Kernel+LibC: Add a DebugLogDevice that forwards everything to I/O port 0xe9.

This is then used to implement the userspace dbgprintf() in a far more
efficient way than what we had before. :^)

Kernel/Devices/DebugLogDevice.cpp

@@ -0,0 +1,28 @@
+#include <Kernel/Devices/DebugLogDevice.h>
+#include <Kernel/IO.h>
+
+static DebugLogDevice* s_the;
+
+DebugLogDevice& DebugLogDevice::the()
+{
+    ASSERT(s_the);
+    return *s_the;
+}
+
+DebugLogDevice::DebugLogDevice()
+    : CharacterDevice(1, 18)
+{
+    s_the = this;
+}
+
+DebugLogDevice::~DebugLogDevice()
+{
+}
+
+ssize_t DebugLogDevice::write(Process&, const byte* data, ssize_t data_size)
+{
+    for (int i = 0; i < data_size; ++i)
+        IO::out8(0xe9, data[i]);
+    return data_size;
+}
+

Kernel/Devices/DebugLogDevice.h

@@ -0,0 +1,17 @@
+#include <Kernel/Devices/CharacterDevice.h>
+
+class DebugLogDevice final : public CharacterDevice {
+public:
+    DebugLogDevice();
+    virtual ~DebugLogDevice() override;
+
+    static DebugLogDevice& the();
+
+private:
+    // ^CharacterDevice
+    virtual ssize_t read(Process&, byte*, ssize_t) override { return 0; }
+    virtual ssize_t write(Process&, const byte*, ssize_t) override;
+    virtual bool can_write(Process&) const override { return true; }
+    virtual bool can_read(Process&) const override { return true; }
+    virtual const char* class_name() const override { return "DebugLogDevice"; }
+};

Kernel/Makefile

@@ -57,6 +57,7 @@ VFS_OBJS = \
     Devices/FullDevice.o \
     Devices/ZeroDevice.o \
     Devices/RandomDevice.o \
+    Devices/DebugLogDevice.o \
     FileSystem/FileSystem.o \
     FileSystem/DiskBackedFileSystem.o \
     FileSystem/Ext2FileSystem.o \

Kernel/init.cpp

@@ -24,6 +24,7 @@
 #include <Kernel/Devices/BXVGADevice.h>
 #include <Kernel/Net/E1000NetworkAdapter.h>
 #include <Kernel/Net/NetworkTask.h>
+#include <Kernel/Devices/DebugLogDevice.h>
 
 #define SPAWN_TERMINAL
 //#define SPAWN_LAUNCHER
@@ -42,6 +43,7 @@ VirtualConsole* tty2;
 VirtualConsole* tty3;
 KeyboardDevice* keyboard;
 PS2MouseDevice* ps2mouse;
+DebugLogDevice* dev_debuglog;
 NullDevice* dev_null;
 VFS* vfs;
 
@@ -151,6 +153,7 @@ extern "C" [[noreturn]] void init()
     init_ksyms();
 
     vfs = new VFS;
+    dev_debuglog = new DebugLogDevice;
 
     auto console = make<Console>();
 

Kernel/sync.sh

@@ -25,6 +25,7 @@ mknod mnt/dev/random c 1 8
 mknod mnt/dev/null c 1 3
 mknod mnt/dev/zero c 1 5
 mknod mnt/dev/full c 1 7
+mknod -m 666 mnt/dev/debuglog c 1 18
 mknod mnt/dev/keyboard c 85 1
 mknod mnt/dev/psaux c 10 1
 mknod -m 666 mnt/dev/ptmx c 5 2

LibC/stdio.cpp

@@ -13,10 +13,11 @@
 
 extern "C" {
 
-static FILE __default_streams[3];
+static FILE __default_streams[4];
 FILE* stdin;
 FILE* stdout;
 FILE* stderr;
+FILE* stddbg;
 
 void init_FILE(FILE& fp, int fd, int mode)
 {
@@ -39,9 +40,16 @@ void __stdio_init()
     stdin = &__default_streams[0];
     stdout = &__default_streams[1];
     stderr = &__default_streams[2];
+    stddbg = &__default_streams[3];
     init_FILE(*stdin, 0, isatty(0) ? _IOLBF : _IOFBF);
     init_FILE(*stdout, 1, isatty(1) ? _IOLBF : _IOFBF);
     init_FILE(*stderr, 2, _IONBF);
+    int fd = open("/dev/debuglog", O_WRONLY);
+    if (fd < 0) {
+        perror("open /dev/debuglog");
+        ASSERT_NOT_REACHED();
+    }
+    init_FILE(*stddbg, fd, _IOLBF);
 }
 
 int setvbuf(FILE* stream, char* buf, int mode, size_t size)
@@ -263,16 +271,11 @@ void rewind(FILE* stream)
     fseek(stream, 0, SEEK_SET);
 }
 
-static void sys_putch(char*&, char ch)
-{
-    syscall(SC_putch, ch);
-}
-
 int dbgprintf(const char* fmt, ...)
 {
     va_list ap;
     va_start(ap, fmt);
-    int ret = printf_internal(sys_putch, nullptr, fmt, ap);
+    int ret = vfprintf(stddbg, fmt, ap);
     va_end(ap);
     return ret;
 }

LibC/stdio.h

@@ -40,6 +40,7 @@ typedef struct __STDIO_FILE FILE;
 extern FILE* stdin;
 extern FILE* stdout;
 extern FILE* stderr;
+extern FILE* stddbg;
 
 typedef size_t fpos_t;