Kernel/SysFS: Add exposing interface for DisplayConnectors

Under normal conditions (when mounting SysFS in /sys), there will be a
new directory in the /sys/devices directory called "graphics".
For now, under that directory there will be only a sub-directory called
"connectors" which will contain all DisplayConnectors' details, each in
its own sub-directory too, distinguished in naming with its minor
number.

Therefore, /sys/devices/graphics/connectors/MINOR_NUMBER/ will contain:
- General device attributes such as mutable_mode_setting_capable,
  double_buffering_capable, flush_support, partial_flush_support and
  refresh_rate_support. These values are exposed in the ioctl interface
  of the DisplayConnector class too, but these can be useful later on
  for command line utilities that want/need to expose these basic
  settings.
- The EDID blob, simply named "edid". This will help userspace to fetch
  the edid without the need of using the ioctl interface later on.

Kernel/FileSystem/SysFS/Subsystems/Devices/Graphics/DisplayConnector/DeviceAttribute.cpp

@@ -0,0 +1,87 @@
+/*
+ * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Bus/PCI/API.h>
+#include <Kernel/Bus/PCI/Access.h>
+#include <Kernel/Debug.h>
+#include <Kernel/FileSystem/SysFS/Subsystems/Devices/Graphics/DisplayConnector/DeviceAttribute.h>
+#include <Kernel/Sections.h>
+
+namespace Kernel {
+
+StringView DisplayConnectorAttributeSysFSComponent::name() const
+{
+    switch (m_type) {
+    case Type::MutableModeSettingCapable:
+        return "mutable_mode_setting_capable"sv;
+    case Type::DoubleFrameBufferingCapable:
+        return "double_framebuffering_capable"sv;
+    case Type::FlushSupport:
+        return "flush_support"sv;
+    case Type::PartialFlushSupport:
+        return "partial_flush_support"sv;
+    case Type::RefreshRateSupport:
+        return "refresh_rate_support"sv;
+    case Type::EDID:
+        return "edid"sv;
+    default:
+        VERIFY_NOT_REACHED();
+    }
+}
+
+NonnullRefPtr<DisplayConnectorAttributeSysFSComponent> DisplayConnectorAttributeSysFSComponent::must_create(DisplayConnectorSysFSDirectory const& device_directory, Type type)
+{
+    return adopt_ref(*new (nothrow) DisplayConnectorAttributeSysFSComponent(device_directory, type));
+}
+
+DisplayConnectorAttributeSysFSComponent::DisplayConnectorAttributeSysFSComponent(DisplayConnectorSysFSDirectory const& device_directory, Type type)
+    : SysFSComponent()
+    , m_device(device_directory.device({}))
+    , m_type(type)
+{
+}
+
+ErrorOr<size_t> DisplayConnectorAttributeSysFSComponent::read_bytes(off_t offset, size_t count, UserOrKernelBuffer& buffer, OpenFileDescription*) const
+{
+    auto blob = TRY(try_to_generate_buffer());
+
+    if ((size_t)offset >= blob->size())
+        return 0;
+
+    ssize_t nread = min(static_cast<off_t>(blob->size() - offset), static_cast<off_t>(count));
+    TRY(buffer.write(blob->data() + offset, nread));
+    return nread;
+}
+
+ErrorOr<NonnullOwnPtr<KBuffer>> DisplayConnectorAttributeSysFSComponent::try_to_generate_buffer() const
+{
+    OwnPtr<KString> value;
+    switch (m_type) {
+    case Type::MutableModeSettingCapable:
+        value = TRY(KString::formatted("{:d}", m_device->mutable_mode_setting_capable()));
+        break;
+    case Type::DoubleFrameBufferingCapable:
+        value = TRY(KString::formatted("{:d}", m_device->double_framebuffering_capable()));
+        break;
+    case Type::FlushSupport:
+        value = TRY(KString::formatted("{:d}", m_device->flush_support()));
+        break;
+    case Type::PartialFlushSupport:
+        value = TRY(KString::formatted("{:d}", m_device->partial_flush_support()));
+        break;
+    case Type::RefreshRateSupport:
+        value = TRY(KString::formatted("{:d}", m_device->refresh_rate_support()));
+        break;
+    case Type::EDID: {
+        auto edid_buffer = TRY(m_device->get_edid());
+        return KBuffer::try_create_with_bytes("SysFS DisplayConnectorAttributeSysFSComponent EDID buffer"sv, edid_buffer.bytes());
+    }
+    default:
+        VERIFY_NOT_REACHED();
+    }
+    return KBuffer::try_create_with_bytes("SysFS DisplayConnectorAttributeSysFSComponent buffer"sv, value->view().bytes());
+}
+}