JSON output support for zfs version and zfs get

This commit adds support for JSON output for zfs version and zfs get
commands. '-j' flag can be used to get output in JSON format.

Information is collected in nvlist objects which is later printed in
JSON format. Existing options that work for zfs get and zfs version
also work with '-j' flag.

man pages for zfs get and zfs version are updated accordingly.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Ameer Hamza <ahamza@ixsystems.com>
Signed-off-by: Umer Saleem <usaleem@ixsystems.com>
Closes #16217

man/man8/zfs-set.8

@@ -46,6 +46,7 @@
 .Cm get
 .Op Fl r Ns | Ns Fl d Ar depth
 .Op Fl Hp
+.Op Fl j Op Ar --json-int
 .Oo Fl o Ar field Ns Oo , Ns Ar field Oc Ns … Oc
 .Oo Fl s Ar source Ns Oo , Ns Ar source Oc Ns … Oc
 .Oo Fl t Ar type Ns Oo , Ns Ar type Oc Ns … Oc
@@ -91,6 +92,7 @@ dataset.
 .Cm get
 .Op Fl r Ns | Ns Fl d Ar depth
 .Op Fl Hp
+.Op Fl j Op Ar --json-int
 .Oo Fl o Ar field Ns Oo , Ns Ar field Oc Ns … Oc
 .Oo Fl s Ar source Ns Oo , Ns Ar source Oc Ns … Oc
 .Oo Fl t Ar type Ns Oo , Ns Ar type Oc Ns … Oc
@@ -128,6 +130,11 @@ The value
 can be used to display all properties that apply to the given dataset's type
 .Pq Sy filesystem , volume , snapshot , No or Sy bookmark .
 .Bl -tag -width "-s source"
+.It Fl j Op Ar --json-int
+Display the output in JSON format.
+Specify
+.Sy --json-int
+to display numbers in integer format instead of strings for JSON output.
 .It Fl H
 Display output in a form more easily parsed by scripts.
 Any headers are omitted, and fields are explicitly separated by a single tab
@@ -283,6 +290,50 @@ The following command gets a single property value:
 on
 .Ed
 .Pp
+The following command gets a single property value recursively in JSON format:
+.Bd -literal -compact -offset Ds
+.No # Nm zfs Cm get Fl j Fl r Sy mountpoint Ar pool/home | Nm jq
+{
+  "output_version": {
+    "command": "zfs get",
+    "vers_major": 0,
+    "vers_minor": 1
+  },
+  "datasets": {
+    "pool/home": {
+      "name": "pool/home",
+      "type": "FILESYSTEM",
+      "pool": "pool",
+      "createtxg": "10",
+      "properties": {
+        "mountpoint": {
+          "value": "/pool/home",
+          "source": {
+            "type": "DEFAULT",
+            "data": "-"
+          }
+        }
+      }
+    },
+    "pool/home/bob": {
+      "name": "pool/home/bob",
+      "type": "FILESYSTEM",
+      "pool": "pool",
+      "createtxg": "1176",
+      "properties": {
+        "mountpoint": {
+          "value": "/pool/home/bob",
+          "source": {
+            "type": "DEFAULT",
+            "data": "-"
+          }
+        }
+      }
+    }
+  }
+}
+.Ed
+.Pp
 The following command lists all properties with local settings for
 .Ar pool/home/bob :
 .Bd -literal -compact -offset Ds

man/man8/zfs.8

@@ -48,6 +48,7 @@
 .Fl ?V
 .Nm
 .Cm version
+.Op Fl j
 .Nm
 .Cm subcommand
 .Op Ar arguments
@@ -153,10 +154,14 @@ Displays a help message.
 .It Xo
 .Nm
 .Cm version
+.Op Fl j
 .Xc
 Displays the software version of the
 .Nm
 userland utility and the zfs kernel module.
+Use
+.Fl j
+option to output in JSON format.
 .El
 .
 .Ss Dataset Management