When I first made VolumeVerifier, I figured that the distinction
between an unsigned ticket and an unsigned TMD was a technical
detail that users would have no reason to care about. However,
while this might be true for discs, it isn't equally true for
WADs, due to the widespread practice of fakesigning tickets to
set the console ID to 0. This practice does not require
fakesigning the TMD (though apparently people do it anyway,
at least sometimes...), and the presence of a correctly signed
TMD is a useful indicator that the contents have not been
tampered with, even if the ticket isn't correctly signed.
It is my opinion that nobody should use NKit disc images without
being aware of the drawbacks of them. Since it seems like almost
nobody who is using NKit disc images knows what NKit is (hmm, now
how could that have happened...?), I am adding a warning to Dolphin
so that you can't run NKit disc images without finding out about the
drawbacks. In case someone really does want to use NKit disc images,
the warning has a "Don't show this again" option. Unfortunately, I
can't retroactively add the warning where it's most needed:
in Dolphin 5.0, which does not support Wii NKit disc images.
This could cause read errors if chunks were laid out a certain
way in the file and the whole chunk wasn't being read at once.
Should fix https://bugs.dolphin-emu.org/issues/12184.
PURGE isn't especially useful, while requiring some annoying
special handling in the file format. If you want no compression,
use NONE. If you want fast compression, use Zstandard.
Gets rid of the need to seek to the end of the file
when opening a file.
The downside of this is that we waste a little space,
since we can't know in advance exactly how much
space the compressed parts of the headers will need.
This is useful for the way Dolphin scrubs Wii discs.
The encrypted data is what gets zeroed out, but this
zeroed out data then gets decrypted before being stored,
and the resulting data does not compress well.
However, each block of decrypted scrubbed data is
identical given the same encryption key, and there's
nothing stopping us from making multiple group entries
point to the same offset in the file, so we only have
to store one copy of this data per partition.
For reference, wit zeroes out the decrypted data,
but Dolphin's WIA writer can't do this because it currently
doesn't know which parts of the disc are scrubbed.
This is also useful for things such as storing Datel discs
full of 0x55 blocks (repesenting unreadable blocks)
without compression enabled.
Shawn Hoffman