perf(zfs): optimise pool listing for pools with many datasets

[lowjoel]

Pull Request template

Please, go through these steps before you submit a PR.

Why is this PR required? What issue does it fix?:

Restricting the zfs list command to depth 1 saves a lot of time for pools with many datasets/zvols.

In my case, before:

$ time zfs list -s name -o name,guid,available -H -p >/dev/null
real    0m3.853s
user    0m0.171s
sys     0m3.539s

After:

$ time zfs list -d 1 -s name -o name,guid,available -H -p >/dev/null
real    0m0.027s
user    0m0.002s
sys     0m0.026s

What this PR does?:

This adds the -d 1 argument to ListZFSPool.

Does this PR require any upgrade changes?:

No, this change should be backward compatible.

If the changes in this PR are manually verified, list down the scenarios covered::

Any additional information for your reviewer? :
Mention if this PR is part of any design or a continuation of previous PRs

[niladrih]

Requires #443

[niladrih]

Requires #443

[lowjoel]

@niladrih should I rebase?

[niladrih]

@niladrih should I rebase?

Yes, you'd have to rebase. But you might want to hold on to this for now. I'll raise a PR to upgrade the Go version. You can rebase then..

[lowjoel]

@niladrih thanks, let me know when that's ready.

[niladrih]

@lowjoel -- Now would be a good time to rebase your PR.

[lowjoel]

@niladrih done, let's see the actions go through!

[avishnu]

Lgtm

[niladrih]

@lowjoel does this issue seem relevant here openzfs/zfs#5594?

[niladrih]

LGTM

[lowjoel]

@lowjoel does this issue seem relevant here openzfs/zfs#5594?

The behaviour described in the issue, i.e. -H modifies the depth argument, doesn't seem true in ZFS 2.1.11. Does it look that way in your testing?

[niladrih]

@lowjoel does this issue seem relevant here openzfs/zfs#5594?

The behaviour described in the issue, i.e. -H modifies the depth argument, doesn't seem true in ZFS 2.1.11. Does it look that way in your testing?

Seems ok to me...