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|
package fs
import (
"errors"
"os"
"path/filepath"
"sync"
"golang.org/x/sys/unix"
"github.com/opencontainers/cgroups"
"github.com/opencontainers/cgroups/internal/path"
)
// The absolute path to the root of the cgroup hierarchies.
var (
cgroupRootLock sync.Mutex
cgroupRoot string
)
const defaultCgroupRoot = "/sys/fs/cgroup"
func initPaths(cg *cgroups.Cgroup) (map[string]string, error) {
root, err := rootPath()
if err != nil {
return nil, err
}
inner, err := path.Inner(cg)
if err != nil {
return nil, err
}
paths := make(map[string]string)
for _, sys := range subsystems {
name := sys.Name()
path, err := subsysPath(root, inner, name)
if err != nil {
// The non-presence of the devices subsystem
// is considered fatal for security reasons.
if cgroups.IsNotFound(err) && (cg.SkipDevices || name != "devices") {
continue
}
return nil, err
}
paths[name] = path
}
return paths, nil
}
func tryDefaultCgroupRoot() string {
var st, pst unix.Stat_t
// (1) it should be a directory...
err := unix.Lstat(defaultCgroupRoot, &st)
if err != nil || st.Mode&unix.S_IFDIR == 0 {
return ""
}
// (2) ... and a mount point ...
err = unix.Lstat(filepath.Dir(defaultCgroupRoot), &pst)
if err != nil {
return ""
}
if st.Dev == pst.Dev {
// parent dir has the same dev -- not a mount point
return ""
}
// (3) ... of 'tmpfs' fs type.
var fst unix.Statfs_t
err = unix.Statfs(defaultCgroupRoot, &fst)
if err != nil || fst.Type != unix.TMPFS_MAGIC {
return ""
}
// (4) it should have at least 1 entry ...
dir, err := os.Open(defaultCgroupRoot)
if err != nil {
return ""
}
defer dir.Close()
names, err := dir.Readdirnames(1)
if err != nil {
return ""
}
if len(names) < 1 {
return ""
}
// ... which is a cgroup mount point.
err = unix.Statfs(filepath.Join(defaultCgroupRoot, names[0]), &fst)
if err != nil || fst.Type != unix.CGROUP_SUPER_MAGIC {
return ""
}
return defaultCgroupRoot
}
// rootPath finds and returns path to the root of the cgroup hierarchies.
func rootPath() (string, error) {
cgroupRootLock.Lock()
defer cgroupRootLock.Unlock()
if cgroupRoot != "" {
return cgroupRoot, nil
}
// fast path
cgroupRoot = tryDefaultCgroupRoot()
if cgroupRoot != "" {
return cgroupRoot, nil
}
// slow path: parse mountinfo
mi, err := cgroups.GetCgroupMounts(false)
if err != nil {
return "", err
}
if len(mi) < 1 {
return "", errors.New("no cgroup mount found in mountinfo")
}
// Get the first cgroup mount (e.g. "/sys/fs/cgroup/memory"),
// use its parent directory.
root := filepath.Dir(mi[0].Mountpoint)
if _, err := os.Stat(root); err != nil {
return "", err
}
cgroupRoot = root
return cgroupRoot, nil
}
func subsysPath(root, inner, subsystem string) (string, error) {
// If the cgroup name/path is absolute do not look relative to the cgroup of the init process.
if filepath.IsAbs(inner) {
mnt, err := cgroups.FindCgroupMountpoint(root, subsystem)
// If we didn't mount the subsystem, there is no point we make the path.
if err != nil {
return "", err
}
// Sometimes subsystems can be mounted together as 'cpu,cpuacct'.
return filepath.Join(root, filepath.Base(mnt), inner), nil
}
// Use GetOwnCgroupPath for dind-like cases, when cgroupns is not
// available. This is ugly.
parentPath, err := cgroups.GetOwnCgroupPath(subsystem)
if err != nil {
return "", err
}
return filepath.Join(parentPath, inner), nil
}
func apply(path string, pid int) error {
if path == "" {
return nil
}
if err := os.MkdirAll(path, 0o755); err != nil {
return err
}
return cgroups.WriteCgroupProc(path, pid)
}
|
