From ff30eddfdbfd558a851425c69f311e210c3c7c6b Mon Sep 17 00:00:00 2001
From: Abtin Keshavarzian <abtink@google.com>
Date: Mon, 18 May 2020 12:03:31 -0700
Subject: [PATCH] [message] update Buffer and MessagePool to use LinkedList
 methods (#4977)

---
 src/core/common/message.cpp | 53 +++++++++++++++++--------------------
 src/core/common/message.hpp | 21 ++++++++++-----
 2 files changed, 40 insertions(+), 34 deletions(-)

diff --git a/src/core/common/message.cpp b/src/core/common/message.cpp
index 1ba41e982..c1b062e0e 100644
--- a/src/core/common/message.cpp
+++ b/src/core/common/message.cpp
@@ -44,22 +44,20 @@ namespace ot {
 
 MessagePool::MessagePool(Instance &aInstance)
     : InstanceLocator(aInstance)
+#if !OPENTHREAD_CONFIG_PLATFORM_MESSAGE_MANAGEMENT
+    , mNumFreeBuffers(kNumBuffers)
+    , mFreeBuffers()
+#endif
 {
-#if OPENTHREAD_CONFIG_PLATFORM_MESSAGE_MANAGEMENT
-    // Initialize Platform buffer pool management.
-    otPlatMessagePoolInit(&GetInstance(), kNumBuffers, sizeof(Buffer));
-#else
+#if !OPENTHREAD_CONFIG_PLATFORM_MESSAGE_MANAGEMENT
     memset(mBuffers, 0, sizeof(mBuffers));
 
-    mFreeBuffers = mBuffers;
-
-    for (uint16_t i = 0; i < kNumBuffers - 1; i++)
+    for (Buffer *cur = &mBuffers[0]; cur < OT_ARRAY_END(mBuffers); cur++)
     {
-        mBuffers[i].SetNextBuffer(&mBuffers[i + 1]);
+        mFreeBuffers.Push(*cur);
     }
-
-    mBuffers[kNumBuffers - 1].SetNextBuffer(NULL);
-    mNumFreeBuffers = kNumBuffers;
+#else
+    otPlatMessagePoolInit(&GetInstance(), kNumBuffers, sizeof(Buffer));
 #endif
 }
 
@@ -134,10 +132,10 @@ Buffer *MessagePool::NewBuffer(uint8_t aPriority)
 
 #else
 
-    if (mFreeBuffers != NULL)
+    buffer = mFreeBuffers.Pop();
+
+    if (buffer != NULL)
     {
-        buffer       = mFreeBuffers;
-        mFreeBuffers = mFreeBuffers->GetNextBuffer();
         buffer->SetNextBuffer(NULL);
         mNumFreeBuffers--;
     }
@@ -157,15 +155,14 @@ void MessagePool::FreeBuffers(Buffer *aBuffer)
 {
     while (aBuffer != NULL)
     {
-        Buffer *tmpBuffer = aBuffer->GetNextBuffer();
+        Buffer *next = aBuffer->GetNextBuffer();
 #if OPENTHREAD_CONFIG_PLATFORM_MESSAGE_MANAGEMENT
         otPlatMessagePoolFree(&GetInstance(), aBuffer);
-#else  // OPENTHREAD_CONFIG_PLATFORM_MESSAGE_MANAGEMENT
-        aBuffer->SetNextBuffer(mFreeBuffers);
-        mFreeBuffers = aBuffer;
+#else
+        mFreeBuffers.Push(*aBuffer);
         mNumFreeBuffers++;
-#endif // OPENTHREAD_CONFIG_PLATFORM_MESSAGE_MANAGEMENT
-        aBuffer = tmpBuffer;
+#endif
+        aBuffer = next;
     }
 }
 
@@ -178,9 +175,9 @@ otError MessagePool::ReclaimBuffers(int aNumBuffers, uint8_t aPriority)
     }
 
 exit:
-#else  // OPENTHREAD_MTD || OPENTHREAD_FTD
+#else
     OT_UNUSED_VARIABLE(aPriority);
-#endif // OPENTHREAD_MTD || OPENTHREAD_FTD
+#endif
 
     // First comparison is to get around issues with comparing
     // signed and unsigned numbers, if aNumBuffers is negative then
@@ -442,9 +439,9 @@ void Message::RemoveHeader(uint16_t aLength)
 
 uint16_t Message::Read(uint16_t aOffset, uint16_t aLength, void *aBuf) const
 {
-    Buffer * curBuffer;
-    uint16_t bytesCopied = 0;
-    uint16_t bytesToCopy;
+    const Buffer *curBuffer;
+    uint16_t      bytesCopied = 0;
+    uint16_t      bytesToCopy;
 
     if (aOffset >= GetLength())
     {
@@ -700,9 +697,9 @@ uint16_t Message::UpdateChecksum(uint16_t aChecksum, const void *aBuf, uint16_t
 
 uint16_t Message::UpdateChecksum(uint16_t aChecksum, uint16_t aOffset, uint16_t aLength) const
 {
-    Buffer * curBuffer;
-    uint16_t bytesCovered = 0;
-    uint16_t bytesToCover;
+    const Buffer *curBuffer;
+    uint16_t      bytesCovered = 0;
+    uint16_t      bytesToCover;
 
     OT_ASSERT(aOffset + aLength <= GetLength());
 
diff --git a/src/core/common/message.hpp b/src/core/common/message.hpp
index 64e8a3bb1..7d019650e 100644
--- a/src/core/common/message.hpp
+++ b/src/core/common/message.hpp
@@ -43,6 +43,7 @@
 
 #include "common/code_utils.hpp"
 #include "common/encoding.hpp"
+#include "common/linked_list.hpp"
 #include "common/locator.hpp"
 #include "common/non_copyable.hpp"
 #include "mac/mac_types.hpp"
@@ -122,7 +123,7 @@ struct MessageInfo
  * This class represents a Message buffer.
  *
  */
-class Buffer : public otMessage
+class Buffer : public otMessage, public LinkedListEntry<Buffer>
 {
     friend class Message;
 
@@ -133,7 +134,15 @@ public:
      * @returns A pointer to the next message buffer.
      *
      */
-    Buffer *GetNextBuffer(void) const { return static_cast<Buffer *>(mNext); }
+    Buffer *GetNextBuffer(void) { return GetNext(); }
+
+    /**
+     * This method returns a pointer to the next message buffer.
+     *
+     * @returns A pointer to the next message buffer.
+     *
+     */
+    const Buffer *GetNextBuffer(void) const { return GetNext(); }
 
     /**
      * This method sets the pointer to the next message buffer.
@@ -141,7 +150,7 @@ public:
      * @param[in] aNext  A pointer to the next buffer.
      *
      */
-    void SetNextBuffer(Buffer *aNext) { mNext = aNext; }
+    void SetNextBuffer(Buffer *aNext) { SetNext(aNext); }
 
 private:
     /**
@@ -1157,9 +1166,9 @@ private:
     otError ReclaimBuffers(int aNumBuffers, uint8_t aPriority);
 
 #if OPENTHREAD_CONFIG_PLATFORM_MESSAGE_MANAGEMENT == 0
-    uint16_t mNumFreeBuffers;
-    Buffer   mBuffers[kNumBuffers];
-    Buffer * mFreeBuffers;
+    uint16_t           mNumFreeBuffers;
+    Buffer             mBuffers[kNumBuffers];
+    LinkedList<Buffer> mFreeBuffers;
 #endif
 };