Protect VPP -> Linux state propagation behind flag

Introduce lcp_main.lcp_sync, which determines if state changes made
to interfaces in VPP do or don't propagate into Linux.

- Add a startup.conf directive 'lcp-sync' to enable at startup time.
- Add CLI.short_help = "lcp lcp-sync [on|enable|off|disable]",
- Show the current value in "show lcp".

Gate changes in mtu, state and address on lcp_lcp_sync().

When the operator issues 'lcp lcp-sync on', it is prudent to do a
one-off sync of all interface attributes from VPP into Linux.
For this, add a lcp_itf_pair_sync_state_all() function.

lcpng.c

@@ -69,6 +69,26 @@ int lcp_set_default_ns(u8 *ns) {
     return 0;
 }
 
+void
+lcp_set_lcp_sync (u8 is_auto)
+{
+  lcp_main_t *lcpm = &lcp_main;
+
+  lcpm->lcp_sync = (is_auto != 0);
+
+  // If we set to 'on', do a one-off sync of LCP interfaces
+  if (is_auto)
+    lcp_itf_pair_sync_state_all ();
+}
+
+int
+lcp_lcp_sync (void)
+{
+  lcp_main_t *lcpm = &lcp_main;
+
+  return lcpm->lcp_sync;
+}
+
 void
 lcp_set_lcp_auto_subint (u8 is_auto)
 {

lcpng.h

@@ -25,6 +25,7 @@ typedef struct lcp_main_s
   u8 default_namespace[LCP_NS_LEN]; /* default namespace if set */
   int default_ns_fd;
   u8 lcp_auto_subint; /* Automatically create/delete LCP sub-interfaces */
+  u8 lcp_sync;	      /* Automatically sync VPP changes to LCP */
   /* Set when Unit testing */
   u8 test_mode;
 } lcp_main_t;
@@ -38,6 +39,11 @@ int lcp_set_default_ns(u8 *ns);
 u8 *lcp_get_default_ns(void); /* Returns NULL or shared string */
 int lcp_get_default_ns_fd(void);
 
+/*
+ * Sync state from VPP into all LCP devices
+ */
+void lcp_itf_pair_sync_state_all ();
+
 #endif
 
 /*

lcpng_if_cli.c

@@ -111,6 +111,37 @@ VLIB_CLI_COMMAND(lcp_itf_pair_create_command, static) = {
     .function = lcp_itf_pair_create_command_fn,
 };
 
+static clib_error_t *
+lcp_lcp_sync_command_fn (vlib_main_t *vm, unformat_input_t *input,
+			 vlib_cli_command_t *cmd)
+{
+  unformat_input_t _line_input, *line_input = &_line_input;
+
+  if (!unformat_user (input, unformat_line_input, line_input))
+    return 0;
+
+  while (unformat_check_input (line_input) != UNFORMAT_END_OF_INPUT)
+    {
+      if (unformat (line_input, "on") || unformat (line_input, "enable"))
+	lcp_set_lcp_sync (1);
+      else if (unformat (line_input, "off") ||
+	       unformat (line_input, "disable"))
+	lcp_set_lcp_sync (0);
+      else
+	return clib_error_return (0, "unknown input `%U'",
+				  format_unformat_error, line_input);
+    }
+
+  unformat_free (line_input);
+  return 0;
+}
+
+VLIB_CLI_COMMAND (lcp_lcp_sync_command, static) = {
+  .path = "lcp lcp-sync",
+  .short_help = "lcp lcp-sync [on|enable|off|disable]",
+  .function = lcp_lcp_sync_command_fn,
+};
+
 static clib_error_t *
 lcp_lcp_auto_subint_command_fn (vlib_main_t *vm, unformat_input_t *input,
 				vlib_cli_command_t *cmd)

lcpng_if_sync.c

@@ -48,6 +48,10 @@ lcp_itf_pair_sync_state (lcp_itf_pair_t *lip)
   vnet_sw_interface_t *sup_sw;
   int curr_ns_fd = -1;
   int vif_ns_fd = -1;
+  u32 mtu;
+
+  if (!lcp_lcp_sync ())
+    return;
 
   sw =
     vnet_get_sw_interface_or_null (vnet_get_main (), lip->lip_phy_sw_if_index);
@@ -72,16 +76,17 @@ lcp_itf_pair_sync_state (lcp_itf_pair_t *lip)
   /* Linux will clamp MTU of children when the parent is lower. VPP is fine
    * with differing MTUs. Reconcile any differences
    */
+  mtu = sw->mtu[VNET_MTU_L3];
   if (sup_sw->mtu[VNET_MTU_L3] < sw->mtu[VNET_MTU_L3])
     {
       LCP_ITF_PAIR_WARN ("sync_state: %U flags %u mtu %u sup-mtu %u: "
 			 "clamping to sup-mtu to satisfy netlink",
 			 format_lcp_itf_pair, lip, sw->flags,
 			 sw->mtu[VNET_MTU_L3], sup_sw->mtu[VNET_MTU_L3]);
-      vnet_sw_interface_set_mtu (vnet_get_main (), sw->sw_if_index,
+      mtu = sup_sw->mtu[VNET_MTU_L3];
-				 sup_sw->mtu[VNET_MTU_L3]);
-      vnet_netlink_set_link_mtu (lip->lip_vif_index, sup_sw->mtu[VNET_MTU_L3]);
     }
+  vnet_sw_interface_set_mtu (vnet_get_main (), sw->sw_if_index, mtu);
+  vnet_netlink_set_link_mtu (lip->lip_vif_index, mtu);
 
   /* Linux will remove IPv6 addresses on children when the master state
    * goes down, so we ensure all IPv4/IPv6 addresses are synced.
@@ -101,7 +106,7 @@ lcp_itf_pair_sync_state (lcp_itf_pair_t *lip)
 }
 
 static walk_rc_t
-lcp_itf_pair_walk_sync_state_cb (index_t lipi, void *ctx)
+lcp_itf_pair_walk_sync_state_all_cb (index_t lipi, void *ctx)
 {
   lcp_itf_pair_t *lip;
   lip = lcp_itf_pair_get (lipi);
@@ -112,6 +117,12 @@ lcp_itf_pair_walk_sync_state_cb (index_t lipi, void *ctx)
   return WALK_CONTINUE;
 }
 
+void
+lcp_itf_pair_sync_state_all ()
+{
+  lcp_itf_pair_walk (lcp_itf_pair_walk_sync_state_all_cb, 0);
+}
+
 static clib_error_t *
 lcp_itf_admin_state_change (vnet_main_t * vnm, u32 sw_if_index, u32 flags)
 {
@@ -122,6 +133,9 @@ lcp_itf_admin_state_change (vnet_main_t * vnm, u32 sw_if_index, u32 flags)
   int curr_ns_fd = -1;
   int vif_ns_fd = -1;
 
+  if (!lcp_lcp_sync ())
+    return 0;
+
   LCP_ITF_PAIR_DBG ("admin_state_change: sw %U %u",
 		  format_vnet_sw_if_index_name, vnm, sw_if_index,
 		  flags);
@@ -163,7 +177,7 @@ lcp_itf_admin_state_change (vnet_main_t * vnm, u32 sw_if_index, u32 flags)
   // change. This is not true in VPP, so we are forced to undo that change by
   // walking the sub-interfaces of a phy and syncing their state back into
   // linux. For simplicity, just walk all interfaces.
-  lcp_itf_pair_walk (lcp_itf_pair_walk_sync_state_cb, 0);
+  lcp_itf_pair_sync_state_all ();
 
   return NULL;
 }   
@@ -178,6 +192,9 @@ lcp_itf_mtu_change (vnet_main_t *vnm, u32 sw_if_index, u32 flags)
   int curr_ns_fd = -1;
   int vif_ns_fd = -1;
 
+  if (!lcp_lcp_sync ())
+    return 0;
+
   LCP_ITF_PAIR_DBG ("mtu_change: sw %U %u", format_vnet_sw_if_index_name, vnm,
 		    sw_if_index, flags);
 
@@ -215,7 +232,7 @@ lcp_itf_mtu_change (vnet_main_t *vnm, u32 sw_if_index, u32 flags)
   // so we are forced to undo that change by walking the sub-interfaces of
   // a phy and syncing their state back into linux.
   // For simplicity, just walk all interfaces.
-  lcp_itf_pair_walk (lcp_itf_pair_walk_sync_state_cb, 0);
+  lcp_itf_pair_sync_state_all ();
 
   return NULL;
 }
@@ -369,6 +386,9 @@ lcp_itf_ip4_add_del_interface_addr (ip4_main_t *im, uword opaque,
   int curr_ns_fd = -1;
   int vif_ns_fd = -1;
 
+  if (!lcp_lcp_sync ())
+    return;
+
   LCP_ITF_PAIR_DBG ("ip4_addr_%s: si:%U %U/%u", is_del ? "del" : "add",
 		    format_vnet_sw_if_index_name, vnet_get_main (),
 		    sw_if_index, format_ip4_address, address, address_length);
@@ -415,6 +435,9 @@ lcp_itf_ip6_add_del_interface_addr (ip6_main_t *im, uword opaque,
   int curr_ns_fd = -1;
   int vif_ns_fd = -1;
 
+  if (!lcp_lcp_sync ())
+    return;
+
   LCP_ITF_PAIR_DBG ("ip6_addr_%s: si:%U %U/%u", is_del ? "del" : "add",
 		    format_vnet_sw_if_index_name, vnet_get_main (),
 		    sw_if_index, format_ip6_address, address, address_length);

lcpng_interface.c

@@ -132,6 +132,7 @@ lcp_itf_pair_show (u32 phy_sw_if_index)
   vlib_cli_output (vm, "lcp default netns %s\n", ns ? (char *) ns : "<unset>");
   vlib_cli_output (vm, "lcp lcp-auto-subint %s\n",
 		   lcp_lcp_auto_subint () ? "on" : "off");
+  vlib_cli_output (vm, "lcp lcp-sync %s\n", lcp_lcp_sync () ? "on" : "off");
 
   if (phy_sw_if_index == ~0)
     {
@@ -568,6 +569,8 @@ lcp_itf_pair_config (vlib_main_t *vm, unformat_input_t *input)
 	}
       else if (unformat (input, "lcp-auto-subint"))
 	lcp_set_lcp_auto_subint (1 /* is_auto */);
+      else if (unformat (input, "lcp-sync"))
+	lcp_set_lcp_sync (1 /* is_auto */);
       else
 	return clib_error_return (0, "unknown input `%U'",
 				  format_unformat_error, input);
@@ -1033,13 +1036,16 @@ lcp_itf_pair_create (u32 phy_sw_if_index, u8 *host_if_name,
 		    host_if_type, ns);
 
   /*
-   * Copy the link state from VPP into the host side.
+   * Copy the link state from VPP into the host side, if lcp-sync is on.
-   * The TAP is shared by many interfaces, always keep it up.
    * This controls whether the host can RX/TX.
+   * The TAP is shared by many interfaces, always keep it up.
    */
   vnet_sw_interface_admin_up (vnm, host_sw_if_index);
-  lip = lcp_itf_pair_get (lcp_itf_pair_find_by_vif(vif_index));
+  if (lcp_lcp_sync ())
-  lcp_itf_pair_sync_state (lip);
+    {
+      lip = lcp_itf_pair_get (lcp_itf_pair_find_by_vif (vif_index));
+      lcp_itf_pair_sync_state (lip);
+    }
 
   if (host_sw_if_indexp)
     *host_sw_if_indexp = host_sw_if_index;

lcpng_interface.h

@@ -170,6 +170,12 @@ lcp_itf_pair_find_by_host (u32 host_sw_if_index)
 void lcp_set_lcp_auto_subint (u8 is_auto);
 int lcp_lcp_auto_subint (void);
 
+/**
+ * sync state changes from VPP into LCP
+ */
+void lcp_set_lcp_sync (u8 is_auto);
+int lcp_lcp_sync (void);
+
 typedef void (*lcp_itf_pair_add_cb_t) (lcp_itf_pair_t *);
 typedef void (*lcp_itf_pair_del_cb_t) (lcp_itf_pair_t *);
 
@@ -199,13 +205,14 @@ void lcp_itf_ip6_add_del_interface_addr (ip6_main_t *im, uword opaque,
 					 u32 address_length,
 					 u32 if_address_index, u32 is_del);
 
-/* Sync all state from VPP to Linux device
+/* Sync all state from VPP to a specific Linux device, or all of them.
  *
  * Note: in some circumstances, this syncer will (have to) make changes to
  * the VPP interface, for example if its MTU is greater than its parent.
  * See the function for rationale.
  */
 void lcp_itf_pair_sync_state (lcp_itf_pair_t *lip);
+void lcp_itf_pair_sync_state_all ();
 
 /*
  * fd.io coding-style-patch-verification: ON