Remove zpl_revalidate

[snajpa]

This patch removes the need for zpl_revalidate altogether.

There were 3 main reasons why we used d_revalidate:

1. periodic automounted snapshots umount deferral
2. negative dentries created before snapshot rollback
3. stale inodes referenced by dentry cache after snapshot rollback

Periodic snapshots deferral solution introduces zfs_exit_fs function, which
is called as a part of ZFS_EXIT(zfsvfs_t) macro.

Negative dentries and stale inodes are solved by flushing the dcache for the
particular dataset on zfs_resume_fs call.

This patch also removes now unused HAVE_S_D_OP configure test.

Fixes #8774

Signed-off-by: Pavel Snajdr [email protected]

How Has This Been Tested?

Locally & together with PR #9414

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.

[behlendorf]

Thanks for splitting this out and addressing the review feedback. This looks good to me after a rebase, and ends up being a nice simplification which is great.

[behlendorf]

nit: Sorry to make you rebase this again, but as part of the ongoing refactoring we've moved these macros in to a platform specific include/os/linux/zfs/sys/zfs_znode_impl.h header. One nice upshot of this is it does provide us more flexibility in adding Linux specific logic to the macro.

[snajpa]

Done :)

[behlendorf]

@cyphar would you mind also reviewing this part of the larger overlayfs work.

[codecov]

Codecov Report

Merging #9549 into master will decrease coverage by 0.29%.
The diff coverage is 66.66%.

@@            Coverage Diff            @@
##           master    #9549     +/-   ##
=========================================
- Coverage   79.35%   79.06%   -0.3%     
=========================================
  Files         418      418             
  Lines      123686   123680      -6     
=========================================
- Hits        98157    97788    -369     
- Misses      25529    25892    +363

Flag	Coverage Δ
#kernel	79.7% <66.66%> (-0.08%)	⬇️
#user	66.84% <ø> (-0.68%)	⬇️

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[tcaputi]

@behlendorf I see you tagged me here for a review. I can take a look if you want, but to be honest I really don't know much about dentries yet. It might be better if we found someone who knew what they were looking at there.

[behlendorf]

@tcaputi no problem. I just wanted to tag you since I thought you might be interested in the changes related to rollback.

[cyphar]

👍 Removing ->d_revalidate solves one of the problems on the path to overlay-on-ZFS support. Assuming that the new invalidation handling is correct (it seems right to me, at least on a surface-level), this looks good overall. Thanks @snajpa.

[ahrens]

I think that this introduced a bug: #9587