[Pearl1594]

Description

This PR adds support for incremental volume snapshots for CLVM-NG

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)
• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Enhancement (improves an existing feature and functionality)
• Cleanup (Code refactoring and cleanup, that may add test cases)
• Build/CI
• Test (unit or integration test code)

Feature/Enhancement Scale or Bug Severity

Feature/Enhancement Scale

• Major
• Minor

Screenshots (if appropriate):

How Has This Been Tested?

• 5-deep ROOT incremental chain with data written between snapshots - File-level: write and change files in the guest across three snapshots; revert to the first incremental and to a mid-chain incremental, files as expected
• Incremental snapshot on a stopped VM (ROOT and data volumes)
• Incremental snapshot on a running VM with the guest writing
• Restore snapshots to new volumes, byte-identical to the source
• Create volume from snapshot; template from snapshot, VM boots
• Delete a middle snapshot: goes Hidden, chain intact
• Delete the last child
• Live VM migration, then incremental snapshot
• Volume migration across VGs, then incremental snapshot and restore
• Revert a data volume, then snapshot (new full after revert)
• ROOT revert after VM migration
• snapshot.delta.max chain rollover
• Live resize, then snapshot and restore
• Hourly snapshot policy
• Snapshot right after boot with the guest writing, then a stopped incremental identical to the LV
• Forced stop VM, restart on another host, then incremental snaps

How did you try to break this feature and the system with this change?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 3.70%. Comparing base (68cff97) to head (d8a5adb).
⚠️ Report is 41 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (68cff97) and HEAD (d8a5adb). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (68cff97)	HEAD (d8a5adb)
unittests	1	0

Additional details and impacted files

@@              Coverage Diff              @@
##               main   #14483       +/-   ##
=============================================
- Coverage     20.21%    3.70%   -16.51%     
=============================================
  Files          6426      493     -5933     
  Lines        580181    42558   -537623     
  Branches      71033     8063    -62970     
=============================================
- Hits         117287     1578   -115709     
+ Misses       450180    40751   -409429     
+ Partials      12714      229    -12485     

Flag	Coverage Δ
uitests	3.70% <ø> (+0.01%)	⬆️
unittests	?

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