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// Copyright 2020 The Prometheus 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 procfs
import (
"bufio"
"bytes"
"fmt"
"strconv"
"strings"
"github.com/prometheus/procfs/internal/util"
)
// Cgroup models one line from /proc/[pid]/cgroup. Each Cgroup struct describes the the placement of a PID inside a
// specific control hierarchy. The kernel has two cgroup APIs, v1 and v2. v1 has one hierarchy per available resource
// controller, while v2 has one unified hierarchy shared by all controllers. Regardless of v1 or v2, all hierarchies
// contain all running processes, so the question answerable with a Cgroup struct is 'where is this process in
// this hierarchy' (where==what path on the specific cgroupfs). By prefixing this path with the mount point of
// *this specific* hierarchy, you can locate the relevant pseudo-files needed to read/set the data for this PID
// in this hierarchy
//
// Also see http://man7.org/linux/man-pages/man7/cgroups.7.html
type Cgroup struct {
// HierarchyID that can be matched to a named hierarchy using /proc/cgroups. Cgroups V2 only has one
// hierarchy, so HierarchyID is always 0. For cgroups v1 this is a unique ID number
HierarchyID int
// Controllers using this hierarchy of processes. Controllers are also known as subsystems. For
// Cgroups V2 this may be empty, as all active controllers use the same hierarchy
Controllers []string
// Path of this control group, relative to the mount point of the cgroupfs representing this specific
// hierarchy
Path string
}
// parseCgroupString parses each line of the /proc/[pid]/cgroup file
// Line format is hierarchyID:[controller1,controller2]:path
func parseCgroupString(cgroupStr string) (*Cgroup, error) {
var err error
fields := strings.Split(cgroupStr, ":")
if len(fields) < 3 {
return nil, fmt.Errorf("at least 3 fields required, found %d fields in cgroup string: %s", len(fields), cgroupStr)
}
cgroup := &Cgroup{
Path: fields[2],
Controllers: nil,
}
cgroup.HierarchyID, err = strconv.Atoi(fields[0])
if err != nil {
return nil, fmt.Errorf("failed to parse hierarchy ID")
}
if fields[1] != "" {
ssNames := strings.Split(fields[1], ",")
cgroup.Controllers = append(cgroup.Controllers, ssNames...)
}
return cgroup, nil
}
// parseCgroups reads each line of the /proc/[pid]/cgroup file
func parseCgroups(data []byte) ([]Cgroup, error) {
var cgroups []Cgroup
scanner := bufio.NewScanner(bytes.NewReader(data))
for scanner.Scan() {
mountString := scanner.Text()
parsedMounts, err := parseCgroupString(mountString)
if err != nil {
return nil, err
}
cgroups = append(cgroups, *parsedMounts)
}
err := scanner.Err()
return cgroups, err
}
// Cgroups reads from /proc/<pid>/cgroups and returns a []*Cgroup struct locating this PID in each process
// control hierarchy running on this system. On every system (v1 and v2), all hierarchies contain all processes,
// so the len of the returned struct is equal to the number of active hierarchies on this system
func (p Proc) Cgroups() ([]Cgroup, error) {
data, err := util.ReadFileNoStat(fmt.Sprintf("/proc/%d/cgroup", p.PID))
if err != nil {
return nil, err
}
return parseCgroups(data)
}
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