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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Large files on 32 and 64 bits ystem
Date: Tue, 26 May 2009 03:22:42 -0700 (PDT)
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Date: 2009-05-26T03:22:42-07:00
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Olivier Scalbert wrote on comp.lang.ada:
> Ludovic Brenta wrote:
> > That line indicates that the GNAT run-time library delegates the write
> > to fwrite(3), so your question really boils down to whether the C run-
> > time library has support for large files or not. =A0What filesystem typ=
e
> > do you use on your machines? (I use XFS which supports files up to 8
> > exabytes :) )
>
> I use ext3.

In this filesystem, files can grow to 16 GiB to 2 TiB depending on
block size.

[1] explains how large file support works in GNU/Linux. Basically, a C
program supports LFS if it is compiled with the -D_FILE_OFFSET_BITS=3D64
preprocessor option on the command line. This changes the definition
of fopen(3), fwrite(3) et al to use 64-bit file offsets instead of the
default 32-bit file offsets.

Unfortunately, the GNAT run-time library directly imports these
functions from glibc without any preprocessor in between, so is
restricted to 32-bit file offsets, and so does not support large
files.

It would be an interesting project for a beginning GCC hacker to
implement LFS in libgnat. This would involve:
- wrapper functions in adaint.c that call fopen(3), fwrite(3), etc.
- compiling adaint.c with -D_FILE_OFFSET_BITS=3D64
- calling the wrappers instead of the glibc functions in
System.File_IO et al. (it may be a little bit tricky to import them
properly on all platforms, with and without LFS).

[1] http://www.suse.de/~aj/linux_lfs.html

--
Ludovic Brenta.