QEMU Barrier Client
Generally, mouse and keyboard are grabbed through the QEMU video interface emulation.
But when we want to use a video graphic adapter via a PCI passthrough there is no way to provide the keyboard and mouse inputs to the VM except by plugging a second set of mouse and keyboard to the host or by installing a KVM software in the guest OS.
The QEMU Barrier client avoids this by implementing directly the Barrier protocol into QEMU.
Barrier is a KVM (Keyboard-Video-Mouse) software forked from Symless’s synergy 1.9 codebase.
This protocol is enabled by adding an input-barrier object to QEMU.
input-barrier,id=<object-id>,name=<guest display name> [,server=<barrier server address>][,port=<barrier server port>] [,x-origin=<x-origin>][,y-origin=<y-origin>] [,width=<width>][,height=<height>]
The object can be added on the QEMU command line, for instance with:
where VM-1 is the name the display configured in the Barrier server on the host providing the mouse and the keyboard events.
<barrier server address> is
<y-origin> are set to
If the Barrier server is stopped QEMU needs to be reconnected manually, by removing and re-adding the input-barrier object, for instance with the help of the HMP monitor:
(qemu) object_del barrier0 (qemu) object_add input-barrier,id=barrier0,name=VM-1