mmbackup dry-run mode

The mmbackup command is intended for highly-scalable backups of IBM Spectrum Scale (SS) filesystems to one or more IBM Spectrum Protect (SP) servers using the SS policy engine to identify files and the SP client software to send them to SP. The command attempts to mimic the behavior of the SP client include/exclude list but has many subtle divergences from that behavior that make it hard to know what files are going to be included or excluded for backups, and which management classes they will be bound to if included. The page https://www.ibm.com/support/pages/considerations-using-ibm-spectrum-protect-include-and-exclude-options-ibm-spectrum-scale-mmbackup-command describes all of these complexities, and is hard to comprehend even with simple rule sets. While the SP client has a "PREVIEW BACKUP" command, this only says what the SP client would backup on its own; mmbackup might very well behave differently and does not have its own preview functionality.

To aid in rule development, it would be very helpful if there were a dry-run mode to mmbackup. There is an undocumented --notsm switch which sort of is a dry-run mode, but it completely ignores SP and uses a default-include policy. Ideally, mmbackup would still interface with SP to get an include/exclude list and translate it into a SP policy rule, leave the files that would be passed to SP clients intact, and then exit. An administrator could then look at the output files and determine which files would be included and their management classes, and which files would be excluded and expired from backups.

Currently, the only option is to let mmbackup start backing up, quickly copy the temporary data in .mmbackupCfg and .mmSharedDir, and hope you can cancel the backup before it does any damage like irrevocably expiring data from SP.