fix empty linux kernel platform information

pkg/util/kernel/platform.go

@@ -8,7 +8,7 @@
 package kernel
 
 import (
-	gopsutilhost "github.com/shirou/gopsutil/v3/host"
+	gopsutilhost "github.com/DataDog/gopsutil/host"
 
 	"github.com/DataDog/datadog-agent/pkg/util/funcs"
 )
@@ -31,7 +31,9 @@ var PlatformVersion = funcs.Memoize(func() (string, error) {
 	return pi.version, err
 })
 
-var platformInformation = funcs.Memoize(func() (platformInfo, error) {
+var platformInformation = funcs.Memoize(getPlatformInformation)
+
+func getPlatformInformation() (platformInfo, error) {
 	platform, family, version, err := gopsutilhost.PlatformInformation()
 	return platformInfo{platform, family, version}, err
-})
+}

pkg/util/kernel/platform_test.go

@@ -0,0 +1,46 @@
+// Unless explicitly stated otherwise all files in this repository are licensed
+// under the Apache License Version 2.0.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2016-present Datadog, Inc.
+
+//go:build linux
+
+package kernel
+
+import (
+	"errors"
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestPlatform(t *testing.T) {
+	osr, err := os.Open("/etc/os-release")
+	if err != nil && errors.Is(err, fs.ErrNotExist) {
+		t.Skip("/etc/os-release does not exist")
+	}
+	require.NoError(t, err)
+	t.Cleanup(func() { _ = osr.Close() })
+
+	tmp := t.TempDir()
+	t.Setenv("HOST_ETC", tmp)
+	require.NoError(t, os.Mkdir(filepath.Join(tmp, "redhat-release"), 0755))
+
+	// copy /etc/os-release to <tmpdir>/os-release
+	dosr, err := os.Create(filepath.Join(tmp, "os-release"))
+	require.NoError(t, err)
+	t.Cleanup(func() { _ = dosr.Close() })
+	_, err = io.Copy(dosr, osr)
+	require.NoError(t, err)
+	_ = dosr.Close()
+
+	pi, err := getPlatformInformation()
+	require.NoError(t, err)
+	require.NotEmpty(t, pi.platform, "platform")
+	require.NotEmpty(t, pi.family, "family")
+	require.NotEmpty(t, pi.version, "version")
+}