Update p4-fs-lab.md

TsinghuaDatabaseGroup · TsinghuaDatabaseGroup · commit 5787ef9ccacf · 2025-04-25T23:29:44.000+08:00
diff --git a/lec9/p4-fs-lab.md b/lec9/p4-fs-lab.md
@@ -888,7 +888,7 @@ pub struct BlockCache {
 3. 从文件系统中获取根目录的 inode 。
 
 ```rust
-lazy_static! {
+lazy_static! {//宏定义静态变量
     pub static ref BLOCK_DEVICE = Arc::new(BlockDeviceImpl::new());
 ......
 lazy_static! {
