Merge pull request #15980 from ncteisen/channelz-subchannel-refs

Channelz Part 3: Subchannel Refs Support for PickFirst

21 files changed, 516 insertions, 116 deletions

diff --git a/include/grpc/support/string_util.h b/include/grpc/support/string_util.h
index 2c7460fa15..2679160c1b 100644
--- a/include/grpc/support/string_util.h
+++ b/include/grpc/support/string_util.h
@@ -21,6 +21,8 @@
 
 #include <grpc/support/port_platform.h>
 
+#include <grpc/impl/codegen/gpr_types.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
diff --git a/src/core/ext/filters/client_channel/client_channel.cc b/src/core/ext/filters/client_channel/client_channel.cc
index 04f7a2c830..024c9d737e 100644
--- a/src/core/ext/filters/client_channel/client_channel.cc
+++ b/src/core/ext/filters/client_channel/client_channel.cc
@@ -3174,6 +3174,16 @@ static void try_to_connect_locked(void* arg, grpc_error* error_ignored) {
   GRPC_CHANNEL_STACK_UNREF(chand->owning_stack, "try_to_connect");
 }
 
+void grpc_client_channel_populate_child_refs(
+    grpc_channel_element* elem, grpc_core::ChildRefsList* child_subchannels,
+    grpc_core::ChildRefsList* child_channels) {
+  channel_data* chand = static_cast<channel_data*>(elem->channel_data);
+  if (chand->lb_policy != nullptr) {
+    chand->lb_policy->FillChildRefsForChannelz(child_subchannels,
+                                               child_channels);
+  }
+}
+
 grpc_connectivity_state grpc_client_channel_check_connectivity_state(
     grpc_channel_element* elem, int try_to_connect) {
   channel_data* chand = static_cast<channel_data*>(elem->channel_data);
diff --git a/src/core/ext/filters/client_channel/client_channel.h b/src/core/ext/filters/client_channel/client_channel.h
index a21e5623a7..0b44a17562 100644
--- a/src/core/ext/filters/client_channel/client_channel.h
+++ b/src/core/ext/filters/client_channel/client_channel.h
@@ -21,6 +21,7 @@
 
 #include <grpc/support/port_platform.h>
 
+#include "src/core/ext/filters/client_channel/client_channel_channelz.h"
 #include "src/core/ext/filters/client_channel/client_channel_factory.h"
 #include "src/core/ext/filters/client_channel/resolver.h"
 #include "src/core/lib/channel/channel_stack.h"
@@ -39,6 +40,10 @@ extern grpc_core::TraceFlag grpc_client_channel_trace;
 
 extern const grpc_channel_filter grpc_client_channel_filter;
 
+void grpc_client_channel_populate_child_refs(
+    grpc_channel_element* elem, grpc_core::ChildRefsList* child_subchannels,
+    grpc_core::ChildRefsList* child_channels);
+
 grpc_connectivity_state grpc_client_channel_check_connectivity_state(
     grpc_channel_element* elem, int try_to_connect);
 
diff --git a/src/core/ext/filters/client_channel/client_channel_channelz.cc b/src/core/ext/filters/client_channel/client_channel_channelz.cc
index 08ceb2dd05..235b8f3207 100644
--- a/src/core/ext/filters/client_channel/client_channel_channelz.cc
+++ b/src/core/ext/filters/client_channel/client_channel_channelz.cc
@@ -63,6 +63,37 @@ void ClientChannelNode::PopulateConnectivityState(grpc_json* json) {
                          false);
 }
 
+void ClientChannelNode::PopulateChildRefs(grpc_json* json) {
+  ChildRefsList child_subchannels;
+  ChildRefsList child_channels;
+  grpc_json* json_iterator = nullptr;
+  grpc_client_channel_populate_child_refs(client_channel_, &child_subchannels,
+                                          &child_channels);
+  if (child_subchannels.size() > 0) {
+    grpc_json* array_parent = grpc_json_create_child(
+        nullptr, json, "subchannelRef", nullptr, GRPC_JSON_ARRAY, false);
+    for (size_t i = 0; i < child_subchannels.size(); ++i) {
+      json_iterator =
+          grpc_json_create_child(json_iterator, array_parent, nullptr, nullptr,
+                                 GRPC_JSON_OBJECT, false);
+      grpc_json_add_number_string_child(json_iterator, nullptr, "subchannelId",
+                                        child_subchannels[i]);
+    }
+  }
+  if (child_channels.size() > 0) {
+    grpc_json* array_parent = grpc_json_create_child(
+        nullptr, json, "channelRef", nullptr, GRPC_JSON_ARRAY, false);
+    json_iterator = nullptr;
+    for (size_t i = 0; i < child_subchannels.size(); ++i) {
+      json_iterator =
+          grpc_json_create_child(json_iterator, array_parent, nullptr, nullptr,
+                                 GRPC_JSON_OBJECT, false);
+      grpc_json_add_number_string_child(json_iterator, nullptr, "channelId",
+                                        child_subchannels[i]);
+    }
+  }
+}
+
 grpc_arg ClientChannelNode::CreateChannelArg() {
   return grpc_channel_arg_pointer_create(
       const_cast<char*>(GRPC_ARG_CHANNELZ_CHANNEL_NODE_CREATION_FUNC),
diff --git a/src/core/ext/filters/client_channel/client_channel_channelz.h b/src/core/ext/filters/client_channel/client_channel_channelz.h
index cf3ef7b6f2..0547109d36 100644
--- a/src/core/ext/filters/client_channel/client_channel_channelz.h
+++ b/src/core/ext/filters/client_channel/client_channel_channelz.h
@@ -22,9 +22,17 @@
 #include <grpc/support/port_platform.h>
 
 #include "src/core/lib/channel/channel_args.h"
+#include "src/core/lib/channel/channel_stack.h"
 #include "src/core/lib/channel/channelz.h"
+#include "src/core/lib/gprpp/inlined_vector.h"
 
 namespace grpc_core {
+
+// TODO(ncteisen), this only contains the uuids of the children for now,
+// since that is all that is strictly needed. In a future enhancement we will
+// add human readable names as in the channelz.proto
+typedef InlinedVector<intptr_t, 10> ChildRefsList;
+
 namespace channelz {
 
 // Subtype of ChannelNode that overrides and provides client_channel specific
@@ -38,6 +46,9 @@ class ClientChannelNode : public ChannelNode {
   // channel connectivity.
   void PopulateConnectivityState(grpc_json* json) override;
 
+  // Override this functionality since client_channels have subchannels
+  void PopulateChildRefs(grpc_json* json) override;
+
   // Helper to create a channel arg to ensure this type of ChannelNode is
   // created.
   static grpc_arg CreateChannelArg();
diff --git a/src/core/ext/filters/client_channel/lb_policy.h b/src/core/ext/filters/client_channel/lb_policy.h
index dab4466b21..3150df8847 100644
--- a/src/core/ext/filters/client_channel/lb_policy.h
+++ b/src/core/ext/filters/client_channel/lb_policy.h
@@ -21,6 +21,7 @@
 
 #include <grpc/support/port_platform.h>
 
+#include "src/core/ext/filters/client_channel/client_channel_channelz.h"
 #include "src/core/ext/filters/client_channel/client_channel_factory.h"
 #include "src/core/ext/filters/client_channel/subchannel.h"
 #include "src/core/lib/gprpp/abstract.h"
@@ -143,6 +144,14 @@ class LoadBalancingPolicy
   /// consider whether this method is still needed.
   virtual void ExitIdleLocked() GRPC_ABSTRACT;
 
+  /// populates child_subchannels and child_channels with the uuids of this
+  /// LB policy's referenced children. This is not invoked from the
+  /// client_channel's combiner. The implementation is responsible for
+  /// providing its own synchronization.
+  virtual void FillChildRefsForChannelz(ChildRefsList* child_subchannels,
+                                        ChildRefsList* child_channels)
+      GRPC_ABSTRACT;
+
   void Orphan() override {
     // Invoke ShutdownAndUnrefLocked() inside of the combiner.
     GRPC_CLOSURE_SCHED(
@@ -196,6 +205,12 @@ class LoadBalancingPolicy
   grpc_pollset_set* interested_parties_;
   /// Callback to force a re-resolution.
   grpc_closure* request_reresolution_;
+
+  // Dummy classes needed for alignment issues.
+  // See https://github.com/grpc/grpc/issues/16032 for context.
+  // TODO(ncteisen): remove this as soon as the issue is resolved.
+  ChildRefsList dummy_list_foo;
+  ChildRefsList dummy_list_bar;
 };
 
 }  // namespace grpc_core
diff --git a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
index 263b51ae89..f757d6057c 100644
--- a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
@@ -135,6 +135,9 @@ class GrpcLb : public LoadBalancingPolicy {
   void HandOffPendingPicksLocked(LoadBalancingPolicy* new_policy) override;
   void PingOneLocked(grpc_closure* on_initiate, grpc_closure* on_ack) override;
   void ExitIdleLocked() override;
+  // TODO(ncteisen): implement this in a follow up PR
+  void FillChildRefsForChannelz(ChildRefsList* child_subchannels,
+                                ChildRefsList* child_channels) override {}
 
  private:
   /// Linked list of pending pick requests. It stores all information needed to
diff --git a/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc b/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
index ff2140e628..c50deb9679 100644
--- a/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
@@ -58,6 +58,8 @@ class PickFirst : public LoadBalancingPolicy {
   void HandOffPendingPicksLocked(LoadBalancingPolicy* new_policy) override;
   void PingOneLocked(grpc_closure* on_initiate, grpc_closure* on_ack) override;
   void ExitIdleLocked() override;
+  void FillChildRefsForChannelz(ChildRefsList* child_subchannels,
+                                ChildRefsList* child_channels) override;
 
  private:
   ~PickFirst();
@@ -103,10 +105,23 @@ class PickFirst : public LoadBalancingPolicy {
     }
   };
 
+  // Helper class to ensure that any function that modifies the child refs
+  // data structures will update the channelz snapshot data structures before
+  // returning.
+  class AutoChildRefsUpdater {
+   public:
+    explicit AutoChildRefsUpdater(PickFirst* pf) : pf_(pf) {}
+    ~AutoChildRefsUpdater() { pf_->UpdateChildRefsLocked(); }
+
+   private:
+    PickFirst* pf_;
+  };
+
   void ShutdownLocked() override;
 
   void StartPickingLocked();
   void DestroyUnselectedSubchannelsLocked();
+  void UpdateChildRefsLocked();
 
   // All our subchannels.
   OrphanablePtr<PickFirstSubchannelList> subchannel_list_;
@@ -122,10 +137,17 @@ class PickFirst : public LoadBalancingPolicy {
   PickState* pending_picks_ = nullptr;
   // Our connectivity state tracker.
   grpc_connectivity_state_tracker state_tracker_;
+
+  /// Lock and data used to capture snapshots of this channels child
+  /// channels and subchannels. This data is consumed by channelz.
+  gpr_mu child_refs_mu_;
+  ChildRefsList child_subchannels_;
+  ChildRefsList child_channels_;
 };
 
 PickFirst::PickFirst(const Args& args) : LoadBalancingPolicy(args) {
   GPR_ASSERT(args.client_channel_factory != nullptr);
+  gpr_mu_init(&child_refs_mu_);
   grpc_connectivity_state_init(&state_tracker_, GRPC_CHANNEL_IDLE,
                                "pick_first");
   if (grpc_lb_pick_first_trace.enabled()) {
@@ -139,6 +161,7 @@ PickFirst::~PickFirst() {
   if (grpc_lb_pick_first_trace.enabled()) {
     gpr_log(GPR_INFO, "Destroying Pick First %p", this);
   }
+  gpr_mu_destroy(&child_refs_mu_);
   GPR_ASSERT(subchannel_list_ == nullptr);
   GPR_ASSERT(latest_pending_subchannel_list_ == nullptr);
   GPR_ASSERT(pending_picks_ == nullptr);
@@ -158,6 +181,7 @@ void PickFirst::HandOffPendingPicksLocked(LoadBalancingPolicy* new_policy) {
 }
 
 void PickFirst::ShutdownLocked() {
+  AutoChildRefsUpdater(this);
   grpc_error* error = GRPC_ERROR_CREATE_FROM_STATIC_STRING("Channel shutdown");
   if (grpc_lb_pick_first_trace.enabled()) {
     gpr_log(GPR_INFO, "Pick First %p Shutting down", this);
@@ -280,7 +304,61 @@ void PickFirst::PingOneLocked(grpc_closure* on_initiate, grpc_closure* on_ack) {
   }
 }
 
+void PickFirst::FillChildRefsForChannelz(
+    ChildRefsList* child_subchannels_to_fill, ChildRefsList* ignored) {
+  mu_guard guard(&child_refs_mu_);
+  for (size_t i = 0; i < child_subchannels_.size(); ++i) {
+    // TODO(ncteisen): implement a de dup loop that is not O(n^2). Might
+    // have to implement lightweight set. For now, we don't care about
+    // performance when channelz requests are made.
+    bool found = false;
+    for (size_t j = 0; j < child_subchannels_to_fill->size(); ++j) {
+      if ((*child_subchannels_to_fill)[j] == child_subchannels_[i]) {
+        found = true;
+        break;
+      }
+    }
+    if (!found) {
+      child_subchannels_to_fill->push_back(child_subchannels_[i]);
+    }
+  }
+}
+
+void PickFirst::UpdateChildRefsLocked() {
+  ChildRefsList cs;
+  if (subchannel_list_ != nullptr) {
+    for (size_t i = 0; i < subchannel_list_->num_subchannels(); ++i) {
+      if (subchannel_list_->subchannel(i)->subchannel() != nullptr) {
+        grpc_core::channelz::SubchannelNode* subchannel_node =
+            grpc_subchannel_get_channelz_node(
+                subchannel_list_->subchannel(i)->subchannel());
+        if (subchannel_node != nullptr) {
+          cs.push_back(subchannel_node->subchannel_uuid());
+        }
+      }
+    }
+  }
+  if (latest_pending_subchannel_list_ != nullptr) {
+    for (size_t i = 0; i < latest_pending_subchannel_list_->num_subchannels();
+         ++i) {
+      if (latest_pending_subchannel_list_->subchannel(i)->subchannel() !=
+          nullptr) {
+        grpc_core::channelz::SubchannelNode* subchannel_node =
+            grpc_subchannel_get_channelz_node(
+                latest_pending_subchannel_list_->subchannel(i)->subchannel());
+        if (subchannel_node != nullptr) {
+          cs.push_back(subchannel_node->subchannel_uuid());
+        }
+      }
+    }
+  }
+  // atomically update the data that channelz will actually be looking at.
+  mu_guard guard(&child_refs_mu_);
+  child_subchannels_ = std::move(cs);
+}
+
 void PickFirst::UpdateLocked(const grpc_channel_args& args) {
+  AutoChildRefsUpdater guard(this);
   const grpc_arg* arg = grpc_channel_args_find(&args, GRPC_ARG_LB_ADDRESSES);
   if (arg == nullptr || arg->type != GRPC_ARG_POINTER) {
     if (subchannel_list_ == nullptr) {
@@ -388,6 +466,7 @@ void PickFirst::UpdateLocked(const grpc_channel_args& args) {
 void PickFirst::PickFirstSubchannelData::ProcessConnectivityChangeLocked(
     grpc_connectivity_state connectivity_state, grpc_error* error) {
   PickFirst* p = static_cast<PickFirst*>(subchannel_list()->policy());
+  AutoChildRefsUpdater guard(p);
   // The notification must be for a subchannel in either the current or
   // latest pending subchannel lists.
   GPR_ASSERT(subchannel_list() == p->subchannel_list_.get() ||
diff --git a/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc b/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc
index 42e8e88ec9..09634a2ad4 100644
--- a/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc
@@ -69,6 +69,9 @@ class RoundRobin : public LoadBalancingPolicy {
   void HandOffPendingPicksLocked(LoadBalancingPolicy* new_policy) override;
   void PingOneLocked(grpc_closure* on_initiate, grpc_closure* on_ack) override;
   void ExitIdleLocked() override;
+  // TODO(ncteisen): implement this in a follow up PR
+  void FillChildRefsForChannelz(ChildRefsList* child_subchannels,
+                                ChildRefsList* child_channels) override {}
 
  private:
   ~RoundRobin();
diff --git a/src/core/ext/filters/client_channel/subchannel.cc b/src/core/ext/filters/client_channel/subchannel.cc
index 8ab3fe40f5..9d608c3c55 100644
--- a/src/core/ext/filters/client_channel/subchannel.cc
+++ b/src/core/ext/filters/client_channel/subchannel.cc
@@ -134,6 +134,9 @@ struct grpc_subchannel {
   bool backoff_begun;
   /** our alarm */
   grpc_timer alarm;
+
+  grpc_core::RefCountedPtr<grpc_core::channelz::SubchannelNode>
+      channelz_subchannel;
 };
 
 struct grpc_subchannel_call {
@@ -178,6 +181,7 @@ static void connection_destroy(void* arg, grpc_error* error) {
 
 static void subchannel_destroy(void* arg, grpc_error* error) {
   grpc_subchannel* c = static_cast<grpc_subchannel*>(arg);
+  c->channelz_subchannel.reset();
   gpr_free((void*)c->filters);
   grpc_channel_args_destroy(c->args);
   grpc_connectivity_state_destroy(&c->state_tracker);
@@ -374,9 +378,22 @@ grpc_subchannel* grpc_subchannel_create(grpc_connector* connector,
   c->backoff.Init(backoff_options);
   gpr_mu_init(&c->mu);
 
+  const grpc_arg* arg =
+      grpc_channel_args_find(c->args, GRPC_ARG_ENABLE_CHANNELZ);
+  bool channelz_enabled = grpc_channel_arg_get_bool(arg, false);
+  if (channelz_enabled) {
+    c->channelz_subchannel =
+        grpc_core::MakeRefCounted<grpc_core::channelz::SubchannelNode>();
+  }
+
   return grpc_subchannel_index_register(key, c);
 }
 
+grpc_core::channelz::SubchannelNode* grpc_subchannel_get_channelz_node(
+    grpc_subchannel* s) {
+  return s->channelz_subchannel.get();
+}
+
 static void continue_connect_locked(grpc_subchannel* c) {
   grpc_connect_in_args args;
   args.interested_parties = c->pollset_set;
diff --git a/src/core/ext/filters/client_channel/subchannel.h b/src/core/ext/filters/client_channel/subchannel.h
index e23aec12df..9e53f7d542 100644
--- a/src/core/ext/filters/client_channel/subchannel.h
+++ b/src/core/ext/filters/client_channel/subchannel.h
@@ -21,6 +21,7 @@
 
 #include <grpc/support/port_platform.h>
 
+#include "src/core/ext/filters/client_channel/client_channel_channelz.h"
 #include "src/core/ext/filters/client_channel/connector.h"
 #include "src/core/lib/channel/channel_stack.h"
 #include "src/core/lib/gpr/arena.h"
@@ -115,6 +116,9 @@ grpc_subchannel_call* grpc_subchannel_call_ref(
 void grpc_subchannel_call_unref(
     grpc_subchannel_call* call GRPC_SUBCHANNEL_REF_EXTRA_ARGS);
 
+grpc_core::channelz::SubchannelNode* grpc_subchannel_get_channelz_node(
+    grpc_subchannel* subchannel);
+
 /** Returns a pointer to the parent data associated with \a subchannel_call.
     The data will be of the size specified in \a parent_data_size
     field of the args passed to \a grpc_connected_subchannel_create_call(). */
diff --git a/src/core/lib/channel/channel_trace.cc b/src/core/lib/channel/channel_trace.cc
index 0f655d8716..c17885a713 100644
--- a/src/core/lib/channel/channel_trace.cc
+++ b/src/core/lib/channel/channel_trace.cc
@@ -131,38 +131,6 @@ void ChannelTrace::AddTraceEventReferencingSubchannel(
 
 namespace {
 
-// returns an allocated string that represents tm according to RFC-3339, and,
-// more specifically, follows:
-// https://developers.google.com/protocol-buffers/docs/proto3#json
-//
-// "Uses RFC 3339, where generated output will always be Z-normalized and uses
-// 0, 3, 6 or 9 fractional digits."
-char* fmt_time(gpr_timespec tm) {
-  char time_buffer[35];
-  char ns_buffer[11];  // '.' + 9 digits of precision
-  struct tm* tm_info = localtime((const time_t*)&tm.tv_sec);
-  strftime(time_buffer, sizeof(time_buffer), "%Y-%m-%dT%H:%M:%S", tm_info);
-  snprintf(ns_buffer, 11, ".%09d", tm.tv_nsec);
-  // This loop trims off trailing zeros by inserting a null character that the
-  // right point. We iterate in chunks of three because we want 0, 3, 6, or 9
-  // fractional digits.
-  for (int i = 7; i >= 1; i -= 3) {
-    if (ns_buffer[i] == '0' && ns_buffer[i + 1] == '0' &&
-        ns_buffer[i + 2] == '0') {
-      ns_buffer[i] = '\0';
-      // Edge case in which all fractional digits were 0.
-      if (i == 1) {
-        ns_buffer[0] = '\0';
-      }
-    } else {
-      break;
-    }
-  }
-  char* full_time_str;
-  gpr_asprintf(&full_time_str, "%s%sZ", time_buffer, ns_buffer);
-  return full_time_str;
-}
-
 const char* severity_string(ChannelTrace::Severity severity) {
   switch (severity) {
     case ChannelTrace::Severity::Info:
@@ -186,9 +154,9 @@ void ChannelTrace::TraceEvent::RenderTraceEvent(grpc_json* json) const {
   json_iterator = grpc_json_create_child(json_iterator, json, "severity",
                                          severity_string(severity_),
                                          GRPC_JSON_STRING, false);
-  json_iterator =
-      grpc_json_create_child(json_iterator, json, "timestamp",
-                             fmt_time(timestamp_), GRPC_JSON_STRING, true);
+  json_iterator = grpc_json_create_child(json_iterator, json, "timestamp",
+                                         gpr_format_timespec(timestamp_),
+                                         GRPC_JSON_STRING, true);
   if (referenced_channel_ != nullptr) {
     char* uuid_str;
     gpr_asprintf(&uuid_str, "%" PRIdPTR, referenced_channel_->channel_uuid());
@@ -216,9 +184,9 @@ grpc_json* ChannelTrace::RenderJSON() const {
   json_iterator =
       grpc_json_create_child(json_iterator, json, "numEventsLogged",
                              num_events_logged_str, GRPC_JSON_STRING, true);
-  json_iterator =
-      grpc_json_create_child(json_iterator, json, "creationTimestamp",
-                             fmt_time(time_created_), GRPC_JSON_STRING, true);
+  json_iterator = grpc_json_create_child(
+      json_iterator, json, "creationTimestamp",
+      gpr_format_timespec(time_created_), GRPC_JSON_STRING, true);
   grpc_json* events = grpc_json_create_child(json_iterator, json, "events",
                                              nullptr, GRPC_JSON_ARRAY, false);
   json_iterator = nullptr;
diff --git a/src/core/lib/channel/channelz.cc b/src/core/lib/channel/channelz.cc
index 2074cb0cc5..79a9220503 100644
--- a/src/core/lib/channel/channelz.cc
+++ b/src/core/lib/channel/channelz.cc
@@ -41,53 +41,6 @@
 namespace grpc_core {
 namespace channelz {
 
-namespace {
-
-// TODO(ncteisen): move this function to a common helper location.
-//
-// returns an allocated string that represents tm according to RFC-3339, and,
-// more specifically, follows:
-// https://developers.google.com/protocol-buffers/docs/proto3#json
-//
-// "Uses RFC 3339, where generated output will always be Z-normalized and uses
-// 0, 3, 6 or 9 fractional digits."
-char* fmt_time(gpr_timespec tm) {
-  char time_buffer[35];
-  char ns_buffer[11];  // '.' + 9 digits of precision
-  struct tm* tm_info = localtime((const time_t*)&tm.tv_sec);
-  strftime(time_buffer, sizeof(time_buffer), "%Y-%m-%dT%H:%M:%S", tm_info);
-  snprintf(ns_buffer, 11, ".%09d", tm.tv_nsec);
-  // This loop trims off trailing zeros by inserting a null character that the
-  // right point. We iterate in chunks of three because we want 0, 3, 6, or 9
-  // fractional digits.
-  for (int i = 7; i >= 1; i -= 3) {
-    if (ns_buffer[i] == '0' && ns_buffer[i + 1] == '0' &&
-        ns_buffer[i + 2] == '0') {
-      ns_buffer[i] = '\0';
-      // Edge case in which all fractional digits were 0.
-      if (i == 1) {
-        ns_buffer[0] = '\0';
-      }
-    } else {
-      break;
-    }
-  }
-  char* full_time_str;
-  gpr_asprintf(&full_time_str, "%s%sZ", time_buffer, ns_buffer);
-  return full_time_str;
-}
-
-// TODO(ncteisen); move this to json library
-grpc_json* add_num_str(grpc_json* parent, grpc_json* it, const char* name,
-                       int64_t num) {
-  char* num_str;
-  gpr_asprintf(&num_str, "%" PRId64, num);
-  return grpc_json_create_child(it, parent, name, num_str, GRPC_JSON_STRING,
-                                true);
-}
-
-}  // namespace
-
 ChannelNode::ChannelNode(grpc_channel* channel, size_t channel_tracer_max_nodes)
     : channel_(channel), target_(nullptr), channel_uuid_(-1) {
   trace_.Init(channel_tracer_max_nodes);
@@ -110,6 +63,8 @@ void ChannelNode::RecordCallStarted() {
 
 void ChannelNode::PopulateConnectivityState(grpc_json* json) {}
 
+void ChannelNode::PopulateChildRefs(grpc_json* json) {}
+
 char* ChannelNode::RenderJSON() {
   // We need to track these three json objects to build our object
   grpc_json* top_level_json = grpc_json_create(GRPC_JSON_OBJECT);
@@ -120,7 +75,8 @@ char* ChannelNode::RenderJSON() {
                                          GRPC_JSON_OBJECT, false);
   json = json_iterator;
   json_iterator = nullptr;
-  json_iterator = add_num_str(json, json_iterator, "channelId", channel_uuid_);
+  json_iterator = grpc_json_add_number_string_child(json, json_iterator,
+                                                    "channelId", channel_uuid_);
   // reset json iterators to top level object
   json = top_level_json;
   json_iterator = nullptr;
@@ -148,17 +104,21 @@ char* ChannelNode::RenderJSON() {
   json_iterator = nullptr;
   // We use -1 as sentinel values since proto default value for integers is
   // zero, and the confuses the parser into thinking the value weren't present
-  json_iterator =
-      add_num_str(json, json_iterator, "callsStarted", calls_started_);
-  json_iterator =
-      add_num_str(json, json_iterator, "callsSucceeded", calls_succeeded_);
-  json_iterator =
-      add_num_str(json, json_iterator, "callsFailed", calls_failed_);
+  json_iterator = grpc_json_add_number_string_child(
+      json, json_iterator, "callsStarted", calls_started_);
+  json_iterator = grpc_json_add_number_string_child(
+      json, json_iterator, "callsSucceeded", calls_succeeded_);
+  json_iterator = grpc_json_add_number_string_child(
+      json, json_iterator, "callsFailed", calls_failed_);
   gpr_timespec ts =
       grpc_millis_to_timespec(last_call_started_millis_, GPR_CLOCK_REALTIME);
   json_iterator =
       grpc_json_create_child(json_iterator, json, "lastCallStartedTimestamp",
-                             fmt_time(ts), GRPC_JSON_STRING, true);
+                             gpr_format_timespec(ts), GRPC_JSON_STRING, true);
+  json = top_level_json;
+  json_iterator = nullptr;
+  PopulateChildRefs(json);
+
   // render and return the over json object
   char* json_str = grpc_json_dump_to_string(top_level_json, 0);
   grpc_json_destroy(top_level_json);
@@ -171,5 +131,13 @@ RefCountedPtr<ChannelNode> ChannelNode::MakeChannelNode(
       channel, channel_tracer_max_nodes);
 }
 
+SubchannelNode::SubchannelNode() {
+  subchannel_uuid_ = ChannelzRegistry::Register(this);
+}
+
+SubchannelNode::~SubchannelNode() {
+  ChannelzRegistry::Unregister(subchannel_uuid_);
+}
+
 }  // namespace channelz
 }  // namespace grpc_core
diff --git a/src/core/lib/channel/channelz.h b/src/core/lib/channel/channelz.h
index 9bd01ece50..7184af93ec 100644
--- a/src/core/lib/channel/channelz.h
+++ b/src/core/lib/channel/channelz.h
@@ -62,6 +62,8 @@ class ChannelNode : public RefCounted<ChannelNode> {
   // instead of lib/
   virtual void PopulateConnectivityState(grpc_json* json);
 
+  virtual void PopulateChildRefs(grpc_json* json);
+
   ChannelTrace* trace() { return trace_.get(); }
 
   void MarkChannelDestroyed() {
@@ -93,6 +95,24 @@ class ChannelNode : public RefCounted<ChannelNode> {
   ManualConstructor<ChannelTrace> trace_;
 };
 
+// Placeholds channelz class for subchannels. All this can do now is track its
+// uuid (this information is needed by the parent channelz class).
+// TODO(ncteisen): build this out to support the GetSubchannel channelz request.
+class SubchannelNode : public RefCounted<SubchannelNode> {
+ public:
+  SubchannelNode();
+  virtual ~SubchannelNode();
+
+  intptr_t subchannel_uuid() { return subchannel_uuid_; }
+
+ protected:
+  GPRC_ALLOW_CLASS_TO_USE_NON_PUBLIC_DELETE
+  GPRC_ALLOW_CLASS_TO_USE_NON_PUBLIC_NEW
+
+ private:
+  intptr_t subchannel_uuid_;
+};
+
 // Creation functions
 
 typedef RefCountedPtr<ChannelNode> (*ChannelNodeCreationFunc)(grpc_channel*,
diff --git a/src/core/lib/gpr/string.cc b/src/core/lib/gpr/string.cc
index ef2a6900b4..0a76fc1f54 100644
--- a/src/core/lib/gpr/string.cc
+++ b/src/core/lib/gpr/string.cc
@@ -23,8 +23,10 @@
 #include <ctype.h>
 #include <limits.h>
 #include <stddef.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <time.h>
 
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
@@ -54,6 +56,32 @@ typedef struct {
   char* data;
 } dump_out;
 
+char* gpr_format_timespec(gpr_timespec tm) {
+  char time_buffer[35];
+  char ns_buffer[11];  // '.' + 9 digits of precision
+  struct tm* tm_info = localtime((const time_t*)&tm.tv_sec);
+  strftime(time_buffer, sizeof(time_buffer), "%Y-%m-%dT%H:%M:%S", tm_info);
+  snprintf(ns_buffer, 11, ".%09d", tm.tv_nsec);
+  // This loop trims off trailing zeros by inserting a null character that the
+  // right point. We iterate in chunks of three because we want 0, 3, 6, or 9
+  // fractional digits.
+  for (int i = 7; i >= 1; i -= 3) {
+    if (ns_buffer[i] == '0' && ns_buffer[i + 1] == '0' &&
+        ns_buffer[i + 2] == '0') {
+      ns_buffer[i] = '\0';
+      // Edge case in which all fractional digits were 0.
+      if (i == 1) {
+        ns_buffer[0] = '\0';
+      }
+    } else {
+      break;
+    }
+  }
+  char* full_time_str;
+  gpr_asprintf(&full_time_str, "%s%sZ", time_buffer, ns_buffer);
+  return full_time_str;
+}
+
 static dump_out dump_out_create(void) {
   dump_out r = {0, 0, nullptr};
   return r;
diff --git a/src/core/lib/gpr/string.h b/src/core/lib/gpr/string.h
index 2e8a4898d9..ce51fe4632 100644
--- a/src/core/lib/gpr/string.h
+++ b/src/core/lib/gpr/string.h
@@ -21,6 +21,8 @@
 
 #include <grpc/support/port_platform.h>
 
+#include <grpc/impl/codegen/gpr_types.h>
+
 #include <stdbool.h>
 #include <stddef.h>
 
@@ -81,6 +83,14 @@ char* gpr_strjoin_sep(const char** strs, size_t nstrs, const char* sep,
 void gpr_string_split(const char* input, const char* sep, char*** strs,
                       size_t* nstrs);
 
+/* Returns an allocated string that represents tm according to RFC-3339, and,
+   more specifically, follows:
+   https://developers.google.com/protocol-buffers/docs/proto3#json
+
+   Uses RFC 3339, where generated output will always be Z-normalized and uses
+   0, 3, 6 or 9 fractional digits. */
+char* gpr_format_timespec(gpr_timespec);
+
 /* A vector of strings... for building up a final string one piece at a time */
 typedef struct {
   char** strs;
diff --git a/src/core/lib/gprpp/abstract.h b/src/core/lib/gprpp/abstract.h
index cc96edc49b..5b7018e07e 100644
--- a/src/core/lib/gprpp/abstract.h
+++ b/src/core/lib/gprpp/abstract.h
@@ -28,7 +28,10 @@
 
 // gRPC currently can't depend on libstdc++, so we can't use "= 0" for
 // pure virtual methods.  Instead, we use this macro.
-#define GRPC_ABSTRACT \
-  { GPR_ASSERT(false); }
+#define GRPC_ABSTRACT                                                        \
+  {                                                                          \
+    gpr_log(GPR_ERROR, "Function marked GRPC_ABSTRACT was not implemented"); \
+    GPR_ASSERT(false);                                                       \
+  }
 
 #endif /* GRPC_CORE_LIB_GPRPP_ABSTRACT_H */
diff --git a/src/core/lib/gprpp/inlined_vector.h b/src/core/lib/gprpp/inlined_vector.h
index 0d2586e507..76e2f0a785 100644
--- a/src/core/lib/gprpp/inlined_vector.h
+++ b/src/core/lib/gprpp/inlined_vector.h
@@ -22,6 +22,7 @@
 #include <grpc/support/port_platform.h>
 
 #include <cassert>
+#include <cstring>
 
 #include "src/core/lib/gprpp/memory.h"
 
@@ -50,9 +51,33 @@ class InlinedVector {
   InlinedVector() { init_data(); }
   ~InlinedVector() { destroy_elements(); }
 
-  // For now, we do not support copying.
-  InlinedVector(const InlinedVector&) = delete;
-  InlinedVector& operator=(const InlinedVector&) = delete;
+  // copy constructor
+  InlinedVector(const InlinedVector& v) {
+    init_data();
+    copy_from(v);
+  }
+
+  InlinedVector& operator=(const InlinedVector& v) {
+    if (this != &v) {
+      clear();
+      copy_from(v);
+    }
+    return *this;
+  }
+
+  // move constructor
+  InlinedVector(InlinedVector&& v) {
+    init_data();
+    move_from(v);
+  }
+
+  InlinedVector& operator=(InlinedVector&& v) {
+    if (this != &v) {
+      clear();
+      move_from(v);
+    }
+    return *this;
+  }
 
   T* data() {
     return dynamic_ != nullptr ? dynamic_ : reinterpret_cast<T*>(inline_);
@@ -98,6 +123,33 @@ class InlinedVector {
 
   void push_back(T&& value) { emplace_back(std::move(value)); }
 
+  void copy_from(const InlinedVector& v) {
+    // if v is allocated, copy over the buffer.
+    if (v.dynamic_ != nullptr) {
+      reserve(v.capacity_);
+      memcpy(dynamic_, v.dynamic_, v.size_ * sizeof(T));
+    } else {
+      memcpy(inline_, v.inline_, v.size_ * sizeof(T));
+    }
+    // copy over metadata
+    size_ = v.size_;
+    capacity_ = v.capacity_;
+  }
+
+  void move_from(InlinedVector& v) {
+    // if v is allocated, then we steal its buffer, else we copy it.
+    if (v.dynamic_ != nullptr) {
+      dynamic_ = v.dynamic_;
+    } else {
+      memcpy(inline_, v.inline_, v.size_ * sizeof(T));
+    }
+    // copy over metadata
+    size_ = v.size_;
+    capacity_ = v.capacity_;
+    // null out the original
+    v.init_data();
+  }
+
   size_t size() const { return size_; }
   bool empty() const { return size_ == 0; }
 
diff --git a/src/core/lib/json/json.cc b/src/core/lib/json/json.cc
index 816241bbf0..6d359573f8 100644
--- a/src/core/lib/json/json.cc
+++ b/src/core/lib/json/json.cc
@@ -18,10 +18,12 @@
 
 #include <grpc/support/port_platform.h>
 
+#include <inttypes.h>
 #include <string.h>
 
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
+#include <grpc/support/string_util.h>
 
 #include "src/core/lib/json/json.h"
 
@@ -84,3 +86,11 @@ grpc_json* grpc_json_create_child(grpc_json* sibling, grpc_json* parent,
   child->key = key;
   return child;
 }
+
+grpc_json* grpc_json_add_number_string_child(grpc_json* parent, grpc_json* it,
+                                             const char* name, int64_t num) {
+  char* num_str;
+  gpr_asprintf(&num_str, "%" PRId64, num);
+  return grpc_json_create_child(it, parent, name, num_str, GRPC_JSON_STRING,
+                                true);
+}
diff --git a/src/core/lib/json/json.h b/src/core/lib/json/json.h
index f93b43048b..8173845c72 100644
--- a/src/core/lib/json/json.h
+++ b/src/core/lib/json/json.h
@@ -91,4 +91,9 @@ grpc_json* grpc_json_create_child(grpc_json* sibling, grpc_json* parent,
                                   const char* key, const char* value,
                                   grpc_json_type type, bool owns_value);
 
+/* Creates a child json string object from the integer num, then links the
+   json object into the parent's json tree */
+grpc_json* grpc_json_add_number_string_child(grpc_json* parent, grpc_json* it,
+                                             const char* name, int64_t num);
+
 #endif /* GRPC_CORE_LIB_JSON_JSON_H */
diff --git a/test/core/gprpp/inlined_vector_test.cc b/test/core/gprpp/inlined_vector_test.cc
index 41f4338f8a..e9d1eb2c76 100644
--- a/test/core/gprpp/inlined_vector_test.cc
+++ b/test/core/gprpp/inlined_vector_test.cc
@@ -17,20 +17,32 @@
  */
 
 #include "src/core/lib/gprpp/inlined_vector.h"
+#include <grpc/support/log.h>
 #include <gtest/gtest.h>
 #include "src/core/lib/gprpp/memory.h"
 #include "test/core/util/test_config.h"
 
 namespace grpc_core {
 namespace testing {
+namespace {
+
+template <typename Vector>
+static void FillVector(Vector* v, int len, int start = 0) {
+  for (int i = 0; i < len; i++) {
+    v->push_back(i + start);
+    EXPECT_EQ(i + 1UL, v->size());
+  }
+  EXPECT_EQ(static_cast<size_t>(len), v->size());
+  EXPECT_LE(static_cast<size_t>(len), v->capacity());
+}
+
+}  // namespace
 
 TEST(InlinedVectorTest, CreateAndIterate) {
   const int kNumElements = 9;
   InlinedVector<int, 2> v;
   EXPECT_TRUE(v.empty());
-  for (int i = 0; i < kNumElements; ++i) {
-    v.push_back(i);
-  }
+  FillVector(&v, kNumElements);
   EXPECT_EQ(static_cast<size_t>(kNumElements), v.size());
   EXPECT_FALSE(v.empty());
   for (int i = 0; i < kNumElements; ++i) {
@@ -42,9 +54,7 @@ TEST(InlinedVectorTest, CreateAndIterate) {
 TEST(InlinedVectorTest, ValuesAreInlined) {
   const int kNumElements = 5;
   InlinedVector<int, 10> v;
-  for (int i = 0; i < kNumElements; ++i) {
-    v.push_back(i);
-  }
+  FillVector(&v, kNumElements);
   EXPECT_EQ(static_cast<size_t>(kNumElements), v.size());
   for (int i = 0; i < kNumElements; ++i) {
     EXPECT_EQ(i, v[i]);
@@ -71,19 +81,13 @@ TEST(InlinedVectorTest, ClearAndRepopulate) {
   const int kNumElements = 10;
   InlinedVector<int, 5> v;
   EXPECT_EQ(0UL, v.size());
-  for (int i = 0; i < kNumElements; ++i) {
-    v.push_back(i);
-    EXPECT_EQ(i + 1UL, v.size());
-  }
+  FillVector(&v, kNumElements);
   for (int i = 0; i < kNumElements; ++i) {
     EXPECT_EQ(i, v[i]);
   }
   v.clear();
   EXPECT_EQ(0UL, v.size());
-  for (int i = 0; i < kNumElements; ++i) {
-    v.push_back(kNumElements + i);
-    EXPECT_EQ(i + 1UL, v.size());
-  }
+  FillVector(&v, kNumElements, kNumElements);
   for (int i = 0; i < kNumElements; ++i) {
     EXPECT_EQ(kNumElements + i, v[i]);
   }
@@ -93,10 +97,7 @@ TEST(InlinedVectorTest, ConstIndexOperator) {
   constexpr int kNumElements = 10;
   InlinedVector<int, 5> v;
   EXPECT_EQ(0UL, v.size());
-  for (int i = 0; i < kNumElements; ++i) {
-    v.push_back(i);
-    EXPECT_EQ(i + 1UL, v.size());
-  }
+  FillVector(&v, kNumElements);
   // The following lambda function is exceptionally allowed to use an anonymous
   // capture due to the erroneous behavior of the MSVC compiler, that refuses to
   // capture the kNumElements constexpr, something allowed by the standard.
@@ -108,6 +109,161 @@ TEST(InlinedVectorTest, ConstIndexOperator) {
   const_func(v);
 }
 
+// the following constants and typedefs are used for copy/move
+// construction/assignment
+const size_t kInlinedLength = 8;
+typedef InlinedVector<int, kInlinedLength> IntVec8;
+const size_t kInlinedFillSize = kInlinedLength - 1;
+const size_t kAllocatedFillSize = kInlinedLength + 1;
+
+TEST(InlinedVectorTest, CopyConstructerInlined) {
+  IntVec8 original;
+  FillVector(&original, kInlinedFillSize);
+  IntVec8 copy_constructed(original);
+  for (size_t i = 0; i < original.size(); ++i) {
+    EXPECT_EQ(original[i], copy_constructed[i]);
+  }
+}
+
+TEST(InlinedVectorTest, CopyConstructerAllocated) {
+  IntVec8 original;
+  FillVector(&original, kAllocatedFillSize);
+  IntVec8 copy_constructed(original);
+  for (size_t i = 0; i < original.size(); ++i) {
+    EXPECT_EQ(original[i], copy_constructed[i]);
+  }
+}
+
+TEST(InlinedVectorTest, CopyAssignementInlinedInlined) {
+  IntVec8 original;
+  FillVector(&original, kInlinedFillSize);
+  IntVec8 copy_assigned;
+  FillVector(&copy_assigned, kInlinedFillSize, 99);
+  copy_assigned = original;
+  for (size_t i = 0; i < original.size(); ++i) {
+    EXPECT_EQ(original[i], copy_assigned[i]);
+  }
+}
+
+TEST(InlinedVectorTest, CopyAssignementInlinedAllocated) {
+  IntVec8 original;
+  FillVector(&original, kInlinedFillSize);
+  IntVec8 copy_assigned;
+  FillVector(&copy_assigned, kAllocatedFillSize, 99);
+  copy_assigned = original;
+  for (size_t i = 0; i < original.size(); ++i) {
+    EXPECT_EQ(original[i], copy_assigned[i]);
+  }
+}
+
+TEST(InlinedVectorTest, CopyAssignementAllocatedInlined) {
+  IntVec8 original;
+  FillVector(&original, kAllocatedFillSize);
+  IntVec8 copy_assigned;
+  FillVector(&copy_assigned, kInlinedFillSize, 99);
+  copy_assigned = original;
+  for (size_t i = 0; i < original.size(); ++i) {
+    EXPECT_EQ(original[i], copy_assigned[i]);
+  }
+}
+
+TEST(InlinedVectorTest, CopyAssignementAllocatedAllocated) {
+  IntVec8 original;
+  FillVector(&original, kAllocatedFillSize);
+  IntVec8 copy_assigned;
+  FillVector(&copy_assigned, kAllocatedFillSize, 99);
+  copy_assigned = original;
+  for (size_t i = 0; i < original.size(); ++i) {
+    EXPECT_EQ(original[i], copy_assigned[i]);
+  }
+}
+
+TEST(InlinedVectorTest, MoveConstructorInlined) {
+  IntVec8 original;
+  FillVector(&original, kInlinedFillSize);
+  IntVec8 tmp(original);
+  auto* old_data = tmp.data();
+  IntVec8 move_constructed(std::move(tmp));
+  for (size_t i = 0; i < original.size(); ++i) {
+    EXPECT_EQ(original[i], move_constructed[i]);
+  }
+  // original data was inlined so it should have been copied, not moved.
+  EXPECT_NE(move_constructed.data(), old_data);
+}
+
+TEST(InlinedVectorTest, MoveConstructorAllocated) {
+  IntVec8 original;
+  FillVector(&original, kAllocatedFillSize);
+  IntVec8 tmp(original);
+  auto* old_data = tmp.data();
+  IntVec8 move_constructed(std::move(tmp));
+  for (size_t i = 0; i < original.size(); ++i) {
+    EXPECT_EQ(original[i], move_constructed[i]);
+  }
+  // original data was allocated, so it should been moved, not copied
+  EXPECT_EQ(move_constructed.data(), old_data);
+}
+
+TEST(InlinedVectorTest, MoveAssignmentInlinedInlined) {
+  IntVec8 original;
+  FillVector(&original, kInlinedFillSize);
+  IntVec8 move_assigned;
+  FillVector(&move_assigned, kInlinedFillSize, 99);  // Add dummy elements
+  IntVec8 tmp(original);
+  auto* old_data = tmp.data();
+  move_assigned = std::move(tmp);
+  for (size_t i = 0; i < original.size(); ++i) {
+    EXPECT_EQ(original[i], move_assigned[i]);
+  }
+  // original data was inlined so it should have been copied, not moved.
+  EXPECT_NE(move_assigned.data(), old_data);
+}
+
+TEST(InlinedVectorTest, MoveAssignmentInlinedAllocated) {
+  IntVec8 original;
+  FillVector(&original, kInlinedFillSize);
+  IntVec8 move_assigned;
+  FillVector(&move_assigned, kAllocatedFillSize, 99);  // Add dummy elements
+  IntVec8 tmp(original);
+  auto* old_data = tmp.data();
+  move_assigned = std::move(tmp);
+  for (size_t i = 0; i < original.size(); ++i) {
+    EXPECT_EQ(original[i], move_assigned[i]);
+  }
+  // original data was inlined so it should have been copied, not moved.
+  EXPECT_NE(move_assigned.data(), old_data);
+}
+
+TEST(InlinedVectorTest, MoveAssignmentAllocatedInlined) {
+  IntVec8 original;
+  FillVector(&original, kAllocatedFillSize);
+  IntVec8 move_assigned;
+  FillVector(&move_assigned, kInlinedFillSize, 99);  // Add dummy elements
+  IntVec8 tmp(original);
+  auto* old_data = tmp.data();
+  move_assigned = std::move(tmp);
+  for (size_t i = 0; i < original.size(); ++i) {
+    EXPECT_EQ(original[i], move_assigned[i]);
+  }
+  // original data was allocated so it should have been moved, not copied.
+  EXPECT_EQ(move_assigned.data(), old_data);
+}
+
+TEST(InlinedVectorTest, MoveAssignmentAllocatedAllocated) {
+  IntVec8 original;
+  FillVector(&original, kAllocatedFillSize);
+  IntVec8 move_assigned;
+  FillVector(&move_assigned, kAllocatedFillSize, 99);  // Add dummy elements
+  IntVec8 tmp(original);
+  auto* old_data = tmp.data();
+  move_assigned = std::move(tmp);
+  for (size_t i = 0; i < original.size(); ++i) {
+    EXPECT_EQ(original[i], move_assigned[i]);
+  }
+  // original data was allocated so it should have been moved, not copied.
+  EXPECT_EQ(move_assigned.data(), old_data);
+}
+
 }  // namespace testing
 }  // namespace grpc_core