Override VRF (#1186)

* Override VRF

New virtual router boolean attribute is introduced to indicate that this is an override VRF and overrides other VRs

Signed-off-by: Jai Kumar <jai.kumar@broadcom.com>

doc/Override-VRF.md

@@ -0,0 +1,114 @@
+Override VRF
+-------------------------------------------------------------------------------
+ Title | SAI Override VRF
+-------------|-----------------------------------------------------------------
+ Authors | Jai Kumar, Broadcom Inc.
+ Status | In review
+ Type | Standards track
+ Created | 02/18/2021
+ SAI-Version | 1.7.2
+
+
+-------------------------------------------------------------------------------
+
+This spec talks about the override VRF usecase.
+
+SAI pipleine define L3 lookup block as an abstracted stage where route lookup is abstracted as a single operation. 
+SAI pipeline do not specify how many parallel L3 lookups a device can/may support.
+
+Typically devices support multiple parallel L3 lookup to provide policy based forwarding.
+Following usecase 1 is already covered in SAI spec. This spec adds support for usecase 2 and 3.
+
+New switch level default override VRF is introduced. 
+```
+ /**
+ * @brief Default SAI Override Virtual Router ID
+ *
+ * Must return #SAI_STATUS_OBJECT_IN_USE when try to delete this VR ID.
+ *
+ * @type sai_object_id_t
+ * @flags READ_ONLY
+ * @objects SAI_OBJECT_TYPE_VIRTUAL_ROUTER
+ * @default internal
+ */
+ SAI_SWITCH_ATTR_DEFAULT_OVERRIDE_VIRTUAL_ROUTER_ID,
+```
+
+
+### Usecase 1: VRF Fallback
+In this case 2 parrallel lookups are performed
+```
+Lookup 1: RIF/ACL -> VRF -> [VRF, DIP] -> R1
+Lookup 2: Switch -> Deafault_VRF -> [Default_VRF, DIP] -> R2
+
+if (R1)
+ use R1;
+elif (R2)
+ use R2;
+else
+ MISS action;
+```
+
+
+
+### Usecase 2: Override VRF
+In this case 2 parallel lookups are performed
+```
+Lookup 1: Switch -> Override_VRF -> [Override_VRF, DIP] -> R1
+Lookup 2: RIF/ACL -> VRF -> [VRF, DIP] -> R2
+
+if (R1)
+ use R1;
+elif (R2)
+ use R2;
+else
+ MISS action;
+```
+
+### Usecase 3: Override VRF and VRF Fallback
+In this case 3 parallel lookups are performed
+```
+Lookup 1: Switch -> Override_VRF -> [Override_VRF, DIP] -> R1
+Lookup 2: RIF/ACL -> VRF -> [VRF, DIP] -> R2
+Lookup 2: Switch -> Deafault_VRF -> [Default_VRF, DIP] -> R3
+
+if (R1)
+ use R1;
+elif (R2)
+ use R2;
+elif (R3)
+ use R3;
+else
+ MISS action;
+```
+
+Example WorkFlow:
+Since SAI_SWITCH_ATTR_DEFAULT_OVERRIDE_VIRTUAL_ROUTER_ID is a READ only attribute, SAI adapter creates a VRF object (virtual_router) during init. This object is emtpy and is returned when application quries for the override VRF.
+Application MUST provide this VRF in the route update API.
+```
+typedef struct _sai_route_entry_t
+{
+ /**
+ * @brief Switch ID
+ *
+ * @objects SAI_OBJECT_TYPE_SWITCH
+ */
+ sai_object_id_t switch_id;
+
+ /**
+ * @brief Virtual Router ID
+ *
+ * @objects SAI_OBJECT_TYPE_VIRTUAL_ROUTER
+ */
+ sai_object_id_t vr_id;
+
+ /**
+ * @brief IP Prefix Destination
+ */
+ sai_ip_prefix_t destination;
+
+} sai_route_entry_t;
+
+```
+
+> SAI adapter should return error if platform do not support SAI_SWITCH_ATTR_DEFAULT_OVERRIDE_VIRTUAL_ROUTER_ID switch attribute

inc/saiswitch.h

@@ -861,6 +861,18 @@ typedef enum _sai_switch_attr_t
  */
  SAI_SWITCH_ATTR_DEFAULT_VIRTUAL_ROUTER_ID,
 
+ /**
+ * @brief Default SAI Override Virtual Router ID
+ *
+ * Must return #SAI_STATUS_OBJECT_IN_USE when try to delete this VR ID.
+ *
+ * @type sai_object_id_t
+ * @flags READ_ONLY
+ * @objects SAI_OBJECT_TYPE_VIRTUAL_ROUTER
+ * @default internal
+ */
+ SAI_SWITCH_ATTR_DEFAULT_OVERRIDE_VIRTUAL_ROUTER_ID,
+
  /**
  * @brief Default .1Q Bridge ID
  *