Hello!
I've discovered that it is possible to create files of size much larger than partition size.
I thought that this is JFS bug, so I've filed a bugreport against it at http://bugzilla.kernel.org/show_bug.cgi?id=4345
Detailed info and testcase program are provided there.
Later I've found that at least XFS and EXT3 filesystems have the same problem (though the resulting filesize is different for each fs). So the problem may be not in fs code but in some other piece of kernel.
Could kernel gurus please investigate the problem?
Your test case isn't writing a full file, it is only writing 4 bytes at various offsets (1^32, 1^40, 1^48, 1^56).
The filesystems you mention support files with "holes" in them, in otherwords they support gaps between data which don't take up any storage.
Even though your test case is creating a huge file, only a couple of bytes are written, the rest of the huge file doesn't take up any space.
The behaviour you're seeing isn't a bug...
Phillip Lougher
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