zvol_wait script should ignore partially received zvols

[pzakha]

Partially received zvols won't have links in /dev/zvol.

Motivation and Context

The zfs-volume-wait service is timing out when there are partially received zvols since they won't have links and /dev/zvol until the zfs receive has completed. As a matter of fact, I believe block device minor nodes won't even be created for them until then.

Description

While a zfs receive is in-progress for a given zvol, it will have a resume token. However, if a zvol already existed before the receive, it should have a block device minor node and a /dev link. In such a case, the receive will be an incremental receive and there will be an invisible clone at <zvol_name>/%recv for the duration of the receive -- we can check if that dataset exists to determine whether or no the zvol should have a dev link.

How Has This Been Tested?

• Ran this on a system with partially received zvols, using both incremental and non-incremental partial receives, and made sure that it behaves as expected.
• Delphix internal testing: ab-pre-push

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.

[pzakha]

cc: @pcd1193182 @jgallag88 @grwilson @shartse @prakashsurya

[codecov]

Codecov Report

Merging #9260 into master will decrease coverage by 1.52%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #9260      +/-   ##
==========================================
- Coverage   79.36%   77.83%   -1.53%     
==========================================
  Files         400      389      -11     
  Lines      122035   121562     -473     
==========================================
- Hits        96848    94617    -2231     
- Misses      25187    26945    +1758

Flag	Coverage Δ
#kernel	77.43% <ø> (-2.43%)	⬇️
#user	66.11% <ø> (-1.15%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9f5c1bc...e482b37. Read the comment docs.