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Message-ID: <3FE2EA13.8020407@lml.ls.fi.upm.es>
Date: Fri, 19 Dec 2003 13:07:47 +0100
From: Manuel Collado <m DOT collado AT aaron DOT ls DOT fi DOT upm DOT es>
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Newsgroups: comp.os.msdos.djgpp
Subject: Re: Detecting system features
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To: djgpp AT delorie DOT com
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Eli Zaretskii wrote:
>>Date: Thu, 18 Dec 2003 13:13:51 +0100
>>From: Manuel Collado <m DOT collado AT aaron DOT ls DOT fi DOT upm DOT es>
>>Newsgroups: comp.os.msdos.djgpp
>>
>>
>>>>2. LFN support (I'm aware of _use_lfn. Any more?)
>>>
>>>What's wrong with _use_lfn?  If you have specific problems with it,
>>>please ask specific questions.
>>
>>Please see below.
> 
> I've read that, but I still don't understand why _use_lfn would not
> suffice.  I think that is what you ned.
> ...

Well, after reading the libc docs again I think _use_lfn will do the 
job. But the usage seems somehow tricky. I assume this is the relevant 
doc fragment:

===
Return Value
------------

If LFN APIs are supported and should be used, it returns 1, else 0.

Note that if the `_CRT0_FLAG_NO_LFN' bit is set, or `LFN' is set to `N'
or `n' in the environment, both `_use_lfn' and `_USE_LFN' will always
return 0 without querying the filesystem.  You can reset the
`_CRT0_FLAG_NO_LFN' bit at runtime to force filesystem to be queried.
===

So to detect the true LFN system capability one should:

- reset CRT0_FLAG_NO_LFN
- call _use_lfn
- restore CRT0_FLAG_NO_LFN to its previous value

Can this be done safely in the middle of a program execution? 
_CRT0_FLAG_NO_LFN is a component of _crt0_startup_flags, and this name 
suggest troubles if changes are intermixed with file (or other) 
operations. What if there are open files while querying for LFN support?

Thanks,
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