diff options
Diffstat (limited to 'sd_login/cgroup_generic.go')
-rw-r--r-- | sd_login/cgroup_generic.go | 163 |
1 files changed, 163 insertions, 0 deletions
diff --git a/sd_login/cgroup_generic.go b/sd_login/cgroup_generic.go new file mode 100644 index 0000000..3842c64 --- /dev/null +++ b/sd_login/cgroup_generic.go @@ -0,0 +1,163 @@ +// 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): PID.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 PID) 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 := PID(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, "_") +} |