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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
type _CgroupTree string
type _CgroupLeaf 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 {
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.
func (pid ProcessID) GetCgroup() (string, error) {
cgVer := cgVersion()
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 := 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
}
func (pid ProcessID) getCgroup() (_Cgroup, error) {
cgroup, err := pid.GetCgroup()
return _Cgroup(cgroup), err
}
// 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.
func cgGetRootPath() (_CgroupTree, error) {
cgroup, err := ProcessID(1).getCgroup()
if err != nil {
return "/", err
}
cgTree := _CgroupTree(trimOneSuffix(string(cgroup),
"/init.scope", // modern systemd
"/system.slice", // legacy systemd
"/system", // even more legacy systemd
))
return cgTree, nil
}
func cgUnescape(s string) string {
return strings.TrimPrefix(s, "_")
}
func cgDecodeUnit(unit string) string {
if len(unit) < 3 {
// because "X.Y" is at least 3 characters
return ""
}
unit = cgUnescape(unit)
if valid_unit_name(unit)&(unit_name_plain|unit_name_instance) == 0 {
return ""
}
return unit
}
func (tree _CgroupTree) Parse(cgroup _Cgroup) (leaf _CgroupLeaf) {
rest, ok := path_startswith(string(cgroup), string(tree))
if ok {
return _CgroupLeaf(rest)
} else {
return ""
}
}
// Even if there is an invalid unit, a slice might still be returned.
func (leaf _CgroupLeaf) Parse() (slice, unit string, extra _CgroupLeaf) {
strLeaf := string(leaf)
slice = "-.slice"
for {
part, rest := split2(strings.TrimLeft(strLeaf, "/"), '/')
if valid_slice_name(part) {
slice = part
strLeaf = rest
} else {
break
}
}
slice = cgDecodeUnit(slice)
if slice == "" {
return
}
unit, extraStr := split2(strings.TrimLeft(strLeaf, "/"), '/')
unit = cgDecodeUnit(unit)
if unit == "" {
return
}
extra = _CgroupLeaf(extraStr)
return
}
func (leaf _CgroupLeaf) GetSlice() string {
slice, _, _ := leaf.Parse()
return slice
}
func (leaf _CgroupLeaf) GetUnit() string {
_, unit, _ := leaf.Parse()
return unit
}
func (leaf _CgroupLeaf) GetRest() _CgroupLeaf {
_, _, extra := leaf.Parse()
return extra
}
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