mm/iob: new function iob_update_pktlen() to update packet length of the iob

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

include/nuttx/mm/iob.h

@@ -554,6 +554,20 @@ int iob_contig(FAR struct iob_s *iob, unsigned int len);
 
 void iob_reserve(FAR struct iob_s *iob, unsigned int reserved);
 
+/****************************************************************************
+ * Name: iob_update_pktlen
+ *
+ * Description:
+ *   This function will update packet length of the iob, it will be
+ *   trimmed if the length of the iob chain is greater than the current
+ *   length.
+ *   This function will not grow the iob link, any grow operation should
+ *   be implemented through iob_copyin()/iob_trycopyin().
+ *
+ ****************************************************************************/
+
+void iob_update_pktlen(FAR struct iob_s *iob, unsigned int pktlen);
+
 /****************************************************************************
  * 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 iob_reserve.c
+CSRCS += iob_get_queue_size.c iob_reserve.c iob_update_pktlen.c
 
 ifeq ($(CONFIG_IOB_NOTIFIER),y)
   CSRCS += iob_notifier.c

mm/iob/iob_update_pktlen.c

@@ -0,0 +1,128 @@
+/****************************************************************************
+ * mm/iob/iob_update_pktlen.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_update_pktlen
+ *
+ * Description:
+ *   This function will update packet length of the iob, it will be
+ *   trimmed if the length of the iob chain is greater than the current
+ *   length.
+ *   This function will not grow the iob link, any grow operation should
+ *   be implemented through iob_copyin()/iob_trycopyin().
+ *
+ ****************************************************************************/
+
+void iob_update_pktlen(FAR struct iob_s *iob, unsigned int pktlen)
+{
+  FAR struct iob_s *penultimate;
+  FAR struct iob_s *next;
+  uint16_t offset = 0;
+  int ninqueue = 0;
+  int nrequire;
+  uint16_t len;
+
+  /* The data offset must be less than CONFIG_IOB_BUFSIZE */
+
+  if (iob == NULL)
+    {
+      return;
+    }
+
+  /* Calculate the total entries of the data in the I/O buffer chain */
+
+  next = iob;
+  while (next != NULL)
+    {
+      ninqueue++;
+      offset += next->io_offset;
+      next    = next->io_flink;
+    }
+
+  /* Trim inqueue entries if needed */
+
+  nrequire = (pktlen + offset + CONFIG_IOB_BUFSIZE - 1) /
+             CONFIG_IOB_BUFSIZE;
+  if (nrequire == 0)
+    {
+      nrequire = 1;
+    }
+
+  if (nrequire < ninqueue)
+    {
+      /* Loop until complete the trim */
+
+      next = iob;
+      penultimate = NULL;
+
+      while (next != NULL)
+        {
+          if (nrequire-- <= 0)
+            {
+              if (penultimate != NULL)
+                {
+                  penultimate->io_flink = NULL;
+                }
+
+              iob_free_chain(next);
+              break;
+            }
+          else
+            {
+              penultimate = next;
+              next = next->io_flink;
+            }
+        }
+    }
+
+  iob->io_pktlen = pktlen;
+
+  /* Update size of each iob */
+
+  next = iob;
+  while (next != NULL && pktlen > 0)
+    {
+      if (pktlen + next->io_offset > CONFIG_IOB_BUFSIZE)
+        {
+          len = CONFIG_IOB_BUFSIZE - next->io_offset;
+        }
+      else
+        {
+          len = pktlen;
+        }
+
+      next->io_len = len;
+      pktlen      -= len;
+      next         = next->io_flink;
+    }
+}