Silence the error log message for SO_RCVLOWAT option.

Removed the unimplemented syscall message for SO_RCVLOWAT option and added a
test for {g,s}etsockopt.

PiperOrigin-RevId: 438145815

pkg/sentry/socket/netstack/netstack.go

@@ -1064,6 +1064,14 @@ func getSockOptSocket(t *kernel.Task, s socket.SocketOps, ep commonEndpoint, fam
 		vP := primitive.Int32(boolToInt32(v))
 		return &vP, nil
 
+	case linux.SO_RCVLOWAT:
+		if outLen < sizeOfInt32 {
+			return nil, syserr.ErrInvalidArgument
+		}
+
+		v := primitive.Int32(ep.SocketOptions().GetRcvlowat())
+		return &v, nil
+
 	default:
 		socket.GetSockOptEmitUnimplementedEvent(t, name)
 	}
@@ -2002,6 +2010,17 @@ func setSockOptSocket(t *kernel.Task, s socket.SocketOps, ep commonEndpoint, nam
 		var v tcpip.SocketDetachFilterOption
 		return syserr.TranslateNetstackError(ep.SetSockOpt(&v))
 
+	// TODO(b/226603727): Add support for SO_RCVLOWAT option. For now, only
+	// the unsupported syscall message is removed.
+	case linux.SO_RCVLOWAT:
+		if len(optVal) < sizeOfInt32 {
+			return syserr.ErrInvalidArgument
+		}
+
+		v := hostarch.ByteOrder.Uint32(optVal)
+		ep.SocketOptions().SetRcvlowat(int32(v))
+		return nil
+
 	default:
 		socket.SetSockOptEmitUnimplementedEvent(t, name)
 	}

pkg/sentry/socket/socket.go

@@ -583,7 +583,6 @@ func emitUnimplementedEvent(t *kernel.Task, name int) {
 		linux.SO_PEEK_OFF,
 		linux.SO_PRIORITY,
 		linux.SO_RCVBUF,
-		linux.SO_RCVLOWAT,
 		linux.SO_RCVTIMEO,
 		linux.SO_REUSEADDR,
 		linux.SO_REUSEPORT,

pkg/tcpip/socketops.go

@@ -245,6 +245,10 @@ type SocketOptions struct {
 	// linger determines the amount of time the socket should linger before
 	// close. We currently implement this option for TCP socket only.
 	linger LingerOption
+
+	// rcvlowat specifies the minimum number of bytes which should be
+	// received to indicate the socket as readable.
+	rcvlowat int32
 }
 
 // InitHandler initializes the handler. This must be called before using the
@@ -702,3 +706,17 @@ func (so *SocketOptions) SetReceiveBufferSize(receiveBufferSize int64, notify bo
 	}
 	so.receiveBufferSize.Store(receiveBufferSize)
 }
+
+// GetRcvlowat gets value for SO_RCVLOWAT option.
+func (so *SocketOptions) GetRcvlowat() int32 {
+	// TODO(b/226603727): Return so.rcvlowat after adding complete support
+	// for SO_RCVLOWAT option. For now, return the default value of 1.
+	defaultRcvlowat := int32(1)
+	return defaultRcvlowat
+}
+
+// SetRcvlowat sets value for SO_RCVLOWAT option.
+func (so *SocketOptions) SetRcvlowat(rcvlowat int32) Error {
+	atomic.StoreInt32(&so.rcvlowat, rcvlowat)
+	return nil
+}

test/syscalls/linux/socket_generic_test_cases.cc

@@ -968,5 +968,35 @@ TEST_P(AllSocketPairTest, GetSocketRcvbufOption) {
     EXPECT_EQ(opt, minRcvBufSizeLinux);
   }
 }
+
+TEST_P(AllSocketPairTest, GetSetSocketRcvlowatOption) {
+  auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
+
+  int opt = 0;
+  socklen_t opt_len = sizeof(opt);
+  constexpr int defaultSz = 1;
+  ASSERT_THAT(
+      getsockopt(sockets->first_fd(), SOL_SOCKET, SO_RCVLOWAT, &opt, &opt_len),
+      SyscallSucceeds());
+  ASSERT_EQ(opt_len, sizeof(opt));
+  EXPECT_EQ(opt, defaultSz);
+
+  int rcvlowatSz = 100;
+  ASSERT_THAT(setsockopt(sockets->first_fd(), SOL_SOCKET, SO_RCVLOWAT,
+                         &rcvlowatSz, sizeof(rcvlowatSz)),
+              SyscallSucceeds());
+
+  ASSERT_THAT(
+      getsockopt(sockets->first_fd(), SOL_SOCKET, SO_RCVLOWAT, &opt, &opt_len),
+      SyscallSucceeds());
+  ASSERT_EQ(opt_len, sizeof(opt));
+
+  if (IsRunningOnGvisor()) {
+    // TODO(b/226603727): Add support for setting SO_RCVLOWAT option in gVisor.
+    EXPECT_EQ(opt, defaultSz);
+  } else {
+    EXPECT_EQ(opt, rcvlowatSz);
+  }
+}
 }  // namespace testing
 }  // namespace gvisor