net/can: Add SO_RCVBUF option for can socket

If the CAN stack receiving packets fast, but the application layer reading packets slow. Then `conn->readahead` will continue to grow, leading to memory leaks. Finally CAN stack potentially starve out all IOB buffers. To prevent memory leaks, users can restrict can socket buffer length.

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

mm/iob/CMakeLists.txt

@@ -44,7 +44,7 @@ if(CONFIG_MM_IOB)
       iob_navail.c
       iob_free_queue_qentry.c
       iob_tailroom.c
-      iob_get_queue_size.c
+      iob_get_queue_info.c
       iob_reserve.c
       iob_update_pktlen.c
       iob_count.c)

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 iob_update_pktlen.c
+CSRCS += iob_get_queue_info.c iob_reserve.c iob_update_pktlen.c
 CSRCS += iob_count.c
 
 ifeq ($(CONFIG_IOB_NOTIFIER),y)

mm/iob/iob_get_queue_info.c

@@ -1,5 +1,5 @@
 /****************************************************************************
- * mm/iob/iob_get_queue_size.c
+ * mm/iob/iob_get_queue_info.c
  *
  * Licensed to the Apache Software Foundation (ASF) under one or more
  * contributor license agreements.  See the NOTICE file distributed with
@@ -55,4 +55,23 @@ unsigned int iob_get_queue_size(FAR struct iob_queue_s *queue)
   return total;
 }
 
+/****************************************************************************
+ * Name: iob_get_queue_entry_count
+ *
+ * Description:
+ *   Queue helper for get the iob queue entry count.
+ *
+ ****************************************************************************/
+
+unsigned int iob_get_queue_entry_count(FAR struct iob_queue_s *queue)
+{
+  FAR struct iob_qentry_s *iobq;
+  unsigned int count;
+
+  for (iobq = queue->qh_head, count = 0; iobq != NULL;
+       iobq = iobq->qe_flink, count++);
+
+  return count;
+}
+
 #endif /* CONFIG_IOB_NCHAINS > 0 */