Fixed #2 -- use a stack buffer for formatting strings in printk (#7)

* Fixed #2 -- use a stack buffer for formatting strings in printk

This avoids a malloc

* fixes

* more compilation fixes

* oops, fix how we call this

* sigh, weird scoping for macros

* sigh, scoping, update use

* Remove unused imports

* fixed output length

* rustfmt

* apparently this isn't required?

* simplify with cmp::min

* review comments

* all our printks are kern_info

Author: alex

src/printk.rs

@@ -1,3 +1,4 @@
+use core::cmp;
 use core::fmt;
 
 use types::c_int;
@@ -8,28 +9,53 @@ extern "C" {
     fn printk_helper(s: *const u8, len: c_int) -> c_int;
 }
 
-impl fmt::Write for KernelConsole {
+pub fn printk(s: &[u8]) {
+    // TODO: I believe printk never fails
+    unsafe { printk_helper(s.as_ptr(), s.len() as c_int) };
+}
+
+// From kernel/print/printk.c
+const LOG_LINE_MAX: usize = 1024 - 32;
+
+pub struct LogLineWriter {
+    data: [u8; LOG_LINE_MAX],
+    pos: usize,
+}
+
+impl LogLineWriter {
+    pub fn new() -> LogLineWriter {
+        LogLineWriter {
+            data: [0u8; LOG_LINE_MAX],
+            pos: 0,
+        }
+    }
+
+    pub fn as_bytes(&self) -> &[u8] {
+        return &self.data[..self.pos];
+    }
+}
+
+impl fmt::Write for LogLineWriter {
     fn write_str(&mut self, s: &str) -> fmt::Result {
-        // TODO: I believe printk never fails
-        unsafe { printk_helper(s.as_ptr(), s.len() as c_int) };
-        Ok(())
+        let copy_len = cmp::min(LOG_LINE_MAX - self.pos, s.as_bytes().len());
+        self.data[self.pos..self.pos + copy_len].copy_from_slice(&s.as_bytes()[..copy_len]);
+        self.pos += copy_len;
+        return Ok(());
     }
 }
 
 #[macro_export]
 macro_rules! println {
     () => ({
-        use ::core::fmt::Write;
-        let _ = $crate::printk::KernelConsole.write_str("\x016\n");
+        $crate::printk::printk("\n".as_bytes());
     });
     ($fmt:expr) => ({
-        use ::core::fmt::Write;
-        let _ = $crate::printk::KernelConsole.write_str(concat!("\x016", $fmt, "\n"));
+        $crate::printk::printk(concat!($fmt, "\n").as_bytes());
     });
     ($fmt:expr, $($arg:tt)*) => ({
-        use ::core::fmt::Write;
-        // TODO: Don't allocate!
-        let s = format!(concat!("\x016", $fmt, "\n"), $($arg)*);
-        let _ = $crate::printk::KernelConsole.write_str(&s);
+        use ::core::fmt;
+        let mut writer = $crate::printk::LogLineWriter::new();
+        let _ = fmt::write(&mut writer, format_args!(concat!($fmt, "\n"), $($arg)*)).unwrap();
+        $crate::printk::printk(writer.as_bytes());
     });
 }

src/printk_helper.c

@@ -2,5 +2,5 @@
 
 int printk_helper(const unsigned char *s, int len)
 {
-	return printk("%.*s", len, (const char *)s);
+	return printk(KERN_INFO "%.*s", len, (const char *)s);
 }