This fixes a weird bug that when sometimes a user tried to switch to
console mode, the screen was frozen on graphics mode. After a hour of
debugging this, it became apparent that the problem was that we left the
y offset of the bochs graphics device in an invalid state, so it was not
zero because the WindowServer changed it, and the framebuffer console
code is not aware of horizontal and vertical offsets of the framebuffer
screen, leading to the problem that the framebuffer console updates the
first framebuffer (y offset = 0), but hardware was indicated to show the
second framebuffer (y offset = first framebuffer height).
Therefore, when doing a switch between these modes, always set the y
offset to be zero.
The DisplayConnector class is meant to replace the FramebufferDevice
class. The advantage of this class over the FramebufferDevice class is:
1. It removes the mmap interface entirely. This interface is unsafe, as
multiple processes could try to use it, and when switching to and from
text console mode, there's no "good" way to revoke a memory mapping from
this interface, let alone when there are multiple processes that call
this interface. Therefore, in the DisplayConnector class there's no
implementation for this method at all.
2. The class uses a new real-world structure called ModeSetting, which
takes into account the fact that real hardware requires more than width,
height and pitch settings to mode-set the display resolution.
3. The class assumes all instances should supply some sort of EDID,
so it facilitates such mechanism to do so. Even if a given driver does
not know what is the actual EDID, it will ask to create default-generic
EDID blob.
3. This class shifts the responsibilies of switching between console
mode and graphical mode from a GraphicsAdapter to the DisplayConnector
class, so when doing the switch, the GraphicsManagement code actually
asks each DisplayConnector object to do the switch and doesn't rely on
the GraphicsAdapter objects at all.
