mm/iob:support iob queue concat to another iob queue

add interface support to merge iob queues, providing support for
subsequent features.

Signed-off-by: wenquan1 <wenquan1@xiaomi.com>

include/nuttx/mm/iob.h

@@ -405,6 +405,19 @@ int iob_add_queue(FAR struct iob_s *iob, FAR struct iob_queue_s *iobq);
 int iob_tryadd_queue(FAR struct iob_s *iob, FAR struct iob_queue_s *iobq);
 #endif /* CONFIG_IOB_NCHAINS > 0 */
 
+/****************************************************************************
+ * Name: iob_concat_queue
+ *
+ * Description:
+ *   Concatenate iob_s queue src to dest
+ *
+ ****************************************************************************/
+
+#if CONFIG_IOB_NCHAINS > 0
+int iob_concat_queue(FAR struct iob_queue_s *dest,
+                     FAR struct iob_queue_s *src);
+#endif /* CONFIG_IOB_NCHAINS > 0 */
+
 /****************************************************************************
  * Name: iob_remove_queue
  *

mm/iob/iob_add_queue.c

@@ -131,4 +131,45 @@ int iob_tryadd_queue(FAR struct iob_s *iob, FAR struct iob_queue_s *iobq)
 
   return iob_add_queue_internal(iob, iobq, qentry);
 }
+
+/****************************************************************************
+ * Name: iob_concat_queue
+ *
+ * Description:
+ *   Concatenate iob_s queue src to dest
+ *
+ ****************************************************************************/
+
+int iob_concat_queue(FAR struct iob_queue_s *dest,
+                     FAR struct iob_queue_s *src)
+{
+  FAR struct iob_qentry_s *qentry;
+  FAR struct iob_qentry_s *tailq;
+
+  /* Detach the list from the queue head so first for safety (should be safe
+   * anyway).
+   */
+
+  qentry = src->qh_head;
+  tailq = src->qh_tail;
+  src->qh_head = NULL;
+  src->qh_tail = NULL;
+
+  if (qentry)
+    {
+      if (!dest->qh_head)
+        {
+          dest->qh_head = qentry;
+          dest->qh_tail = tailq;
+        }
+      else
+        {
+          DEBUGASSERT(dest->qh_tail);
+          dest->qh_tail->qe_flink = qentry;
+          dest->qh_tail = tailq;
+        }
+    }
+
+  return 0;
+}
 #endif /* CONFIG_IOB_NCHAINS > 0 */