Bug#586883: libc6: printf doesn't return a negative value in case of output error

[Vincent Lefevre <vincent@vinc17.net>]

Package: libc6
Version: 2.11.2-1
Severity: normal

For fprintf (thus printf), the C standard says:

  The fprintf function returns the number of characters transmitted,
  or a negative value if an output or encoding error occurred.

But in glibc, printf doesn't return a negative value in case of output
error (at least not in some cases). For instance:

#include <stdio.h>

int main (void)
{
  int r;
  r = printf ("%10000s\n", "foo");
  fprintf (stderr, "%d\n", r);
  return 0;
}

Then I get:

$ ./out > /dev/null
10001
$ ./out >&-
8196

The first case is correct (anything can be written to /dev/null),
but in the second case (where the fd is closed), there's obviously
an output error (the return value is not 10001), but in such a case,
r should have been negative.

-- System Information:
Debian Release: squeeze/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.32-5-amd64 (SMP w/8 CPU cores)
Locale: LANG=POSIX, LC_CTYPE=en_US.ISO8859-1 (charmap=ISO-8859-1)
Shell: /bin/sh linked to /bin/dash

Versions of packages libc6 depends on:
ii  libc-bin                      2.11.2-1   Embedded GNU C Library: Binaries
ii  libgcc1                       1:4.4.4-5  GCC support library

libc6 recommends no packages.

Versions of packages libc6 suggests:
ii  debconf [debconf-2.0]         1.5.32     Debian configuration management sy
ii  glibc-doc                     2.11.2-1   Embedded GNU C Library: Documentat
ii  locales                       2.11.2-1   Embedded GNU C Library: National L

-- debconf information:
  glibc/upgrade: true
  glibc/disable-screensaver:
  glibc/restart-failed:
* glibc/restart-services: gdm exim4 cups cron atd