fix diskio and memory bugs under windows (elastic#21992)

(cherry picked from commit 6955665)

metricbeat/module/system/diskio/diskio.go

@@ -21,6 +21,7 @@ package diskio
 
 import (
 	"fmt"
+	"runtime"
 
 	"github.com/elastic/beats/v7/libbeat/common"
 	"github.com/elastic/beats/v7/libbeat/metric/system/diskio"
@@ -114,7 +115,7 @@ func (m *MetricSet) Fetch(r mb.ReporterV2) error {
 		diskWriteBytes += counters.WriteBytes
 
 		//Add linux-only data if agent is off as not to make breaking changes.
-		if !m.IsAgent {
+		if !m.IsAgent && runtime.GOOS == "linux" {
 			result, err := m.statistics.CalcIOStatistics(counters)
 			if err != nil {
 				return errors.Wrap(err, "error calculating iostat")

metricbeat/module/system/memory/memory.go

@@ -42,7 +42,7 @@ func init() {
 // MetricSet for fetching system memory metrics.
 type MetricSet struct {
 	mb.BaseMetricSet
-	IsFleet bool
+	IsAgent bool
 }
 
 // New is a mb.MetricSetFactory that returns a memory.MetricSet.
@@ -53,7 +53,7 @@ func New(base mb.BaseMetricSet) (mb.MetricSet, error) {
 		return nil, fmt.Errorf("unexpected module type")
 	}
 
-	return &MetricSet{BaseMetricSet: base, IsFleet: systemModule.IsAgent}, nil
+	return &MetricSet{BaseMetricSet: base, IsAgent: systemModule.IsAgent}, nil
 }
 
 // Fetch fetches memory metrics from the OS.
@@ -117,7 +117,7 @@ func (m *MetricSet) Fetch(r mb.ReporterV2) error {
 	}
 
 	// for backwards compatibility, only report if we're not in fleet mode
-	if !m.IsFleet {
+	if !m.IsAgent {
 		err := linux.FetchLinuxMemStats(memory)
 		if err != nil {
 			return errors.Wrap(err, "error getting page stats")

metricbeat/module/system/process/process.go

@@ -156,10 +156,12 @@ func (m *MetricSet) Fetch(r mb.ReporterV2) error {
 		// There's some more Windows memory quirks we need to deal with.
 		// "rss" is a linux concept, but "wss" is a direct match on Windows.
 		// "share" is also unavailable on Windows.
+		if runtime.GOOS == "windows" {
+			proc.Delete("memory.share")
+		}
 
 		if m.IsAgent {
 			if runtime.GOOS == "windows" {
-				proc.Delete("memory.share")
 				if setSize := getAndRemove(proc, "memory.rss"); setSize != nil {
 					proc.Put("memory.wss", setSize)
 				}