package cgroups
import (
"errors"
"fmt"
"os"
"path/filepath"
"strings"
"sync"
"syscall"
securejoin "github.com/cyphar/filepath-securejoin"
"github.com/moby/sys/mountinfo"
"golang.org/x/sys/unix"
)
// Code in this source file are specific to cgroup v1,
// and must not be used from any cgroup v2 code.
const (
CgroupNamePrefix = "name="
defaultPrefix = "/sys/fs/cgroup"
)
var (
errUnified = errors.New("not implemented for cgroup v2 unified hierarchy")
ErrV1NoUnified = errors.New("invalid configuration: cannot use unified on cgroup v1")
readMountinfoOnce sync.Once
readMountinfoErr error
cgroupMountinfo []*mountinfo.Info
)
type NotFoundError struct {
Subsystem string
}
func (e *NotFoundError) Error() string {
return fmt.Sprintf("mountpoint for %s not found", e.Subsystem)
}
func NewNotFoundError(sub string) error {
return &NotFoundError{
Subsystem: sub,
}
}
func IsNotFound(err error) bool {
var nfErr *NotFoundError
return errors.As(err, &nfErr)
}
func tryDefaultPath(cgroupPath, subsystem string) string {
if !strings.HasPrefix(defaultPrefix, cgroupPath) {
return ""
}
// remove possible prefix
subsystem = strings.TrimPrefix(subsystem, CgroupNamePrefix)
// Make sure we're still under defaultPrefix, and resolve
// a possible symlink (like cpu -> cpu,cpuacct).
path, err := securejoin.SecureJoin(defaultPrefix, subsystem)
if err != nil {
return ""
}
// (1) path should be a directory.
st, err := os.Lstat(path)
if err != nil || !st.IsDir() {
return ""
}
// (2) path should be a mount point.
pst, err := os.Lstat(filepath.Dir(path))
if err != nil {
return ""
}
if st.Sys().(*syscall.Stat_t).Dev == pst.Sys().(*syscall.Stat_t).Dev {
// parent dir has the same dev -- path is not a mount point
return ""
}
// (3) path should have 'cgroup' fs type.
fst := unix.Statfs_t{}
err = unix.Statfs(path, &fst)
if err != nil || fst.Type != unix.CGROUP_SUPER_MAGIC {
return ""
}
return path
}
// readCgroupMountinfo returns a list of cgroup v1 mounts (i.e. the ones
// with fstype of "cgroup") for the current running process.
//
// The results are cached (to avoid re-reading mountinfo which is relatively
// expensive), so it is assumed that cgroup mounts are not being changed.
func readCgroupMountinfo() ([]*mountinfo.Info, error) {
readMountinfoOnce.Do(func() {
cgroupMountinfo, readMountinfoErr = mountinfo.GetMounts(
mountinfo.FSTypeFilter("cgroup"),
)
})
return cgroupMountinfo, readMountinfoErr
}
// https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt
func FindCgroupMountpoint(cgroupPath, subsystem string) (string, error) {
if IsCgroup2UnifiedMode() {
return "", errUnified
}
// If subsystem is empty, we look for the cgroupv2 hybrid path.
if len(subsystem) == 0 {
return hybridMountpoint, nil
}
// Avoid parsing mountinfo by trying the default path first, if possible.
if path := tryDefaultPath(cgroupPath, subsystem); path != "" {
return path, nil
}
mnt, _, err := FindCgroupMountpointAndRoot(cgroupPath, subsystem)
return mnt, err
}
func FindCgroupMountpointAndRoot(cgroupPath, subsystem string) (string, string, error) {
if IsCgroup2UnifiedMode() {
return "", "", errUnified
}
mi, err := readCgroupMountinfo()
if err != nil {
return "", "", err
}
return findCgroupMountpointAndRootFromMI(mi, cgroupPath, subsystem)
}
func findCgroupMountpointAndRootFromMI(mounts []*mountinfo.Info, cgroupPath, subsystem string) (string, string, error) {
for _, mi := range mounts {
if strings.HasPrefix(mi.Mountpoint, cgroupPath) {
for _, opt := range strings.Split(mi.VFSOptions, ",") {
if opt == subsystem {
return mi.Mountpoint, mi.Root, nil
}
}
}
}
return "", "", NewNotFoundError(subsystem)
}
func (m Mount) GetOwnCgroup(cgroups map[string]string) (string, error) {
if len(m.Subsystems) == 0 {
return "", errors.New("no subsystem for mount")
}
return getControllerPath(m.Subsystems[0], cgroups)
}
func getCgroupMountsHelper(ss map[string]bool, mounts []*mountinfo.Info, all bool) ([]Mount, error) {
res := make([]Mount, 0, len(ss))
numFound := 0
for _, mi := range mounts {
m := Mount{
Mountpoint: mi.Mountpoint,
Root: mi.Root,
}
for _, opt := range strings.Split(mi.VFSOptions, ",") {
seen, known := ss[opt]
if !known || (!all && seen) {
continue
}
ss[opt] = true
opt = strings.TrimPrefix(opt, CgroupNamePrefix)
m.Subsystems = append(m.Subsystems, opt)
numFound++
}
if len(m.Subsystems) > 0 || all {
res = append(res, m)
}
if !all && numFound >= len(ss) {
break
}
}
return res, nil
}
func getCgroupMountsV1(all bool) ([]Mount, error) {
mi, err := readCgroupMountinfo()
if err != nil {
return nil, err
}
allSubsystems, err := ParseCgroupFile("/proc/self/cgroup")
if err != nil {
return nil, err
}
allMap := make(map[string]bool)
for s := range allSubsystems {
allMap[s] = false
}
return getCgroupMountsHelper(allMap, mi, all)
}
// GetOwnCgroup returns the relative path to the cgroup docker is running in.
func GetOwnCgroup(subsystem string) (string, error) {
if IsCgroup2UnifiedMode() {
return "", errUnified
}
cgroups, err := ParseCgroupFile("/proc/self/cgroup")
if err != nil {
return "", err
}
return getControllerPath(subsystem, cgroups)
}
func GetOwnCgroupPath(subsystem string) (string, error) {
cgroup, err := GetOwnCgroup(subsystem)
if err != nil {
return "", err
}
// If subsystem is empty, we look for the cgroupv2 hybrid path.
if len(subsystem) == 0 {
return hybridMountpoint, nil
}
return getCgroupPathHelper(subsystem, cgroup)
}
func GetInitCgroup(subsystem string) (string, error) {
if IsCgroup2UnifiedMode() {
return "", errUnified
}
cgroups, err := ParseCgroupFile("/proc/1/cgroup")
if err != nil {
return "", err
}
return getControllerPath(subsystem, cgroups)
}
func GetInitCgroupPath(subsystem string) (string, error) {
cgroup, err := GetInitCgroup(subsystem)
if err != nil {
return "", err
}
return getCgroupPathHelper(subsystem, cgroup)
}
func getCgroupPathHelper(subsystem, cgroup string) (string, error) {
mnt, root, err := FindCgroupMountpointAndRoot("", subsystem)
if err != nil {
return "", err
}
// This is needed for nested containers, because in /proc/self/cgroup we
// see paths from host, which don't exist in container.
relCgroup, err := filepath.Rel(root, cgroup)
if err != nil {
return "", err
}
return filepath.Join(mnt, relCgroup), nil
}
func getControllerPath(subsystem string, cgroups map[string]string) (string, error) {
if IsCgroup2UnifiedMode() {
return "", errUnified
}
if p, ok := cgroups[subsystem]; ok {
return p, nil
}
if p, ok := cgroups[CgroupNamePrefix+subsystem]; ok {
return p, nil
}
return "", NewNotFoundError(subsystem)
}
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