  if (fread(&readvalue, sizeof(variable), 1, mem) != 1) {
    perror("fread");
    exit(EXIT_FAILURE);
  }
  
  printf("Localvar=%d, read value=%d\n", variable, readvalue);
  
  return 0;
}
"

-- System Information:
Debian Release: 3.1
  APT prefers testing
  APT policy: (990, 'testing')
Architecture: i386 (i686)
Kernel: Linux 2.6.9-1-686
Locale: LANG=sv_SE, LC_CTYPE=sv_SE (charmap=ISO-8859-1)

Versions of packages libc6 depends on:
ii  libdb1-compat                 2.1.3-7    The Berkeley database routines [gl

-- no debconf information

---------------------------------------
Received: (at 287824-done) by bugs.debian.org; 26 Jan 2005 14:01:31 +0000
>From gotom@debian.or.jp Wed Jan 26 06:01:31 2005
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Date: Wed, 26 Jan 2005 23:01:28 +0900
Message-ID: <81acqwp9vr.wl@omega.webmasters.gr.jp>
From: GOTO Masanori <gotom@debian.or.jp>
To: Johan Walles <walles@mailblocks.com>, 287824-done@bugs.debian.org
Cc: gotom@debian.or.jp
Subject: Re: Bug#287824: libc6: fseek() fails and returns -1 without setting errno
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> I send my interpretation to debian-kernel to make sure.  Debian-kernel
> guys, if you don't agree with my thought, please let me know.
> Otherwise, I'll close this bug.

I believe this report does not focus the correct usage for using
/proc/self/mem + fseek().  I close this bug.  Johan, if you have doubt
about this close, please read again my reply.

Regards,
-- gotom



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