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container_linux.go
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container_linux.go
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// Unless explicitly stated otherwise all files in this repository are licensed
// under the Apache License Version 2.0.
// This product includes software developed at Datadog (https://www.datadoghq.com/).
// Copyright 2016 Datadog, Inc.
//go:build linux
package internal
import (
"bufio"
"fmt"
"io"
"os"
"path"
"regexp"
"strings"
"syscall"
)
const (
// cgroupPath is the path to the cgroup file where we can find the container id if one exists.
cgroupPath = "/proc/self/cgroup"
// cgroupV1BaseController is the base controller used to identify the cgroup v1 mount point in the cgroupMounts map.
cgroupV1BaseController = "memory"
// defaultCgroupMountPath is the path to the cgroup mount point.
defaultCgroupMountPath = "/sys/fs/cgroup"
uuidSource = "[0-9a-f]{8}[-_][0-9a-f]{4}[-_][0-9a-f]{4}[-_][0-9a-f]{4}[-_][0-9a-f]{12}|[0-9a-f]{8}(?:-[0-9a-f]{4}){4}$"
containerSource = "[0-9a-f]{64}"
taskSource = "[0-9a-f]{32}-\\d+"
// From https://github.com/torvalds/linux/blob/5859a2b1991101d6b978f3feb5325dad39421f29/include/linux/proc_ns.h#L41-L49
// Currently, host namespace inode number are hardcoded, which can be used to detect
// if we're running in host namespace or not (does not work when running in DinD)
hostCgroupNamespaceInode = 0xEFFFFFFB
)
var (
// expLine matches a line in the /proc/self/cgroup file. It has a submatch for the last element (path), which contains the container ID.
expLine = regexp.MustCompile(`^\d+:[^:]*:(.+)$`)
// expContainerID matches contained IDs and sources. Source: https://github.com/Qard/container-info/blob/master/index.js
expContainerID = regexp.MustCompile(fmt.Sprintf(`(%s|%s|%s)(?:.scope)?$`, uuidSource, containerSource, taskSource))
// containerID is the containerID read at init from /proc/self/cgroup
containerID string
// entityID is the entityID to use for the container. It is the `cid-<containerID>` if the container id available,
// otherwise the cgroup node controller's inode prefixed with `in-` or an empty string on incompatible OS.
// We use the memory controller on cgroupv1 and the root cgroup on cgroupv2.
entityID string
)
func init() {
containerID = readContainerID(cgroupPath)
entityID = readEntityID(defaultCgroupMountPath, cgroupPath, isHostCgroupNamespace())
}
// parseContainerID finds the first container ID reading from r and returns it.
func parseContainerID(r io.Reader) string {
scn := bufio.NewScanner(r)
for scn.Scan() {
path := expLine.FindStringSubmatch(scn.Text())
if len(path) != 2 {
// invalid entry, continue
continue
}
if parts := expContainerID.FindStringSubmatch(path[1]); len(parts) == 2 {
return parts[1]
}
}
return ""
}
// readContainerID attempts to return the container ID from the provided file path or empty on failure.
func readContainerID(fpath string) string {
f, err := os.Open(fpath)
if err != nil {
return ""
}
defer f.Close()
return parseContainerID(f)
}
// ContainerID attempts to return the container ID from /proc/self/cgroup or empty on failure.
func ContainerID() string {
return containerID
}
// parseCgroupNodePath parses /proc/self/cgroup and returns a map of controller to its associated cgroup node path.
func parseCgroupNodePath(r io.Reader) map[string]string {
res := make(map[string]string)
scn := bufio.NewScanner(r)
for scn.Scan() {
line := scn.Text()
tokens := strings.Split(line, ":")
if len(tokens) != 3 {
continue
}
if tokens[1] == cgroupV1BaseController || tokens[1] == "" {
res[tokens[1]] = tokens[2]
}
}
return res
}
// getCgroupInode returns the cgroup controller inode if it exists otherwise an empty string.
// The inode is prefixed by "in-" and is used by the agent to retrieve the container ID.
// We first try to retrieve the cgroupv1 memory controller inode, if it fails we try to retrieve the cgroupv2 inode.
func getCgroupInode(cgroupMountPath, procSelfCgroupPath string) string {
// Parse /proc/self/cgroup to retrieve the paths to the memory controller (cgroupv1) and the cgroup node (cgroupv2)
f, err := os.Open(procSelfCgroupPath)
if err != nil {
return ""
}
defer f.Close()
cgroupControllersPaths := parseCgroupNodePath(f)
// Retrieve the cgroup inode from /sys/fs/cgroup + controller + cgroupNodePath
for _, controller := range []string{cgroupV1BaseController, ""} {
cgroupNodePath, ok := cgroupControllersPaths[controller]
if !ok {
continue
}
inode := inodeForPath(path.Join(cgroupMountPath, controller, cgroupNodePath))
if inode != "" {
return inode
}
}
return ""
}
// inodeForPath returns the inode for the provided path or empty on failure.
func inodeForPath(path string) string {
fi, err := os.Stat(path)
if err != nil {
return ""
}
stats, ok := fi.Sys().(*syscall.Stat_t)
if !ok {
return ""
}
return fmt.Sprintf("in-%d", stats.Ino)
}
// readEntityID attempts to return the cgroup node inode or empty on failure.
func readEntityID(mountPath, cgroupPath string, isHostCgroupNamespace bool) string {
// First try to emit the containerID if available. It will be retrieved if the container is
// running in the host cgroup namespace, independently of the cgroup version.
if containerID != "" {
return "cid-" + containerID
}
// Rely on the inode if we're not running in the host cgroup namespace.
if isHostCgroupNamespace {
return ""
}
return getCgroupInode(mountPath, cgroupPath)
}
// EntityID attempts to return the container ID or the cgroup node controller's inode if the container ID
// is not available. The cid is prefixed with `cid-` and the inode with `in-`.
func EntityID() string {
return entityID
}
// isHostCgroupNamespace checks if the agent is running in the host cgroup namespace.
func isHostCgroupNamespace() bool {
fi, err := os.Stat("/proc/self/ns/cgroup")
if err != nil {
return false
}
stat, ok := fi.Sys().(*syscall.Stat_t)
if ok {
return stat.Ino == hostCgroupNamespaceInode
}
return false
}