If on Windows, we require the 'largefile' resource.
If not on Windows, we use a test that actually writes a byte beyond
the 2BG limit -- seeking alone is not sufficient, since on some
systems (e.g. Linux with glibc 2.2) the sytem call interface supports
large seek offsets but not all filesystem implementations do.
Note that on Windows, we do not use the write test: on Win2K, that
test can take a minute trying to zero all those blocks on disk, and on
Windows our code always supports large seek offsets (but again, not
all filesystems do). This may mean that on Win95, or on certain other
backward filesystems, test_largefile will *fail*.
1. That seeking beyond the end of a file increases the size of a file.
2. That files so extended are magically filled with null bytes.
I find no support for either in the C std, and #2 in particular turns out
not to be true on Win32 (you apparently see whatever trash happened to be
on disk). Left #1 intact, but changed the test to check only bytes it
explicitly wrote. Also fiddled the "expected" vs "got" failure reports
to consistently use repr (%r) -- they weren't readable otherwise.
Curious: the MS docs say stati64 etc are supported even on Win95, but
Win95 doesn't support a filesystem that allows partitions > 2 Gb.
test_largefile: This was opening its test file in text mode. I have no
idea how that worked under Win64, but it sure needs binary mode on Win98.
BTW, on Win98 test_largefile runs quickly (under a second).
catch IOError as well as OverflowError. I found that on Tru64 Unix
this was raised; probably because the OS (or libc) doesn't support
large files but the architecture is 64 bits!
Guido van Rossum
Tim Peters
Barry Warsaw
Fred Drake
Trent Mick