rootless, spec: allow resources with cgroup v2

We were always raising an error when the rootless user attempted to
setup resources, but this is not the case anymore with cgroup v2.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

3 files changed, 36 insertions, 3 deletions

diff --git a/pkg/spec/spec.go b/pkg/spec/spec.go
index 20c649f9a..c2c5e0900 100644
--- a/pkg/spec/spec.go
+++ b/pkg/spec/spec.go
@@ -7,6 +7,7 @@ import (
 
 	"github.com/containers/libpod/libpod"
 	"github.com/containers/libpod/pkg/rootless"
+	"github.com/containers/libpod/pkg/util"
 	pmount "github.com/containers/storage/pkg/mount"
 	"github.com/docker/docker/oci/caps"
 	"github.com/docker/go-units"
@@ -347,10 +348,13 @@ func (config *CreateConfig) createConfigToOCISpec(runtime *libpod.Runtime, userM
 	}
 
 	if rootless.IsRootless() {
-		if addedResources {
-			return nil, errors.New("invalid configuration, cannot set resources with rootless containers")
+		cgroup2, err := util.IsCgroup2UnifiedMode()
+		if err != nil {
+			return nil, err
+		}
+		if addedResources && !cgroup2 {
+			return nil, errors.New("invalid configuration, cannot set resources with rootless containers not using cgroups v2 unified mode")
 		}
-		configSpec.Linux.Resources = &spec.LinuxResources{}
 	}
 
 	// Make sure that the bind mounts keep options like nosuid, noexec, nodev.
diff --git a/pkg/util/utils_supported.go b/pkg/util/utils_supported.go
index af5e67fc1..8b98658c2 100644
--- a/pkg/util/utils_supported.go
+++ b/pkg/util/utils_supported.go
@@ -11,9 +11,33 @@ import (
 	"github.com/pkg/errors"
 	"os"
 	"path/filepath"
+	"sync"
 	"syscall"
 )
 
+const (
+	_cgroup2SuperMagic = 0x63677270
+)
+
+var (
+	isUnifiedOnce sync.Once
+	isUnified     bool
+	isUnifiedErr  error
+)
+
+// IsCgroup2UnifiedMode returns whether we are running in cgroup 2 unified mode.
+func IsCgroup2UnifiedMode() (bool, error) {
+	isUnifiedOnce.Do(func() {
+		var st syscall.Statfs_t
+		if err := syscall.Statfs("/sys/fs/cgroup", &st); err != nil {
+			isUnified, isUnifiedErr = false, err
+		} else {
+			isUnified, isUnifiedErr = st.Type == _cgroup2SuperMagic, nil
+		}
+	})
+	return isUnified, isUnifiedErr
+}
+
 // GetRootlessRuntimeDir returns the runtime directory when running as non root
 func GetRootlessRuntimeDir() (string, error) {
 	var rootlessRuntimeDirError error
diff --git a/pkg/util/utils_windows.go b/pkg/util/utils_windows.go
index 1e9ccea90..b33733da9 100644
--- a/pkg/util/utils_windows.go
+++ b/pkg/util/utils_windows.go
@@ -10,3 +10,8 @@ import (
 func GetRootlessRuntimeDir() (string, error) {
 	return "", errors.New("this function is not implemented for windows")
 }
+
+// IsCgroup2UnifiedMode returns whether we are running in cgroup 2 unified mode.
+func IsCgroup2UnifiedMode() (bool, error) {
+	return false, errors.New("this function is not implemented for windows")
+}