SBFS version two adds directories out of space each entry had already set
aside: two of the four reserved bytes become a parent, and one of the seven
spare flag bits says an entry is a directory. The entry is still thirty two
bytes, so it still divides two hundred and fifty six and still never straddles
a block, and nothing in the block layer knows anything happened.
A directory is an entry with no blocks. That is what keeps the flat array of
entries the whole allocation map, which is the property the format is built
on: with files laid down contiguously, every block is inside some entry's
range or it is not, and an entry with no range is in nobody's way. There is
still no allocation table to consult and none to keep right.
THE PARENT IS AN INDEX PLUS ONE, so zero means the root. A version one disk has
zeroes in those bytes, and "in the root" is exactly where every file on a flat
disk is - so a version one image is already a valid version two image, with
nothing to convert and no tool to convert it with.
A disk is at the lowest version that describes what is on it. format makes a
version one disk and mkdir is what raises it, so everything built here stays
readable by a reader that has never heard of a directory right up until it
really does have one. That is what lets this land before the machine knows
anything: the whole existing suite passes untouched.
The tool gains mkdir and rmdir, and list, put, get and delete take paths. list
also now reports entries used against entries available, because a disk has two
ceilings and the entry one is the one nobody notices until it bites.
rmdir refuses a directory with anything in it, and that is not politeness:
parents are entry indices, a freed index gets handed out again, and the
children of a removed directory would reappear inside whatever took its place.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
AnachronautandClaude Opus 5
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