NAS-132930 / 24.10.2 / add get_name implementation for exports. (#16833)

[anodos325]

This fixes a serious performance problem with NFS handling of large directories, as the new get_name code is much more efficient than the default zfs_readdir. This is actually part of
20232ec in 2.3. But I've taken only the minimum code to implement get_name, and not the rest of the long name changes.

Reviewed-by: Alexander Motin [email protected]
Reviewed by: Brian Behlendorf [email protected]
Reviewed by: Brian Behlendorf [email protected]
Reviewed-by: Tony Hutter [email protected]

Motivation and Context

Description

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)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[bugclerk]

Jira URL: https://ixsystems.atlassian.net/browse/NAS-132930

[anodos325]

This is targeted fix for issue rather than backport of entire ZFS long name commit.

[bugclerk]

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