3 files changed, 54 insertions, 2 deletions

diff --git a/test/syscalls/linux/cgroup.cc b/test/syscalls/linux/cgroup.cc
index a1006a978..862328f5b 100644
--- a/test/syscalls/linux/cgroup.cc
+++ b/test/syscalls/linux/cgroup.cc
@@ -15,6 +15,7 @@
 // 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 <limits.h>
 #include <sys/mount.h>
 #include <unistd.h>
 
@@ -35,8 +36,9 @@ using ::testing::_;
 using ::testing::Ge;
 using ::testing::Gt;
 
-std::vector<std::string> known_controllers = {"cpu", "cpuset", "cpuacct",
-                                              "memory"};
+std::vector<std::string> known_controllers = {
+    "cpu", "cpuset", "cpuacct", "job", "memory",
+};
 
 bool CgroupsAvailable() {
   return IsRunningOnGvisor() && !IsRunningWithVFS1() &&
@@ -257,6 +259,35 @@ TEST(CPUAcctCgroup, CPUAcctStat) {
   EXPECT_THAT(Atoi<int64_t>(sys_tokens[1]), IsPosixErrorOkAndHolds(Ge(0)));
 }
 
+// WriteAndVerifyControlValue attempts to write val to a cgroup file at path,
+// and verify the value by reading it afterwards.
+PosixError WriteAndVerifyControlValue(const Cgroup& c, std::string_view path,
+                                      int64_t val) {
+  RETURN_IF_ERRNO(c.WriteIntegerControlFile(path, val));
+  ASSIGN_OR_RETURN_ERRNO(int64_t newval, c.ReadIntegerControlFile(path));
+  if (newval != val) {
+    return PosixError(
+        EINVAL,
+        absl::StrFormat(
+            "Unexpected value for control file '%s': expected %d, got %d", path,
+            val, newval));
+  }
+  return NoError();
+}
+
+TEST(JobCgroup, ReadWriteRead) {
+  SKIP_IF(!CgroupsAvailable());
+
+  Mounter m(ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()));
+  Cgroup c = ASSERT_NO_ERRNO_AND_VALUE(m.MountCgroupfs("job"));
+
+  EXPECT_THAT(c.ReadIntegerControlFile("job.id"), IsPosixErrorOkAndHolds(0));
+  EXPECT_NO_ERRNO(WriteAndVerifyControlValue(c, "job.id", 1234));
+  EXPECT_NO_ERRNO(WriteAndVerifyControlValue(c, "job.id", -1));
+  EXPECT_NO_ERRNO(WriteAndVerifyControlValue(c, "job.id", LLONG_MIN));
+  EXPECT_NO_ERRNO(WriteAndVerifyControlValue(c, "job.id", LLONG_MAX));
+}
+
 TEST(ProcCgroups, Empty) {
   SKIP_IF(!CgroupsAvailable());
 
diff --git a/test/util/cgroup_util.cc b/test/util/cgroup_util.cc
index 65d9c4986..d8d3fe471 100644
--- a/test/util/cgroup_util.cc
+++ b/test/util/cgroup_util.cc
@@ -17,6 +17,7 @@
 #include <sys/syscall.h>
 #include <unistd.h>
 
+#include "absl/strings/str_cat.h"
 #include "absl/strings/str_split.h"
 #include "test/util/fs_util.h"
 #include "test/util/mount_util.h"
@@ -50,6 +51,18 @@ PosixErrorOr<int64_t> Cgroup::ReadIntegerControlFile(
   return val;
 }
 
+PosixError Cgroup::WriteControlFile(absl::string_view name,
+                                    const std::string& value) const {
+  ASSIGN_OR_RETURN_ERRNO(FileDescriptor fd, Open(Relpath(name), O_WRONLY));
+  RETURN_ERROR_IF_SYSCALL_FAIL(WriteFd(fd.get(), value.c_str(), value.size()));
+  return NoError();
+}
+
+PosixError Cgroup::WriteIntegerControlFile(absl::string_view name,
+                                           int64_t value) const {
+  return WriteControlFile(name, absl::StrCat(value));
+}
+
 PosixErrorOr<absl::flat_hash_set<pid_t>> Cgroup::Procs() const {
   ASSIGN_OR_RETURN_ERRNO(std::string buf, ReadControlFile("cgroup.procs"));
   return ParsePIDList(buf);
diff --git a/test/util/cgroup_util.h b/test/util/cgroup_util.h
index b049559df..c6e4303e1 100644
--- a/test/util/cgroup_util.h
+++ b/test/util/cgroup_util.h
@@ -45,6 +45,14 @@ class Cgroup {
   // to parse it as an integer.
   PosixErrorOr<int64_t> ReadIntegerControlFile(absl::string_view name) const;
 
+  // Writes a string to a cgroup control file.
+  PosixError WriteControlFile(absl::string_view name,
+                              const std::string& value) const;
+
+  // Writes an integer value to a cgroup control file.
+  PosixError WriteIntegerControlFile(absl::string_view name,
+                                     int64_t value) const;
+
   // Returns the thread ids of the leaders of thread groups managed by this
   // cgroup.
   PosixErrorOr<absl::flat_hash_set<pid_t>> Procs() const;