#1687 Dynamic VHD parser: real vs supposed behavior

[maxpat78]

Let’s assume we have a Dynamic VHD and we fill a specific sector N of the emulated disk with a pattern.

Subsequently, in the bitmap related to the VHD block containing sector N, we alternately set the bit corresponding to N to 0 and 1 before attempting to read N back.

At this point, we discover that the behavior of Windows 11 (and, likely, previous editions) differs from 86box (MiniVHD library) and 7-Zip.

Windows 11, in fact, ignores the bitmap and retrieves the physical sector from the block regardless, returning the original pattern.

MiniVHD and 7-Zip, on the other hand, honor the VHD 1.0 specification and, finding the bit set to zero, return an empty (zeroed-out) sector.

This might be a bug, or another chance to consider whether to prioritize specs over real-world user behavior.