fix(zfs) zfs arcstats.p on FreeBSD 14.0+ (#2754)

* dongjiang, fix zfs arcstats.p

Signed-off-by: dongjiang1989 <dongjiang1989@126.com>

* dongjiang, fix gofmt -s

Signed-off-by: dongjiang1989 <dongjiang1989@126.com>

* change warn log to debug log by code review

Signed-off-by: dongjiang1989 <dongjiang1989@126.com>

---------

Signed-off-by: dongjiang1989 <dongjiang1989@126.com>

collector/zfs_freebsd.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 
 	"github.com/go-kit/log"
+	"github.com/go-kit/log/level"
 	"github.com/prometheus/client_golang/prometheus"
 
 	"golang.org/x/sys/unix"
@@ -241,6 +242,7 @@ func NewZfsCollector(logger log.Logger) (Collector, error) {
 				valueType:   prometheus.GaugeValue,
 				labels:      nil,
 			},
+			// when FreeBSD 14.0+, `meta/pm/pd` install of `p`.
 			{
 				name:        "arcstats_p_bytes",
 				description: "ZFS ARC MRU target size",
@@ -249,6 +251,27 @@ func NewZfsCollector(logger log.Logger) (Collector, error) {
 				valueType:   prometheus.GaugeValue,
 				labels:      nil,
 			},
+			{
+				name:        "arcstats_meta_bytes",
+				description: "ZFS ARC metadata target frac ",
+				mib:         "kstat.zfs.misc.arcstats.meta",
+				dataType:    bsdSysctlTypeUint64,
+				valueType:   prometheus.GaugeValue,
+			},
+			{
+				name:        "arcstats_pd_bytes",
+				description: "ZFS ARC data MRU target frac",
+				mib:         "kstat.zfs.misc.arcstats.pd",
+				dataType:    bsdSysctlTypeUint64,
+				valueType:   prometheus.GaugeValue,
+			},
+			{
+				name:        "arcstats_pm_bytes",
+				description: "ZFS ARC meta MRU target frac",
+				mib:         "kstat.zfs.misc.arcstats.pm",
+				dataType:    bsdSysctlTypeUint64,
+				valueType:   prometheus.GaugeValue,
+			},
 			{
 				name:        "arcstats_size_bytes",
 				description: "ZFS ARC size",
@@ -282,7 +305,9 @@ func (c *zfsCollector) Update(ch chan<- prometheus.Metric) error {
 	for _, m := range c.sysctls {
 		v, err := m.Value()
 		if err != nil {
-			return fmt.Errorf("couldn't get sysctl: %w", err)
+			// debug logging
+			level.Debug(c.logger).Log("name", m.name, "couldn't get sysctl:", err)
+			continue
 		}
 
 		ch <- prometheus.MustNewConstMetric(