mm: Implement malloc_usable_size

defined here:
https://man7.org/linux/man-pages/man3/malloc_usable_size.3.html

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
Change-Id: I5988bb28375626188312bd0a0ba3fc12db66f644

include/malloc.h

@@ -25,6 +25,8 @@
  * Included Files
  ****************************************************************************/
 
+#include <stdlib.h>
+
 /****************************************************************************
  * Pre-processor Definitions
  ****************************************************************************/
@@ -55,6 +57,7 @@ extern "C"
 #endif
 
 struct mallinfo mallinfo(void);
+size_t malloc_usable_size(FAR void *ptr);
 
 #if defined(__cplusplus)
 }

mm/mm_heap/Make.defs

@@ -36,7 +36,7 @@
 # Core heap allocator logic
 
 CSRCS += mm_initialize.c mm_sem.c mm_addfreechunk.c mm_size2ndx.c
-CSRCS += mm_shrinkchunk.c
+CSRCS += mm_malloc_usable_size.c mm_shrinkchunk.c
 CSRCS += mm_brkaddr.c mm_calloc.c mm_extend.c mm_free.c mm_mallinfo.c
 CSRCS += mm_malloc.c mm_memalign.c mm_realloc.c mm_zalloc.c mm_heapmember.c
 

mm/mm_heap/mm_malloc_usable_size.c

@@ -0,0 +1,57 @@
+/****************************************************************************
+ * mm/mm_heap/mm_malloc_usable_size.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 <assert.h>
+#include <debug.h>
+#include <malloc.h>
+
+#include <nuttx/mm/mm.h>
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+size_t malloc_usable_size(FAR void *mem)
+{
+  FAR struct mm_freenode_s *node;
+
+  /* Protect against attempts to query a NULL reference */
+
+  if (!mem)
+    {
+      return 0;
+    }
+
+  /* Map the memory chunk into a free node */
+
+  node = (FAR struct mm_freenode_s *)((FAR char *)mem - SIZEOF_MM_ALLOCNODE);
+
+  /* Sanity check against double-frees */
+
+  DEBUGASSERT(node->preceding & MM_ALLOC_BIT);
+
+  return node->size - SIZEOF_MM_ALLOCNODE;
+}