From 64bca780a708f592c73ec5993351db9bc6b1b29f Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Thu, 30 Mar 2023 21:19:16 +0200
Subject: [PATCH] kernel: Add /dev/zero

---
 apps/init.cpp                            |  1 +
 kernel/CMakeLists.txt                    |  1 +
 kernel/src/fs/devices/DeviceRegistry.cpp |  2 ++
 kernel/src/fs/devices/ZeroDevice.cpp     |  6 +++++
 kernel/src/fs/devices/ZeroDevice.h       | 28 ++++++++++++++++++++++++
 5 files changed, 38 insertions(+)
 create mode 100644 kernel/src/fs/devices/ZeroDevice.cpp
 create mode 100644 kernel/src/fs/devices/ZeroDevice.h

diff --git a/apps/init.cpp b/apps/init.cpp
index 9e485d40..5062fba1 100644
--- a/apps/init.cpp
+++ b/apps/init.cpp
@@ -19,6 +19,7 @@ static void populate_devfs()
 
     xmknod("/dev/console", 0666, 1, 0);
     xmknod("/dev/null", 0666, 2, 0);
+    xmknod("/dev/zero", 0666, 2, 1);
 }
 
 int main()
diff --git a/kernel/CMakeLists.txt b/kernel/CMakeLists.txt
index 1c929c39..b9708673 100644
--- a/kernel/CMakeLists.txt
+++ b/kernel/CMakeLists.txt
@@ -38,6 +38,7 @@ set(SOURCES
     src/fs/tmpfs/FileSystem.cpp
     src/fs/devices/DeviceRegistry.cpp
     src/fs/devices/NullDevice.cpp
+    src/fs/devices/ZeroDevice.cpp
     src/fs/devices/ConsoleDevice.cpp
     src/InitRD.cpp
     src/ELF.cpp
diff --git a/kernel/src/fs/devices/DeviceRegistry.cpp b/kernel/src/fs/devices/DeviceRegistry.cpp
index a4eab963..059376b5 100644
--- a/kernel/src/fs/devices/DeviceRegistry.cpp
+++ b/kernel/src/fs/devices/DeviceRegistry.cpp
@@ -2,6 +2,7 @@
 #include "Log.h"
 #include "fs/devices/ConsoleDevice.h"
 #include "fs/devices/NullDevice.h"
+#include "fs/devices/ZeroDevice.h"
 #include <luna/Vector.h>
 
 struct DeviceDescriptor
@@ -42,6 +43,7 @@ namespace DeviceRegistry
     {
         // Hardcode default devices.
         TRY(register_special_device(DeviceMajorTypes::Memory, 0, NullDevice::create));
+        TRY(register_special_device(DeviceMajorTypes::Memory, 1, ZeroDevice::create));
         TRY(register_special_device(DeviceMajorTypes::Console, 0, ConsoleDevice::create));
 
         return {};
diff --git a/kernel/src/fs/devices/ZeroDevice.cpp b/kernel/src/fs/devices/ZeroDevice.cpp
new file mode 100644
index 00000000..f1a4c151
--- /dev/null
+++ b/kernel/src/fs/devices/ZeroDevice.cpp
@@ -0,0 +1,6 @@
+#include "fs/devices/ZeroDevice.h"
+
+Result<SharedPtr<Device>> ZeroDevice::create()
+{
+    return (SharedPtr<Device>)TRY(make_shared<ZeroDevice>());
+}
diff --git a/kernel/src/fs/devices/ZeroDevice.h b/kernel/src/fs/devices/ZeroDevice.h
new file mode 100644
index 00000000..33da86d8
--- /dev/null
+++ b/kernel/src/fs/devices/ZeroDevice.h
@@ -0,0 +1,28 @@
+#pragma once
+#include "fs/devices/DeviceRegistry.h"
+
+class ZeroDevice : public Device
+{
+  public:
+    // Initializer for DeviceRegistry.
+    static Result<SharedPtr<Device>> create();
+
+    Result<usize> read(u8* buf, usize, usize length) const override
+    {
+        __builtin_memset(buf, 0, length);
+
+        return length;
+    }
+
+    Result<usize> write(const u8*, usize, usize) override
+    {
+        return 0;
+    }
+
+    bool blocking() const override
+    {
+        return false;
+    }
+
+    virtual ~ZeroDevice() = default;
+};