mm/iob: new function iob_reserve() to adjust headroom offset

Signed-off-by: chao an <anchao@xiaomi.com>

include/nuttx/mm/iob.h

@@ -544,6 +544,16 @@ FAR struct iob_s *iob_pack(FAR struct iob_s *iob);
 
 int iob_contig(FAR struct iob_s *iob, unsigned int len);
 
+/****************************************************************************
+ * Name: iob_reserve
+ *
+ * Description:
+ *   Adjust headroom offset of iobs by reducing the tail room.
+ *
+ ****************************************************************************/
+
+void iob_reserve(FAR struct iob_s *iob, unsigned int reserved);
+
 /****************************************************************************
  * Name: iob_dump
  *

mm/iob/Make.defs

@@ -28,7 +28,7 @@ CSRCS += iob_free_chain.c iob_free_qentry.c iob_free_queue.c
 CSRCS += iob_initialize.c iob_pack.c iob_peek_queue.c iob_remove_queue.c
 CSRCS += iob_statistics.c iob_trimhead.c iob_trimhead_queue.c iob_trimtail.c
 CSRCS += iob_navail.c iob_free_queue_qentry.c iob_tailroom.c
-CSRCS += iob_get_queue_size.c
+CSRCS += iob_get_queue_size.c iob_reserve.c
 
 ifeq ($(CONFIG_IOB_NOTIFIER),y)
   CSRCS += iob_notifier.c

mm/iob/iob_reserve.c

@@ -0,0 +1,82 @@
+/****************************************************************************
+ * mm/iob/iob_reserve.c
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+#include <nuttx/mm/iob.h>
+
+#include "iob.h"
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: iob_reserve
+ *
+ * Description:
+ *   Adjust headroom offset of iobs by reducing the tail room.
+ *
+ ****************************************************************************/
+
+void iob_reserve(FAR struct iob_s *iob, unsigned int reserved)
+{
+  unsigned int offset;
+
+  /* Empty iob buffer is allowed, update packet length. */
+
+  if (iob->io_pktlen > reserved)
+    {
+      iob->io_pktlen -= reserved;
+    }
+  else
+    {
+      iob->io_pktlen = 0;
+    }
+
+  /* Update offset and reducing the tail room */
+
+  while (iob != NULL && reserved > 0)
+    {
+      if (reserved > CONFIG_IOB_BUFSIZE)
+        {
+          offset = CONFIG_IOB_BUFSIZE;
+        }
+      else
+        {
+          offset = reserved;
+        }
+
+      if (iob->io_len > offset)
+        {
+          iob->io_len -= offset;
+        }
+      else
+        {
+          iob->io_len = 0;
+        }
+
+      iob->io_offset = offset;
+      iob = iob->io_flink;
+    }
+}