1 files changed, 111 insertions, 0 deletions
diff --git a/pkg/sentry/hostmm/cgroup.go b/pkg/sentry/hostmm/cgroup.go
new file mode 100644
index 000000000..e5cc26ab2
--- /dev/null
+++ b/pkg/sentry/hostmm/cgroup.go
@@ -0,0 +1,111 @@
+// Copyright 2019 The gVisor 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 hostmm
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"path"
+	"strings"
+)
+
+// currentCgroupDirectory returns the directory for the cgroup for the given
+// controller in which the calling process resides.
+func currentCgroupDirectory(ctrl string) (string, error) {
+	root, err := cgroupRootDirectory(ctrl)
+	if err != nil {
+		return "", err
+	}
+	cg, err := currentCgroup(ctrl)
+	if err != nil {
+		return "", err
+	}
+	return path.Join(root, cg), nil
+}
+
+// cgroupRootDirectory returns the root directory for the cgroup hierarchy in
+// which the given cgroup controller is mounted in the calling process' mount
+// namespace.
+func cgroupRootDirectory(ctrl string) (string, error) {
+	const path = "/proc/self/mounts"
+	file, err := os.Open(path)
+	if err != nil {
+		return "", err
+	}
+	defer file.Close()
+
+	// Per proc(5) -> fstab(5):
+	// Each line of /proc/self/mounts describes a mount.
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		// Each line consists of 6 space-separated fields. Find the line for
+		// which the third field (fs_vfstype) is cgroup, and the fourth field
+		// (fs_mntops, a comma-separated list of mount options) contains
+		// ctrl.
+		var spec, file, vfstype, mntopts, freq, passno string
+		const nrfields = 6
+		line := scanner.Text()
+		n, err := fmt.Sscan(line, &spec, &file, &vfstype, &mntopts, &freq, &passno)
+		if err != nil {
+			return "", fmt.Errorf("failed to parse %s: %v", path, err)
+		}
+		if n != nrfields {
+			return "", fmt.Errorf("failed to parse %s: line %q: got %d fields, wanted %d", path, line, n, nrfields)
+		}
+		if vfstype != "cgroup" {
+			continue
+		}
+		for _, mntopt := range strings.Split(mntopts, ",") {
+			if mntopt == ctrl {
+				return file, nil
+			}
+		}
+	}
+	return "", fmt.Errorf("no cgroup hierarchy mounted for controller %s", ctrl)
+}
+
+// currentCgroup returns the cgroup for the given controller in which the
+// calling process resides. The returned string is a path that should be
+// interpreted as relative to cgroupRootDirectory(ctrl).
+func currentCgroup(ctrl string) (string, error) {
+	const path = "/proc/self/cgroup"
+	file, err := os.Open(path)
+	if err != nil {
+		return "", err
+	}
+	defer file.Close()
+
+	// Per proc(5) -> cgroups(7):
+	// Each line of /proc/self/cgroups describes a cgroup hierarchy.
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		// Each line consists of 3 colon-separated fields. Find the line for
+		// which the second field (controller-list, a comma-separated list of
+		// cgroup controllers) contains ctrl.
+		line := scanner.Text()
+		const nrfields = 3
+		fields := strings.Split(line, ":")
+		if len(fields) != nrfields {
+			return "", fmt.Errorf("failed to parse %s: line %q: got %d fields, wanted %d", path, line, len(fields), nrfields)
+		}
+		for _, controller := range strings.Split(fields[1], ",") {
+			if controller == ctrl {
+				return fields[2], nil
+			}
+		}
+	}
+	return "", fmt.Errorf("not a member of a cgroup hierarchy for controller %s", ctrl)
+}