zhack: Fix importing large allocation profiles on small pools

[0mp]

This patch fixes a segmentation fault in zhack metaslab leak which might be triggered by feeding zhack with a fragmentation profile that's exported from a pool larger than the target pool.

Fixes: 8f15d2e
Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.

Motivation and Context

Currently, if you export an allocation profile from pool A and you import that allocation profile into pool B, then zhack will segfault if pool A was larger than pool B. This patch fixes that.

Description

The way this fix works is that the allocation profile's allocations targeting metaslabs, which are not present in the pool, are ignored.

How Has This Been Tested?

I've tested this manually by importing the allocation profile of a larger pool into a smaller pool.

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.