Kernel: Implement generic VGA device using multiboot info

This implements a very basic VGA device using the information provided
to us by the bootloader in the multiboot header. This allows Serenity to
boot to the desktop on basically any halfway modern system.

Kernel/Devices/MBVGADevice.cpp

@@ -0,0 +1,102 @@
+#include <Kernel/Devices/MBVGADevice.h>
+#include <Kernel/Process.h>
+#include <Kernel/VM/AnonymousVMObject.h>
+#include <Kernel/VM/MemoryManager.h>
+#include <LibC/errno_numbers.h>
+#include <LibC/sys/ioctl_numbers.h>
+
+static MBVGADevice* s_the;
+
+MBVGADevice& MBVGADevice::the()
+{
+    return *s_the;
+}
+
+MBVGADevice::MBVGADevice(PhysicalAddress addr, int pitch, int width, int height)
+    : BlockDevice(29, 0)
+    , m_framebuffer_address(addr)
+    , m_framebuffer_pitch(pitch)
+    , m_framebuffer_width(width)
+    , m_framebuffer_height(height)
+{
+    s_the = this;
+}
+
+KResultOr<Region*> MBVGADevice::mmap(Process& process, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t size, int prot)
+{
+    ASSERT(offset == 0);
+    ASSERT(size == framebuffer_size_in_bytes());
+    auto vmo = AnonymousVMObject::create_for_physical_range(m_framebuffer_address, framebuffer_size_in_bytes());
+    auto* region = process.allocate_region_with_vmo(
+        preferred_vaddr,
+        framebuffer_size_in_bytes(),
+        move(vmo),
+        0,
+        "MBVGA Framebuffer",
+        prot);
+    kprintf("MBVGA: %s(%u) created Region{%p} with size %u for framebuffer P%x with vaddr L%x\n",
+        process.name().characters(), process.pid(),
+        region, region->size(), m_framebuffer_address.as_ptr(), region->vaddr().get());
+    ASSERT(region);
+    return region;
+}
+
+int MBVGADevice::ioctl(FileDescription&, unsigned request, unsigned arg)
+{
+    switch (request) {
+    case FB_IOCTL_GET_SIZE_IN_BYTES: {
+        auto* out = (size_t*)arg;
+        if (!current->process().validate_write_typed(out))
+            return -EFAULT;
+        *out = framebuffer_size_in_bytes();
+        return 0;
+    }
+    case FB_IOCTL_GET_BUFFER: {
+        auto* index = (int*)arg;
+        if (!current->process().validate_write_typed(index))
+            return -EFAULT;
+        *index = 0;
+        return 0;
+    }
+    case FB_IOCTL_GET_RESOLUTION: {
+        auto* resolution = (FBResolution*)arg;
+        if (!current->process().validate_write_typed(resolution))
+            return -EFAULT;
+        resolution->pitch = m_framebuffer_pitch;
+        resolution->width = m_framebuffer_width;
+        resolution->height = m_framebuffer_height;
+        return 0;
+    }
+    case FB_IOCTL_SET_RESOLUTION: {
+        auto* resolution = (FBResolution*)arg;
+        if (!current->process().validate_read_typed(resolution) || !current->process().validate_write_typed(resolution))
+            return -EFAULT;
+        resolution->pitch = m_framebuffer_pitch;
+        resolution->width = m_framebuffer_width;
+        resolution->height = m_framebuffer_height;
+        return 0;
+    }
+    default:
+        return -EINVAL;
+    };
+}
+
+bool MBVGADevice::can_read(FileDescription&) const
+{
+    ASSERT_NOT_REACHED();
+}
+
+bool MBVGADevice::can_write(FileDescription&) const
+{
+    ASSERT_NOT_REACHED();
+}
+
+ssize_t MBVGADevice::read(FileDescription&, u8*, ssize_t)
+{
+    ASSERT_NOT_REACHED();
+}
+
+ssize_t MBVGADevice::write(FileDescription&, const u8*, ssize_t)
+{
+    ASSERT_NOT_REACHED();
+}