Add a console output stream and a separate stream for user errors

The user errors stream is disabled by default.

Add a console output stream and a separate stream for user errors
e0824a1c · Austin Clements · Silas Boyd-Wickizer · 8c2334c1 · e0824a1c · e0824a1c
--- a/include/kstream.hh
+++ b/include/kstream.hh
+#pragma once
+
+#include "pstream.hh"
+
+class console_stream : public print_stream
+{
+public:
+  constexpr console_stream(bool enabled = true)
+    : print_stream(enabled) { }
+
+protected:
+  void write(char c);
+  void write(sbuf buf);
+};
+
+extern console_stream console;
+
+// Errors caused by user processes (page faults, failed system calls,
+// etc.)
+extern console_stream uerr;
--- a/kernel/Makefrag
+++ b/kernel/Makefrag
@@ -57,6 +57,7 @@ OBJS = \
        zalloc.o \
 	incbin.o \
 	sysvectors.o \
+	pstream.o

 ifeq ($(EXCEPTIONS),y)
 OBJS += \

--- a/kernel/console.cc
+++ b/kernel/console.cc
@@ -19,6 +19,7 @@
 #include "sperf.hh"
 #include "wq.hh"
 #include "major.h"
+#include "kstream.hh"

 #define BACKSPACE 0x100

@@ -336,6 +337,24 @@ consoleread(struct inode *ip, char *dst, u32 off, u32 n)
  return target - n;
 }

+// Console stream support
+
+void
+console_stream::write(char c)
+{
+  consputc(c);
+}
+
+void
+console_stream::write(sbuf buf)
+{
+  for (size_t i = 0; i < buf.len; i++)
+    consputc(buf.base[i]);
+}
+
+console_stream console;
+console_stream uerr(false);
+
 void
 initconsole(void)
 {