Extend 'zfs holds -r' to accept a dataset, instead of only a snapshot as input

[allanjude]

Test Plan

zfs holds dataset@snapshot
zfs holds -r dataset@snapshot
zfs holds -r dataset

[dteske]

Nice work. I gauge this on style(9) rules (NULL used properly; '\0' used properly; proper comparison of pointer to NULL versus treating it as boolean; et cetera), validation of logic-reversal (== becomes !=), validation of removal of error message given context of change (allow dataset arguments as well as snapshots), and of course this change meets the goal of minimal-changes to reach desired effect.

Short of actually running the code myself, I'd say this patch looks dandy. [Again,] Nice work!

[mahrens]

This is a good start, but you also need to update the manpage and help message (see get_usage()).

Once this is in FreeBSD, would you consider upstreaming it to OpenZFS? (https://github.com/openzfs/openzfs)

[allanjude]

Updated with feedback from mahrens

add support for -d, to limit depth of search
add support for -p, to print values as literals (raw timestamp instead of date text)
update usage message
update man page

[allanjude]

In D3994#83328, @mahrens wrote:

This is a good start, but you also need to update the manpage and help message (see get_usage()).

done (and more)

Once this is in FreeBSD, would you consider upstreaming it to OpenZFS? (https://github.com/openzfs/openzfs)

Of course.

[mahrens]

cddl/contrib/opensolaris/cmd/zfs/zfs.8

275–278

I think you should also add a detailed description of the new -H, -p, and -d flags. (feel free to copy/paste the descriptions from "zfs list").

[allanjude]

Add missing text to man page