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// Copyright (C) 2016-2017 Luke Shumaker <lukeshu@sbcglobal.net>
//
// 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 sd_login
import (
"bufio"
"fmt"
"io"
"os"
"strings"
"golang.org/x/sys/unix"
)
type _Cgroup string
var cgVersion_cache uint
func cgVersion() uint {
if cgVersion_cache == 0 {
fs, err := statfs("/sys/fs/cgroup/")
if err != nil {
return 0
}
if fs.Type == magic_CGROUP2_SUPER {
cgVersion_cache = 2
} else if fs.Type == magic_TMPFS {
// XXX: systemd-specific cgroup v1 logic
fs, err = statfs("/sys/fs/cgroup/systemd/")
if err != nil {
return 0
}
if fs.Type == magic_CGROUP2_SUPER {
cgVersion_cache = 2
} else {
cgVersion_cache = 1
}
}
}
return cgVersion_cache
}
// getCgroup returns the cgroup path of the process, relative to the
// root of the cgroup hierarchy.
//
// In cgroup v2, there is a only one cgroup hierarchy, so the behavior
// is obvious.
//
// However, in cgroup v1, there were multiple cgroup hierarchies, so
// this function must decide which hierarchy to use. We chooses the
// first hierarchy with either the "name=systemd" controller or the
// "name=elogind" controller attached to it[1]. If no such hierarchy
// exists, then an error is returned.
//
// However, it is possible to generally use cgroup v1, but use a
// single (named) v2 hierarchy alongside many v1 hierarchies. In this
// case, we use the v2 hierarchy iff it is named "systemd", otherwise
// we use the cgroup v1 behavior.
//
// [1]: The "first" in that sentence is worrying; shouldn't the choice
// of hierarchy not depend on the undefined order that controllers are
// listed in? Well, a controller may be attached to only one
// hierarchy at a time. So there is only an ambiguity for "first" to
// come in if both "name=systemd" and "name=elogind" controllers
// exist. Systemd and elogind cannot be used together, so this isn't
// a concern.
//
// BUG(lukeshu): ProcessID.getCgroup: Has systemd-specific logic. However,
// it is only for "legacy" cgroup v1 compatibility; the cgroup v2
// logic is totally implementation-agnostic. Unfortunately(?), no
// distro seems to be using cgroup v2 (introduced in Linux 4.5) yet by
// default.
func (pid ProcessID) getCgroup() (_Cgroup, error) {
cgVer := cgVersion()
var cgroupFilename string
if pid == 0 {
cgroupFilename = "/proc/self/cgroup"
} else {
cgroupFilename = fmt.Sprintf("/proc/%d/cgroup", pid)
}
f, err := os.Open(cgroupFilename)
if err != nil {
return "", err
}
defer f.Close()
bf := bufio.NewReader(f)
for {
line, err := bf.ReadString('\n')
if err == io.EOF {
break
}
if err != nil {
return "", err
}
line = strings.TrimSuffix(line, "\n")
parts := strings.SplitN(line, ":", 3)
if len(parts) != 3 {
continue
}
hierarchy := parts[0]
controllers := parts[1]
path := _Cgroup(parts[2])
switch cgVer {
case 1:
for _, controller := range strings.Split(controllers, ",") {
if controller == "name=systemd" || controller == "name=elogind" {
return path, nil
}
}
case 2:
if hierarchy != "0" {
continue
}
return path, nil
}
}
return "", unix.ENODATA
}
// cgGetRootPath determines the cgroup that all other cgroups belong
// to. The common case is just "/", but it could be something else if
// we are inside of a container, but have a view of the entier cgroup
// hierarchy.
//
// BUG(lukeshu): cgGetRootPath: works correctly on systemd and
// elogind, but I'm not sure it's general.
func cgGetRootPath() (_Cgroup, error) {
cgpath, err := ProcessID(1).getCgroup()
if err != nil {
return "/", err
}
cgpath = _Cgroup(trimOneSuffix(string(cgpath),
"/init.scope", // modern systemd
"/system.slice", // legacy systemd
"/system", // even more legacy systemd
))
return cgpath, nil
}
func cgUnescape(s string) string {
return strings.TrimPrefix(s, "_")
}
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