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// -*- Mode: Go; indent-tabs-mode: t -*-
/*
* Copyright (C) 2022 Canonical Ltd
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 3 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
package cgroup
import (
"bufio"
"errors"
"fmt"
"os"
"path/filepath"
"strings"
)
var (
// path where v1 controllers are listed, see
// https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/index.html
// and cgroups(7)
cgroupV1ControllersPath = "/proc/cgroups"
// path where v2 controllers are listed, at the root of the hierarchy tree,
// see https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html
cgroupV2ControllersPath = filepath.Join(cgroupMountPoint, "cgroup.controllers")
errMemoryControllerDisabled = errors.New("cgroup memory controller is disabled on this system")
)
// CheckMemoryCgroup checks if the memory cgroup is enabled. It will return
// an error if not.
//
// Since the control groups can be enabled/disabled without the kernel config the only
// way to identify the status of memory control groups is via /proc/cgroups
// "cat /proc/cgroups | grep memory" returns the active status of memory control group
// and the 3rd parameter is the status
// 0 => false => disabled
// 1 => true => enabled
func CheckMemoryCgroup() error {
var supp bool
var err error
if IsUnified() {
supp, err = checkV2CgroupMemoryController()
} else {
supp, err = checkV1CgroupMemoryController()
}
if err != nil {
return err
}
if supp {
return nil
}
// no errors so far but found no evidence of memory controller to be enabled
return errMemoryControllerDisabled
}
func checkV1CgroupMemoryController() (bool, error) {
cgroupsFile, err := os.Open(filepath.Join(rootPath, cgroupV1ControllersPath))
if err != nil {
return false, fmt.Errorf("cannot open cgroups file: %w", err)
}
defer cgroupsFile.Close()
scanner := bufio.NewScanner(cgroupsFile)
for scanner.Scan() {
line := scanner.Text()
if strings.HasPrefix(line, "memory\t") {
memoryCgroupValues := strings.Fields(line)
if len(memoryCgroupValues) < 4 {
// change in size, should investigate the new structure
return false, fmt.Errorf("cannot parse cgroups file: invalid line %q", line)
}
isMemoryEnabled := memoryCgroupValues[3] == "1"
return isMemoryEnabled, nil
}
}
if err := scanner.Err(); err != nil {
return false, fmt.Errorf("cannot read %s contents: %w", cgroupV1ControllersPath, err)
}
return false, nil
}
func checkV2CgroupMemoryController() (bool, error) {
// check at the root controller
f, err := os.Open(filepath.Join(rootPath, cgroupV2ControllersPath))
if err != nil {
return false, err
}
defer f.Close()
scanner := bufio.NewScanner(f)
scanner.Split(bufio.ScanWords)
// expecting a single line
for scanner.Scan() {
if ctrl := scanner.Text(); ctrl == "memory" {
return true, nil
}
}
if err := scanner.Err(); err != nil {
return false, err
}
return false, nil
}
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