Re: [Qemu-devel] [PATCH 3/3] xenfb: Add "feature-no-abs-rescale" for Windows PV frontend

[Owen Smith]

> -----Original Message-----
> From: Stefano Stabellini [mailto:address@hidden
> Sent: 11 September 2014 02:23
> To: Owen Smith
> Cc: address@hidden; address@hidden; Stefano Stabellini
> Subject: Re: [PATCH 3/3] xenfb: Add "feature-no-abs-rescale" for Windows
> PV frontend
> 
> On Wed, 10 Sep 2014, Owen smith wrote:
> > Windows PV frontend requires absolute mouse values in the range [0,
> > 0x7fff]. Add a feature to not rescale the axes to DisplaySurface size.
> > Also allows Windows PV frontend to connect without a vfb device. Moves
> > the rescaling of axes to a seperate function with additional
> > null-pointer checks.
> >
> > Signed-off-by: Owen smith <address@hidden>
> > ---
> >  hw/display/xenfb.c | 52
> > +++++++++++++++++++++++++++++++++++++---------------
> >  1 file changed, 37 insertions(+), 15 deletions(-)
> >
> > diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c index
> > c4375c8..65c373b 100644
> > --- a/hw/display/xenfb.c
> > +++ b/hw/display/xenfb.c
> > @@ -61,6 +61,7 @@ struct common {
> >  struct XenInput {
> >      struct common c;
> >      int abs_pointer_wanted; /* Whether guest supports absolute
> > pointer */
> > +    int no_abs_rescale;     /* Whether guest wants rescaled abs axes */
> >      int button_state;       /* Last seen pointer button state */
> >      int extended;
> >      QEMUPutKbdEntry *qkbd;
> > @@ -325,6 +326,25 @@ static void xenfb_key_event(void *opaque, int
> scancode)
> >      xenfb_send_key(xenfb, down, scancode2linux[scancode]);  }
> >
> > +static void xenfb_rescale_mouse(struct XenInput *xenfb, int *dx, int
> > +*dy) {
> > +    DisplaySurface *surface;
> > +    int dw, dh;
> > +
> > +    if (xenfb->c.con == NULL) {
> > +        return;
> > +    }
> > +    surface = qemu_console_surface(xenfb->c.con);
> > +    if (surface == NULL) {
> > +        return;
> > +    }
> > +    dw = surface_width(surface);
> > +    dh = surface_height(surface);
> > +
> > +    *dx = *dx * (dw - 1) / 0x7fff;
> > +    *dy = *dy * (dh - 1) / 0x7fff;
> > +}
> > +
> >  /*
> >   * Send a mouse event from the client to the guest OS
> >   *
> > @@ -338,18 +358,16 @@ static void xenfb_mouse_event(void *opaque,
> >                           int dx, int dy, int dz, int button_state)  {
> >      struct XenInput *xenfb = opaque;
> > -    DisplaySurface *surface = qemu_console_surface(xenfb->c.con);
> > -    int dw = surface_width(surface);
> > -    int dh = surface_height(surface);
> >      int i;
> >
> > -    if (xenfb->abs_pointer_wanted)
> > -   xenfb_send_position(xenfb,
> > -                       dx * (dw - 1) / 0x7fff,
> > -                       dy * (dh - 1) / 0x7fff,
> > -                       dz);
> > -    else
> > +    if (xenfb->abs_pointer_wanted) {
> > +        if (!xenfb->no_abs_rescale) {
> > +            xenfb_rescale_mouse(xenfb, &dx, &dy);
> > +        }
> > +        xenfb_send_position(xenfb, dx, dy, dz);
> > +    } else {
> >     xenfb_send_motion(xenfb, dx, dy, dz);
> > +    }
> >
> >      for (i = 0 ; i < 8 ; i++) {
> >     int lastDown = xenfb->button_state & (1 << i); @@ -366,6 +382,7
> @@
> > static void xenfb_mouse_event(void *opaque,  static int
> > input_init(struct XenDevice *xendev)  {
> >      xenstore_write_be_int(xendev, "feature-abs-pointer", 1);
> > +    xenstore_write_be_int(xendev, "feature-no-abs-rescale", 1);
> >      return 0;
> >  }
> >
> > @@ -374,7 +391,17 @@ static int input_initialise(struct XenDevice
> *xendev)
> >      struct XenInput *in = container_of(xendev, struct XenInput, c.xendev);
> >      int rc;
> >
> > -    if (!in->c.con) {
> > +    if (xenstore_read_fe_int(xendev, "request-abs-pointer",
> > +                             &in->abs_pointer_wanted) == -1) {
> > +        in->abs_pointer_wanted = 0;
> > +    }
> > +
> > +    if (xenstore_read_fe_int(xendev, "request-no-abs-rescale",
> > +                             &in->no_abs_rescale) == -1) {
> > +        in->no_abs_rescale = 0;
> > +    }
> 
> I don't think is safe to move checking for "request-abs-pointer" so
> early: what if the guest writes request-abs-pointer after initialise but 
> before
> connect?
> 
> Also it would be nice to document this protocol extension somewhere. I do
> realize that the existing documentation on vfb is somewhat lacking.
> 

I'll change this to read the feature flags during the input_connected for v2. 
I've spotted that neither feature has anything in the xen header, so I'll 
include 
a patch to document this with v2.

> 
> > +    if (!in->c.con && !in->no_abs_rescale) {
> 
> Why this change?
> 

Without an additional check here, the frontend would not connect. in->c.con is
not initialised without a vfb device. Overloading no_abs_rescale here is not 
right,
I'll add an option that the frontend can set to ignore the absence of the 
console.


> 
> >          xen_be_printf(xendev, 1, "ds not set (yet)\n");
> >          return -1;
> >      }
> > @@ -390,11 +417,6 @@ static void input_connected(struct XenDevice
> > *xendev)  {
> >      struct XenInput *in = container_of(xendev, struct XenInput,
> > c.xendev);
> >
> > -    if (xenstore_read_fe_int(xendev, "request-abs-pointer",
> > -                             &in->abs_pointer_wanted) == -1) {
> > -        in->abs_pointer_wanted = 0;
> > -    }
> > -
> >      if (in->qmouse) {
> >          qemu_remove_mouse_event_handler(in->qmouse);
> >      }
> > --
> > 2.1.0
> >