rename CtranVcImpl to CtranIbQpUtils to be reused by ibgda init process

Summary:
The functions in CtranIbVcImpl can be reused for any QP initialization, move them to a standalone library and rename to `CtranIbQpUtils` to be reused

```
folly::Expected<ibverbx::IbvQp, ibverbx::Error> ctranIbQpCreate(
    const ibverbx::IbvPd* ibvPd,
    ibverbx::ibv_cq* cq);

folly::Expected<folly::Unit, ibverbx::Error>
ctranIbQpInit(ibverbx::IbvQp& ibvQp, int port, int qp_access_flags);

folly::Expected<folly::Unit, ibverbx::Error> ctranIbQpRTR(
    const CtranIbRemoteQpInfo& remoteQpInfo,
    ibverbx::IbvQp& ibvQp,
    uint8_t trafficClass);

folly::Expected<folly::Unit, ibverbx::Error> ctranIbQpRTS(
    ibverbx::IbvQp& ibvQp);
```

Reviewed By: dmwu

Differential Revision: D83687865

fbshipit-source-id: 48c5a03e4be690d82a83acebf906db3e52f0c58b

Author: GirasoleY

comms/ctran/backends/ib/CtranIbLocalVc.cc

@@ -2,7 +2,7 @@
 
 #include "comms/ctran/backends/ib/CtranIbLocalVc.h"
 #include "comms/ctran/backends/ib/CtranIb.h"
-#include "comms/ctran/backends/ib/CtranIbVcImpl.h"
+#include "comms/ctran/backends/ib/CtranIbQpUtils.h"
 #include "comms/ctran/backends/ib/IbvWrap.h"
 #include "comms/ctran/utils/Checks.h"
 #include "comms/utils/logger/LogUtils.h"

comms/ctran/backends/ib/CtranIbVcImpl.cc renamed to comms/ctran/backends/ib/CtranIbQpUtils.cc

@@ -1,8 +1,9 @@
 // Copyright (c) Meta Platforms, Inc. and affiliates.
-#include "comms/ctran/backends/ib/CtranIbVcImpl.h"
-#include "comms/ctran/utils/Checks.h"
+
 #include "comms/utils/cvars/nccl_cvars.h"
 
+#include "comms/ctran/backends/ib/CtranIbQpUtils.h"
+
 namespace ctran::ib {
 folly::Expected<ibverbx::IbvQp, ibverbx::Error> ctranIbQpCreate(
     const ibverbx::IbvPd* ibvPd,

comms/ctran/backends/ib/CtranIbQpUtils.h

@@ -0,0 +1,59 @@
+// Copyright (c) Meta Platforms, Inc. and affiliates.
+
+#pragma once
+
+#include "comms/ctran/ibverbx/Ibverbx.h"
+
+namespace ctran::ib {
+
+/**
+ * Common utility functions for InfiniBand Queue Pair (QP) management.
+ *
+ * These functions provide a reusable interface for QP creation and state
+ * transitions that can be used across different components of the Ctran IB
+ * backend. They were extracted from CtranIbVcImpl to enable reuse in other QP
+ * initialization scenarios.
+ */
+
+constexpr int MAX_CONTROL_MSGS{128};
+constexpr int MAX_SEND_WR{256};
+
+struct CtranIbRemoteQpInfo {
+  enum ibverbx::ibv_mtu mtu;
+  uint32_t qpn;
+  uint8_t port;
+  int linkLayer;
+  union {
+    struct {
+      uint64_t spn;
+      uint64_t iid;
+    } eth;
+    struct {
+      uint16_t lid;
+    } ib;
+  } u;
+};
+
+// ctranIbQpCreate - Creates a new Reliable Connection (RC) QP
+folly::Expected<ibverbx::IbvQp, ibverbx::Error> ctranIbQpCreate(
+    const ibverbx::IbvPd* ibvPd,
+    ibverbx::ibv_cq* cq);
+
+// ctranIbQpInit - Transitions QP to INIT state with port and access
+// configuration
+folly::Expected<folly::Unit, ibverbx::Error>
+ctranIbQpInit(ibverbx::IbvQp& ibvQp, int port, int qp_access_flags);
+
+// ctranIbQpRTR - Transitions QP to Ready To Receive (RTR) state with remote
+// endpoint info
+folly::Expected<folly::Unit, ibverbx::Error> ctranIbQpRTR(
+    const CtranIbRemoteQpInfo& remoteQpInfo,
+    ibverbx::IbvQp& ibvQp,
+    uint8_t trafficClass);
+
+// ctranIbQpRTS - Transitions QP to Ready To Send (RTS) state for active
+// communication
+folly::Expected<folly::Unit, ibverbx::Error> ctranIbQpRTS(
+    ibverbx::IbvQp& ibvQp);
+
+} // namespace ctran::ib

comms/ctran/backends/ib/CtranIbVc.cc

@@ -8,8 +8,8 @@
 #include "comms/ctran/backends/CtranCtrl.h"
 #include "comms/ctran/backends/ib/CtranIb.h"
 #include "comms/ctran/backends/ib/CtranIbBase.h"
+#include "comms/ctran/backends/ib/CtranIbQpUtils.h"
 #include "comms/ctran/backends/ib/CtranIbVc.h"
-#include "comms/ctran/backends/ib/CtranIbVcImpl.h"
 #include "comms/ctran/utils/Checks.h"
 
 #include "comms/utils/cvars/nccl_cvars.h"

comms/ctran/backends/ib/CtranIbVc.h

@@ -9,8 +9,8 @@
 #include <vector>
 #include "comms/ctran/CtranComm.h"
 #include "comms/ctran/backends/ib/CtranIbBase.h"
+#include "comms/ctran/backends/ib/CtranIbQpUtils.h"
 #include "comms/ctran/backends/ib/CtranIbSingleton.h"
-#include "comms/ctran/backends/ib/CtranIbVcImpl.h"
 #include "comms/ctran/backends/ib/IbvWrap.h"
 #include "comms/ctran/mapper/CtranMapperTypes.h"
 #include "comms/ctran/utils/Checks.h"
@@ -24,7 +24,63 @@
 // a QpUniqueId is defined by a pair of <qpnum, ibDeviceId>
 typedef std::pair<int, int> QpUniqueId;
 
-using ctran::ib::CtrlPacket;
+// Fix-sized payload buffer for IB transport to prepare and register the
+// temporary buffers for control messages
+constexpr int MAX_PAYLOAD_SIZE{4096};
+struct CtrlPacket {
+  int type{0}; // for callback check
+  size_t size{0}; // size of actual data in payload
+  char payload[MAX_PAYLOAD_SIZE];
+
+  inline void
+  copyFrom(const int srcType, const void* srcPayload, const size_t srcSize) {
+    FB_CHECKABORT(
+        srcSize <= sizeof(payload),
+        "Unexpected payload size {} > packet max payload size {}",
+        srcSize,
+        sizeof(payload));
+
+    memcpy(payload, srcPayload, srcSize);
+    size = srcSize;
+    type = srcType;
+  }
+
+  inline void copyTo(void* dstPayload, const size_t dstSize) {
+    FB_CHECKABORT(
+        size == dstSize,
+        "Unexpected packet payload size {} != input payload size {}",
+        size,
+        dstSize);
+
+    memcpy(dstPayload, payload, dstSize);
+  }
+
+  inline void copyFrom(const CtrlPacket& src) {
+    type = src.type;
+    size = src.size;
+    memcpy(payload, src.payload, src.size);
+  }
+
+  inline void copyTo(CtrlPacket& dst) {
+    dst.type = type;
+    dst.size = size;
+    memcpy(dst.payload, payload, size);
+  }
+
+  inline size_t getPacketSize() const {
+    return offsetof(CtrlPacket, payload) +
+        size; // transfer header + actual size of payload
+  }
+
+  std::string toString() const {
+    return fmt::format(
+        "addr {} type {} payloadSize {} packetSize {}",
+        (void*)this,
+        type,
+        size,
+        getPacketSize());
+  }
+};
 
 /**
  * Virtual connection internal work request (WR) structure holding a pending