Add CLOCK_BOOTTIME as a CLOCK_MONOTONIC alias

Makes CLOCK_BOOTTIME available with
* clock_gettime
* timerfd_create
* clock_gettime vDSO

CLOCK_BOOTTIME is implemented as an alias to CLOCK_MONOTONIC.
CLOCK_MONOTONIC already keeps track of time across save
and restore. This is the closest possible behavior to Linux
CLOCK_BOOTIME, as there is no concept of suspend/resume.

Updates google/gvisor#218

5 files changed, 19 insertions, 6 deletions

diff --git a/pkg/sentry/syscalls/linux/sys_time.go b/pkg/sentry/syscalls/linux/sys_time.go
index fe8725191..0f36e4cd0 100644
--- a/pkg/sentry/syscalls/linux/sys_time.go
+++ b/pkg/sentry/syscalls/linux/sys_time.go
@@ -121,8 +121,13 @@ func getClock(t *kernel.Task, clockID int32) (ktime.Clock, error) {
 	switch clockID {
 	case linux.CLOCK_REALTIME, linux.CLOCK_REALTIME_COARSE:
 		return t.Kernel().RealtimeClock(), nil
-	case linux.CLOCK_MONOTONIC, linux.CLOCK_MONOTONIC_COARSE, linux.CLOCK_MONOTONIC_RAW:
+	case linux.CLOCK_MONOTONIC, linux.CLOCK_MONOTONIC_COARSE,
+		linux.CLOCK_MONOTONIC_RAW, linux.CLOCK_BOOTTIME:
 		// CLOCK_MONOTONIC approximates CLOCK_MONOTONIC_RAW.
+		// CLOCK_BOOTTIME is internally mapped to CLOCK_MONOTONIC, as:
+		// - CLOCK_BOOTTIME should behave as CLOCK_MONOTONIC while also including suspend time.
+		// - gVisor has no concept of suspend/resume.
+		// - CLOCK_MONOTONIC already includes save/restore time, which is the closest to suspend time.
 		return t.Kernel().MonotonicClock(), nil
 	case linux.CLOCK_PROCESS_CPUTIME_ID:
 		return t.ThreadGroup().CPUClock(), nil
diff --git a/pkg/sentry/syscalls/linux/sys_timerfd.go b/pkg/sentry/syscalls/linux/sys_timerfd.go
index ea6d44315..b889a2a93 100644
--- a/pkg/sentry/syscalls/linux/sys_timerfd.go
+++ b/pkg/sentry/syscalls/linux/sys_timerfd.go
@@ -38,7 +38,7 @@ func TimerfdCreate(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel
 	switch clockID {
 	case linux.CLOCK_REALTIME:
 		c = t.Kernel().RealtimeClock()
-	case linux.CLOCK_MONOTONIC:
+	case linux.CLOCK_MONOTONIC, linux.CLOCK_BOOTTIME:
 		c = t.Kernel().MonotonicClock()
 	default:
 		return 0, nil, syserror.EINVAL
diff --git a/test/syscalls/linux/clock_gettime.cc b/test/syscalls/linux/clock_gettime.cc
index 335a38d41..9efd20b1a 100644
--- a/test/syscalls/linux/clock_gettime.cc
+++ b/test/syscalls/linux/clock_gettime.cc
@@ -132,6 +132,9 @@ std::string PrintClockId(::testing::TestParamInfo<clockid_t> info) {
       return "CLOCK_MONOTONIC_COARSE";
     case CLOCK_MONOTONIC_RAW:
       return "CLOCK_MONOTONIC_RAW";
+    case CLOCK_BOOTTIME:
+      // CLOCK_BOOTTIME is a monotonic clock.
+      return "CLOCK_BOOTTIME";
     default:
       return absl::StrCat(info.param);
   }
@@ -140,15 +143,14 @@ std::string PrintClockId(::testing::TestParamInfo<clockid_t> info) {
 INSTANTIATE_TEST_SUITE_P(ClockGettime, MonotonicClockTest,
                          ::testing::Values(CLOCK_MONOTONIC,
                                            CLOCK_MONOTONIC_COARSE,
-                                           CLOCK_MONOTONIC_RAW),
+                                           CLOCK_MONOTONIC_RAW,
+                                           CLOCK_BOOTTIME),
                          PrintClockId);
 
 TEST(ClockGettime, UnimplementedReturnsEINVAL) {
   SKIP_IF(!IsRunningOnGvisor());
 
   struct timespec tp;
-  EXPECT_THAT(clock_gettime(CLOCK_BOOTTIME, &tp),
-              SyscallFailsWithErrno(EINVAL));
   EXPECT_THAT(clock_gettime(CLOCK_REALTIME_ALARM, &tp),
               SyscallFailsWithErrno(EINVAL));
   EXPECT_THAT(clock_gettime(CLOCK_BOOTTIME_ALARM, &tp),
diff --git a/test/syscalls/linux/vdso_clock_gettime.cc b/test/syscalls/linux/vdso_clock_gettime.cc
index 759a50569..7e56c3de0 100644
--- a/test/syscalls/linux/vdso_clock_gettime.cc
+++ b/test/syscalls/linux/vdso_clock_gettime.cc
@@ -39,6 +39,8 @@ std::string PrintClockId(::testing::TestParamInfo<clockid_t> info) {
       return "CLOCK_MONOTONIC";
     case CLOCK_REALTIME:
       return "CLOCK_REALTIME";
+    case CLOCK_BOOTTIME:
+      return "CLOCK_BOOTTIME";
     default:
       return absl::StrCat(info.param);
   }
@@ -95,7 +97,9 @@ TEST_P(CorrectVDSOClockTest, IsCorrect) {
 }
 
 INSTANTIATE_TEST_SUITE_P(ClockGettime, CorrectVDSOClockTest,
-                         ::testing::Values(CLOCK_MONOTONIC, CLOCK_REALTIME),
+                         ::testing::Values(CLOCK_MONOTONIC,
+                                           CLOCK_REALTIME,
+                                           CLOCK_BOOTTIME),
                          PrintClockId);
 
 }  // namespace
diff --git a/vdso/vdso.cc b/vdso/vdso.cc
index 6265ad217..0bded13ac 100644
--- a/vdso/vdso.cc
+++ b/vdso/vdso.cc
@@ -33,6 +33,8 @@ int __common_clock_gettime(clockid_t clock, struct timespec* ts) {
       ret = ClockRealtime(ts);
       break;
 
+    // Fallthrough, CLOCK_BOOTTIME is an alias for CLOCK_MONOTONIC
+    case CLOCK_BOOTTIME:
     case CLOCK_MONOTONIC:
       ret = ClockMonotonic(ts);
       break;