mm/iob: add a helper function to get iob count in chain

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

Documentation/reference/os/iob.rst

@@ -177,6 +177,7 @@ Public Function Prototypes
   - :c:func:`iob_trimtail()`
   - :c:func:`iob_pack()`
   - :c:func:`iob_contig()`
+  - :c:func:`iob_count()`
   - :c:func:`iob_dump()`
 
 .. c:function:: void iob_initialize(void);
@@ -324,6 +325,10 @@ Public Function Prototypes
   space at the beginning of the I/O buffer chain starting at
   ``iob``.
 
+.. c:function:: int iob_count(FAR struct iob_s *iob);
+
+  Get ``iob`` entries count in chain.
+
 .. c:function:: void iob_dump(FAR const char *msg, FAR struct iob_s *iob, unsigned int len, \
                  unsigned int offset);
 

include/nuttx/mm/iob.h

@@ -593,6 +593,16 @@ void iob_reserve(FAR struct iob_s *iob, unsigned int reserved);
 
 void iob_update_pktlen(FAR struct iob_s *iob, unsigned int pktlen);
 
+/****************************************************************************
+ * Name: iob_count
+ *
+ * Description:
+ *   Get iob entries count in chain.
+ *
+ ****************************************************************************/
+
+int iob_count(FAR struct iob_s *iob);
+
 /****************************************************************************
  * Name: iob_dump
  *

mm/iob/Make.defs

@@ -29,6 +29,7 @@ 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 iob_reserve.c iob_update_pktlen.c
+CSRCS += iob_count.c
 
 ifeq ($(CONFIG_IOB_NOTIFIER),y)
   CSRCS += iob_notifier.c

mm/iob/iob_count.c

@@ -0,0 +1,49 @@
+/****************************************************************************
+ * mm/iob/iob_count.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_count
+ *
+ * Description:
+ *   Get iob entries count in chain.
+ *
+ ****************************************************************************/
+
+int iob_count(FAR struct iob_s *iob)
+{
+  int count;
+
+  for (count = 0; iob != NULL;
+       iob = iob->io_flink, count++);
+
+  return count;
+}