Added methods to query filesystem for size

Added methods totalBytes() and usedBytes() for obtaining flash
filesystem overall size and available space, like those found in SPIFFS.
Also added usedBlocks() method for good measure.

libraries/Adafruit_LittleFS/src/Adafruit_LittleFS.cpp

@@ -239,6 +239,32 @@ bool Adafruit_LittleFS::rmdir_r (char const *filepath)
   return LFS_ERR_OK == err;
 }
 
+static int _lfs_count(void *p, lfs_block_t block) {
+  *(size_t *)p += 1;
+	return 0;
+}
+
+size_t Adafruit_LittleFS::usedBlocks() {
+  _lockFS();
+
+  size_t blocks = 0;
+  lfs_traverse(&_lfs, _lfs_count, &blocks);
+
+  _unlockFS();
+  return blocks;
+}
+
+size_t Adafruit_LittleFS::usedBytes() {
+  if (nullptr == _lfs_cfg) return 0;
+	const size_t blocks_used = usedBlocks();
+	return _lfs_cfg->block_size * blocks_used;
+}
+
+size_t Adafruit_LittleFS::totalBytes() {
+  if (nullptr == _lfs_cfg) return 0;
+	return _lfs_cfg->block_size * _lfs_cfg->block_count;
+}
+
 //------------- Debug -------------//
 #if CFG_DEBUG
 

libraries/Adafruit_LittleFS/src/Adafruit_LittleFS.h

@@ -70,6 +70,10 @@ class Adafruit_LittleFS
     // format file system
     bool format (void);
 
+    size_t usedBlocks();
+    size_t usedBytes();
+    size_t totalBytes();
+
     /*------------------------------------------------------------------*/
     /* INTERNAL USAGE ONLY
      * Although declare as public, it is meant to be invoked by internal