tap: allow change of carrier state on host

Type: feature

Add a function to adjust the link state of the host side of a tap
interface. If an application (e.g. route protocol daemons) running on
the host uses netlink to monitor interface state, a plugin
could use this function to communicate a loss of connectivity
to the application by making the interface appear to go down.

Requires a somewhat recent kernel. E.g. it does not have any effect
on CentOS 7 but it works on CentOS 8.

Change-Id: I677ee7889d2eb142e2395bea98f0b4d7e7e7f810
Signed-off-by: Matthew Smith <mgsmith@netgate.com>

1 files changed, 41 insertions, 0 deletions

diff --git a/src/vnet/devices/tap/tap.c b/src/vnet/devices/tap/tap.c
index aa9182a58f7..94a91e5509a 100644
--- a/src/vnet/devices/tap/tap.c
+++ b/src/vnet/devices/tap/tap.c
@@ -751,6 +751,12 @@ tap_create_if (vlib_main_t * vm, tap_create_if_args_t * args)
   vif->flags |= VIRTIO_IF_FLAG_ADMIN_UP;
   vnet_hw_interface_set_flags (vnm, vif->hw_if_index,
 			       VNET_HW_INTERFACE_FLAG_LINK_UP);
+  /*
+   * Host tun/tap driver link carrier state is "up" at creation. The
+   * driver never changes this unless the backend (VPP) changes it using
+   * TUNSETCARRIER ioctl(). See tap_set_carrier().
+   */
+  vif->host_carrier_up = 1;
   vif->cxq_vring = NULL;
 
   goto done;
@@ -987,6 +993,41 @@ tap_dump_ifs (tap_interface_details_t ** out_tapids)
   return 0;
 }
 
+/*
+ * Set host tap/tun interface carrier state so it will appear to host
+ * applications that the interface's link state changed.
+ *
+ * If the kernel we're building against does not have support for the
+ * TUNSETCARRIER ioctl command, do nothing.
+ */
+int
+tap_set_carrier (u32 hw_if_index, u32 carrier_up)
+{
+  int ret = 0;
+#ifdef TUNSETCARRIER
+  vnet_main_t *vnm = vnet_get_main ();
+  vnet_hw_interface_t *hi = vnet_get_hw_interface (vnm, hw_if_index);
+  virtio_main_t *mm = &virtio_main;
+  virtio_if_t *vif;
+  int *fd;
+
+  vif = pool_elt_at_index (mm->interfaces, hi->dev_instance);
+  vec_foreach (fd, vif->tap_fds)
+  {
+    ret = ioctl (*fd, TUNSETCARRIER, &carrier_up);
+    if (ret < 0)
+      {
+	clib_warning ("ioctl (TUNSETCARRIER) returned %d", ret);
+	break;
+      }
+  }
+  if (!ret)
+    vif->host_carrier_up = (carrier_up != 0);
+#endif
+
+  return ret;
+}
+
 static clib_error_t *
 tap_mtu_config (vlib_main_t * vm, unformat_input_t * input)
 {