First Impression: dvd_align.c is empty....
This is why I refer to it as a *framework*. As already mentioned real code will be implemented as time permits. So far regression tests can be and *were* made by simply modifying the return value from DVDLayerAlignment() and observing whole DVD-Video contents sliding toward the end of the resulting image, yet keeping layout sane.
For the rest, I'll have to check and need more time....
Few human-readable comments. Note that proposed code adds extra integrity check by comparing scheduled extent for the file to be written with current value of last_written_extent ("out of sync" fatal condition). As 'else' clause to the this check it automatically pads previous file (or directory) to current last_written_extent. The latter effectively obsoletes the current padding code. Finally note that by moving blk[SECTOR_SIZE] from stack to .bss I address potential privacy issue by padding with *zeros* and not current stack contents. A.