I've pushed changes to my repository that address a few things you brought
up:
- compiler warnings addressed
- decompression memory allocated on heap rather than stack
- a couple optimizations for decompression speed
I'll take a closer look at the interaction with the NTFS-3g driver when I
have time.
On Tue, Sep 22, 2015 at 10:49 PM, Eric Biggers <ebigge...@gmail.com> wrote:
> Hi,
>
> "WOF compression" is as good as the other names. It still seems slightly
> wrong
> because WOF (the "Windows Overlay Filesystem Filter") is a more general
> feature,
> and this is actually the *second* compression technology that Microsoft has
> built on top of it (the first was "WIMBoot"). For now, I'll keep the code
> the
> way it is, using the "system compression" name. It could be that
> Microsoft will
> release more documentation for this.
>
> Yes, your reparse data indicates XPRESS4K compression (the fourth 32-bit
> little
> endian word is 0). FYI, here are the compressed sizes I get with the
> Silesia
> corpus (uncompressed size: 211,938,580 bytes total):
>
> LZNT1 (NTFS compression): 121,049,088 bytes
> XPRESS4K: 104,124,416 bytes
> XPRESS8K: 95,465,472 bytes
> XPRESS16K: 90,460,160 bytes
> LZX: 69,144,576 bytes
>
> Even though FUSE makes big reads, it would be nice to not have to allocate
> a
> decompression context for every read. That would avoid doing all of the
> following on a per-read basis:
> - open WofCompressedData attribute
> - allocate heap memory for ntfs_system_decompression_ctx
> - allocate heap memory for XPRESS or LZX
> - read chunk offsets from the compressed file's chunk table
>
> Having an external tool to create "system compressed" files, if people
> want that
> support, is probably the way to go. Probably that would be possible even
> with
> no changes in libntfs-3g.
>
> Eric
>
>
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