Side-project feature request for 'hammer mirror-*' functions

[Thomas Nikolajsen]

>If you do a hammer mirror-copy or hammer mirror-stream
>to a target HAMMER filesystem the code checks that the target is a PFS
>slave with the same shared UUID as the master's UUID.
>
>I want a feature that asks the user whether he wants to create a
>conforming PFS on the target at that point, if the target directory
>does not exist, instead of exiting with an error.

Ideas for more automagic:
 - It should also make a null mount for new PFS, as this is recommended way to use PFSs.
 - It should set snapshots PFS option
(maybe `hammer pfs-slave' should just set this option by default;
a unique <name> could be derived from PFS name)

Then an already setup `hammer cleanup' will also manage new PFS.

Or, do we need to snapshot/prune/reblock a PFS slave,
if same retension policy as master is intended?

 -thomas