should "man feature_test_macros" mention _LARGEFILE_SOURCE?

should "man feature_test_macros" mention _LARGEFILE_SOURCE?

[Robert P. J. Day]

  just noticed under /usr/include on my fedora rawhide system the
following:

/usr/include/bits/environments.h:# define __ILP32_OFFBIG_CFLAGS	"-m32 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64"
/usr/include/python3.3m/pyconfig-64.h:#define _LARGEFILE_SOURCE 1
/usr/include/features.h:   _LARGEFILE_SOURCE	Some more functions for correct standard I/O.
/usr/include/features.h:#  undef _LARGEFILE_SOURCE
/usr/include/features.h:#  define _LARGEFILE_SOURCE	1
/usr/include/features.h:#ifdef _LARGEFILE_SOURCE
/usr/include/python2.7/pyconfig-64.h:#define _LARGEFILE_SOURCE 1

but there's no mention of "_LARGEFILE_SOURCE" in "man
feature_test_macros". is that assumed to be implied by
_LARGEFILE64_SOURCE? it's not clear.

rday

-- 

========================================================================
Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
LinkedIn:                               http://ca.linkedin.com/in/rpjday
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Re: should "man feature_test_macros" mention _LARGEFILE_SOURCE?

[Michael Kerrisk (man-pages)]

On Tue, Mar 18, 2014 at 8:46 PM, Robert P. J. Day <rpjday-L09J2beyid0N/H6P543EQg@public.gmane.org> wrote:
>
>   just noticed under /usr/include on my fedora rawhide system the
> following:
>
> /usr/include/bits/environments.h:# define __ILP32_OFFBIG_CFLAGS "-m32 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64"
> /usr/include/python3.3m/pyconfig-64.h:#define _LARGEFILE_SOURCE 1
> /usr/include/features.h:   _LARGEFILE_SOURCE    Some more functions for correct standard I/O.
> /usr/include/features.h:#  undef _LARGEFILE_SOURCE
> /usr/include/features.h:#  define _LARGEFILE_SOURCE     1
> /usr/include/features.h:#ifdef _LARGEFILE_SOURCE
> /usr/include/python2.7/pyconfig-64.h:#define _LARGEFILE_SOURCE 1
>
> but there's no mention of "_LARGEFILE_SOURCE" in "man
> feature_test_macros". is that assumed to be implied by
> _LARGEFILE64_SOURCE? it's not clear.

I don't know the answer, but when you do, send a patch!

Cheers,

Michael

-- 
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Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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Re: should "man feature_test_macros" mention _LARGEFILE_SOURCE?

[Mike Frysinger]

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On Tue 18 Mar 2014 15:46:43 Robert P. J. Day wrote:
>   just noticed under /usr/include on my fedora rawhide system the
> following:
> 
> /usr/include/bits/environments.h:# define __ILP32_OFFBIG_CFLAGS	"-m32
> -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64"
> /usr/include/python3.3m/pyconfig-64.h:#define _LARGEFILE_SOURCE 1
> /usr/include/features.h:   _LARGEFILE_SOURCE	Some more functions for 
correct
> standard I/O. /usr/include/features.h:#  undef _LARGEFILE_SOURCE
> /usr/include/features.h:#  define _LARGEFILE_SOURCE	1
> /usr/include/features.h:#ifdef _LARGEFILE_SOURCE
> /usr/include/python2.7/pyconfig-64.h:#define _LARGEFILE_SOURCE 1
> 
> but there's no mention of "_LARGEFILE_SOURCE" in "man
> feature_test_macros". is that assumed to be implied by
> _LARGEFILE64_SOURCE? it's not clear.

nope, none of the three LFS flags imply each other, nor should they.  they're 
related, but orthogonal by design.

i could have sworn i saw a description of them in POSIX, but i can't find it 
now.  the GNU C library manual covers it though:
https://www.gnu.org/software/libc/manual/html_node/Feature-Test-Macros.html

here's a terse summary off the top of my head:

_LARGEFILE_SOURCE: expose prototypes for new funcs which POSIX got wrong 
originally.  e.g. fseek & ftell utilize "long", so fseeko & ftello were added 
which use "off_t".

_LARGEFILE64_SOURCE: expose prototypes for 64-bit variant funcs w/out 
affecting any existing funcs.  e.g. you now have fseeko64 & ftello64 which 
take explicit off64_t types while fseeko and ftello are unchanged.  makes 
sense when sizeof(off_t) == 4 && sizeof(off64_t) == 8.

_FILE_OFFSET_BITS: explicitly set the off_t size.  set it to 32 if you want 
sizeof(off_t) == 4, or set it to 64 if you want sizeof(off_t) == 8.

in the ideal world, _FILE_OFFSET_BITS should default to 64 and 
_LARGEFILE_SOURCE should default to defined.  in our crap world, apps should 
be always building with these in their CPPFLAGS.
-mike

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Re: should "man feature_test_macros" mention _LARGEFILE_SOURCE?

[Robert P. J. Day]

On Tue, 18 Mar 2014, Mike Frysinger wrote:

> On Tue 18 Mar 2014 15:46:43 Robert P. J. Day wrote:
> >   just noticed under /usr/include on my fedora rawhide system the
> > following:
> >
> > /usr/include/bits/environments.h:# define __ILP32_OFFBIG_CFLAGS	"-m32
> > -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64"
> > /usr/include/python3.3m/pyconfig-64.h:#define _LARGEFILE_SOURCE 1
> > /usr/include/features.h:   _LARGEFILE_SOURCE	Some more functions for
> correct
> > standard I/O. /usr/include/features.h:#  undef _LARGEFILE_SOURCE
> > /usr/include/features.h:#  define _LARGEFILE_SOURCE	1
> > /usr/include/features.h:#ifdef _LARGEFILE_SOURCE
> > /usr/include/python2.7/pyconfig-64.h:#define _LARGEFILE_SOURCE 1
> >
> > but there's no mention of "_LARGEFILE_SOURCE" in "man
> > feature_test_macros". is that assumed to be implied by
> > _LARGEFILE64_SOURCE? it's not clear.
>
> nope, none of the three LFS flags imply each other, nor should they.
> they're related, but orthogonal by design.

... snip ...

  i mentioned this only because the current features.h header file
mentions this macro near the top in the documentatiin:

   ...
   _LARGEFILE_SOURCE    Some more functions for correct standard I/O.
   _LARGEFILE64_SOURCE  Additional functionality from LFS for large files.
   _FILE_OFFSET_BITS=N  Select default filesystem interface.
   ...

but the man page for "feature_test_macros" says nothing about it. just
an observation.

rday

-- 

========================================================================
Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
LinkedIn:                               http://ca.linkedin.com/in/rpjday
========================================================================

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Re: should "man feature_test_macros" mention _LARGEFILE_SOURCE?

[Michael Kerrisk (man-pages)]

On 03/19/2014 03:48 AM, Mike Frysinger wrote:
> On Tue 18 Mar 2014 15:46:43 Robert P. J. Day wrote:
>>   just noticed under /usr/include on my fedora rawhide system the
>> following:
>>
>> /usr/include/bits/environments.h:# define __ILP32_OFFBIG_CFLAGS	"-m32
>> -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64"
>> /usr/include/python3.3m/pyconfig-64.h:#define _LARGEFILE_SOURCE 1
>> /usr/include/features.h:   _LARGEFILE_SOURCE	Some more functions for 
> correct
>> standard I/O. /usr/include/features.h:#  undef _LARGEFILE_SOURCE
>> /usr/include/features.h:#  define _LARGEFILE_SOURCE	1
>> /usr/include/features.h:#ifdef _LARGEFILE_SOURCE
>> /usr/include/python2.7/pyconfig-64.h:#define _LARGEFILE_SOURCE 1
>>
>> but there's no mention of "_LARGEFILE_SOURCE" in "man
>> feature_test_macros". is that assumed to be implied by
>> _LARGEFILE64_SOURCE? it's not clear.
> 
> nope, none of the three LFS flags imply each other, nor should they.  they're 
> related, but orthogonal by design.
> 
> i could have sworn i saw a description of them in POSIX, but i can't find it 
> now.  the GNU C library manual covers it though:
> https://www.gnu.org/software/libc/manual/html_node/Feature-Test-Macros.html
> 
> here's a terse summary off the top of my head:
> 
> _LARGEFILE_SOURCE: expose prototypes for new funcs which POSIX got wrong 
> originally.  e.g. fseek & ftell utilize "long", so fseeko & ftello were added 
> which use "off_t".

Thanks, Mike. I'd forgotten those details.

So, as far as I can see, _LARGEFILE_SOURCE is largely of (ancient) historical
interest, so I don't think I'll bother adding it to the FTM(7) page.

Cheers,

Michael



> _LARGEFILE64_SOURCE: expose prototypes for 64-bit variant funcs w/out 
> affecting any existing funcs.  e.g. you now have fseeko64 & ftello64 which 
> take explicit off64_t types while fseeko and ftello are unchanged.  makes 
> sense when sizeof(off_t) == 4 && sizeof(off64_t) == 8.
> 
> _FILE_OFFSET_BITS: explicitly set the off_t size.  set it to 32 if you want 
> sizeof(off_t) == 4, or set it to 64 if you want sizeof(off_t) == 8.
> 
> in the ideal world, _FILE_OFFSET_BITS should default to 64 and 
> _LARGEFILE_SOURCE should default to defined.  in our crap world, apps should 
> be always building with these in their CPPFLAGS.
> -mike
> 


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Re: should "man feature_test_macros" mention _LARGEFILE_SOURCE?

[Mike Frysinger]

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On Wed 19 Mar 2014 14:37:51 Michael Kerrisk wrote:
> On 03/19/2014 03:48 AM, Mike Frysinger wrote:
> > On Tue 18 Mar 2014 15:46:43 Robert P. J. Day wrote:
> >>   just noticed under /usr/include on my fedora rawhide system the
> >> 
> >> following:
> >> 
> >> /usr/include/bits/environments.h:# define __ILP32_OFFBIG_CFLAGS	"-m32
> >> -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64"
> >> /usr/include/python3.3m/pyconfig-64.h:#define _LARGEFILE_SOURCE 1
> >> /usr/include/features.h:   _LARGEFILE_SOURCE	Some more functions for
> > 
> > correct
> > 
> >> standard I/O. /usr/include/features.h:#  undef _LARGEFILE_SOURCE
> >> /usr/include/features.h:#  define _LARGEFILE_SOURCE	1
> >> /usr/include/features.h:#ifdef _LARGEFILE_SOURCE
> >> /usr/include/python2.7/pyconfig-64.h:#define _LARGEFILE_SOURCE 1
> >> 
> >> but there's no mention of "_LARGEFILE_SOURCE" in "man
> >> feature_test_macros". is that assumed to be implied by
> >> _LARGEFILE64_SOURCE? it's not clear.
> > 
> > nope, none of the three LFS flags imply each other, nor should they. 
> > they're related, but orthogonal by design.
> > 
> > i could have sworn i saw a description of them in POSIX, but i can't find
> > it now.  the GNU C library manual covers it though:
> > https://www.gnu.org/software/libc/manual/html_node/Feature-Test-Macros.htm
> > l
> > 
> > here's a terse summary off the top of my head:
> > 
> > _LARGEFILE_SOURCE: expose prototypes for new funcs which POSIX got wrong
> > originally.  e.g. fseek & ftell utilize "long", so fseeko & ftello were
> > added which use "off_t".
> 
> Thanks, Mike. I'd forgotten those details.
> 
> So, as far as I can see, _LARGEFILE_SOURCE is largely of (ancient)
> historical interest, so I don't think I'll bother adding it to the FTM(7)
> page.

would be nice to document it ... i tend to get more confused when something is 
left out entirely even if it was done on purpose.  especially since it'd give 
us the opportunity to discourage people from using it and drive people towards 
the One True Way when it comes to LFS flags.
-mike

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Re: should "man feature_test_macros" mention _LARGEFILE_SOURCE?

[Michael Kerrisk (man-pages)]

On 03/19/2014 08:15 PM, Mike Frysinger wrote:
> On Wed 19 Mar 2014 14:37:51 Michael Kerrisk wrote:
>> On 03/19/2014 03:48 AM, Mike Frysinger wrote:
>>> On Tue 18 Mar 2014 15:46:43 Robert P. J. Day wrote:
>>>>   just noticed under /usr/include on my fedora rawhide system the
>>>>
>>>> following:
>>>>
>>>> /usr/include/bits/environments.h:# define __ILP32_OFFBIG_CFLAGS	"-m32
>>>> -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64"
>>>> /usr/include/python3.3m/pyconfig-64.h:#define _LARGEFILE_SOURCE 1
>>>> /usr/include/features.h:   _LARGEFILE_SOURCE	Some more functions for
>>>
>>> correct
>>>
>>>> standard I/O. /usr/include/features.h:#  undef _LARGEFILE_SOURCE
>>>> /usr/include/features.h:#  define _LARGEFILE_SOURCE	1
>>>> /usr/include/features.h:#ifdef _LARGEFILE_SOURCE
>>>> /usr/include/python2.7/pyconfig-64.h:#define _LARGEFILE_SOURCE 1
>>>>
>>>> but there's no mention of "_LARGEFILE_SOURCE" in "man
>>>> feature_test_macros". is that assumed to be implied by
>>>> _LARGEFILE64_SOURCE? it's not clear.
>>>
>>> nope, none of the three LFS flags imply each other, nor should they. 
>>> they're related, but orthogonal by design.
>>>
>>> i could have sworn i saw a description of them in POSIX, but i can't find
>>> it now.  the GNU C library manual covers it though:
>>> https://www.gnu.org/software/libc/manual/html_node/Feature-Test-Macros.htm
>>> l
>>>
>>> here's a terse summary off the top of my head:
>>>
>>> _LARGEFILE_SOURCE: expose prototypes for new funcs which POSIX got wrong
>>> originally.  e.g. fseek & ftell utilize "long", so fseeko & ftello were
>>> added which use "off_t".
>>
>> Thanks, Mike. I'd forgotten those details.
>>
>> So, as far as I can see, _LARGEFILE_SOURCE is largely of (ancient)
>> historical interest, so I don't think I'll bother adding it to the FTM(7)
>> page.
> 
> would be nice to document it ... i tend to get more confused when something is 
> left out entirely even if it was done on purpose.  especially since it'd give 
> us the opportunity to discourage people from using it and drive people towards 
> the One True Way when it comes to LFS flags.

Fair enough. I added the following:

       _LARGEFILE_SOURCE
              This macro was historically used to expose certain func‐
              tions   (specifically   fseeko(3)  and  ftello(3))  that
              address  limitations  of  earlier  APIs   (feek(3)   and
              ftell(3))  that  use  long  int  for file offsets.  This
              macro is implicitly defined if _XOPEN_SOURCE is  defined
              with a value greater than or equal to 500.  New programs
              should not employ this macro; defining _XOPEN_SOURCE  as
              just  described  or  defining _FILE_OFFSET_BITS with the
              value 64 is the preferred mechanism to achieve the  same
              result.

Cheers,

Michael


-- 
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Linux/UNIX System Programming Training: http://man7.org/training/
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