Support weights_disallowed field in P4Info (#563)

Signed-off-by: Matthew Lam <[email protected]>

Author: matthewtlam

docs/v1/P4Runtime-Spec.adoc

@@ -1506,13 +1506,22 @@ The `ActionProfile` message includes the following fields:
 
 
 PSA programs can use the `@selector_size_semantics` annotation with one of
-`sum_of_weights` or `sum_of_members` to specify this value for Action Selectors. In the `sum_of_members` case, the `@max_member_weight` annotation
+`sum_of_weights` or `sum_of_members` to specify this value for Action Selectors.
+In the `sum_of_members` case, the `@max_member_weight` annotation
 can be used to specify `max_member_weight`. Unless otherwise specified, the
 value of `selector_size_semantics` should default to `sum_of_weights`.
 However, an unset `selector_size_semantics` should also be treated as
 `sum_of_weights` for backwards compatibility in Action Selectors. In Action
 Profiles, this value must be unset.
 
+* `weights_disallowed`,  a boolean flag indicating whether the controller
+  programs the weights (false) or the switch determines them through some other
+  mechanism (true). One such mechanism is dynamic load balancing or adaptive
+  routing (See e.g. link:https://sonic.software/sai/group__SAIARS.html[SAI API]).
+  The `@weights_disallowed` annotation can be added to action selectors in P4
+  programs to set this value to true. In Action Profiles, this value must be unset
+  (i.e. false).
+
 ==== `Counter` & `DirectCounter`
 
 `Counter` and `DirectCounter` messages are used to specify all possible
@@ -3777,9 +3786,11 @@ An `ActionProfileGroup` entity update message has the following fields:
   group. For each member in a group, the controller must define the following
   fields:
     ** `member_id` for looking up the member table in the selector.
-    ** `weight` specifying the probability of the member's selection at
-      runtime. 0 is not a valid `weight` value and the server must return
-      `INVALID_ARGUMENT` if the client attempts to use it.
+    ** `weight` specifying the probability of the member's selection at runtime.
+       If `weights_disallowed` is set to true, then 0 (unset) is the only valid
+       `weight`. If `weights_disallowed` is false, then 0 is not a valid
+       `weight`. The server must return `INVALID_ARGUMENT` if the client attempts
+       to use invalid `weight`s.
     ** `watch_port` is the controller-defined port that the member's
       liveness depends on. At runtime, the member must be excluded from
       selection if the watch port is down.  See <<#action-selector-constraints>> for notes on the behavior if all members in
@@ -3884,16 +3895,18 @@ Each `ActionProfileAction` message has the following fields:
 * `action` is one of the actions specified by the table that is being
   programmed.
 
-* `weight` specifying the probability of the action's selection at runtime. 0 is
-  not a valid `weight` value and the server must return `INVALID_ARGUMENT` if
-  the client attempts to use it. If `selector_size_semantics` is
-  `sum_of_weights`, then the sum of all weights across all `ActionProfileAction`
-  messages for that `ActionProfileActionSet` message must not exceed the
-  `max_group_size` specified in the P4Info (if greater than 0), or the server
-  must return `INVALID_ARGUMENT`. If `selector_size_semantics` is
-  `sum_of_members`, the individual weight of each member must not exceed
-  `max_member_weight` (if greater than 0), or the server must return
-  `INVALID_ARGUMENT`.
+* `weight` specifying the probability of the action's selection at runtime.
+  If `weights_disallowed` is set to true, then 0 (unset) is the only valid
+  `weight`. If `weights_disallowed` is false, then 0 is not a valid `weight`.
+  The server must return `INVALID_ARGUMENT` if the client attempts to use invalid
+  `weight`s.
+  If `selector_size_semantics` is `sum_of_weights`, then the sum of all weights
+  across all `ActionProfileAction` messages for that `ActionProfileActionSet`
+  message must not exceed the `max_group_size` specified in the P4Info
+  (if greater than 0), or the server must return `INVALID_ARGUMENT`.
+  If `selector_size_semantics` is `sum_of_members`, the individual weight of
+  each member must not exceed `max_member_weight` (if greater than 0), or the
+  server must return `INVALID_ARGUMENT`.
 
 * `watch_port` is the controller-defined port that the action's liveness depends
   on. At runtime, the action must be excluded from selection if the watch port