Clear screen before passing control to kernel

Author: phil-opp

src/main.rs

@@ -100,6 +100,7 @@ pub extern "C" fn load_elf(kernel_start: PhysAddr, kernel_size: u64,
     enable_write_protect_bit();
 
     let entry_point = VirtAddr::new(elf_file.header.pt2.entry_point());
+    printer::PRINTER.lock().clear_screen();
     unsafe { context_switch(p4_addr, entry_point, stack_end, boot_info_addr) };
 }
 

src/printer.rs

@@ -1,31 +1,45 @@
-use core::fmt::{Write, Result};
-use core::slice;
-use spin::Mutex;
-
-pub static PRINTER: Mutex<Printer> = Mutex::new(Printer::new());
-
-pub struct Printer {
-    index: usize,
-}
-
-impl Printer {
-    pub const fn new() -> Printer {
-        Printer {
-            index: 0,
-        }
-    }
-}
-
-impl Write for Printer {
-    fn write_str(&mut self, s: &str) -> Result {
-        const VGA_BUFFER: *mut u8 = 0xb8000 as *mut _;
-        let vga_buffer = unsafe { slice::from_raw_parts_mut(VGA_BUFFER, 80 * 25 * 2) };
-        for byte in s.bytes() {
-            vga_buffer[self.index] = byte;
-            vga_buffer[self.index + 1] = 0x4f;
-            self.index += 2;
-        }
-
-        Ok(())
-    }
-}
+use core::fmt::{Write, Result};
+use core::slice;
+use spin::Mutex;
+
+const VGA_BUFFER: *mut u8 = 0xb8000 as *mut _;
+const SCREEN_SIZE: usize = 80 * 25;
+
+pub static PRINTER: Mutex<Printer> = Mutex::new(Printer::new());
+
+pub struct Printer {
+    index: usize,
+}
+
+impl Printer {
+    pub const fn new() -> Printer {
+        Printer {
+            index: 0,
+        }
+    }
+
+    pub fn clear_screen(&mut self) {
+        let vga_buffer = Self::vga_buffer();
+        for byte in vga_buffer {
+            *byte = 0;
+        }
+        self.index = 0;
+    }
+
+    fn vga_buffer() -> &'static mut [u8] {
+         unsafe { slice::from_raw_parts_mut(VGA_BUFFER, SCREEN_SIZE * 2) }
+    }
+}
+
+impl Write for Printer {
+    fn write_str(&mut self, s: &str) -> Result {
+        let vga_buffer = Self::vga_buffer();
+        for byte in s.bytes() {
+            vga_buffer[self.index] = byte;
+            vga_buffer[self.index + 1] = 0x4f;
+            self.index += 2;
+        }
+
+        Ok(())
+    }
+}