Import cgroup2 support & use generics to improve pparser's interface

.github/workflows/go.yml

@@ -8,17 +8,17 @@ jobs:
     strategy:
       matrix:
         os: [macOS-latest, ubuntu-latest]
-        goversion: [1.17, 1.18, 1.19]
+        goversion: ['1.22', '1.23']
     steps:
 
     - name: Set up Go ${{matrix.goversion}} on ${{matrix.os}}
-      uses: actions/setup-go@v3
+      uses: actions/setup-go@v5
       with:
         go-version: ${{matrix.goversion}}
       id: go
 
     - name: Check out code into the Go module directory
-      uses: actions/checkout@v1
+      uses: actions/checkout@v4
 
     - name: gofmt
       run: |

.github/workflows/staticcheck.yml

@@ -6,9 +6,9 @@ jobs:
     name: "staticcheck"
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v4
       with:
         fetch-depth: 1
-    - uses: dominikh/staticcheck-action@v1.1.0
+    - uses: dominikh/staticcheck-action@v1.3.1
       with:
-        version: "2022.1.3"
+        version: "2024.1.1"

cgresolver/cg_path.go

@@ -0,0 +1,106 @@
+// package cgresolver contains helpers and types for resolving the CGroup associated with specific subsystems
+// If you don't know what cgroup subsystems are, you probably want one of the higher-level interfaces in the parent package.
+package cgresolver
+
+import (
+	"fmt"
+	"os"
+	"slices"
+	"strconv"
+	"strings"
+)
+
+// CGMode is an enum indicating which cgroup type is active for the returned controller
+type CGMode uint8
+
+const (
+	CGModeUnknown CGMode = iota
+	// CGroup V1
+	CGModeV1
+	// CGroup V2
+	CGModeV2
+)
+
+func cgroup2Mode(iscg2 bool) CGMode {
+	if iscg2 {
+		return CGModeV2
+	}
+	return CGModeV1
+}
+
+// CGroupPath includes information about a cgroup.
+type CGroupPath struct {
+	AbsPath   string
+	MountPath string
+	Mode      CGMode
+}
+
+// Parent returns a CGroupPath for the parent directory as long as it wouldn't pass the root of the mountpoint.
+// second return indicates whether a new path was returned.
+func (c *CGroupPath) Parent() (CGroupPath, bool) {
+	// Remove any trailing slash
+	path := strings.TrimSuffix(c.AbsPath, string(os.PathSeparator))
+	mnt := strings.TrimSuffix(c.MountPath, string(os.PathSeparator))
+	if mnt == path {
+		return CGroupPath{
+			AbsPath:   path,
+			MountPath: mnt,
+			Mode:      c.Mode,
+		}, false
+	}
+	lastSlashIdx := strings.LastIndexByte(path, byte(os.PathSeparator))
+	if lastSlashIdx == -1 {
+		// This shouldn't happen
+		panic("invalid state: path \"" + path + "\" has no slashes and doesn't match the mountpoint")
+	}
+	return CGroupPath{
+		AbsPath:   path[:lastSlashIdx],
+		MountPath: mnt, // Strip any trailing slash in case one snuck in
+		Mode:      c.Mode,
+	}, true
+}
+
+// SelfSubsystemPath returns a CGroupPath for the cgroup associated with a specific subsystem for the current process.
+func SelfSubsystemPath(subsystem string) (CGroupPath, error) {
+	return subsystemPath("self", subsystem)
+}
+
+// PIDSubsystemPath returns a CGroupPath for the cgroup associated with a specific subsystem for the specified PID
+func PIDSubsystemPath(pid int, subsystem string) (CGroupPath, error) {
+	return subsystemPath(strconv.Itoa(pid), subsystem)
+}
+
+func subsystemPath(procSubDir string, subsystem string) (CGroupPath, error) {
+	cgSubSyses, cgSubSysReadErr := ParseReadCGSubsystems()
+	if cgSubSysReadErr != nil {
+		return CGroupPath{}, fmt.Errorf("failed to resolve subsystems to hierarchies: %w", cgSubSysReadErr)
+	}
+	cgIdx := slices.IndexFunc(cgSubSyses, func(c CGroupSubsystem) bool {
+		return c.Subsys == subsystem
+	})
+	if cgIdx == -1 {
+		return CGroupPath{}, fmt.Errorf("no cgroup hierarchy associated with subsystem %q", subsystem)
+	}
+	cgHierID := cgSubSyses[cgIdx].Hierarchy
+
+	procCGs, procCGsErr := resolveProcCGControllers(procSubDir)
+	if procCGsErr != nil {
+		return CGroupPath{}, fmt.Errorf("failed to resolve cgroup controllers: %w", procCGsErr)
+	}
+
+	procCGIdx := slices.IndexFunc(procCGs, func(cg CGProcHierarchy) bool { return cg.HierarchyID == cgHierID })
+	if procCGIdx == -1 {
+		return CGroupPath{}, fmt.Errorf("failed to resolve process cgroup controllers: %w", procCGsErr)
+	}
+
+	cgMountInfo, mountInfoParseErr := CGroupMountInfo()
+	if mountInfoParseErr != nil {
+		return CGroupPath{}, fmt.Errorf("failed to parse mountinfo: %w", mountInfoParseErr)
+	}
+
+	cgPath, cgPathErr := procCGs[procCGIdx].cgPath(cgMountInfo)
+	if cgPathErr != nil {
+		return CGroupPath{}, fmt.Errorf("failed to resolve filesystem path for cgroup %+v: %w", procCGs[procCGIdx], cgPathErr)
+	}
+	return cgPath, nil
+}

cgresolver/cg_path_test.go

@@ -0,0 +1,93 @@
+package cgresolver
+
+import "testing"
+
+func TestCGroupPathParent(t *testing.T) {
+	for _, tbl := range []struct {
+		name         string
+		in           CGroupPath
+		expParent    CGroupPath
+		expNewParent bool
+	}{
+		{
+			name: "cgroup_mount_root",
+			in: CGroupPath{
+				AbsPath:   "/sys/fs/cgroup",
+				MountPath: "/sys/fs/cgroup",
+				Mode:      CGModeV2,
+			},
+			expParent: CGroupPath{
+				AbsPath:   "/sys/fs/cgroup",
+				MountPath: "/sys/fs/cgroup",
+				Mode:      CGModeV2,
+			},
+			expNewParent: false,
+		},
+		{
+			name: "cgroup_mount_root_strip_trailing_slashes",
+			in: CGroupPath{
+				AbsPath:   "/sys/fs/cgroup/",
+				MountPath: "/sys/fs/cgroup/",
+				Mode:      CGModeV2,
+			},
+			expParent: CGroupPath{
+				AbsPath:   "/sys/fs/cgroup",
+				MountPath: "/sys/fs/cgroup",
+				Mode:      CGModeV2,
+			},
+			expNewParent: false,
+		},
+		{
+			name: "cgroup_mount_sub_cgroup_cgv1",
+			in: CGroupPath{
+				AbsPath:   "/sys/fs/cgroup/a/b/c",
+				MountPath: "/sys/fs/cgroup",
+				Mode:      CGModeV1,
+			},
+			expParent: CGroupPath{
+				AbsPath:   "/sys/fs/cgroup/a/b",
+				MountPath: "/sys/fs/cgroup",
+				Mode:      CGModeV1,
+			},
+			expNewParent: true,
+		},
+		{
+			name: "cgroup_mount_sub_cgroup_cgv2",
+			in: CGroupPath{
+				AbsPath:   "/sys/fs/cgroup/a/b/c",
+				MountPath: "/sys/fs/cgroup",
+				Mode:      CGModeV2,
+			},
+			expParent: CGroupPath{
+				AbsPath:   "/sys/fs/cgroup/a/b",
+				MountPath: "/sys/fs/cgroup",
+				Mode:      CGModeV2,
+			},
+			expNewParent: true,
+		},
+		{
+			name: "cgroup_mount_sub_cgroup_strip_trailing_slash",
+			in: CGroupPath{
+				AbsPath:   "/sys/fs/cgroup/a/b/c/",
+				MountPath: "/sys/fs/cgroup",
+				Mode:      CGModeV2,
+			},
+			expParent: CGroupPath{
+				AbsPath:   "/sys/fs/cgroup/a/b",
+				MountPath: "/sys/fs/cgroup",
+				Mode:      CGModeV2,
+			},
+			expNewParent: true,
+		},
+	} {
+		t.Run(tbl.name, func(t *testing.T) {
+			par, np := tbl.in.Parent()
+			if np != tbl.expNewParent {
+				t.Errorf("unexpected OK value: %t; expected %t", np, tbl.expNewParent)
+			}
+			if par != tbl.expParent {
+				t.Errorf("unexpected parent CGroupPath:\n  got %+v\n want %+v", par, tbl.expParent)
+			}
+		})
+	}
+}

cgresolver/mountinfo_parse.go

@@ -0,0 +1,137 @@
+package cgresolver
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+// Mount represents a cgroup or cgroup2 mount.
+// Subsystems will be nil if the mount is for a unified hierarchy/cgroup v2
+// in that case, CGroupV2 will be true.
+type Mount struct {
+	Mountpoint string
+	Root       string
+	Subsystems []string
+	CGroupV2   bool // true if this is a cgroup2 mount
+}
+
+const (
+	mountinfoPath = "/proc/self/mountinfo"
+)
+
+// CGroupMountInfo parses /proc/self/mountinfo and returns info about all cgroup and cgroup2 mounts
+func CGroupMountInfo() ([]Mount, error) {
+	mountinfoContents, mntInfoReadErr := os.ReadFile(mountinfoPath)
+	if mntInfoReadErr != nil {
+		return nil, fmt.Errorf("failed to read contents of %s: %w",
+			mountinfoPath, mntInfoReadErr)
+	}
+
+	mounts, mntsErr := getCGroupMountsFromMountinfo(string(mountinfoContents))
+	if mntsErr != nil {
+		return nil, fmt.Errorf("failed to list cgroupfs mounts: %w", mntsErr)
+	}
+
+	return mounts, nil
+}
+
+func getCGroupMountsFromMountinfo(mountinfo string) ([]Mount, error) {
+	// mountinfo is line-delimited, then space-delimited
+	mountinfoLines := strings.Split(mountinfo, "\n")
+	if len(mountinfoLines) == 0 {
+		return nil, fmt.Errorf("unexpectedly empty mountinfo (one line): %q", mountinfo)
+	}
+	out := make([]Mount, 0, len(mountinfoLines))
+	for _, line := range mountinfoLines {
+		if len(line) == 0 {
+			continue
+		}
+		sections := strings.SplitN(line, " - ", 2)
+		if len(sections) < 2 {
+			return nil, fmt.Errorf("missing section separator in line %q", line)
+		}
+		s2Fields := strings.SplitN(sections[1], " ", 3)
+		if len(s2Fields) < 3 {
+			return nil, fmt.Errorf("line %q contains %d fields in second section, expected 3",
+				line, len(s2Fields))
+
+		}
+		isCG2 := false
+		switch s2Fields[0] {
+		case "cgroup":
+			isCG2 = false
+		case "cgroup2":
+			isCG2 = true
+		default:
+			// skip anything that's not a cgroup
+			continue
+		}
+		s1Fields := strings.Split(sections[0], " ")
+		if len(s1Fields) < 5 {
+			return nil, fmt.Errorf("too few fields in line %q before optional separator: %d; expected 5",
+				line, len(s1Fields))
+		}
+		mntpnt, mntPntUnescapeErr := unOctalEscape(s1Fields[4])
+		if mntPntUnescapeErr != nil {
+			return nil, fmt.Errorf("failed to unescape mountpoint %q: %w", s1Fields[4], mntPntUnescapeErr)
+		}
+		rootPath, rootUnescErr := unOctalEscape(s1Fields[3])
+		if rootUnescErr != nil {
+			return nil, fmt.Errorf("failed to unescape mount root %q: %w", s1Fields[3], rootUnescErr)
+		}
+		mnt := Mount{
+			CGroupV2:   isCG2,
+			Mountpoint: mntpnt,
+			Root:       rootPath,
+			Subsystems: nil,
+		}
+		// only bother with the mount options to find subsystems if cgroup v1
+		if !isCG2 {
+			for _, mntOpt := range strings.Split(s2Fields[2], ",") {
+				switch mntOpt {
+				case "ro", "rw":
+					// These mount options are lies, (or at least
+					// only reflect the original mount, without
+					// considering the layering of later bind-mounts)
+					continue
+				case "":
+					continue
+				default:
+					mnt.Subsystems = append(mnt.Subsystems, mntOpt)
+				}
+			}
+		}
+
+		out = append(out, mnt)
+
+	}
+	return out, nil
+}
+
+func unOctalEscape(str string) (string, error) {
+	b := strings.Builder{}
+	b.Grow(len(str))
+	for {
+		backslashIdx := strings.IndexByte(str, byte('\\'))
+		if backslashIdx == -1 {
+			b.WriteString(str)
+			return b.String(), nil
+		}
+		b.WriteString(str[:backslashIdx])
+		// if the end of the escape is beyond the end of the string, abort!
+		if backslashIdx+3 >= len(str) {
+			return "", fmt.Errorf("invalid offset: %d+3 >= len %d", backslashIdx, len(str))
+		}
+		// slice out the octal 3-digit component
+		esc := str[backslashIdx+1 : backslashIdx+4]
+		asciiVal, parseUintErr := strconv.ParseUint(esc, 8, 8)
+		if parseUintErr != nil {
+			return "", fmt.Errorf("failed to parse escape value %q: %w", esc, parseUintErr)
+		}
+		b.WriteByte(byte(asciiVal))
+		str = str[backslashIdx+4:]
+	}
+
+}