You can find some information in the Disk & File Recovery chapter of the QNX 4 Installation & Configuration guide. There’s another version – which looks suspiciously similar – in the Backing Up and Recovering Data chapter of the Neutrino User’s Guide.
I can’t find chapter “Backing Up and Recovering Data” in QNX 6.2.1 PE!
In chapter “Disk & File Recovery” I found indormation about
QNX4FS_FILE_USED and QNX4FS_FILE_LINK. All other flags are not documented!!!
I also heard that the QNX 4 System Architecture is very helpful on understanding the QNX4FS. Actually, the Linux QNX4fs driver was written based on the information from that book.