staging: usbip: vhci: handle EAGAIN from SO_RCVTIMEO

If there is a receive timeout without any active
requests, we can tell the connection was idle and
ignore the timeout.

If there are active requests for which we expect
to receive a reply we close the connection.

This makes it possible to set an upper bound on
the time a usbip device may be unresponsive.

This is a workaround for the lack of heart-beat
messages in the USBIP protocol.

Extending the protocol would break compatibility
with all previous stub versions, so this seems like
the lesser evil.

Signed-off-by: Max Vozeler <[e-mail]>
Tested-by: Mark Wehby <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/usbip/vhci_rx.c

···
 	return;
 }
 
+static int vhci_priv_tx_empty(struct vhci_device *vdev)
+{
+	int empty = 0;
+
+	spin_lock(&vdev->priv_lock);
+
+	empty = list_empty(&vdev->priv_rx);
+
+	spin_unlock(&vdev->priv_lock);
+
+	return empty;
+}
+
 /* recv a pdu */
 static void vhci_rx_pdu(struct usbip_device *ud)
 {
···
 	if (ret < 0) {
 		if (ret == -ECONNRESET)
 			usbip_uinfo("connection reset by peer\n");
-		else if (ret != -ERESTARTSYS)
+		else if (ret == -EAGAIN) {
+			/* ignore if connection was idle */
+			if (vhci_priv_tx_empty(vdev))
+				return;
+			usbip_uinfo("connection timed out with pending urbs\n");
+		} else if (ret != -ERESTARTSYS)
 			usbip_uinfo("xmit failed %d\n", ret);
+
 		usbip_event_add(ud, VDEV_EVENT_ERROR_TCP);
 		return;
 	}