Add Port.linkScanMode

Summary:
Adds the per-port `linkScanMode` config that later diffs use to pick the
linkscan mode. This diff is config and state plumbing only -- nothing reads the
setting yet, so behavior is unchanged.

- `switch_config.thrift`: new `LinkScanMode` enum (`SOFTWARE` / `HARDWARE`) plus
  `PortConfig.linkScanMode` (field 45). Leaving the field unset means FBOSS
  never programs the mode and leaves whatever the SDK came up with alone; either
  value is written down to the SDK.
- `switch_state.thrift` / `state/Port.h`: matching `PortFields` field 73 plus
  getter/setter, so the setting is warmboot-serialized like the rest of the port
  fields.
- `ApplyThriftConfig.cpp`: propagates config to switch state.

`fsdb_model_thriftpath.h` is regenerated via
`buck2 run fbcode//fboss/fsdb/if/oss:sync_model_thriftpath`, as its CI verify
step requires.

Reviewed By: jasmeetbagga

Differential Revision: D116373299

fbshipit-source-id: bd32ee3006c9227f69dd011e489f0613d4e6328d

Author: huruinan

fboss/agent/ApplyThriftConfig.cpp

@@ -3241,6 +3241,7 @@ shared_ptr<Port> ThriftConfigApplier::updatePort(
           orig->getRxPrecoding().value_or(false) &&
       portConf->rxPrecoding().has_value() ==
           orig->getRxPrecoding().has_value() &&
+      portConf->linkScanMode().to_optional() == orig->getLinkScanMode() &&
       portConf->portDownHoldoffTimeMs().value_or(0) ==
           orig->getPortDownHoldoffTimeMs().value_or(0) &&
       portConf->portDownHoldoffTimeMs().has_value() ==
@@ -3358,6 +3359,7 @@ shared_ptr<Port> ThriftConfigApplier::updatePort(
   } else {
     newPort->setRxPrecoding(std::nullopt);
   }
+  newPort->setLinkScanMode(portConf->linkScanMode().to_optional());
   if (portConf->portDownHoldoffTimeMs().has_value()) {
     auto v = portConf->portDownHoldoffTimeMs().value();
     if (v < 0) {

fboss/agent/state/Port.h

@@ -941,6 +941,23 @@ class Port : public ThriftStructNode<Port, state::PortFields> {
     }
   }
 
+  /** @brief Get who notices link status changes: the SDK or the ASIC */
+  std::optional<cfg::LinkScanMode> getLinkScanMode() const {
+    if (auto linkScanMode = cref<switch_state_tags::linkScanMode>()) {
+      return linkScanMode->toThrift();
+    }
+    return std::nullopt;
+  }
+
+  /** @brief Set who notices link status changes: the SDK or the ASIC */
+  void setLinkScanMode(std::optional<cfg::LinkScanMode> linkScanMode) {
+    if (!linkScanMode.has_value()) {
+      ref<switch_state_tags::linkScanMode>().reset();
+    } else {
+      set<switch_state_tags::linkScanMode>(linkScanMode.value());
+    }
+  }
+
   std::optional<int32_t> getPortSwitchId() const {
     if (auto portSwitchId = cref<switch_state_tags::portSwitchId>()) {
       return portSwitchId->cref();

fboss/agent/state/tests/PortTests.cpp

@@ -1474,6 +1474,50 @@ TEST(Port, precodingConfig) {
   EXPECT_EQ(serializedPort->getRxPrecoding(), true);
 }
 
+TEST(Port, linkScanModeConfig) {
+  auto platform = createMockPlatform();
+  auto state = make_shared<SwitchState>();
+  registerPort(state, PortID(1), "port1", scope());
+
+  auto applyAndVerify = [&](std::optional<cfg::LinkScanMode> newMode) {
+    auto oldMode = state->getPorts()->getNodeIf(PortID(1))->getLinkScanMode();
+    cfg::SwitchConfig config;
+    config.ports()->resize(1);
+    preparedMockPortConfig(
+        config.ports()[0], 1, "port1", cfg::PortState::DISABLED);
+    if (newMode.has_value()) {
+      config.ports()[0].linkScanMode() = newMode.value();
+    }
+    auto newState = publishAndApplyConfig(state, &config, platform.get());
+
+    if (oldMode == newMode) {
+      EXPECT_EQ(nullptr, newState);
+      return;
+    }
+    ASSERT_NE(nullptr, newState);
+    state = newState;
+    EXPECT_EQ(
+        state->getPorts()->getNodeIf(PortID(1))->getLinkScanMode(), newMode);
+  };
+
+  EXPECT_EQ(
+      std::nullopt, state->getPorts()->getNodeIf(PortID(1))->getLinkScanMode());
+
+  applyAndVerify(cfg::LinkScanMode::HARDWARE);
+  applyAndVerify(cfg::LinkScanMode::SOFTWARE);
+  applyAndVerify(cfg::LinkScanMode::SOFTWARE);
+  // Dropping the field from config clears it from switch state
+  applyAndVerify(std::nullopt);
+
+  auto newPort = state->getPorts()->getNodeIf(PortID(1))->clone();
+  newPort->setLinkScanMode(cfg::LinkScanMode::HARDWARE);
+  auto serializedPort = std::make_shared<Port>(newPort->toThrift());
+  EXPECT_EQ(serializedPort->getLinkScanMode(), cfg::LinkScanMode::HARDWARE);
+
+  newPort->setLinkScanMode(std::nullopt);
+  EXPECT_FALSE(newPort->toThrift().linkScanMode().has_value());
+}
+
 // Test holdoff timer fields: default values, applyConfig propagation,
 // getter/setter methods, and serialization/deserialization.
 TEST(Port, holdoffTimerConfig) {

fboss/agent/switch_config.thrift

@@ -1183,6 +1183,18 @@ enum PortDrainState {
   DRAINED = 1,
 }
 
+/*
+ * Who notices that a port's link status changed: the SDK's software
+ * linkscan thread, or the ASIC itself.
+ *
+ * Unset leaves whatever the SDK came up with alone - FBOSS never
+ * programs the mode. Either value is written down to the SDK.
+ */
+enum LinkScanMode {
+  SOFTWARE = 1,
+  HARDWARE = 2,
+}
+
 /**
  * Configuration for a single logical port
  */
@@ -1415,6 +1427,13 @@ struct Port {
   // Controls whether RX precoding settings from the platform mapping are
   // applied to the port.
   44: optional bool rxPrecoding;
+
+  /*
+   * Whether link status changes on this port are noticed by the SDK's
+   * software linkscan thread or by the ASIC.
+   * Unset = leave whatever the SDK came up with untouched.
+   */
+  45: optional LinkScanMode linkScanMode;
 }
 
 enum LacpPortRate {

fboss/agent/switch_state.thrift

@@ -190,6 +190,9 @@ struct PortFields {
   71: optional bool txPrecoding;
   // Whether platform mapping RX precoding settings are applied to this port
   72: optional bool rxPrecoding;
+  // Whether the SDK's software linkscan thread or the ASIC notices link
+  // status changes on this port. Unset = leave SDK default untouched.
+  73: optional switch_config.LinkScanMode linkScanMode;
 }
 
 typedef ctrl.SystemPortThrift SystemPortFields

fboss/fsdb/if/oss/fsdb_model_thriftpath.h

@@ -4272,6 +4272,7 @@ class ChildThriftPath<::facebook::fboss::state::PortFields, ::facebook::fboss::f
     STRUCT_CHILD_GETTERS(llrConfig, 70);
     STRUCT_CHILD_GETTERS(txPrecoding, 71);
     STRUCT_CHILD_GETTERS(rxPrecoding, 72);
+    STRUCT_CHILD_GETTERS(linkScanMode, 73);
 };
 
 
@@ -5069,6 +5070,7 @@ class ChildThriftPath<::facebook::fboss::cfg::Port, ::facebook::fboss::fsdb::Fsd
     STRUCT_CHILD_GETTERS(llrConfigName, 42);
     STRUCT_CHILD_GETTERS(txPrecoding, 43);
     STRUCT_CHILD_GETTERS(rxPrecoding, 44);
+    STRUCT_CHILD_GETTERS(linkScanMode, 45);
 };