OK, let's do the background... on Unix systems where by default off_t is
a "long", a 32-bit integer, there are two different ways to get "large
file" support, i.e. the ability to manipulate files bigger than 2Gb:
1) you compile using -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64. This
makes sys/types.h expose off_t as a "long long", a 64-bit integer, and
changes the size of a few other types too. The C library headers
automatically arrange to expose a correct implementation of functions
like lseek() which take off_t parameters.
2) you compile using -D_LARGEFILE64_SOURCE, and use what is called the
"transitional" interface. This means that the system headers expose a
new type, "off64_t", which is a long long, but the size of off_t is not
changed. A bunch of new functions like lseek64() are exposed by the C
library headers, which take off64_t parameters in place of off_t.
Perl built with -Duselargefiles uses approach (1).
APR HEAD uses (2) by default. APR 0.9 does not by default use either
approach, but random users can take a httpd-2.0.49 tarball, and do:
export CPPFLAGS="-D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64"
./configure
to build a copy of apr/httpd which uses approach (1), though this isn't
really a supported configuration.
The problem that mod_perl has to work around is when you take a package
built with approach (1), i.e. Perl, and any package which was *not*
built with (1), i.e. APR, and want to interface between them. [1]
So what you want to know is whether APR was built using approach (1) or
not. APR_HAS_LARGE_FILES in HEAD just tells you whether APR was built
using approach (2) or not, which isn't useful in solving this problem.
Does that make sense?
joe
[1]: In some cases, it may be OK to interface between packages which use
(1) and packages which use (2). APR HEAD is currently not such a case,
since the size of apr_ino_t is still changing when _FILE_OFFSET_BITS is
defined.
If you want to see how this matters, get some httpd function to do at
the very beginning of main():
printf("sizeof(request_rec) = %lu, sizeof(apr_finfo_t) = %ul",
sizeof(request_rec), sizeof(apr_finfo_t));
and then put the same printf in mod_perl somewhere, and see the
differences. This is why it is a really terribly silly idea to ever use
approach (1) in anything other than an entirely self-contained
application.
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