ZTS: new kstat helper

[robn]

[Sponsors: Klara, Inc., Wasabi Technology, Inc.]

Motivation and Context

Tests use a wide range of methods to get at kstat values. This is error prone, and usually ends up limiting the test to a single platform.

This came up again in #16947, and I decided to just fix it.

Description

libtest.shlib had a kstat helper that was barely used, I suspect in part because it was very limited in the kinds of kstats it could gather. This adds new functions to replace it, for each kind of thing that can have stats: global, pool and dataset. There's options in there to get a single stat value, or all values within a group.

Most importantly, the interface is the same for both platforms. This is quite complicated, but will be worth it when its very easy to use kstats from within test.

See comments at stop of kstat.shlib for the detail..

After that, all existing uses of kstats, through either the old kstat or get_arcstat helpers, or directly through /proc/spl/kstat/zfs or sysctl, have been updated to use the new functions.

Actually, almost all. I've left the procfs test suite for now, since it is explicitly testing the /proc/spl/kstat/zfs interface.

Mostly this has been a mechanical conversion, but some tests have been adjusted slightly to not assume things about kstat name structure or data format.

I have not looked closely, but this also might make it easier for some of the platform-specific tests to work everywhere. That's an exercise for the future.

How Has This Been Tested?

All modified tests have passed on Linux and FreeBSD.

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.

[amotin]

Thanks for doing this. Few issues I spotted:

[tonyhutter]

Nice cleanup!

I suspect future generations will re-implement get_arcstat as a helper function though. Did you consider keeping it in place but just doing?:

function get_arcstat # stat
{
	kstat arcstats.$1
}

[robn]

Alright, here's v2, dealing with some of the complications. Top post updated.

[robn]

I suspect future generations will re-implement get_arcstat as a helper function though. Did you consider keeping it in place but just doing?

I did at first (as you see, it's removed in a separate commit). It seemed not worth keeping - it did nothing of interest, but looked different to other things, inviting questions like "why is this special?" and "why aren't other things not special?"

I don't think anyone will bother implementing it, because there's nothing gained from doing so, and nothing in the existing code to even give the idea. But, if they do, at least it will work properly :)

[amotin]

Cool! Just few comments: