fs: add support of .. operation in devfs

Author: equation314

Cargo.toml

@@ -8,7 +8,7 @@ authors = ["Yuekai Jia <[email protected]>"]
 
 [dependencies]
 cfg-if = "1.0"
-bitflags = "2.0"
+bitflags = "2.1"
 memory_addr = { path = "../memory_addr" }
 
 [target.'cfg(target_arch = "x86_64")'.dependencies]