AF_XDP/XSK UDP client transport (fleet-safe re-land)

Summary:
Re-land of the AF_XDP/XSK UDP client transport for the ucache fast path (originally D109703046), now with a fix for the fleet-wide breakage that forced the backout (D110310180, see T277941128).

What this adds: the `mc_xdp_protocol` transport plumbing — `XdpTransport` (single-threaded, per-EVB, AsyncUDPSocket-based, fiber/baton reply demux under `facebook/`), the `xdp` protocol enum + parse cases, the `xdp_tx_truncate_bytes` mcrouter option, and the `McRouteHandleProvider` wiring.

Why the first version broke the fleet: `McRouteHandleProvider` (linked by nearly everything via memcache/ServiceRouter) instantiates `createDestinationRoute<XdpTransport>`, which pulls in `UdpWireFormat.h`. That single header unconditionally included the generated TAO and Ucache carbon message codegen, so via `mcrouter-core -> xdp_transport -> udp_wire_format -> carbon-Ucache-messages` every mcrouter dependent was forced to build the Ucache protocol codegen. Ucache protocol sits architecturally above mcrouter, so this dragged a heavy, effectively-cyclic subtree into the fleet and broke 100+ unrelated targets. (TAO codegen was already reachable fleet-wide via `carbon-Memcache-messages`, so it was not part of the regression; the new fleet edge was `carbon-Ucache-messages`.)

The fix: split `UdpWireFormat.h` by protocol family. The core header keeps framing, the `MessageType` enum, the generic `serializeWithId`/`deserializeWithId`/`peek` helpers, and the Memcache `MessageTypeTag` specialisations (Memcache is the only family reachable through the universal `MemcacheRouterInfo` path). The TAO and Ucache tags move to `UdpWireFormatTao.h` / `UdpWireFormatUcache.h` behind their own `udp_wire_format_tao` / `udp_wire_format_ucache` targets, taken only by consumers that actually (de)serialise those families (the ucache XSK server). No ODR risk: each type tag is defined in exactly one header. Net effect: `mcrouter-core -> xdp_transport -> udp_wire_format` adds zero new codegen to mcrouter dependents.

Reviewed By: lenar-f

Differential Revision: D110316229

fbshipit-source-id: 533b603b4c57c4a5330340424b2e0b1a388eec7f

Author: Stuart Clark

mcrouter/ProxyDestination-inl.h

@@ -303,6 +303,7 @@ void ProxyDestination<Transport>::initializeTransport() {
     options.qosPath = qosPath();
   }
   options.useJemallocNodumpAllocator = opts.jemalloc_nodump_buffers;
+  options.xdpTxTruncateBytes = opts.xdp_tx_truncate_bytes;
   if (accessPoint()->compressed()) {
     if (auto codecManager = proxy().router().getCodecManager()) {
       options.compressionCodecMap =

mcrouter/lib/mc/protocol.h

@@ -19,6 +19,7 @@ typedef enum mc_protocol_e {
   mc_binary_protocol = 2,
   mc_caret_protocol = 4,
   mc_thrift_protocol = 5,
+  mc_xdp_protocol = 6,
   mc_nprotocols, // placeholder
 } mc_protocol_t;
 
@@ -31,6 +32,8 @@ static inline mc_protocol_t mc_string_to_protocol(const char* str) {
     return mc_caret_protocol;
   } else if (!strcmp(str, "thrift")) {
     return mc_thrift_protocol;
+  } else if (!strcmp(str, "xdp")) {
+    return mc_xdp_protocol;
   } else {
     return mc_unknown_protocol;
   }
@@ -46,6 +49,8 @@ static inline const char* mc_protocol_to_string(const mc_protocol_t value) {
       return "caret";
     case mc_thrift_protocol:
       return "thrift";
+    case mc_xdp_protocol:
+      return "xdp";
     case mc_unknown_protocol:
     case mc_nprotocols:
     default:

mcrouter/lib/network/AccessPoint.cpp

@@ -59,6 +59,8 @@ mc_protocol_t parseProtocol(folly::StringPiece str) {
     return mc_caret_protocol;
   } else if (str == "thrift") {
     return mc_thrift_protocol;
+  } else if (str == "xdp") {
+    return mc_xdp_protocol;
   }
   throw std::runtime_error("Invalid protocol");
 }

mcrouter/lib/network/ConnectionOptions.h

@@ -146,6 +146,13 @@ struct ConnectionOptions {
    * iff thriftCompression is enabled.
    */
   size_t thriftCompressionThreshold{0};
+
+  /**
+   * AF_XDP/XSK client: max request datagram payload in bytes before the
+   * request is rejected with LOCAL_ERROR. 0 means no cap (clamp to the jumbo
+   * buffer size). Plumbed from the xdp_tx_truncate_bytes mcrouter option.
+   */
+  size_t xdpTxTruncateBytes{0};
 };
 } // namespace memcache
 } // namespace facebook

mcrouter/mcrouter_options_list.h

@@ -881,6 +881,16 @@ MCROUTER_OPTION_INTEGER(
     "Payloads >= thriftCompressionTreshold will be compressed "
     "iff thriftCompression is enabled.")
 
+MCROUTER_OPTION_INTEGER(
+    size_t,
+    xdp_tx_truncate_bytes,
+    3072,
+    "xdp-tx-truncate-bytes",
+    no_short,
+    "AF_XDP/XSK client: max request datagram payload in bytes before the "
+    "request is rejected with LOCAL_ERROR. 0 means no cap (clamp to the jumbo "
+    "buffer size). Default 3072 (3K).")
+
 MCROUTER_OPTION_TOGGLE(
     enable_axonlog,
     false,

mcrouter/routes/McRouteHandleProvider-inl.h

@@ -28,6 +28,9 @@
 #include "mcrouter/lib/network/FailureDomains.h"
 #include "mcrouter/lib/network/SecurityOptions.h"
 #include "mcrouter/lib/network/ThriftTransport.h"
+#if defined(__linux__) && !defined(ANDROID) && !defined(MCROUTER_OSS_BUILD)
+#include "mcrouter/lib/network/facebook/XdpTransport.h"
+#endif
 #include "mcrouter/lib/network/gen/MemcacheRouterInfo.h"
 #include "mcrouter/routes/AllFastestRouteFactory.h"
 #include "mcrouter/routes/AsynclogRoute.h"
@@ -405,6 +408,25 @@ McRouteHandleProvider<RouterInfo>::makePool(
               idx);
           accessPointsSet.insert(destResult.second);
           addDestination(std::move(destResult.first));
+#if defined(__linux__) && !defined(ANDROID) && !defined(MCROUTER_OSS_BUILD)
+        } else if (ap->getProtocol() == mc_xdp_protocol) {
+          using Transport = XdpTransport;
+          auto destResult = createDestinationRoute<Transport>(
+              std::move(ap),
+              timeout,
+              connectTimeout,
+              qosClass,
+              qosPath,
+              nameSp,
+              i,
+              poolStatIndex,
+              disableRequestDeadlineCheck,
+              poolTkoTracker,
+              keepRoutingPrefix,
+              idx);
+          accessPointsSet.insert(destResult.second);
+          addDestination(std::move(destResult.first));
+#endif
         } else {
           using Transport = AsyncMcClient;
           auto destResult = createDestinationRoute<Transport>(

mcrouter/routes/McRouteHandleProvider.cpp

@@ -79,6 +79,8 @@ std::shared_ptr<CommonAccessPointAttributes> getCommonAccessPointAttributes(
       protocol = mc_caret_protocol;
     } else if (equalStr("thrift", str, folly::AsciiCaseInsensitive())) {
       protocol = mc_thrift_protocol;
+    } else if (equalStr("xdp", str, folly::AsciiCaseInsensitive())) {
+      protocol = mc_xdp_protocol;
     } else {
       throwLogic("Unknown protocol '{}'", str);
     }