xorg.conf how to set to mirror mode

[Jason Wu]

I would like to have mirror display across both monitor ,
with A monitor connect to intel display card,
and B monitor connect to a usb to vga dongle.

on KDE or GNOME i can have both screen working in extend mode,
but i want both screen have exactly the same output, which is mirror mode
how to do the setup? or should i add any code in my xf86-displaylink driver?

here's my xorg.conf
##########################################
Section "Device"
        Identifier      "DisplayLinkDevice"
        driver          "displaylink"
        Option  "fbdev" "/dev/fb1"
EndSection

Section "Monitor"
        Identifier      "DisplayLinkMonitor"
EndSection

Section "Screen"
        Identifier      "DisplayLinkScreen"
    Device          "DisplayLinkDevice"
        Monitor         "DisplayLinkMonitor"
    SubSection  "Display"
                Modes   "1024x768"
        EndSubSection
EndSection

############### Card1 Intel ##################
Section "Device"
    Identifier  "Card1"
Driver      "intel"
BusID       "PCI:0:2:0"
EndSection

Section "Monitor"
Identifier   "Monitor1"
EndSection

Section "Screen"
    Identifier "Screen1"
Device     "Card1"
Monitor    "Monitor1"
EndSection

############### Server Layout ###############
Section "ServerLayout"
Identifier     "X.org Configured"
Screen         0 "DisplayLinkScreen" 0 0
Screen         1 "Screen1" RightOf "DisplayLinkScreen"
#Screen 0 "Screen1" 0 0
#Screen 1 "DisplayLinkScreen" Leftof "Screen1"
       Option         "Xinerama" "true"
EndSection
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