common/pkg/cgroups: Replace handler interface with stat functions

Replace the controllerHandler interface with a simple statFunc type
and convert all handler structs to plain functions. This eliminates
unnecessary abstraction since all handlers only implemented a single
Stat method.

Changes:
- Replace controllerHandler interface with statFunc type
- Convert linuxBlkioHandler, linuxCPUHandler, linuxMemHandler, and
  linuxPidHandler structs to blkioStat, cpuStat, memoryStat, and
  pidsStat functions
- Remove init() function and factory methods (getBlkioHandler, etc.)
- Simplify handlers map to direct function references
- Update Stat() method to call functions directly
- Update AvailableControllers signature to use statFunc type

Signed-off-by: Lokesh Mandvekar <[email protected]>

Author: lsm5

common/pkg/cgroups/blkio_linux.go

@@ -9,15 +9,8 @@ import (
 	"github.com/opencontainers/cgroups"
 )
 
-type linuxBlkioHandler struct {
-}
-
-func getBlkioHandler() *linuxBlkioHandler {
-	return &linuxBlkioHandler{}
-}
-
-// Stat fills a metrics structure with usage stats for the controller.
-func (c *linuxBlkioHandler) Stat(ctr *CgroupControl, m *cgroups.Stats) error {
+// blkioStat fills a metrics structure with usage stats for the blkio controller.
+func blkioStat(ctr *CgroupControl, m *cgroups.Stats) error {
 	var ioServiceBytesRecursive []cgroups.BlkioStatEntry
 
 	// more details on the io.stat file format:X https://facebookmicrosites.github.io/cgroup2/docs/io-controller.html

common/pkg/cgroups/cgroups_linux.go

@@ -42,9 +42,8 @@ type CgroupControl struct {
 	systemd bool
 }
 
-type controllerHandler interface {
-	Stat(*CgroupControl, *cgroups.Stats) error
-}
+// statFunc is a function that gathers statistics for a cgroup controller.
+type statFunc func(*CgroupControl, *cgroups.Stats) error
 
 const (
 	cgroupRoot = "/sys/fs/cgroup"
@@ -58,15 +57,11 @@ const (
 	Blkio = "blkio"
 )
 
-var handlers map[string]controllerHandler
-
-func init() {
-	handlers = map[string]controllerHandler{
-		CPU:    getCPUHandler(),
-		Memory: getMemoryHandler(),
-		Pids:   getPidsHandler(),
-		Blkio:  getBlkioHandler(),
-	}
+var handlers = map[string]statFunc{
+	CPU:    cpuStat,
+	Memory: memoryStat,
+	Pids:   pidsStat,
+	Blkio:  blkioStat,
 }
 
 // getAvailableControllers get the available controllers.
@@ -95,7 +90,7 @@ func getAvailableControllers() ([]string, error) {
 }
 
 // AvailableControllers get string:bool map of all the available controllers.
-func AvailableControllers(exclude map[string]controllerHandler) ([]string, error) {
+func AvailableControllers(exclude map[string]statFunc) ([]string, error) {
 	return getAvailableControllers()
 }
 
@@ -312,8 +307,8 @@ func (c *CgroupControl) Update(resources *cgroups.Resources) error {
 func (c *CgroupControl) Stat() (*cgroups.Stats, error) {
 	m := cgroups.Stats{}
 	found := false
-	for _, h := range handlers {
-		if err := h.Stat(c, &m); err != nil {
+	for _, statFunc := range handlers {
+		if err := statFunc(c, &m); err != nil {
 			if !errors.Is(err, os.ErrNotExist) {
 				return nil, err
 			}

common/pkg/cgroups/cpu_linux.go

@@ -8,15 +8,8 @@ import (
 	"github.com/opencontainers/cgroups"
 )
 
-type linuxCPUHandler struct {
-}
-
-func getCPUHandler() *linuxCPUHandler {
-	return &linuxCPUHandler{}
-}
-
-// Stat fills a metrics structure with usage stats for the controller.
-func (c *linuxCPUHandler) Stat(ctr *CgroupControl, m *cgroups.Stats) error {
+// cpuStat fills a metrics structure with usage stats for the cpu controller.
+func cpuStat(ctr *CgroupControl, m *cgroups.Stats) error {
 	cpu := cgroups.CpuStats{}
 	values, err := readCgroup2MapFile(ctr, "cpu.stat")
 	if err != nil {

common/pkg/cgroups/memory_linux.go

@@ -8,15 +8,8 @@ import (
 	"github.com/opencontainers/cgroups"
 )
 
-type linuxMemHandler struct {
-}
-
-func getMemoryHandler() *linuxMemHandler {
-	return &linuxMemHandler{}
-}
-
-// Stat fills a metrics structure with usage stats for the controller.
-func (c *linuxMemHandler) Stat(ctr *CgroupControl, m *cgroups.Stats) error {
+// memoryStat fills a metrics structure with usage stats for the memory controller.
+func memoryStat(ctr *CgroupControl, m *cgroups.Stats) error {
 	var err error
 	memUsage := cgroups.MemoryStats{}
 

common/pkg/cgroups/pids_linux.go

@@ -8,15 +8,8 @@ import (
 	"github.com/opencontainers/cgroups"
 )
 
-type linuxPidHandler struct {
-}
-
-func getPidsHandler() *linuxPidHandler {
-	return &linuxPidHandler{}
-}
-
-// Stat fills a metrics structure with usage stats for the controller.
-func (c *linuxPidHandler) Stat(ctr *CgroupControl, m *cgroups.Stats) error {
+// pidsStat fills a metrics structure with usage stats for the pids controller.
+func pidsStat(ctr *CgroupControl, m *cgroups.Stats) error {
 	if ctr.config.Path == "" {
 		// nothing we can do to retrieve the pids.current path
 		return nil