Re: [PATCH v3] xen,input: add xen-kbdfront module parameter for setting resolution

[Juergen Gross <jgross@suse.com>]

On 12/04/17 20:26, Juergen Gross wrote:
> On 12/04/17 18:24, Dmitry Torokhov wrote:
>> On Wed, Apr 12, 2017 at 06:04:30PM +0200, Juergen Gross wrote:
>>> On 12/04/17 17:16, Dmitry Torokhov wrote:
>>>> Hi Juergen,
>>>>
>>>> On Tue, Apr 11, 2017 at 02:30:37PM +0200, Juergen Gross wrote:
>>>>> Add a parameter for setting the resolution of xen-kbdfront in order to
>>>>> be able to cope with a (virtual) frame buffer of arbitrary resolution.
>>>>>
>>>>> While at it remove the pointless second reading of parameters from
>>>>> Xenstore in the device connection phase: all parameters are available
>>>>> during device probing already and that is where they should be read.
>>>>>
>>>>> Signed-off-by: Juergen Gross <jgross@suse.com>
>>>>> ---
>>>>> V3: - merged the two patches
>>>>>     - read Xenstore parameters during probing of the device only
>>>>
>>>> I guess 2 module parameters are not big deal, but could you tell me why
>>>> you can't always have them specified in Xenstore?
>>>
>>> This will depend on Xen version then. I'd prefer to have a way to
>>> specify the resolution in case a new kernel is running as a guest
>>> of an old Xen version.
>>
>> Who would be seeting up the kernel parameters in this case? User
>> manually in guest bootloader config?
> 
> Either the guest administrator through guest boot loader or the Xen
> administrator in the guest config file.
> 
> In the case where the problem has been reported (automatic tests of
> graphical tools) this would be in the guest config file.
> 
>>>> Also, I still think you are going in the wrong direction here. Can your
>>>> framebuffer size change after booting the guest? If it can, you have to
>>>> reconcile the new size and the coordinates reported by the pointing
>>>> device, and I think guest should be doing it. If you look, for example,
>>>> at vmmouse driver, they do not try to match coordinates it reports to
>>>> the screen.
>>>
>>> I'm no expert in input driver interface. Can you tell me how the mouse
>>> pointer is positioned in case of the vmmouse driver? Are the real limits
>>> used just the minimum of pointing device and screen size limits? So
>>> specifying a size of 0xffff * 0xffff like the vmmouse driver does will
>>> work with any screen size being smaller than that?
>>
>> I think 0xffff is just the limits for coordinates reported through this
>> interface; the expectation is that guest window size is not larger than
>> that. I do not recall if the backend reports real screen pointer
>> position, of offset from the (0,0) of guest's window, Thomas might tel
>> you. IIRC code in vmware tools package (that runs in guest) gets
>> notifications about screen changes and reacts accordingly.
> 
> So a small test revealed that only with a resolution matching that of
> the virtual console the virtual mouse pointer will be at the same
> position as the real mouse pointer. Working with different resolutions
> will require some sort of scaling available only if _both_ resolutions
> are known. And as you don't like the input driver knowing about the
> console I'm limited to fixed values via module parameters (taking into
> account the embedded scenario without udev).

Dmitry, are you okay with this now?

I'd _really_ like to get this in - I'm trying for 3 months now.


Juergen