Direct filesystem updates ignore the changed-track list and attempt a full-disk write

[rjburrows]

Summary

FluxSectorInterface::flushChanges() gathers only modified tracks and passes them to writeDiskCommand(), but writeDiskCommand() discards that list and recreates a list of every logical track in the layout.

This makes a direct filesystem update attempt to rewrite the entire disk, even though only the modified tracks have been loaded.

Reproduction

A direct Roland D-20 filesystem update:

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

After reading the directory, FluxEngine attempted a full-disk write and failed before writing because the untouched tracks were absent from the in-memory image:

Error: sector 0.0.0 is missing from the image

This appears generic to direct filesystem modifications, not Roland-specific.

Cause

The overload with a location argument currently reconstructs all logical locations:

auto sectorLocations =
    std::ranges::views::keys(diskLayout.layoutByLogicalLocation);
auto chs = std::vector(sectorLocations.begin(), sectorLocations.end());

It then writes chs, ignoring the supplied list.

Proposed fix

Use the supplied logical-location list:

void writeDiskCommand(
    const DiskLayout& diskLayout,
    const Image& image,
    Encoder& encoder,
    FluxSinkFactory& fluxSinkFactory,
    Decoder* decoder,
    FluxSource* fluxSource,
    const std::vector<CylinderHead>& logicalLocations)
{
    if (fluxSource && decoder)
        writeTracksAndVerify(
            diskLayout, fluxSinkFactory, encoder,
            *fluxSource, *decoder, image, logicalLocations);
    else
        writeTracks(
            diskLayout, fluxSinkFactory, encoder,
            image, logicalLocations);
}

The existing overload with no list can continue to construct and pass all logical tracks for full-disk write operations.

[davidgiven]

Thanks --- that's fixed in the new Java version: https://github.com/davidgiven/fluxengine/blob/java/java/com/cowlark/fluxengine/algorithms/ReadWriteFluxOperation.java#L828