Re: [Xen-devel] [PATCH] kbdif.h: Introduce feature-vkbd-standalone

[Owen Smith <owen.smith@xxxxxxxxxx>]

Hi Oleksandr,

 

The reason I’m proposing the additional feature flag is to differentiate between

older, broken, backends that will not connect without the vfb device

(qemu-upstream’s implementation in hw/display/xenfb.c) and fixed backends

(like patches I’ve posted to fix the qemu backend). Without a differentiator,

a frontend I’ve developed will get stuck waiting for the backend to connect,

and under Windows this effectively hangs the system.

The Qemu backend should be fixed to make the vkbd and vfb independent

devices. This proposal will help detect an incompatible backend and avoid a

VM hang.

 

(frontend WIP: http://xenbits.xen.org/gitweb/?p=pvdrivers/win/xenvkbd.git;a=tree)

Owen

 

From: Oleksandr Andrushchenko
Sent: 12 June 2017 08:07
To: Owen Smith; xen-devel@xxxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] [PATCH] kbdif.h: Introduce feature-vkbd-standalone

 

Hi, Owen!

On 06/08/2017 04:09 PM, Owen Smith wrote:
> Backends set "feature-vkbd-standalone" to 1 if they can connect
> without waiting for the PV framebuffer. If this value is missing
> or not 1, then a backend will wait for the PV framebuffer before
> connecting, potentially causing the frontend to wait indefinitely.
This means that by the new option we *fix an existing
backend* and its particular behavior. What is more,
we introduce knowledge of virtual fb into generic virtual
kbd/ptr protocol which seems to be not correct (IMO).
For the reasons above, I would recommend fixing the
corresponding backend instead, for example by configuring
it appropriately wrt use-case you have.
> Frontends set "request-vkbd-standalone" to 1 to request that the
> backend does not wait for the PV framebuffer. Frontends that
> require a standalone vkbd device should not attempt to connect
> unless the backend advertises "feature-vkbd-standalone", and
> should set "request-vkbd-standalone".
Again, this looks very use-case specific
> Backends that are standalone (i.e. do not have an associated PV
> framebuffer) do not rescale absolute mouse or touch coordinates
> to a the size of the (non-existant) PV framebuffer, and use the
> range of [0, 0x7fff] for absolute values.
>
> Signed-off-by: Owen Smith <owen.smith@xxxxxxxxxx>
> ---
>   xen/include/public/io/kbdif.h | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
>
> diff --git a/xen/include/public/io/kbdif.h b/xen/include/public/io/kbdif.h
> index dcbd71a..ca09080 100644
> --- a/xen/include/public/io/kbdif.h
> +++ b/xen/include/public/io/kbdif.h
> @@ -63,6 +63,12 @@
>    *      Backends, which support reporting of multi-touch events
>    *      should set this to 1.
>    *
> + * feature-vkbd-standalone
> + *      Values:         <uint>
> + *
> + *      Backends, which support a standalone vkbd, without requiring a vfb
> + *      device, should set this to 1.
> + *
>    *------------------------- Pointer Device Parameters ------------------------
>    *
>    * width
> @@ -98,6 +104,13 @@
>    *
>    *      Request backend to report multi-touch events.
>    *
> + * request-vkbd-standalone
> + *      Values:         <uint>
> + *
> + *      Request backend to connect vkbd device without waiting for the
> + *      vfb device. Any absolute coordinates will NOT be scaled to
> + *      screen size, and will remain in the range [0, 0x7fff]
> + *
>    *----------------------- Request Transport Parameters -----------------------
>    *
>    * event-channel
> @@ -165,8 +178,10 @@
>  
>   #define XENKBD_FIELD_FEAT_ABS_POINTER  "feature-abs-pointer"
>   #define XENKBD_FIELD_FEAT_MTOUCH       "feature-multi-touch"
> +#define XENKBD_FIELD_FEAT_STANDALONE   "feature-vkbd-standalone"
>   #define XENKBD_FIELD_REQ_ABS_POINTER   "request-abs-pointer"
>   #define XENKBD_FIELD_REQ_MTOUCH        "request-multi-touch"
> +#define XENKBD_FIELD_REQ_STANDALONE    "request-vkbd-standalone"
>   #define XENKBD_FIELD_RING_GREF         "page-gref"
>   #define XENKBD_FIELD_EVT_CHANNEL       "event-channel"
>   #define XENKBD_FIELD_WIDTH             "width"
Thank you,
Oleksandr

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