lvm: add bd_lvm_vgchange function

[accumulator]

There's currently no way to access vgchange functionality through BD.

Missing

• bd_lvm_vgchange function(s)
• VG attributes in BDLVMVGdata struct
• VG tags in BDLVMVGdata struct
• additional VG properties like activationmode, max number of LVs, max physical volumes, PV metadata copies etc in BDLVMVGdata struct

[vojtechtrefny]

We plan to release 3.0 in few months, so it would be a good opportunity to change some of the structs (because it's an ABI change). Can you list attributes you'd like to access using libblockdev and the vgchange functionality you need? I'd like to avoid adding all the vg properties and adding ~10 new "vgchange" function if noone needs these.

Also we are using the LVM DBus API (https://github.com/tasleson/lvm-dubstep/blob/master/api.md) so if it doesn't provide the API we need, it needs to be added there first.

[accumulator]

I left this bugreport/feature request during my investigation into porting KVPM away from the DWAR (Deprecation Without A Replacement) of liblvm2app. KVPM is a LVM management tool that accesses basically all features of LVM.

Since both the DBus API and libblockdev do not provide access to most LVM functionality yet, I've parked this idea for now, so it's up to you to decide if you think it's worth it to include parts or all of the LVM feature set in this ABI change opportunity.