Sparsely populated, just the way I like it

The NTFS filesystem has support for sparse files, but this has to be specially enabled when creating a file. I was originally linked to a blog post on the idea, but unfortunately the license pretty much forbids me from using that code.

So I spent most of yesterday evening and this morning googling API documentation and eventually came up with a fairly basic implementation of sparse file support. The only two operations supported are:

1. Creating a sparse file
2. Setting the size of the sparse data.

The benefits of this are seen only on the NTFS filesystem, but what it gives you is the ability to write pieces at arbitrary places in the file without having to preallocate up to that point. There's a bit of overhead, but other than that you only use up the space which you've actually written to, i.e. only the pieces which have been downloaded.

Finally, if you don't have an NTFS filesystem supporting sparse files, you will not be affected by this. Those of you on HFS+ can never get this support, and those of you on ext3, I'm unsure how to enable sparse files. I think it's enabled by default, but if not, any recommendations on setting this up would be appreciated.