Allow resolver to pass channel args to LB policy.

src/core/ext/client_config/client_channel.c

@@ -179,6 +179,8 @@ static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
     grpc_lb_policy_args lb_policy_args;
     lb_policy_args.addresses =
         grpc_resolver_result_get_addresses(chand->resolver_result);
+    lb_policy_args.additional_args =
+        grpc_resolver_result_get_lb_policy_args(chand->resolver_result);
     lb_policy_args.client_channel_factory = chand->client_channel_factory;
     lb_policy = grpc_lb_policy_create(
         exec_ctx,

src/core/ext/client_config/lb_policy_factory.h

@@ -47,9 +47,12 @@ struct grpc_lb_policy_factory {
   const grpc_lb_policy_factory_vtable *vtable;
 };
 
+// TODO(roth, ctiller): Consider replacing this struct with
+// grpc_channel_args.  See comment in resolver_result.h for details.
 typedef struct grpc_lb_policy_args {
   grpc_addresses *addresses;
   grpc_client_channel_factory *client_channel_factory;
+  grpc_channel_args *additional_args;
 } grpc_lb_policy_args;
 
 struct grpc_lb_policy_factory_vtable {

src/core/ext/client_config/resolver_result.c

@@ -36,6 +36,8 @@
 #include <grpc/support/alloc.h>
 #include <grpc/support/string_util.h>
 
+#include "src/core/lib/channel/channel_args.h"
+
 grpc_addresses* grpc_addresses_create(size_t num_addresses) {
   grpc_addresses* addresses = gpr_malloc(sizeof(grpc_addresses));
   addresses->num_addresses = num_addresses;
@@ -71,15 +73,18 @@ struct grpc_resolver_result {
   gpr_refcount refs;
   grpc_addresses* addresses;
   char* lb_policy_name;
+  grpc_channel_args* lb_policy_args;
 };
 
-grpc_resolver_result* grpc_resolver_result_create(grpc_addresses* addresses,
-                                                  const char* lb_policy_name) {
+grpc_resolver_result* grpc_resolver_result_create(
+    grpc_addresses* addresses, const char* lb_policy_name,
+    grpc_channel_args* lb_policy_args) {
   grpc_resolver_result* result = gpr_malloc(sizeof(*result));
   memset(result, 0, sizeof(*result));
   gpr_ref_init(&result->refs, 1);
   result->addresses = addresses;
   result->lb_policy_name = gpr_strdup(lb_policy_name);
+  result->lb_policy_args = lb_policy_args;
   return result;
 }
 
@@ -92,6 +97,7 @@ void grpc_resolver_result_unref(grpc_exec_ctx* exec_ctx,
   if (gpr_unref(&result->refs)) {
     grpc_addresses_destroy(result->addresses);
     gpr_free(result->lb_policy_name);
+    grpc_channel_args_destroy(result->lb_policy_args);
     gpr_free(result);
   }
 }
@@ -105,3 +111,8 @@ const char* grpc_resolver_result_get_lb_policy_name(
     grpc_resolver_result* result) {
   return result->lb_policy_name;
 }
+
+grpc_channel_args* grpc_resolver_result_get_lb_policy_args(
+    grpc_resolver_result* result) {
+  return result->lb_policy_args;
+}

src/core/ext/client_config/resolver_result.h

@@ -37,6 +37,16 @@
 #include "src/core/ext/client_config/lb_policy.h"
 #include "src/core/lib/iomgr/resolve_address.h"
 
+// TODO(roth, ctiller): In the long term, we are considering replacing
+// the resolver_result data structure with grpc_channel_args.  The idea is
+// that the resolver will return a set of channel args that contains the
+// information that is currently in the resolver_result struct.  For
+// example, there will be specific args indicating the set of addresses
+// and the name of the LB policy to instantiate.  Note that if we did
+// this, we would probably want to change the data structure of
+// grpc_channel_args such to a hash table or AVL or some other data
+// structure that does not require linear search to find keys.
+
 /// Used to represent addresses returned by the resolver.
 typedef struct grpc_address {
   grpc_resolved_address address;
@@ -63,9 +73,10 @@ void grpc_addresses_destroy(grpc_addresses* addresses);
 /// Results reported from a grpc_resolver.
 typedef struct grpc_resolver_result grpc_resolver_result;
 
-/// Takes ownership of \a addresses.
-grpc_resolver_result* grpc_resolver_result_create(grpc_addresses* addresses,
-                                                  const char* lb_policy_name);
+/// Takes ownership of \a addresses and \a lb_policy_args.
+grpc_resolver_result* grpc_resolver_result_create(
+    grpc_addresses* addresses, const char* lb_policy_name,
+    grpc_channel_args* lb_policy_args);
 void grpc_resolver_result_ref(grpc_resolver_result* result);
 void grpc_resolver_result_unref(grpc_exec_ctx* exec_ctx,
                                 grpc_resolver_result* result);
@@ -78,4 +89,8 @@ grpc_addresses* grpc_resolver_result_get_addresses(
 const char* grpc_resolver_result_get_lb_policy_name(
     grpc_resolver_result* result);
 
+/// Caller does NOT take ownership of result.
+grpc_channel_args* grpc_resolver_result_get_lb_policy_args(
+    grpc_resolver_result* result);
+
 #endif /* GRPC_CORE_EXT_CLIENT_CONFIG_RESOLVER_RESULT_H */

src/core/ext/resolver/dns/native/dns_resolver.c

@@ -174,7 +174,7 @@ static void dns_on_resolved(grpc_exec_ctx *exec_ctx, void *arg,
                                  false /* is_balancer */);
     }
     grpc_resolved_addresses_destroy(r->addresses);
-    result = grpc_resolver_result_create(addresses, r->lb_policy_name);
+    result = grpc_resolver_result_create(addresses, r->lb_policy_name, NULL);
   } else {
     gpr_timespec now = gpr_now(GPR_CLOCK_MONOTONIC);
     gpr_timespec next_try = gpr_backoff_step(&r->backoff_state, now);

src/core/ext/resolver/sockaddr/sockaddr_resolver.c

@@ -121,7 +121,7 @@ static void sockaddr_maybe_finish_next_locked(grpc_exec_ctx *exec_ctx,
   if (r->next_completion != NULL && !r->published) {
     r->published = true;
     *r->target_result = grpc_resolver_result_create(
-        grpc_addresses_copy(r->addresses), r->lb_policy_name);
+        grpc_addresses_copy(r->addresses), r->lb_policy_name, NULL);
     grpc_exec_ctx_sched(exec_ctx, r->next_completion, GRPC_ERROR_NONE, NULL);
     r->next_completion = NULL;
   }