OpenZFS 8070 Add some ZFS comments

[bunder2015]

Authored by: Alan Somers asomers@gmail.com
Reviewed by: Yuri Pankov yuri.pankov@gmail.com
Reviewed by: Matthew Ahrens mahrens@delphix.com
Approved by: Robert Mustacchi rm@joyent.com
Ported-by: bunder2015 omfgbunder@gmail.com

OpenZFS-issue: https://www.illumos.org/issues/8070
OpenZFS-commit: openzfs/openzfs@40713f2

Description

Porting some changes from the OpenZFS tracker

Motivation and Context

How Has This Been Tested?

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)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commit messages are properly formatted and contain Signed-off-by.
• Change has been approved by a ZFS on Linux member.

[mention-bot]

@bunder2015, thanks for your PR! By analyzing the history of the files in this pull request, we identified @behlendorf, @ahrens and @grwilson to be potential reviewers.

[dinatale2]

Patch LGTM. Please fix the commit message.