Use the sysutil library's printf code also for the kernel.

kernel/kprintf.c

@@ -0,0 +1,71 @@
+/*
+ * printf for the kernel
+ *
+ * Changes:
+ *   Dec 10, 2004   kernel printing to circular buffer  (Jorrit N. Herder)
+ * 
+ * This file contains the routines that take care of kernel messages, i.e.,
+ * diagnostic output within the kernel. Kernel messages are not directly
+ * displayed on the console, because this must be done by the output driver. 
+ * Instead, the kernel accumulates characters in a buffer and notifies the
+ * output driver when a new message is ready. 
+ */
+
+#include "kernel.h"
+#include "proc.h"
+#include <signal.h>
+
+#define printf kprintf
+
+#include "../lib/sysutil/kprintf.c"
+
+#define END_OF_KMESS 	0
+FORWARD _PROTOTYPE( void ser_putc, (char c));
+
+/*===========================================================================*
+ *				kputc				     	     *
+ *===========================================================================*/
+PUBLIC void kputc(c)
+int c;					/* character to append */
+{
+/* Accumulate a single character for a kernel message. Send a notification
+ * to the output driver if an END_OF_KMESS is encountered. 
+ */
+  if (c != END_OF_KMESS) {
+      if (do_serial_debug)
+      	ser_putc(c);
+      kmess.km_buf[kmess.km_next] = c;	/* put normal char in buffer */
+      if (kmess.km_size < KMESS_BUF_SIZE)
+          kmess.km_size += 1;		
+      kmess.km_next = (kmess.km_next + 1) % KMESS_BUF_SIZE;
+  } else {
+      int p, outprocs[] = OUTPUT_PROCS_ARRAY;
+      for(p = 0; outprocs[p] != NONE; p++) {
+	 if(isokprocn(outprocs[p]) && !isemptyn(outprocs[p])) {
+           send_sig(outprocs[p], SIGKMESS);
+	 }
+      }
+  }
+}
+
+#define COM1_BASE	0x3F8
+#define COM1_THR	(COM1_BASE + 0)
+#define	  LSR_THRE	0x20
+#define COM1_LSR	(COM1_BASE + 5)
+
+PRIVATE void ser_putc(char c)
+{
+	int i;
+	int lsr, thr;
+
+	return;
+
+	lsr= COM1_LSR;
+	thr= COM1_THR;
+	for (i= 0; i<100000; i++)
+	{
+		if (inb(lsr) & LSR_THRE)
+			break;
+	}
+	outb(thr, c);
+}