Use `LOG` env to set log level

Makefile

@@ -2,6 +2,8 @@
 # 	make run					Run in debug
 #	make run int=1				Run with interrupt info by QEMU
 # 	make run mode=release		Run in release
+#	make run LOG=error			Run with log level: error
+#									LOG = off | error | warn | info | debug | trace
 # 	make doc					Generate docs
 # 	make asm					Open the deassemble file of the last build
 # 	make clean					Clean
@@ -24,6 +26,7 @@ user_object_files := $(patsubst user/%.img, build/user/%.o, $(user_image_files))
 qemu_opts := -cdrom $(iso) -smp 4 -serial mon:stdio
 features := use_apic
 
+LOG ?= debug
 link_user = 1
 
 ifdef link_user

src/io/mod.rs

@@ -6,7 +6,14 @@ mod vga_writer;
 pub fn init() {
     static LOGGER: SimpleLogger = SimpleLogger;
     log::set_logger(&LOGGER).unwrap();
-    log::set_max_level(LevelFilter::Debug);
+    log::set_max_level(match option_env!("LOG") {
+        Some("off") => LevelFilter::Off,
+        Some("error") => LevelFilter::Error,
+        Some("warn") => LevelFilter::Warn,
+        Some("info") => LevelFilter::Info,
+        Some("trace") => LevelFilter::Trace,
+        Some("debug") | _ => LevelFilter::Debug,
+    });
 }
 
 macro_rules! print {