mufs: add mufs_shrink_tree() to shrink a file tree to a specific size in terms of VAS

source/fs/mufs/tree.c

@@ -116,3 +116,47 @@ int mufs_extend_tree(struct mufs *fs, struct mufs_tree *tree, uint8_t depth)
 
 	return 0;
 }
+
+int mufs_shrink_tree(struct mufs *fs, struct mufs_tree *tree, uint32_t max_size)
+{
+	char data[1 << fs->dev->log2_block_size];
+	uint32_t *table = (uint32_t *)data;
+	size_t index;
+	uint32_t base, size;
+	uint8_t log2_nentries = fs->dev->log2_block_size - ilog2(sizeof(uint32_t));
+	uint8_t depth;
+
+	base = tree->root;
+
+	for (depth = tree->depth; depth; --depth) {
+		size = 1 << (depth * log2_nentries + fs->dev->log2_block_size);
+
+		if (size < max_size)
+			return 0;
+
+		index = max_size >> ((depth - 1) * log2_nentries +
+			fs->dev->log2_block_size);
+
+		if (flash_read(fs->dev, base, data, sizeof data) == 0)
+			return -1;
+
+		if (index <= 1) {
+			tree->root = table[0];
+			--tree->depth;
+
+			mufs_free_block(fs, base);
+
+			continue;
+		}
+
+		for (; index < (UINT32_C(1) << log2_nentries); ++index) {
+			table[index] = 0;
+		}
+
+		if (flash_write(fs->dev, base << fs->dev->log2_block_size, data,
+			sizeof data) == 0)
+			return -1;
+	}
+
+	return 0;
+}

source/fs/mufs/tree.h

@@ -6,3 +6,4 @@ int mufs_alloc_page(struct mufs *fs, struct mufs_tree *tree, uint32_t *page,
 	uint32_t va);
 void mufs_free_page(struct mufs *fs, struct mufs_tree *tree, uint32_t va);
 int mufs_extend_tree(struct mufs *fs, struct mufs_tree *tree, uint8_t depth);
+int mufs_shrink_tree(struct mufs *fs, struct mufs_tree *tree, uint32_t max_size);