cgroups.go

// Copyright 2018 Authors of Cilium
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package cgroups

import (
	"fmt"
	"os"
	"sync"
	"syscall"

	"github.com/cilium/cilium/pkg/defaults"
	"github.com/cilium/cilium/pkg/logging"
	"github.com/cilium/cilium/pkg/logging/logfields"
	"github.com/cilium/cilium/pkg/mountinfo"
)

var (
	// Path to where cgroup is mounted
	cgroupRoot = defaults.DefaultCgroupRoot

	// Only mount a single instance
	cgrpMountOnce sync.Once
)

var log = logging.DefaultLogger.WithField(logfields.LogSubsys, "cgroups")

// setCgroupRoot will set the path to mount cgroupv2
func setCgroupRoot(path string) {
	cgroupRoot = path
}

// GetCgroupRoot returns the path for the cgroupv2 mount
func GetCgroupRoot() string {
	return cgroupRoot
}

// mountCgroup mounts the Cgroup v2 filesystem into the desired cgroupRoot directory.
func mountCgroup() error {
	cgroupRootStat, err := os.Stat(cgroupRoot)
	if err != nil {
		if os.IsNotExist(err) {
			if err := os.MkdirAll(cgroupRoot, 0755); err != nil {
				return fmt.Errorf("Unable to create cgroup mount directory: %s", err)
			}
		} else {
			return fmt.Errorf("Failed to stat the mount path %s: %s", cgroupRoot, err)
		}
	} else if !cgroupRootStat.IsDir() {
		return fmt.Errorf("%s is a file which is not a directory", cgroupRoot)
	}

	if err := syscall.Mount("none", cgroupRoot, mountinfo.FilesystemTypeCgroup2, 0, ""); err != nil {
		return fmt.Errorf("failed to mount %s: %s", cgroupRoot, err)
	}

	return nil
}

// checkOrMountCustomLocation tries to check or mount the BPF filesystem in the
// given path.
func cgrpCheckOrMountLocation(cgroupRoot string) error {
	setCgroupRoot(cgroupRoot)

	// Check whether the custom location has a mount.
	mounted, cgroupInstance, err := mountinfo.IsMountFS(mountinfo.FilesystemTypeCgroup2, cgroupRoot)
	if err != nil {
		return err
	}

	// If the custom location has no mount, let's mount there.
	if !mounted {
		if err := mountCgroup(); err != nil {
			return err
		}
	}

	if !cgroupInstance {
		return fmt.Errorf("Mount in the custom directory %s has a different filesystem than cgroup2", cgroupRoot)
	}
	return nil
}

// CheckOrMountCgrpFS this checks if the cilium cgroup2 root mount point is
// mounted and if not mounts it. If mapRoot is "" it will mount the default
// location. It is harmless to have multiple cgroupv2 root mounts so unlike
// BPFFS case we simply mount at the cilium default regardless if the system
// has another mount created by systemd or otherwise.
func CheckOrMountCgrpFS(mapRoot string) {
	cgrpMountOnce.Do(func() {
		if mapRoot == "" {
			mapRoot = cgroupRoot
		}
		err := cgrpCheckOrMountLocation(mapRoot)
		// Failed cgroup2 mount is not a fatal error, sockmap will be disabled however
		if err == nil {
			log.Infof("Mounted cgroupv2 filesystem at %s", mapRoot)
		}
	})
}