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Re: [PATCH] fdopendir: work around FreeBSD bug

From: Eric Blake
Subject: Re: [PATCH] fdopendir: work around FreeBSD bug
Date: Mon, 29 Mar 2010 16:43:32 -0600
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[re-adding the list]

On 03/29/2010 04:39 PM, Christian Weisgerber wrote:
>> I'm still trying to get access to a FreeBSD 7 box to test this out
>> myself (my current FreeBSD access is running 8.0, but that does not
>> have the bug).
> Well, you can temporarily remove the prototype for fdopendir() from
> <dirent.h>.
> Your changes look correct to me, and I've wedged them into GNU tar
> 1.23 on my FreeBSD 7.3/amd64 box and they work.

Thanks for the feedback.  Yeah, I suppose I could temporarily corrupt a
non-FreeBSD system for an equally effective test.

> Minor remarks:
>> --- a/m4/fdopendir.m4
>> +++ b/m4/fdopendir.m4
>> @@ -35,4 +35,9 @@ AC_DEFUN([gl_FUNC_FDOPENDIR],
>>        AC_LIBOBJ([fdopendir])
>>      fi
>>    fi
>> +  dnl FreeBSD 7.3 has the function, but failed to declare it.
>> +  AC_CHECK_DECLS([fdopendir], [], [HAVE_DECL_FDOPENDIR=0], [[
>> +#include <dirent.h>
>> +#include <fcntl.h>
>> +    ]])
>>  ])
> The <fcntl.h> is useless; the preceding test only uses it to pull
> in O_RDONLY.  *BSD documents that <sys/types> should be included
> before <dirent.h>, but in practice that isn't necessary.

Thanks for the pointers.  We haven't yet encountered a system where
<dirent.h> in isolation fails to compile, but I will fix the <fcntl.h>

> If you are really paranoid, you need to provide a prototype here...
>     [int fd = open ("conftest.c", O_RDONLY);
>      if (fd < 0) return 2;
>      return !!fdopendir (fd);])],
> ... because fdopendir() could return a valid pointer whose lower
> 32 bits just happen to be 0, as unlikely as that is in practice.
> But then only some versions of FreeBSD lack the prototype, and
> FreeBSD's fdopendir() does not accept a file handle from a non-directory
> file.

Worth incorporating into my patch, then.  I'll post my respin, once I've
tested locally.

Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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