the QEMU frontend (e.g. the VNC server or the SDL window) is in charge of
translating user events
into emulated hardware ones. Most generally, this will mean emulating a
keyboard or mouse IRQ
and the associated i/o protocol. Exact details depend on which hardware you
want to emulate.

For example, when emulating a PC with PS/2 keyboard and mouse, the code in
hw/ps2.c will be used.

Here's a concrete example:

   - The VNC server receives packets from the client (see
   protocol_client_msg in vnc.c).
   Some of them correspond to keyboard events (processed in key_event() in
   the same file),
   which end up calling kbd_put_keycode() after translating the VNC
   keycode/state into
   a different key scancode.


   - kbd_put_keycode() is defined in vl.c and calls the hardware-specific
   keycode translator.


   - For PC emulation, this happens to be ps2_put_keycode() defined in
   hw/ps2.c, and
   registered at startup by ps2_kbd_init() in the same file. It probably is
   a different function
   for different emulated hardware.


   - The implementation of ps2_put_keycode() will end up enqueue-ing a
   keycode into
   a queue then raising an IRQ.

   - The guest kernel responds to the IRQ by running its keyboard driver
   code, the latter
   will try to read data from the PS/2 queue


The SDL front-end receives user events differently, but still ends up
calling kbd_put_keycode().
Same thing happens for mouse events, and about anything that needs to
emulate hardware
(e.g. serial/usb/bluetooth/etc...) but implementations and specifics may
differ.

Hope this helps

On Wed, Sep 2, 2009 at 5:55 AM, Amey Moghe <amey1288@gmail.com> wrote:

> Hello all,
>
> I am new to QEMU.While reading about qemu , I came across one statement:
> "QEMU does not depend on the presence of graphical output methods on the
> host system. Instead, it allows one to access the screen of the guest OS via
> VNC. It can also use an emulated serial line, without any screen, with
> applicable operating systems." on following link :
>
> http://en.wikipedia.org/wiki/QEMU
>
> So please can anybodys tell me how does qemu use VNC server for receiving
> events and if yes then how does it receive events from host OS? Or is there
> any other way with which QEMU receives input events from host OS?