Generic Table First draft

docs/v1/GenericTable.md

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+# GenericTable example p4info
+
+Below is an example for realizing MulticastGroupEntry as a GenericTable.
+The key (MatchFields) comprise of only the group_id. 2 different ways of
+defining the data fields has been presented. Only 1 of them is required.
+
+```
+generic_tables {
+  type_id : 145
+  type_name : "MulticastGroup"
+  properties : {
+    "indexed"
+  }
+  instances {
+    preamble {
+      id: 45332650
+      name: "MulticastGroup"
+      alias: "multicast_group"
+    }
+    generic_match_fields {
+      id: 1
+      name: "multicast_group_id"
+      match_type: EXACT
+      type_spec {
+        bitstring {
+          bit {
+            bitwidth : 32
+          }
+        }
+      }
+    }
+    union_refs {
+      id: 23557840
+      scope: TABLE_AND_DEFAULT
+    }
+    size: 1024
+  }
+}
+```
+
+In the below one, both `instance` and `port` are separate
+repeated fields. So the check on `len(instance_array) == len(port_array)`
+needs to be a runtime check. This however keeps implementation simpler
+and faster since we avoid further recursive nesting.
+
+`port` is a varbytes of max size 64 bits each. The field is a list so
+it is defined as list of varbits through p4info.
+
+```
+unions {
+  preamble {
+    id: 23557840
+    name: "multicast_group_member_add"
+    alias: "multicast_group_member_add"
+  }
+  params {
+    id: 1
+    name: "instance"
+    type_spec {
+      list {
+        element_type_spec {
+          bitstring {
+            bit {
+              bitwidth : 32
+            }
+          }
+        }
+        max_size : 10
+      }
+    }
+  }
+  params {
+    id: 2
+    name: "port"
+    type_spec {
+      list {
+        type_spec {
+          bitstring {
+            varbit {
+              max_bitwidth : 64
+            }
+          }
+        }
+        max_size : 10
+      }
+    }
+  }
+}
+
+```
+
+The below one is similar to the above but both `instance` and `port` have
+been converted to a list of structs.
+
+```
+unions {
+  preamble {
+    id: 23557841
+    name: "multicast_group_member_add_2"
+    alias: "multicast_group_member_add_2"
+  }
+  params {
+    id: 1
+    name: "replica"
+    type_spec {
+      list {
+        element_type_spec {
+          struct {
+            members {
+              id : 1
+              name : "instance"
+              type_spec {
+                bitstring {
+                  bit {
+                    bitwidth : 32
+                  }
+                }
+              }
+            }
+            members {
+              id : 2
+              name : "port"
+              type_spec {
+                bitstring {
+                  varbit {
+                    max_bitwidth : 64
+                  }
+                }
+              }
+            }
+          }
+        }
+        max_size : 10
+      }
+    }
+  }
+}
+```