fs: allow to configure per-alloaction heap overhead

The size of overhead for each heap allocation can change after
heap implementation change and such change impacts automatic
calculation of heap size for littleFS.
This patch allows per-alloaction overhead to be configurable and then
automatic heap size calculation can be adjusted without code change.
This is a temporary fix until per-alloaction overhead value will be
available from kernel internals.

Fixes #36962

Signed-off-by: Artur Lipowski <[email protected]>

Author: r2r0

subsys/fs/Kconfig.littlefs

@@ -89,4 +89,19 @@ config FS_LITTLEFS_FC_HEAP_SIZE
 	  support up to FS_LITTLE_FS_NUM_FILES blocks of
 	  FS_LITTLEFS_CACHE_SIZE bytes.
 
+if FS_LITTLEFS_FC_HEAP_SIZE <= 0
+
+config FS_LITTLEFS_HEAP_PER_ALLOC_OVERHEAD_SIZE
+	int "Size of per-allocation overhead for littleFS heap in bytes"
+	default 32
+	help
+	  In case when total size of littleFS heap is automatically calculated
+	  we need to take into account overhead caused per block allocation.
+	  For the purpose of heap size calculation the size of each cache block
+	  will be increased by this value.
+	  NOTE: when your app fails to open pre-defined number of files, as set
+	  by FS_LITTLEFS_NUM_FILES, try to increase the value.
+
+endif # FS_LITTLEFS_FC_HEAP_SIZE <= 0
+
 endif # FILE_SYSTEM_LITTLEFS

subsys/fs/littlefs_fs.c

@@ -41,10 +41,13 @@ static K_MEM_SLAB_DEFINE(lfs_dir_pool, sizeof(struct lfs_dir),
  * the filecache heap.  This relates to the CHUNK_UNIT parameter in
  * the heap implementation, but that value is not visible outside the
  * kernel.
+ * FIXME: value for this macro should be rather taken from the Kernel
+ * internals than set by user, but we do not have a way to do so now.
  */
-#define FC_HEAP_PER_ALLOC_OVERHEAD 24U
+#define FC_HEAP_PER_ALLOC_OVERHEAD CONFIG_FS_LITTLEFS_HEAP_PER_ALLOC_OVERHEAD_SIZE
 
 #if (CONFIG_FS_LITTLEFS_FC_HEAP_SIZE - 0) <= 0
+BUILD_ASSERT((CONFIG_FS_LITTLEFS_HEAP_PER_ALLOC_OVERHEAD_SIZE % 8) == 0);
 /* Auto-generate heap size from cache size and number of files */
 #undef CONFIG_FS_LITTLEFS_FC_HEAP_SIZE
 #define CONFIG_FS_LITTLEFS_FC_HEAP_SIZE						\