layout.txt

Total file size (including headers and indexes) can't be larger than 2**64.

Everything except the HEAD section (including the compression and
encryption data, if any) is encrytpted using the encryption method.

Only file data is compressed.

Besides the header part of the HEAD section that has to be at the
beginning of a file, everything else can be stored in any arbitrary
order since every reference is done via absolute offsets from the
beginning of the file.


HEAD

 0-8  | magic
 8-16 | root inode offset
16-17 | version major
17-18 | version minor
18-19 | compression type
19-20 | encryption type
20-32 | <padding> // checksum?

If major version differs, then incompatible on-disk format
If minor version differs, then possibly new values for some types, but no format changes.

encryption types

0 = NONE
1 = ChaCha20 (stream mode, no AEAD)

compression types

0 = NONE

If the encryption or compression layers require additional data, they
should make sure that some space is unreserved in the image and store
their data there.

FILEDATA

Files are optionally dedupped, then compressed, then encrypted

Each encryption and compression is done per-file so that they can be
easily retrived individually


INODE

 0-8  | parent inode
 8-16 | offset
16-24 | size
24-25 | inode type
25-32 | <padding>

padding may be allocated to some use in the future, for now, the value
of the bytes stored there do not matter.

DIRENTS

 0-8  | name offset
 8-16 | inode offset

dirents for a single directory MUST be contiguous and sorted by
name. The names can be stored before or after, in any order. The names
should not include '.' or '..' since those entries can be sythesized
from other data.

Name are stored with a terminating NUL byte since filenames can't
contain NUL. Other than that name are arbitry byte strings and don't
have to be valid in any specific text encoding.