Test cancelling a removal in ZTS

[sdimitro]

This patch adds a new test that sanity checks cancelling a removal.

Signed-off-by: Serapheim Dimitropoulos serapheim@delphix.com

Description

A variation of this test has existed in DelphixOS for a while. It has helped detect bugs where there are faults in operations like forgetting to walk the ms_freeing or the ms_unflushed_frees trees from svr_allocd_segs when cancelling a removal. The variation that we had in DelphixOS was that instead of having zfs_removal_suspend_progress that just suspends removals right away (without potentially having done any copy whatsoever and thus having svr_allocd_segs empty to begin with) we had zfs_remove_max_bytes_pause which would pause removals AFTER having copied some data away from the removed device. zfs_removal_suspend_progress (ZoL) and zfs_remove_max_bytes_pause (DelphixOS) are in the same exact places in the source which makes me think that when upstreaming device removal to ZoL, people preferred the former over the latter. In any case, in order to "emulate"(/hack our way) zfs_remove_max_bytes_pause, we try to do enough writes in the device to be removed, so once the removal is issued we sleep for 1 second and then raise zfs_removal_suspend_progress to stop the removal mid-way.

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.

[codecov]

Codecov Report

Merging #9101 into master will decrease coverage by 0.29%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #9101     +/-   ##
=========================================
- Coverage   79.32%   79.03%   -0.3%     
=========================================
  Files         400      400             
  Lines      121640   121640             
=========================================
- Hits        96493    96139    -354     
- Misses      25147    25501    +354

Flag	Coverage Δ
#kernel	79.66% <ø> (-0.14%)	⬇️
#user	66.9% <ø> (-0.64%)	⬇️

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