Roland D-20 filesystem updates can exceed bounds and corrupt filenames

[rjburrows]

Summary

Direct filesystem updates on Roland D-20 disks can select out-of-bounds blocks and rewrite existing filenames incorrectly.

Reproduction

fluxengine putfile -c rolandd20 -f drive:1 \  -l TESTSND.333 -p TESTSND2.333

The disk uses the rolandd20 profile and a Greaseweazle-connected 80-track PC drive.

Observed behavior

1. The initial write failed with:

Error: invalid filesystem: sector 972 is out of bounds

The D-20 format has 78 tracks × 12 sectors, so sector 972 is outside its filesystem.

2. After the allocation issue was worked around, a directory rewrite changed existing names while retaining their original byte counts and file data:

TESTALL.111  -> TESTALL.11.1
TESTSONG.222 -> TESTSONG.2.22
TESTSND.333  -> TESTSND.33.3
TESTRHY.444  -> TESTRHY.44.4

The newly added name TESTSND2.333 was correct.

Likely causes and proposed fixes

Allocation bounds

RolandFsFilesystem::init() derives its allocation count from the drive-probed sector count. A physical probe can expose extra tracks that are not part of the D-20 filesystem, allowing allocation to target an invalid block.

For the current Roland GCRDOS layout, allocation should be bounded by the tracks arranged around the directory track:

_filesystemBlocks = _config.directory_track() * 2;
_midBlock = _config.directory_track();

A more general option would be an explicit filesystem-block-count field in RolandFsProto.

Filename encoding

RolandDirent::filename should remain the human-readable name. It is currently sometimes pre-mangled before directory serialization, while existing entries are human-readable after mounting. Rewriting then puts the literal dot in the fixed 13-byte on-disk field, shifting the extension when the disk is read again.

Suggested changes:

// putFile
auto de = std::make_shared<RolandDirent>(path.front());

// moveFile
de->rename(newName.front());

// rewriteDirectory
const std::string mangledFilename = mangleFilename(de->filename);
bw.append(mangledFilename);
bw.pad(13 - mangledFilename.size(), '_');

This keeps file data and directory metadata separate and preserves names through directory rewrites.