support typed restriction of lv creation to specific pvs

[sielicki]

lvcreate accepts a trailing argument [PhysicalVolumePath[:PE[-PE]]...] which can be used to restrict logical volume creation to specific physical volume(s).

This is the only really sensible way to create tiered storage for eg: cache creation, #421, but it can be useful in other complex scenarios.

Nothing prevents this from being used today via extraArguments, but it would drop types, ie: would rely on just using the same device string in extraArguments to pv creation as one used for the lv.

[iFreilicht]

I don't quite understand what the final API is supposed to look like. Could you show an example of what you would like to add to a configuration?

Also, are you sure this is possible right now? extraArgs does exist on lvm_vg and is passed to lvmcreate, but lvm_pv does not have an option like that. Would adding this already be sufficient?

[TheSlothyBR]

I don't quite understand what the final API is supposed to look like. Could you show an example of what you would like to add to a configuration?

Also, are you sure this is possible right now? extraArgs does exist on lvm_vg and is passed to lvmcreate, but lvm_pv does not have an option like that. Would adding this already be sufficient?

Based on the lvm documentation, the very last argument passed to the command "lvcreate" should be the physical volume(s) it will be created from. Maybe it can be done by adding something like ${lib.optionalString } right after this line, using the values passed to here to generate an enum for the option?

[sielicki]

After running into performance issues with any complex layout on the system where I originally wanted this, I have no personal interest in this use-case anymore and would leave it up to others to comment on what schema would make sense.

If this is a rare-enough option that it shouldn't be in the spec in the first place, might just be worth commenting with an example of how to use hooks to accomplish this and closing.

Thank you for your time.