Re: [Qemu-devel] How does QEMU kernel receive any input events from host OS

[David Turner <digit@google.com>]

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I think you are confused about what clients/servers are in VNC.

On Fri, Sep 4, 2009 at 2:58 AM, Amey Moghe <amey1288@gmail.com> wrote:

> Hello,
>
> Thanks for the details.I understood how any input event is processed.
> But if I pressed a key in guest OS environment


You never "press a key in a guest OS environment", the guest doesn't have
access
to a real keyboard.


> then how does client
> i.e. guest OS ( with reference to VNC server )   come to know that it
> has to send key_event to VNC server?


The guest OS is not a VNC client at all. The qemu program implements a VNC
server,
that can be accessed from VNC clients running on the host, or even from
different machines,
but that is totally oblivious to the guest OS.

A VNC Client is a standalone application, which generally converts user
input into RFB
protocol messages, which are then sent to the VNC server (running in QEMU),
which translates
them into emulated hardware i/o. The guest OS doesn't know if the user is
really using a
VNC client, the qemu SDL frontend, or anything else, it just believes there
was some hardware
activity.


> Does client through qemu,
> recognise it either from X server running on host OS (e.g. linux ) or
> directly from host OS's kernel ?
>
>
I don't really understand this question, but if you want to know how a
typical VNC client
translates a real user event into a VNC message sent to the server, you
should read the
RFB protocol specification. Try
http://en.wikipedia.org/wiki/RFB_protocolfor a start.


>
> Thanks,
> Amey.
>
> On 9/3/09, David Turner <digit@google.com> wrote:
> > 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?
> >
>
>
>

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