Re: PATCH: linux-generic dup2 behaviour

[Chris Metcalf <cmetcalf at tilera dot com>]

Linas, you might want to grab the version we have up on our website and
diff it with the sources you have, because this bug was in fact fixed a
while ago (Nov 2010) in our code.  The current body of dup2() looks like this:

int
__dup2 (int fd, int fd2)
{
  /* For the degenerate case, check if the fd is valid (by trying to
     get the file status flags) and return it, or else return EBADF.  */
  if (fd == fd2)
    return __libc_fcntl(fd, F_GETFL, 0) < 0 ? -1 : fd;

  return INLINE_SYSCALL(dup3, 3, fd, fd2, 0);
}

As I've mentioned before, our website has:

http://www.tilera.com/scm/glibc-2.11.2.tar.bz2

In addition, I also just uploaded the much smaller (100 KB) bzipped patch
file we are using relative to RHEL 6's libc for our next release:

http://www.tilera.com/scm/glibc-2.12.get.bz2

This is what we would be starting with for a community return -- though not
yet worth going through with a fine-tooth comb, as (in addition to being
behind the git head) there are a couple of known minor bugs I'd like to
fix, and it needs a style review, copyright fixes, and changelog work.

On 9/13/2011 5:43 PM, Linas Vepstas wrote:
> Argh, patch below is bad; here's why:
>
> There is another m4 test case which closes stderr, on purpose,
> then does a dup2(2,2) and expects to get back EBADF
> Should I emulate this kind of behavior in glibc? If not, then
> the question arises: what is the correct way of mapping
> expected dup2() behavior to non-deprecated syscalls?
>
> --linas
>
>
> On 13 September 2011 16:10, Linas Vepstas <linasvepstas@gmail.com> wrote:
>> Chris, here's another:
>>
>> man dup2 states that:
>>   If  oldfd  is a valid file descriptor, and newfd has the same value as
>>   oldfd, then dup2() does nothing, and returns newfd.
>>
>> while the linux kernel does this in fs/fcntl.c:
>>  if (unlikely(oldfd == newfd)) return -EINVAL;
>>
>> Which I presume is correct for dup3.
>> Thus, dup2 needs fixing. Note that m4 test suite catches this.
>>
>>
>> ---
>>  sysdeps/unix/sysv/linux/generic/dup2.c |    2 ++
>>  1 file changed, 2 insertions(+)
>>
>> Index: glibc-2.14/sysdeps/unix/sysv/linux/generic/dup2.c
>> ===================================================================
>> --- glibc-2.14.orig/sysdeps/unix/sysv/linux/generic/dup2.c  2011-09-13
>> 15:39:03.000000000 -0500
>> +++ glibc-2.14/sysdeps/unix/sysv/linux/generic/dup2.c 2011-09-13
>> 15:40:09.000000000 -0500
>> @@ -26,6 +26,8 @@
>>  int
>>  __dup2 (int fd, int fd2)
>>  {
>> +  /* if fd's are equal, preserve documented dup2 response */
>> +  if (fd == fd2) return fd;
>>   return INLINE_SYSCALL(dup3, 3, fd, fd2, 0);
>>  }
>>  libc_hidden_def (__dup2)
>>

-- 
Chris Metcalf, Tilera Corp.
http://www.tilera.com