add support for the backup catalog

[keithgh1]

Now that we have support for primary catalog processing, it would be nice, especially when there's corruption present within that catalog, to be able to process the backup catalog.

The primary catalog is stored at the beginning of the first backup floppy. The backup catalog is only written in certain cases and normally is written to the last disk of the backup. The task requires

• Identifying the overall combined file offset the backup catalog is located. The likely easiest way is to located the "Qbc2" indicator, possibly searching from the bottom up. The offset to the start of the dirfib entries is approximately 222.
• Modifying the command line argument to accept a backup option. It defaults to primary now, and backup just reports "unsupported"
• Determining which functions, if any, have to be modified to support passing an argument for a new offset.
• The existing functions should process it normally once started in the right location.

[merlin555]

With this backup, the last diskette is not required for the catalog. But I remember that I already had certain backups with QB.

[keithgh1]

Right. Definitely not required.

They give you a second copy of the catalog at the end, in case your primary has been corrupted.

[merlin555]

Understand. Good to know.