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// Copyright 2019 The gVisor Authors.
//
// 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 hostmm
import (
"bufio"
"fmt"
"os"
"path"
"strings"
)
// currentCgroupDirectory returns the directory for the cgroup for the given
// controller in which the calling process resides.
func currentCgroupDirectory(ctrl string) (string, error) {
root, err := cgroupRootDirectory(ctrl)
if err != nil {
return "", err
}
cg, err := currentCgroup(ctrl)
if err != nil {
return "", err
}
return path.Join(root, cg), nil
}
// cgroupRootDirectory returns the root directory for the cgroup hierarchy in
// which the given cgroup controller is mounted in the calling process' mount
// namespace.
func cgroupRootDirectory(ctrl string) (string, error) {
const path = "/proc/self/mounts"
file, err := os.Open(path)
if err != nil {
return "", err
}
defer file.Close()
// Per proc(5) -> fstab(5):
// Each line of /proc/self/mounts describes a mount.
scanner := bufio.NewScanner(file)
for scanner.Scan() {
// Each line consists of 6 space-separated fields. Find the line for
// which the third field (fs_vfstype) is cgroup, and the fourth field
// (fs_mntops, a comma-separated list of mount options) contains
// ctrl.
var spec, file, vfstype, mntopts, freq, passno string
const nrfields = 6
line := scanner.Text()
n, err := fmt.Sscan(line, &spec, &file, &vfstype, &mntopts, &freq, &passno)
if err != nil {
return "", fmt.Errorf("failed to parse %s: %v", path, err)
}
if n != nrfields {
return "", fmt.Errorf("failed to parse %s: line %q: got %d fields, wanted %d", path, line, n, nrfields)
}
if vfstype != "cgroup" {
continue
}
for _, mntopt := range strings.Split(mntopts, ",") {
if mntopt == ctrl {
return file, nil
}
}
}
return "", fmt.Errorf("no cgroup hierarchy mounted for controller %s", ctrl)
}
// currentCgroup returns the cgroup for the given controller in which the
// calling process resides. The returned string is a path that should be
// interpreted as relative to cgroupRootDirectory(ctrl).
func currentCgroup(ctrl string) (string, error) {
const path = "/proc/self/cgroup"
file, err := os.Open(path)
if err != nil {
return "", err
}
defer file.Close()
// Per proc(5) -> cgroups(7):
// Each line of /proc/self/cgroups describes a cgroup hierarchy.
scanner := bufio.NewScanner(file)
for scanner.Scan() {
// Each line consists of 3 colon-separated fields. Find the line for
// which the second field (controller-list, a comma-separated list of
// cgroup controllers) contains ctrl.
line := scanner.Text()
const nrfields = 3
fields := strings.Split(line, ":")
if len(fields) != nrfields {
return "", fmt.Errorf("failed to parse %s: line %q: got %d fields, wanted %d", path, line, len(fields), nrfields)
}
for _, controller := range strings.Split(fields[1], ",") {
if controller == ctrl {
return fields[2], nil
}
}
}
return "", fmt.Errorf("not a member of a cgroup hierarchy for controller %s", ctrl)
}
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