Initial cgroupfs support for subcontainers

Allow creation and management of subcontainers through cgroupfs
directory syscalls. Also add a mechanism to specify a default root
container to start new jobs in.

This implements the filesystem support for subcontainers, but doesn't
implement hierarchical resource accounting or task migration.

PiperOrigin-RevId: 390254870

4 files changed, 47 insertions, 3 deletions

diff --git a/test/syscalls/linux/cgroup.cc b/test/syscalls/linux/cgroup.cc
index f29891571..ca23dfeee 100644
--- a/test/syscalls/linux/cgroup.cc
+++ b/test/syscalls/linux/cgroup.cc
@@ -279,6 +279,23 @@ TEST(Cgroup, UnmountRepeated) {
   EXPECT_THAT(umount(c.Path().c_str()), SyscallFailsWithErrno(EINVAL));
 }
 
+TEST(Cgroup, Create) {
+  SKIP_IF(!CgroupsAvailable());
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup c = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs(""));
+  ASSERT_NO_ERRNO(c.CreateChild("child1"));
+  EXPECT_TRUE(ASSERT_NO_ERRNO_AND_VALUE(Exists(c.Path())));
+}
+
+TEST(Cgroup, SubcontainerInitiallyEmpty) {
+  SKIP_IF(!CgroupsAvailable());
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup c = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs(""));
+  Cgroup child = ASSERT_NO_ERRNO_AND_VALUE(c.CreateChild("child1"));
+  auto procs = ASSERT_NO_ERRNO_AND_VALUE(child.Procs());
+  EXPECT_TRUE(procs.empty());
+}
+
 TEST(MemoryCgroup, MemoryUsageInBytes) {
   SKIP_IF(!CgroupsAvailable());
 
diff --git a/test/util/cgroup_util.cc b/test/util/cgroup_util.cc
index 977993f41..df3c57b87 100644
--- a/test/util/cgroup_util.cc
+++ b/test/util/cgroup_util.cc
@@ -25,12 +25,26 @@
 namespace gvisor {
 namespace testing {
 
-Cgroup::Cgroup(std::string_view path) : cgroup_path_(path) {
+Cgroup::Cgroup(absl::string_view path) : cgroup_path_(path) {
   id_ = ++Cgroup::next_id_;
   std::cerr << absl::StreamFormat("[cg#%d] <= %s", id_, cgroup_path_)
             << std::endl;
 }
 
+PosixErrorOr<Cgroup> Cgroup::RecursivelyCreate(absl::string_view path) {
+  RETURN_IF_ERRNO(RecursivelyCreateDir(path));
+  return Cgroup(path);
+}
+
+PosixErrorOr<Cgroup> Cgroup::Create(absl::string_view path) {
+  RETURN_IF_ERRNO(Mkdir(path));
+  return Cgroup(path);
+}
+
+PosixErrorOr<Cgroup> Cgroup::CreateChild(absl::string_view name) const {
+  return Cgroup::Create(JoinPath(Path(), name));
+}
+
 PosixErrorOr<std::string> Cgroup::ReadControlFile(
     absl::string_view name) const {
   std::string buf;
@@ -93,7 +107,7 @@ 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) {
+  for (const absl::string_view& line : lines) {
     if (line.empty()) {
       continue;
     }
diff --git a/test/util/cgroup_util.h b/test/util/cgroup_util.h
index e3f696a89..ccc7219e3 100644
--- a/test/util/cgroup_util.h
+++ b/test/util/cgroup_util.h
@@ -34,8 +34,20 @@ class Cgroup {
 
   uint64_t id() const { return id_; }
 
+  // RecursivelyCreate creates cgroup specified by path, including all
+  // components leading up to path. Path should end inside a cgroupfs mount. If
+  // path already exists, RecursivelyCreate does nothing and silently succeeds.
+  static PosixErrorOr<Cgroup> RecursivelyCreate(std::string_view path);
+
+  // Creates a new cgroup at path. The parent directory must exist and be a
+  // cgroupfs directory.
+  static PosixErrorOr<Cgroup> Create(std::string_view path);
+
   const std::string& Path() const { return cgroup_path_; }
 
+  // Creates a child cgroup under this cgroup with the given name.
+  PosixErrorOr<Cgroup> CreateChild(std::string_view name) const;
+
   std::string Relpath(absl::string_view leaf) const {
     return JoinPath(cgroup_path_, leaf);
   }
diff --git a/test/util/fs_util.cc b/test/util/fs_util.cc
index 483ae848d..253411858 100644
--- a/test/util/fs_util.cc
+++ b/test/util/fs_util.cc
@@ -201,7 +201,8 @@ PosixError UnlinkAt(const FileDescriptor& dfd, absl::string_view path,
 PosixError Mkdir(absl::string_view path, int mode) {
   int res = mkdir(std::string(path).c_str(), mode);
   if (res < 0) {
-    return PosixError(errno, absl::StrCat("mkdir ", path, " mode ", mode));
+    return PosixError(errno,
+                      absl::StrFormat("mkdir \"%s\" mode %#o", path, mode));
   }
 
   return NoError();