Implement cgroupfs.

A skeleton implementation of cgroupfs. It supports trivial cpu and
memory controllers with no support for hierarchies.

PiperOrigin-RevId: 366561126

8 files changed, 803 insertions, 0 deletions

diff --git a/test/syscalls/BUILD b/test/syscalls/BUILD
index ef299799e..3bd93df70 100644
--- a/test/syscalls/BUILD
+++ b/test/syscalls/BUILD
@@ -995,3 +995,7 @@ syscall_test(
 syscall_test(
     test = "//test/syscalls/linux:processes_test",
 )
+
+syscall_test(
+    test = "//test/syscalls/linux:cgroup_test",
+)
diff --git a/test/syscalls/linux/BUILD b/test/syscalls/linux/BUILD
index 043ada583..a9fa93437 100644
--- a/test/syscalls/linux/BUILD
+++ b/test/syscalls/linux/BUILD
@@ -4205,3 +4205,24 @@ cc_binary(
         "//test/util:test_util",
     ],
 )
+
+cc_binary(
+    name = "cgroup_test",
+    testonly = 1,
+    srcs = ["cgroup.cc"],
+    linkstatic = 1,
+    deps = [
+        "//test/util:capability_util",
+        "//test/util:cgroup_util",
+        "//test/util:file_descriptor",
+        "//test/util:fs_util",
+        "@com_google_absl//absl/strings",
+        gtest,
+        "//test/util:posix_error",
+        "//test/util:temp_path",
+        "//test/util:test_main",
+        "//test/util:test_util",
+        "@com_google_absl//absl/container:flat_hash_map",
+        "@com_google_absl//absl/container:flat_hash_set",
+    ],
+)
diff --git a/test/syscalls/linux/cgroup.cc b/test/syscalls/linux/cgroup.cc
new file mode 100644
index 000000000..3a51348ba
--- /dev/null
+++ b/test/syscalls/linux/cgroup.cc
@@ -0,0 +1,370 @@
+// Copyright 2021 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.
+
+// All tests in this file rely on being about to mount and unmount cgroupfs,
+// which isn't expected to work, or be safe on a general linux system.
+
+#include <sys/mount.h>
+#include <unistd.h>
+
+#include "gtest/gtest.h"
+#include "absl/container/flat_hash_map.h"
+#include "absl/container/flat_hash_set.h"
+#include "test/util/capability_util.h"
+#include "test/util/cgroup_util.h"
+#include "test/util/temp_path.h"
+#include "test/util/test_util.h"
+
+namespace gvisor {
+namespace testing {
+namespace {
+
+using ::testing::_;
+using ::testing::Gt;
+
+std::vector<std::string> known_controllers = {"cpu", "cpuset", "cpuacct",
+                                              "memory"};
+
+bool CgroupsAvailable() {
+  return IsRunningOnGvisor() && !IsRunningWithVFS1() &&
+         TEST_CHECK_NO_ERRNO_AND_VALUE(HaveCapability(CAP_SYS_ADMIN));
+}
+
+TEST(Cgroup, MountSucceeds) {
+  SKIP_IF(!CgroupsAvailable());
+
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup c = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs(""));
+  EXPECT_NO_ERRNO(c.ContainsCallingProcess());
+}
+
+TEST(Cgroup, SeparateMounts) {
+  SKIP_IF(!CgroupsAvailable());
+
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+
+  for (const auto& ctl : known_controllers) {
+    Cgroup c = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs(ctl));
+    EXPECT_NO_ERRNO(c.ContainsCallingProcess());
+  }
+}
+
+TEST(Cgroup, AllControllersImplicit) {
+  SKIP_IF(!CgroupsAvailable());
+
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup c = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs(""));
+
+  absl::flat_hash_map<std::string, CgroupsEntry> cgroups_entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcCgroupsEntries());
+  for (const auto& ctl : known_controllers) {
+    EXPECT_TRUE(cgroups_entries.contains(ctl))
+        << absl::StreamFormat("ctl=%s", ctl);
+  }
+  EXPECT_EQ(cgroups_entries.size(), known_controllers.size());
+}
+
+TEST(Cgroup, AllControllersExplicit) {
+  SKIP_IF(!CgroupsAvailable());
+
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup c = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs("all"));
+
+  absl::flat_hash_map<std::string, CgroupsEntry> cgroups_entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcCgroupsEntries());
+  for (const auto& ctl : known_controllers) {
+    EXPECT_TRUE(cgroups_entries.contains(ctl))
+        << absl::StreamFormat("ctl=%s", ctl);
+  }
+  EXPECT_EQ(cgroups_entries.size(), known_controllers.size());
+}
+
+TEST(Cgroup, ProcsAndTasks) {
+  SKIP_IF(!CgroupsAvailable());
+
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup c = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs(""));
+  absl::flat_hash_set<pid_t> pids = ASSERT_NO_ERRNO_AND_VALUE(c.Procs());
+  absl::flat_hash_set<pid_t> tids = ASSERT_NO_ERRNO_AND_VALUE(c.Tasks());
+
+  EXPECT_GE(tids.size(), pids.size()) << "Found more processes than threads";
+
+  // Pids should be a strict subset of tids.
+  for (auto it = pids.begin(); it != pids.end(); ++it) {
+    EXPECT_TRUE(tids.contains(*it))
+        << absl::StreamFormat("Have pid %d, but no such tid", *it);
+  }
+}
+
+TEST(Cgroup, ControllersMustBeInUniqueHierarchy) {
+  SKIP_IF(!CgroupsAvailable());
+
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  // Hierarchy #1: all controllers.
+  Cgroup all = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs(""));
+  // Hierarchy #2: memory.
+  //
+  // This should conflict since memory is already in hierarchy #1, and the two
+  // hierarchies have different sets of controllers, so this mount can't be a
+  // view into hierarchy #1.
+  EXPECT_THAT(m.MountCgroupfs("memory"), PosixErrorIs(EBUSY, _))
+      << "Memory controller mounted on two hierarchies";
+  EXPECT_THAT(m.MountCgroupfs("cpu"), PosixErrorIs(EBUSY, _))
+      << "CPU controller mounted on two hierarchies";
+}
+
+TEST(Cgroup, UnmountFreesControllers) {
+  SKIP_IF(!CgroupsAvailable());
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup all = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs(""));
+  // All controllers are now attached to all's hierarchy. Attempting new mount
+  // with any individual controller should fail.
+  EXPECT_THAT(m.MountCgroupfs("memory"), PosixErrorIs(EBUSY, _))
+      << "Memory controller mounted on two hierarchies";
+
+  // Unmount the "all" hierarchy. This should enable any controller to be
+  // mounted on a new hierarchy again.
+  ASSERT_NO_ERRNO(m.Unmount(all));
+  EXPECT_NO_ERRNO(m.MountCgroupfs("memory"));
+  EXPECT_NO_ERRNO(m.MountCgroupfs("cpu"));
+}
+
+TEST(Cgroup, OnlyContainsControllerSpecificFiles) {
+  SKIP_IF(!CgroupsAvailable());
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup mem = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs("memory"));
+  EXPECT_THAT(Exists(mem.Relpath("memory.usage_in_bytes")),
+              IsPosixErrorOkAndHolds(true));
+  // CPU files shouldn't exist in memory cgroups.
+  EXPECT_THAT(Exists(mem.Relpath("cpu.cfs_period_us")),
+              IsPosixErrorOkAndHolds(false));
+  EXPECT_THAT(Exists(mem.Relpath("cpu.cfs_quota_us")),
+              IsPosixErrorOkAndHolds(false));
+  EXPECT_THAT(Exists(mem.Relpath("cpu.shares")), IsPosixErrorOkAndHolds(false));
+
+  Cgroup cpu = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs("cpu"));
+  EXPECT_THAT(Exists(cpu.Relpath("cpu.cfs_period_us")),
+              IsPosixErrorOkAndHolds(true));
+  EXPECT_THAT(Exists(cpu.Relpath("cpu.cfs_quota_us")),
+              IsPosixErrorOkAndHolds(true));
+  EXPECT_THAT(Exists(cpu.Relpath("cpu.shares")), IsPosixErrorOkAndHolds(true));
+  // Memory files shouldn't exist in cpu cgroups.
+  EXPECT_THAT(Exists(cpu.Relpath("memory.usage_in_bytes")),
+              IsPosixErrorOkAndHolds(false));
+}
+
+TEST(Cgroup, InvalidController) {
+  SKIP_IF(!CgroupsAvailable());
+
+  TempPath mountpoint = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir());
+  std::string mopts = "this-controller-is-invalid";
+  EXPECT_THAT(
+      mount("none", mountpoint.path().c_str(), "cgroup", 0, mopts.c_str()),
+      SyscallFailsWithErrno(EINVAL));
+}
+
+TEST(Cgroup, MoptAllMustBeExclusive) {
+  SKIP_IF(!CgroupsAvailable());
+
+  TempPath mountpoint = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir());
+  std::string mopts = "all,cpu";
+  EXPECT_THAT(
+      mount("none", mountpoint.path().c_str(), "cgroup", 0, mopts.c_str()),
+      SyscallFailsWithErrno(EINVAL));
+}
+
+TEST(MemoryCgroup, MemoryUsageInBytes) {
+  SKIP_IF(!CgroupsAvailable());
+
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup c = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs("memory"));
+  EXPECT_THAT(c.ReadIntegerControlFile("memory.usage_in_bytes"),
+              IsPosixErrorOkAndHolds(Gt(0)));
+}
+
+TEST(CPUCgroup, ControlFilesHaveDefaultValues) {
+  SKIP_IF(!CgroupsAvailable());
+
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup c = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs("cpu"));
+  EXPECT_THAT(c.ReadIntegerControlFile("cpu.cfs_quota_us"),
+              IsPosixErrorOkAndHolds(-1));
+  EXPECT_THAT(c.ReadIntegerControlFile("cpu.cfs_period_us"),
+              IsPosixErrorOkAndHolds(100000));
+  EXPECT_THAT(c.ReadIntegerControlFile("cpu.shares"),
+              IsPosixErrorOkAndHolds(1024));
+}
+
+TEST(ProcCgroups, Empty) {
+  SKIP_IF(!CgroupsAvailable());
+
+  absl::flat_hash_map<std::string, CgroupsEntry> entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcCgroupsEntries());
+  // No cgroups mounted yet, we should have no entries.
+  EXPECT_TRUE(entries.empty());
+}
+
+TEST(ProcCgroups, ProcCgroupsEntries) {
+  SKIP_IF(!CgroupsAvailable());
+
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+
+  Cgroup mem = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs("memory"));
+  absl::flat_hash_map<std::string, CgroupsEntry> entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcCgroupsEntries());
+  EXPECT_EQ(entries.size(), 1);
+  ASSERT_TRUE(entries.contains("memory"));
+  CgroupsEntry mem_e = entries["memory"];
+  EXPECT_EQ(mem_e.subsys_name, "memory");
+  EXPECT_GE(mem_e.hierarchy, 1);
+  // Expect a single root cgroup.
+  EXPECT_EQ(mem_e.num_cgroups, 1);
+  // Cgroups are currently always enabled when mounted.
+  EXPECT_TRUE(mem_e.enabled);
+
+  // Add a second cgroup, and check for new entry.
+
+  Cgroup cpu = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs("cpu"));
+  entries = ASSERT_NO_ERRNO_AND_VALUE(ProcCgroupsEntries());
+  EXPECT_EQ(entries.size(), 2);
+  EXPECT_TRUE(entries.contains("memory"));  // Still have memory entry.
+  ASSERT_TRUE(entries.contains("cpu"));
+  CgroupsEntry cpu_e = entries["cpu"];
+  EXPECT_EQ(cpu_e.subsys_name, "cpu");
+  EXPECT_GE(cpu_e.hierarchy, 1);
+  EXPECT_EQ(cpu_e.num_cgroups, 1);
+  EXPECT_TRUE(cpu_e.enabled);
+
+  // Separate hierarchies, since controllers were mounted separately.
+  EXPECT_NE(mem_e.hierarchy, cpu_e.hierarchy);
+}
+
+TEST(ProcCgroups, UnmountRemovesEntries) {
+  SKIP_IF(!CgroupsAvailable());
+
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup cg = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs("cpu,memory"));
+  absl::flat_hash_map<std::string, CgroupsEntry> entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcCgroupsEntries());
+  EXPECT_EQ(entries.size(), 2);
+
+  ASSERT_NO_ERRNO(m.Unmount(cg));
+
+  entries = ASSERT_NO_ERRNO_AND_VALUE(ProcCgroupsEntries());
+  EXPECT_TRUE(entries.empty());
+}
+
+TEST(ProcPIDCgroup, Empty) {
+  SKIP_IF(!CgroupsAvailable());
+
+  absl::flat_hash_map<std::string, PIDCgroupEntry> entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcPIDCgroupEntries(getpid()));
+  EXPECT_TRUE(entries.empty());
+}
+
+TEST(ProcPIDCgroup, Entries) {
+  SKIP_IF(!CgroupsAvailable());
+
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup c = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs("memory"));
+
+  absl::flat_hash_map<std::string, PIDCgroupEntry> entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcPIDCgroupEntries(getpid()));
+  EXPECT_EQ(entries.size(), 1);
+  PIDCgroupEntry mem_e = entries["memory"];
+  EXPECT_GE(mem_e.hierarchy, 1);
+  EXPECT_EQ(mem_e.controllers, "memory");
+  EXPECT_EQ(mem_e.path, "/");
+
+  Cgroup c1 = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs("cpu"));
+  entries = ASSERT_NO_ERRNO_AND_VALUE(ProcPIDCgroupEntries(getpid()));
+  EXPECT_EQ(entries.size(), 2);
+  EXPECT_TRUE(entries.contains("memory"));  // Still have memory entry.
+  PIDCgroupEntry cpu_e = entries["cpu"];
+  EXPECT_GE(cpu_e.hierarchy, 1);
+  EXPECT_EQ(cpu_e.controllers, "cpu");
+  EXPECT_EQ(cpu_e.path, "/");
+
+  // Separate hierarchies, since controllers were mounted separately.
+  EXPECT_NE(mem_e.hierarchy, cpu_e.hierarchy);
+}
+
+TEST(ProcPIDCgroup, UnmountRemovesEntries) {
+  SKIP_IF(!CgroupsAvailable());
+
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup all = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs(""));
+
+  absl::flat_hash_map<std::string, PIDCgroupEntry> entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcPIDCgroupEntries(getpid()));
+  EXPECT_GT(entries.size(), 0);
+
+  ASSERT_NO_ERRNO(m.Unmount(all));
+
+  entries = ASSERT_NO_ERRNO_AND_VALUE(ProcPIDCgroupEntries(getpid()));
+  EXPECT_TRUE(entries.empty());
+}
+
+TEST(ProcCgroup, PIDCgroupMatchesCgroups) {
+  SKIP_IF(!CgroupsAvailable());
+
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup c = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs("memory"));
+  Cgroup c1 = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs("cpu"));
+
+  absl::flat_hash_map<std::string, CgroupsEntry> cgroups_entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcCgroupsEntries());
+  absl::flat_hash_map<std::string, PIDCgroupEntry> pid_entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcPIDCgroupEntries(getpid()));
+
+  CgroupsEntry cgroup_mem = cgroups_entries["memory"];
+  PIDCgroupEntry pid_mem = pid_entries["memory"];
+
+  EXPECT_EQ(cgroup_mem.hierarchy, pid_mem.hierarchy);
+
+  CgroupsEntry cgroup_cpu = cgroups_entries["cpu"];
+  PIDCgroupEntry pid_cpu = pid_entries["cpu"];
+
+  EXPECT_EQ(cgroup_cpu.hierarchy, pid_cpu.hierarchy);
+  EXPECT_NE(cgroup_mem.hierarchy, cgroup_cpu.hierarchy);
+  EXPECT_NE(pid_mem.hierarchy, pid_cpu.hierarchy);
+}
+
+TEST(ProcCgroup, MultiControllerHierarchy) {
+  SKIP_IF(!CgroupsAvailable());
+
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup c = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs("memory,cpu"));
+
+  absl::flat_hash_map<std::string, CgroupsEntry> cgroups_entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcCgroupsEntries());
+
+  CgroupsEntry mem_e = cgroups_entries["memory"];
+  CgroupsEntry cpu_e = cgroups_entries["cpu"];
+
+  // Both controllers should have the same hierarchy ID.
+  EXPECT_EQ(mem_e.hierarchy, cpu_e.hierarchy);
+
+  absl::flat_hash_map<std::string, PIDCgroupEntry> pid_entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcPIDCgroupEntries(getpid()));
+
+  // Expecting an entry listing both controllers, that matches the previous
+  // hierarchy ID. Note that the controllers are listed in alphabetical order.
+  PIDCgroupEntry pid_e = pid_entries["cpu,memory"];
+  EXPECT_EQ(pid_e.hierarchy, mem_e.hierarchy);
+}
+
+}  // namespace
+}  // namespace testing
+}  // namespace gvisor
diff --git a/test/util/BUILD b/test/util/BUILD
index e561f3daa..383de00ed 100644
--- a/test/util/BUILD
+++ b/test/util/BUILD
@@ -94,6 +94,7 @@ cc_library(
         ":file_descriptor",
         ":posix_error",
         "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/time",
         gtest,
     ],
 )
@@ -368,3 +369,20 @@ cc_library(
     testonly = 1,
     hdrs = ["temp_umask.h"],
 )
+
+cc_library(
+    name = "cgroup_util",
+    testonly = 1,
+    srcs = ["cgroup_util.cc"],
+    hdrs = ["cgroup_util.h"],
+    deps = [
+        ":cleanup",
+        ":fs_util",
+        ":mount_util",
+        ":posix_error",
+        ":temp_path",
+        "@com_google_absl//absl/container:flat_hash_map",
+        "@com_google_absl//absl/container:flat_hash_set",
+        "@com_google_absl//absl/strings",
+    ],
+)
diff --git a/test/util/cgroup_util.cc b/test/util/cgroup_util.cc
new file mode 100644
index 000000000..65d9c4986
--- /dev/null
+++ b/test/util/cgroup_util.cc
@@ -0,0 +1,223 @@
+// Copyright 2021 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.
+
+#include "test/util/cgroup_util.h"
+
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#include "absl/strings/str_split.h"
+#include "test/util/fs_util.h"
+#include "test/util/mount_util.h"
+
+namespace gvisor {
+namespace testing {
+
+Cgroup::Cgroup(std::string path) : cgroup_path_(path) {
+  id_ = ++Cgroup::next_id_;
+  std::cerr << absl::StreamFormat("[cg#%d] <= %s", id_, cgroup_path_)
+            << std::endl;
+}
+
+PosixErrorOr<std::string> Cgroup::ReadControlFile(
+    absl::string_view name) const {
+  std::string buf;
+  RETURN_IF_ERRNO(GetContents(Relpath(name), &buf));
+
+  const std::string alias_path = absl::StrFormat("[cg#%d]/%s", id_, name);
+  std::cerr << absl::StreamFormat("<contents of %s>", alias_path) << std::endl;
+  std::cerr << buf;
+  std::cerr << absl::StreamFormat("<end of %s>", alias_path) << std::endl;
+
+  return buf;
+}
+
+PosixErrorOr<int64_t> Cgroup::ReadIntegerControlFile(
+    absl::string_view name) const {
+  ASSIGN_OR_RETURN_ERRNO(const std::string buf, ReadControlFile(name));
+  ASSIGN_OR_RETURN_ERRNO(const int64_t val, Atoi<int64_t>(buf));
+  return val;
+}
+
+PosixErrorOr<absl::flat_hash_set<pid_t>> Cgroup::Procs() const {
+  ASSIGN_OR_RETURN_ERRNO(std::string buf, ReadControlFile("cgroup.procs"));
+  return ParsePIDList(buf);
+}
+
+PosixErrorOr<absl::flat_hash_set<pid_t>> Cgroup::Tasks() const {
+  ASSIGN_OR_RETURN_ERRNO(std::string buf, ReadControlFile("tasks"));
+  return ParsePIDList(buf);
+}
+
+PosixError Cgroup::ContainsCallingProcess() const {
+  ASSIGN_OR_RETURN_ERRNO(const absl::flat_hash_set<pid_t> procs, Procs());
+  ASSIGN_OR_RETURN_ERRNO(const absl::flat_hash_set<pid_t> tasks, Tasks());
+  const pid_t pid = getpid();
+  const pid_t tid = syscall(SYS_gettid);
+  if (!procs.contains(pid)) {
+    return PosixError(
+        ENOENT, absl::StrFormat("Cgroup doesn't contain process %d", pid));
+  }
+  if (!tasks.contains(tid)) {
+    return PosixError(ENOENT,
+                      absl::StrFormat("Cgroup doesn't contain task %d", tid));
+  }
+  return NoError();
+}
+
+PosixErrorOr<absl::flat_hash_set<pid_t>> Cgroup::ParsePIDList(
+    absl::string_view data) const {
+  absl::flat_hash_set<pid_t> res;
+  std::vector<absl::string_view> lines = absl::StrSplit(data, '\n');
+  for (const std::string_view& line : lines) {
+    if (line.empty()) {
+      continue;
+    }
+    ASSIGN_OR_RETURN_ERRNO(const int32_t pid, Atoi<int32_t>(line));
+    res.insert(static_cast<pid_t>(pid));
+  }
+  return res;
+}
+
+int64_t Cgroup::next_id_ = 0;
+
+PosixErrorOr<Cgroup> Mounter::MountCgroupfs(std::string mopts) {
+  ASSIGN_OR_RETURN_ERRNO(TempPath mountpoint,
+                         TempPath::CreateDirIn(root_.path()));
+  ASSIGN_OR_RETURN_ERRNO(
+      Cleanup mount, Mount("none", mountpoint.path(), "cgroup", 0, mopts, 0));
+  const std::string mountpath = mountpoint.path();
+  std::cerr << absl::StreamFormat(
+                   "Mount(\"none\", \"%s\", \"cgroup\", 0, \"%s\", 0) => OK",
+                   mountpath, mopts)
+            << std::endl;
+  Cgroup cg = Cgroup(mountpath);
+  mountpoints_[cg.id()] = std::move(mountpoint);
+  mounts_[cg.id()] = std::move(mount);
+  return cg;
+}
+
+PosixError Mounter::Unmount(const Cgroup& c) {
+  auto mount = mounts_.find(c.id());
+  auto mountpoint = mountpoints_.find(c.id());
+
+  if (mount == mounts_.end() || mountpoint == mountpoints_.end()) {
+    return PosixError(
+        ESRCH, absl::StrFormat("No mount found for cgroupfs containing cg#%d",
+                               c.id()));
+  }
+
+  std::cerr << absl::StreamFormat("Unmount([cg#%d])", c.id()) << std::endl;
+
+  // Simply delete the entries, their destructors will unmount and delete the
+  // mountpoint. Note the order is important to avoid errors: mount then
+  // mountpoint.
+  mounts_.erase(mount);
+  mountpoints_.erase(mountpoint);
+
+  return NoError();
+}
+
+constexpr char kProcCgroupsHeader[] =
+    "#subsys_name\thierarchy\tnum_cgroups\tenabled";
+
+PosixErrorOr<absl::flat_hash_map<std::string, CgroupsEntry>>
+ProcCgroupsEntries() {
+  std::string content;
+  RETURN_IF_ERRNO(GetContents("/proc/cgroups", &content));
+
+  bool found_header = false;
+  absl::flat_hash_map<std::string, CgroupsEntry> entries;
+  std::vector<std::string> lines = absl::StrSplit(content, '\n');
+  std::cerr << "<contents of /proc/cgroups>" << std::endl;
+  for (const std::string& line : lines) {
+    std::cerr << line << std::endl;
+
+    if (!found_header) {
+      EXPECT_EQ(line, kProcCgroupsHeader);
+      found_header = true;
+      continue;
+    }
+    if (line.empty()) {
+      continue;
+    }
+
+    // Parse a single entry from /proc/cgroups.
+    //
+    // Example entries, fields are tab separated in the real file:
+    //
+    // #subsys_name    hierarchy       num_cgroups     enabled
+    // cpuset  12      35      1
+    // cpu     3       222     1
+    //   ^     ^       ^       ^
+    //   0     1       2       3
+
+    CgroupsEntry entry;
+    std::vector<std::string> fields =
+        StrSplit(line, absl::ByAnyChar(": \t"), absl::SkipEmpty());
+
+    entry.subsys_name = fields[0];
+    ASSIGN_OR_RETURN_ERRNO(entry.hierarchy, Atoi<uint32_t>(fields[1]));
+    ASSIGN_OR_RETURN_ERRNO(entry.num_cgroups, Atoi<uint64_t>(fields[2]));
+    ASSIGN_OR_RETURN_ERRNO(const int enabled, Atoi<int>(fields[3]));
+    entry.enabled = enabled != 0;
+
+    entries[entry.subsys_name] = entry;
+  }
+  std::cerr << "<end of /proc/cgroups>" << std::endl;
+
+  return entries;
+}
+
+PosixErrorOr<absl::flat_hash_map<std::string, PIDCgroupEntry>>
+ProcPIDCgroupEntries(pid_t pid) {
+  const std::string path = absl::StrFormat("/proc/%d/cgroup", pid);
+  std::string content;
+  RETURN_IF_ERRNO(GetContents(path, &content));
+
+  absl::flat_hash_map<std::string, PIDCgroupEntry> entries;
+  std::vector<std::string> lines = absl::StrSplit(content, '\n');
+
+  std::cerr << absl::StreamFormat("<contents of %s>", path) << std::endl;
+  for (const std::string& line : lines) {
+    std::cerr << line << std::endl;
+
+    if (line.empty()) {
+      continue;
+    }
+
+    // Parse a single entry from /proc/<pid>/cgroup.
+    //
+    // Example entries:
+    //
+    // 2:cpu:/path/to/cgroup
+    // 1:memory:/
+
+    PIDCgroupEntry entry;
+    std::vector<std::string> fields =
+        absl::StrSplit(line, absl::ByChar(':'), absl::SkipEmpty());
+
+    ASSIGN_OR_RETURN_ERRNO(entry.hierarchy, Atoi<uint32_t>(fields[0]));
+    entry.controllers = fields[1];
+    entry.path = fields[2];
+
+    entries[entry.controllers] = entry;
+  }
+  std::cerr << absl::StreamFormat("<end of %s>", path) << std::endl;
+
+  return entries;
+}
+
+}  // namespace testing
+}  // namespace gvisor
diff --git a/test/util/cgroup_util.h b/test/util/cgroup_util.h
new file mode 100644
index 000000000..b049559df
--- /dev/null
+++ b/test/util/cgroup_util.h
@@ -0,0 +1,111 @@
+// Copyright 2021 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.
+
+#ifndef GVISOR_TEST_UTIL_CGROUP_UTIL_H_
+#define GVISOR_TEST_UTIL_CGROUP_UTIL_H_
+
+#include <unistd.h>
+
+#include "absl/container/flat_hash_map.h"
+#include "absl/container/flat_hash_set.h"
+#include "absl/strings/string_view.h"
+#include "test/util/cleanup.h"
+#include "test/util/fs_util.h"
+#include "test/util/temp_path.h"
+
+namespace gvisor {
+namespace testing {
+
+// Cgroup represents a cgroup directory on a mounted cgroupfs.
+class Cgroup {
+ public:
+  Cgroup(std::string path);
+
+  uint64_t id() const { return id_; }
+
+  std::string Relpath(absl::string_view leaf) const {
+    return JoinPath(cgroup_path_, leaf);
+  }
+
+  // Returns the contents of a cgroup control file with the given name.
+  PosixErrorOr<std::string> ReadControlFile(absl::string_view name) const;
+
+  // Reads the contents of a cgroup control with the given name, and attempts
+  // to parse it as an integer.
+  PosixErrorOr<int64_t> ReadIntegerControlFile(absl::string_view name) const;
+
+  // Returns the thread ids of the leaders of thread groups managed by this
+  // cgroup.
+  PosixErrorOr<absl::flat_hash_set<pid_t>> Procs() const;
+
+  PosixErrorOr<absl::flat_hash_set<pid_t>> Tasks() const;
+
+  // ContainsCallingProcess checks whether the calling process is part of the
+  PosixError ContainsCallingProcess() const;
+
+ private:
+  PosixErrorOr<absl::flat_hash_set<pid_t>> ParsePIDList(
+      absl::string_view data) const;
+
+  static int64_t next_id_;
+  int64_t id_;
+  const std::string cgroup_path_;
+};
+
+// Mounter is a utility for creating cgroupfs mounts. It automatically manages
+// the lifetime of created mounts.
+class Mounter {
+ public:
+  Mounter(TempPath root) : root_(std::move(root)) {}
+
+  PosixErrorOr<Cgroup> MountCgroupfs(std::string mopts);
+
+  PosixError Unmount(const Cgroup& c);
+
+ private:
+  // The destruction order of these members avoids errors during cleanup. We
+  // first unmount (by executing the mounts_ cleanups), then delete the
+  // mountpoint subdirs, then delete the root.
+  TempPath root_;
+  absl::flat_hash_map<int64_t, TempPath> mountpoints_;
+  absl::flat_hash_map<int64_t, Cleanup> mounts_;
+};
+
+// Represents a line from /proc/cgroups.
+struct CgroupsEntry {
+  std::string subsys_name;
+  uint32_t hierarchy;
+  uint64_t num_cgroups;
+  bool enabled;
+};
+
+// Returns a parsed representation of /proc/cgroups.
+PosixErrorOr<absl::flat_hash_map<std::string, CgroupsEntry>>
+ProcCgroupsEntries();
+
+// Represents a line from /proc/<pid>/cgroup.
+struct PIDCgroupEntry {
+  uint32_t hierarchy;
+  std::string controllers;
+  std::string path;
+};
+
+// Returns a parsed representation of /proc/<pid>/cgroup.
+PosixErrorOr<absl::flat_hash_map<std::string, PIDCgroupEntry>>
+ProcPIDCgroupEntries(pid_t pid);
+
+}  // namespace testing
+}  // namespace gvisor
+
+#endif  // GVISOR_TEST_UTIL_CGROUP_UTIL_H_
diff --git a/test/util/fs_util.cc b/test/util/fs_util.cc
index 5f1ce0d8a..483ae848d 100644
--- a/test/util/fs_util.cc
+++ b/test/util/fs_util.cc
@@ -28,6 +28,8 @@
 #include "absl/strings/str_cat.h"
 #include "absl/strings/str_split.h"
 #include "absl/strings/string_view.h"
+#include "absl/time/clock.h"
+#include "absl/time/time.h"
 #include "test/util/cleanup.h"
 #include "test/util/file_descriptor.h"
 #include "test/util/posix_error.h"
@@ -366,6 +368,48 @@ PosixErrorOr<std::vector<std::string>> ListDir(absl::string_view abspath,
   return files;
 }
 
+PosixError DirContains(absl::string_view path,
+                       const std::vector<std::string>& expect,
+                       const std::vector<std::string>& exclude) {
+  ASSIGN_OR_RETURN_ERRNO(auto listing, ListDir(path, false));
+
+  for (auto& expected_entry : expect) {
+    auto cursor = std::find(listing.begin(), listing.end(), expected_entry);
+    if (cursor == listing.end()) {
+      return PosixError(ENOENT, absl::StrFormat("Failed to find '%s' in '%s'",
+                                                expected_entry, path));
+    }
+  }
+  for (auto& excluded_entry : exclude) {
+    auto cursor = std::find(listing.begin(), listing.end(), excluded_entry);
+    if (cursor != listing.end()) {
+      return PosixError(ENOENT, absl::StrCat("File '", excluded_entry,
+                                             "' found in path '", path, "'"));
+    }
+  }
+  return NoError();
+}
+
+PosixError EventuallyDirContains(absl::string_view path,
+                                 const std::vector<std::string>& expect,
+                                 const std::vector<std::string>& exclude) {
+  constexpr int kRetryCount = 100;
+  const absl::Duration kRetryDelay = absl::Milliseconds(100);
+
+  for (int i = 0; i < kRetryCount; ++i) {
+    auto res = DirContains(path, expect, exclude);
+    if (res.ok()) {
+      return res;
+    }
+    if (i < kRetryCount - 1) {
+      // Sleep if this isn't the final iteration.
+      absl::SleepFor(kRetryDelay);
+    }
+  }
+  return PosixError(ETIMEDOUT,
+                    "Timed out while waiting for directory to contain files ");
+}
+
 PosixError RecursivelyDelete(absl::string_view path, int* undeleted_dirs,
                              int* undeleted_files) {
   ASSIGN_OR_RETURN_ERRNO(bool exists, Exists(path));
diff --git a/test/util/fs_util.h b/test/util/fs_util.h
index 2190c3bca..bb2d1d3c8 100644
--- a/test/util/fs_util.h
+++ b/test/util/fs_util.h
@@ -129,6 +129,18 @@ PosixError WalkTree(
 PosixErrorOr<std::vector<std::string>> ListDir(absl::string_view abspath,
                                                bool skipdots);
 
+// Check that a directory contains children nodes named in expect, and does not
+// contain any children nodes named in exclude.
+PosixError DirContains(absl::string_view path,
+                       const std::vector<std::string>& expect,
+                       const std::vector<std::string>& exclude);
+
+// Same as DirContains, but adds a retry. Suitable for checking a directory
+// being modified asynchronously.
+PosixError EventuallyDirContains(absl::string_view path,
+                                 const std::vector<std::string>& expect,
+                                 const std::vector<std::string>& exclude);
+
 // Attempt to recursively delete a directory or file. Returns an error and
 // the number of undeleted directories and files. If either
 // undeleted_dirs or undeleted_files is nullptr then it will not be used.