feat: simple drawing board GUI

os/src/drivers/bus/mod.rs

@@ -1 +1 @@
-pub mod virtio;
+pub mod virtio;

os/src/drivers/bus/virtio.rs

@@ -1,9 +1,9 @@
-use alloc::vec::Vec;
 use crate::mm::{
     frame_alloc, frame_dealloc, kernel_token, FrameTracker, PageTable, PhysAddr, PhysPageNum,
     StepByOne, VirtAddr,
 };
 use crate::sync::UPIntrFreeCell;
+use alloc::vec::Vec;
 use lazy_static::*;
 use virtio_drivers::Hal;
 
@@ -49,4 +49,4 @@ impl Hal for VirtioHal {
             .unwrap()
             .0
     }
-}
+}