Kernel+Userland: Provide bytes count for a DisplayConnector framebuffer

This value will be used later on by WindowServer to reject resolutions
that will request a mapping that will overflow the hardware framebuffer
max length.

Kernel/Graphics/DisplayConnector.cpp

@@ -301,12 +301,14 @@ ErrorOr<void> DisplayConnector::ioctl(OpenFileDescription&, unsigned request, Us
         return {};
     }
     case GRAPHICS_IOCTL_GET_PROPERTIES: {
+        VERIFY(m_shared_framebuffer_vmobject);
         auto user_properties = static_ptr_cast<GraphicsConnectorProperties*>(arg);
         GraphicsConnectorProperties properties {};
         properties.flushing_support = flush_support();
         properties.doublebuffer_support = double_framebuffering_capable();
         properties.partial_flushing_support = partial_flush_support();
         properties.refresh_rate_support = refresh_rate_support();
+        properties.max_buffer_bytes = m_shared_framebuffer_vmobject->size();
 
         return copy_to_user(user_properties, &properties);
     }

Userland/Libraries/LibC/sys/ioctl_numbers.h

@@ -24,6 +24,7 @@ struct GraphicsConnectorProperties {
     unsigned char flushing_support;
     unsigned char partial_flushing_support;
     unsigned char refresh_rate_support;
+    unsigned max_buffer_bytes;
 };
 
 struct GraphicsHeadModeSetting {

Userland/Services/WindowServer/HardwareScreenBackend.cpp

@@ -33,6 +33,7 @@ ErrorOr<void> HardwareScreenBackend::open()
     m_can_device_flush_buffers = (properties.partial_flushing_support != 0);
     m_can_device_flush_entire_framebuffer = (properties.flushing_support != 0);
     m_can_set_head_buffer = (properties.doublebuffer_support != 0);
+    m_max_size_in_bytes = properties.max_buffer_bytes;
     return {};
 }
 

Userland/Services/WindowServer/ScreenBackend.h

@@ -43,6 +43,7 @@ public:
 
     Gfx::ARGB32* m_framebuffer { nullptr };
     size_t m_size_in_bytes { 0 };
+    size_t m_max_size_in_bytes { 0 };
     size_t m_back_buffer_offset { 0 };
 
     int m_pitch { 0 };