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>

4 files changed, 45 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)
 {
diff --git a/src/vnet/devices/tap/tap.h b/src/vnet/devices/tap/tap.h
index 46f13a4e274..42283281448 100644
--- a/src/vnet/devices/tap/tap.h
+++ b/src/vnet/devices/tap/tap.h
@@ -108,6 +108,8 @@ int
 tap_csum_offload_enable_disable (vlib_main_t * vm, u32 sw_if_index,
 				 int enable_disable);
 int tap_dump_ifs (tap_interface_details_t ** out_tapids);
+int tap_set_carrier (u32 hw_if_index, u32 carrier_up);
+
 
 #endif /* _VNET_DEVICES_VIRTIO_TAP_H_ */
 
diff --git a/src/vnet/devices/virtio/virtio.c b/src/vnet/devices/virtio/virtio.c
index 8209a46b52f..925ad092b91 100644
--- a/src/vnet/devices/virtio/virtio.c
+++ b/src/vnet/devices/virtio/virtio.c
@@ -345,6 +345,7 @@ virtio_show (vlib_main_t * vm, u32 * hw_if_indices, u8 show_descr, u32 type)
 	  if (type == VIRTIO_IF_TYPE_TAP)
 	    vlib_cli_output (vm, "  host-mac-addr: %U",
 			     format_ethernet_address, vif->host_mac_addr);
+	  vlib_cli_output (vm, "  host-carrier-up: %u", vif->host_carrier_up);
 
 	  vec_foreach_index (i, vif->vhost_fds)
 	    str = format (str, " %d", vif->vhost_fds[i]);
diff --git a/src/vnet/devices/virtio/virtio.h b/src/vnet/devices/virtio/virtio.h
index 86660a1f933..fda72365db9 100644
--- a/src/vnet/devices/virtio/virtio.h
+++ b/src/vnet/devices/virtio/virtio.h
@@ -169,6 +169,7 @@ typedef struct
       ip4_address_t host_ip4_addr;
       u8 host_ip4_prefix_len;
       u8 host_ip6_prefix_len;
+      u8 host_carrier_up;	/* host tun/tap driver link carrier state */
     };
     struct			/* native virtio */
     {