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