Further improve 'zpool labelclear' command

[martymac]

Hello,

That patch follows : #8500 to further improve the labelclear command.

It is an updated version of my my previous patch for OpenZFS :

openzfs/openzfs#424

Description

Basically, the patch adds the following :

• ability to clear a specific label (options -b, -e and -i)
• label invalidation using a single-byte modification (use -w to zeroe the label as before)
• option -ff to force invalidation even for invalid labels

How Has This Been Tested?

The patch has been tested on Debian 9 with a file-backed zpool.

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)
• Documentation (a change to man pages or other documentation)

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.

[ahrens]

I haven't often had need for zpool labelclear, but when I have, it's worked just fine. Personally, I don't see the use case for these expanded options, but maybe I just haven't run into enough weird situations :-). Can you elaborate on when this flexibility is needed? In the absence of additional input, I would be inclined to close this PR.

[martymac]

Hello Matthew,

Thanks for the update.

The original idea was :

• to avoid breaking an existing underlying filesystem by destroying the pool with minimal writes (in case of a mistake)
• to add flexibility by allowing manipulating specific labels only
  but there have been nearly no reaction to this patch so I presume I am the only one feeling this could be useful :p I have no special case in mind but just wanted to prevent our customers from destroying data by mistake.

If you think this is not worth updating that patch, feel free to close that PR.

Best regards,

Ganael.

[tonyhutter]

@martymac I have a PR (#12474) that adds a zpool labelclear -f --unsafe option to allow clearing the label on active pools. I'm not clear if that's the same as your -ff option. Just wanted to give you a heads-up.

[martymac]

Hello @tonyhutter,

Thanks !

Our patches do not act on the same things : your patch focuses on allowing clearing valid labels from active pools while mine allows clearing invalid labels (see: 7c62008#diff-8f1a174ac28c3b0269336b69d4cbd5d057fb6e65b62321f54c4dce5c8ab2d14bR1168 and 7c62008#diff-4d1ee8409af09d86d05eb396741ef7c3a1ba2cad77a58777164c4866084fb140R177). They can be seen as complementary if we really want to avoid using dd to clear labels.

Cheers,

Ganael.

[ahrens]

I think that we would need to find a specific use case for this, otherwise we'll close this PR.

[martymac]

Hello Matthew,

As there has been no interest shown in the features brought by the patch, I presume we can close that PR.

Best regards,

Ganael.

[ahrens]

Thanks Ganael, if you have other ideas for how to improve OpenZFS please let us know by opening a PR or discussing them at our monthly meeting.