Restrict cloning with different properties

[amotin]

While technically its not a problem to clone between datasets with different properties, it might create expectation of new properties being applied during data move, while actually it won't happen. For copies and checksum it may mean incorrect safety expectations. For dedup, compression and special_small_blocks -- performance and space usage. New zfs_bclone_strict_properties tunable controls it.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Quality assurance (non-breaking change which makes the code more robust against bugs)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[robn]

Yeah, that's fair. I had thought about arguing to disallow it only if the result would be worse (eg source has higher copies= than dest), especially after seeing that its strict by default. But I'm not going to, because this is a small and easy-to-understand change, chooses safety every time, and for most people probably won't come up anyway. Works for me!

[behlendorf]

Yes, I'm good with this. However, instead of removing the block_diff* tests let's use this as an opportunity to test that the new option works by setting zfs_bclone_strict_properties=0 for these tests.