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Use sync.OnceFunc, sync.OnceValue[s] #5261

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65fddb5
libct/apparmor: simplify isEnabled
kolyshkin Apr 23, 2026
53e72e1
libct/utils: use sync.OnceValue
kolyshkin Apr 23, 2026
fe2f15d
libcontainer/configs/validate: use early return
kolyshkin Apr 23, 2026
4bb3a0d
libct/intelrdt: remove newManager
kolyshkin Apr 30, 2026
ae72c82
libct/configs/validate: simplify intelrtd tests
kolyshkin Apr 23, 2026
789c1fb
libct/intelrdt: use sync.OnceFunc and sync.OnceValues
kolyshkin Apr 23, 2026
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21 changes: 7 additions & 14 deletions libcontainer/apparmor/apparmor_linux.go
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Original file line number Diff line number Diff line change
Expand Up @@ -11,21 +11,14 @@ import (
"github.com/opencontainers/runc/internal/pathrs"
)

var (
appArmorEnabled bool
checkAppArmor sync.Once
)

// isEnabled returns true if apparmor is enabled for the host.
func isEnabled() bool {
checkAppArmor.Do(func() {
if _, err := os.Stat("/sys/kernel/security/apparmor"); err == nil {
buf, err := os.ReadFile("/sys/module/apparmor/parameters/enabled")
appArmorEnabled = err == nil && len(buf) > 1 && buf[0] == 'Y'
}
})
return appArmorEnabled
}
var isEnabled = sync.OnceValue(func() bool {
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@thaJeztah thaJeztah Apr 24, 2026

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one pattern I also used in some places is to have a regular function (instead of the rather ad-hoc style for these), and then wrap it in a sync.OnceValue - sometimes useful for testing (where you may not want the "once") and to keep it as a "function", not a variable that happens to be a function, i.e.;

var something = sync.OnceValue(doSomething)

func doSomething() bool {
    return true
}

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@kolyshkin kolyshkin Apr 30, 2026

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Yes, if the bare (unwrapped) functionality is needed for e.g. test or a benchmark.

Not the case here so I'd rather keep this as is.

if _, err := os.Stat("/sys/kernel/security/apparmor"); err != nil {
return false
}
buf, err := os.ReadFile("/sys/module/apparmor/parameters/enabled")
return err == nil && len(buf) > 0 && buf[0] == 'Y'
})

func setProcAttr(attr, value string) error {
attr = pathrs.LexicallyCleanPath(attr)
Expand Down
41 changes: 6 additions & 35 deletions libcontainer/configs/validate/intelrdt.go
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Original file line number Diff line number Diff line change
@@ -1,41 +1,12 @@
package validate

import (
"sync"

"github.com/opencontainers/runc/libcontainer/intelrdt"
)

// Cache the result of intelrdt IsEnabled functions to avoid repeated sysfs
// access and enable mocking for unit tests.
type intelRdtStatus struct {
sync.Once
rdtEnabled bool
catEnabled bool
mbaEnabled bool
}

var intelRdt = &intelRdtStatus{}

func (i *intelRdtStatus) init() {
i.Do(func() {
i.rdtEnabled = intelrdt.IsEnabled()
i.catEnabled = intelrdt.IsCATEnabled()
i.mbaEnabled = intelrdt.IsMBAEnabled()
})
}

func (i *intelRdtStatus) isEnabled() bool {
i.init()
return i.rdtEnabled
}

func (i *intelRdtStatus) isCATEnabled() bool {
i.init()
return i.catEnabled
}

func (i *intelRdtStatus) isMBAEnabled() bool {
i.init()
return i.mbaEnabled
}
// Allow mocking for TestValidateIntelRdt.
var (
intelRdtIsEnabled = intelrdt.IsEnabled
intelRdtIsCATEnabled = intelrdt.IsCATEnabled
intelRdtIsMBAEnabled = intelrdt.IsMBAEnabled
)
16 changes: 10 additions & 6 deletions libcontainer/configs/validate/intelrdt_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -4,12 +4,10 @@ import (
"testing"

"github.com/opencontainers/runc/libcontainer/configs"
"github.com/opencontainers/runc/libcontainer/intelrdt"
)

func TestValidateIntelRdt(t *testing.T) {
// Call init to trigger the sync.Once and enable overriding the rdt status
intelRdt.init()

testCases := []struct {
name string
rdtEnabled bool
Expand Down Expand Up @@ -90,11 +88,17 @@ func TestValidateIntelRdt(t *testing.T) {
},
},
}

for _, tc := range testCases {
t.Run(tc.name, func(t *testing.T) {
intelRdt.rdtEnabled = tc.rdtEnabled
intelRdt.catEnabled = tc.catEnabled
intelRdt.mbaEnabled = tc.mbaEnabled
t.Cleanup(func() {
intelRdtIsEnabled = intelrdt.IsEnabled
intelRdtIsCATEnabled = intelrdt.IsCATEnabled
intelRdtIsMBAEnabled = intelrdt.IsMBAEnabled
})
intelRdtIsEnabled = func() bool { return tc.rdtEnabled }
intelRdtIsCATEnabled = func() bool { return tc.catEnabled }
intelRdtIsMBAEnabled = func() bool { return tc.mbaEnabled }

config := &configs.Config{
Rootfs: "/var",
Expand Down
30 changes: 15 additions & 15 deletions libcontainer/configs/validate/validator.go
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Original file line number Diff line number Diff line change
Expand Up @@ -306,22 +306,22 @@ func sysctl(config *configs.Config) error {
}

func intelrdtCheck(config *configs.Config) error {
if config.IntelRdt != nil {
if !intelRdt.isEnabled() {
return fmt.Errorf("intelRdt is specified in config, but Intel RDT is not enabled")
}

switch clos := config.IntelRdt.ClosID; {
case clos == ".", clos == "..", len(clos) > 1 && strings.Contains(clos, "/"):
return fmt.Errorf("invalid intelRdt.ClosID %q", clos)
}
if config.IntelRdt == nil {
return nil
}
if !intelRdtIsEnabled() {
return fmt.Errorf("intelRdt is specified in config, but Intel RDT is not enabled")
}

if !intelRdt.isCATEnabled() && config.IntelRdt.L3CacheSchema != "" {
return errors.New("intelRdt.l3CacheSchema is specified in config, but Intel RDT/CAT is not enabled")
}
if !intelRdt.isMBAEnabled() && config.IntelRdt.MemBwSchema != "" {
return errors.New("intelRdt.memBwSchema is specified in config, but Intel RDT/MBA is not enabled")
}
switch clos := config.IntelRdt.ClosID; {
case clos == ".", clos == "..", len(clos) > 1 && strings.Contains(clos, "/"):
return fmt.Errorf("invalid intelRdt.ClosID %q", clos)
}
if !intelRdtIsCATEnabled() && config.IntelRdt.L3CacheSchema != "" {
return errors.New("intelRdt.l3CacheSchema is specified in config, but Intel RDT/CAT is not enabled")
}
if !intelRdtIsMBAEnabled() && config.IntelRdt.MemBwSchema != "" {
return errors.New("intelRdt.memBwSchema is specified in config, but Intel RDT/MBA is not enabled")
}

return nil
Expand Down
128 changes: 54 additions & 74 deletions libcontainer/intelrdt/intelrdt.go
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Expand Up @@ -162,7 +162,7 @@ func NewManager(config *configs.Config, id, path string) *Manager {
return nil
}

rootPath, err := Root()
rootPath, err := root()
if err != nil {
return nil
}
Expand All @@ -180,12 +180,6 @@ func NewManager(config *configs.Config, id, path string) *Manager {
}
}

return newManager(config, id, path)
}

// newManager is the same as NewManager, except it does not check if the feature
// is actually available. Used by unit tests that mock intelrdt paths.
func newManager(config *configs.Config, id, path string) *Manager {
return &Manager{
config: config,
id: id,
Expand All @@ -203,47 +197,42 @@ var (
// The flag to indicate if Intel RDT/MBA is enabled
mbaEnabled bool

// For Intel RDT initialization
initOnce sync.Once

errNotFound = errors.New("Intel RDT not available")
)

// Check if Intel RDT sub-features are enabled in featuresInit()
func featuresInit() {
initOnce.Do(func() {
// 1. Check if Intel RDT "resource control" filesystem is available.
// The user guarantees to mount the filesystem.
root, err := Root()
if err != nil {
return
}
var featuresInit = sync.OnceFunc(func() {
// 1. Check if Intel RDT "resource control" filesystem is available.
// The user guarantees to mount the filesystem.
root, err := root()
if err != nil {
return
}

// 2. Check if Intel RDT sub-features are available in "resource
// control" filesystem. Intel RDT sub-features can be
// selectively disabled or enabled by kernel command line
// (e.g., rdt=!l3cat,mba) in 4.14 and newer kernel
if _, err := os.Stat(filepath.Join(root, "info", "L3")); err == nil {
catEnabled = true
}
if _, err := os.Stat(filepath.Join(root, "info", "MB")); err == nil {
mbaEnabled = true
}
if _, err := os.Stat(filepath.Join(root, "info", "L3_MON")); err != nil {
return
}
enabledMonFeatures, err = getMonFeatures(root)
if err != nil {
return
}
if enabledMonFeatures.mbmTotalBytes || enabledMonFeatures.mbmLocalBytes {
mbmEnabled = true
}
if enabledMonFeatures.llcOccupancy {
cmtEnabled = true
}
})
}
// 2. Check if Intel RDT sub-features are available in "resource
// control" filesystem. Intel RDT sub-features can be
// selectively disabled or enabled by kernel command line
// (e.g., rdt=!l3cat,mba) in 4.14 and newer kernel
if _, err := os.Stat(filepath.Join(root, "info", "L3")); err == nil {
catEnabled = true
}
if _, err := os.Stat(filepath.Join(root, "info", "MB")); err == nil {
mbaEnabled = true
}
if _, err := os.Stat(filepath.Join(root, "info", "L3_MON")); err != nil {
return
}
enabledMonFeatures, err = getMonFeatures(root)
if err != nil {
return
}
if enabledMonFeatures.mbmTotalBytes || enabledMonFeatures.mbmLocalBytes {
mbmEnabled = true
}
if enabledMonFeatures.llcOccupancy {
cmtEnabled = true
}
})

// findIntelRdtMountpointDir returns the mount point of the Intel RDT "resource control" filesystem.
func findIntelRdtMountpointDir() (string, error) {
Expand All @@ -264,43 +253,34 @@ func findIntelRdtMountpointDir() (string, error) {
return mi[0].Mountpoint, nil
}

// For Root() use only.
var (
intelRdtRoot string
intelRdtRootErr error
rootOnce sync.Once
)

// The kernel creates this (empty) directory if resctrl is supported by the
// hardware and kernel. The user is responsible for mounting the resctrl
// filesystem, and they could mount it somewhere else if they wanted to.
const defaultResctrlMountpoint = "/sys/fs/resctrl"

// Root returns the Intel RDT "resource control" filesystem mount point.
func Root() (string, error) {
rootOnce.Do(func() {
// Does this system support resctrl?
var statfs unix.Statfs_t
if err := unix.Statfs(defaultResctrlMountpoint, &statfs); err != nil {
if errors.Is(err, unix.ENOENT) {
err = errNotFound
}
intelRdtRootErr = err
return
}
return root()
}

// Has the resctrl fs been mounted to the default mount point?
if statfs.Type == unix.RDTGROUP_SUPER_MAGIC {
intelRdtRoot = defaultResctrlMountpoint
return
var root = sync.OnceValues(func() (string, error) {
// Does this system support resctrl?
var statfs unix.Statfs_t
if err := unix.Statfs(defaultResctrlMountpoint, &statfs); err != nil {
if errors.Is(err, unix.ENOENT) {
err = errNotFound
}
return "", err
}

// The resctrl fs could have been mounted somewhere nonstandard.
intelRdtRoot, intelRdtRootErr = findIntelRdtMountpointDir()
})
// Has the resctrl fs been mounted to the default mount point?
if statfs.Type == unix.RDTGROUP_SUPER_MAGIC {
return defaultResctrlMountpoint, nil
}

return intelRdtRoot, intelRdtRootErr
}
// The resctrl fs could have been mounted somewhere nonstandard.
return findIntelRdtMountpointDir()
})

// Gets a single uint64 value from the specified file.
func getIntelRdtParamUint(path, file string) (uint64, error) {
Expand Down Expand Up @@ -331,7 +311,7 @@ func getIntelRdtParamString(path, file string) (string, error) {
func getL3CacheInfo() (*L3CacheInfo, error) {
l3CacheInfo := &L3CacheInfo{}

rootPath, err := Root()
rootPath, err := root()
if err != nil {
return l3CacheInfo, err
}
Expand Down Expand Up @@ -361,7 +341,7 @@ func getL3CacheInfo() (*L3CacheInfo, error) {
func getMemBwInfo() (*MemBwInfo, error) {
memBwInfo := &MemBwInfo{}

rootPath, err := Root()
rootPath, err := root()
if err != nil {
return memBwInfo, err
}
Expand Down Expand Up @@ -394,7 +374,7 @@ func getMemBwInfo() (*MemBwInfo, error) {

// Get diagnostics for last filesystem operation error from file info/last_cmd_status
func getLastCmdStatus() (string, error) {
rootPath, err := Root()
rootPath, err := root()
if err != nil {
return "", err
}
Expand Down Expand Up @@ -425,7 +405,7 @@ func WriteIntelRdtTasks(dir string, pid int) error {

// IsEnabled checks if Intel RDT is enabled.
func IsEnabled() bool {
fsroot, err := Root()
fsroot, err := root()
return err == nil && fsroot != ""
}

Expand Down Expand Up @@ -544,7 +524,7 @@ func (m *Manager) GetStats() (*Stats, error) {
defer m.mu.Unlock()
stats := newStats()

rootPath, err := Root()
rootPath, err := root()
if err != nil {
return nil, err
}
Expand Down
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