Re: [Qemu-devel] [PULL 10/14] ui: fix VNC client throttling when audio capture is active

[Paolo Bonzini]

On 18/01/2018 15:50, Peter Maydell wrote:
> On 18 January 2018 at 14:46, Paolo Bonzini <address@hidden> wrote:
>> On 18/01/2018 15:12, Daniel P. Berrange wrote:
>>>> In addition to that, do we support a >= 2 GiB framebuffer at all? (Even
>>>> with unsigned ints, Coverity would rightly complain about a truncated
>>>> 32-bit multiplication being assigned to a 64-bit value).
>>> client_width/client_height are values that are initialized from the
>>> graphics card frontend config, and thus limited by amount of video
>>> RAM QEMU allows.   bytes_per_pixel is limited to 8/16/32.
>>>
>>> So I think we're safe from 2GB overflow in any normal case.
>>>
>>> That said, VGA RAM size is configurable, so I'm curious what would happen
>>> if someone configured an insanely large VGA RAM and asked for a big frame
>>> buffer in guest.
>>>
>>> VNC is protocol limited to uint16 for width/height size, and so is X11
>>> so I imagine some exploding behavour would follow :-)
>>
>> Indeed, and even 2^16 x 2^16 * 32bpp is already 34 bits.  So perhaps we
>> should limit VNC to 16384 pixels on each axis (maximum frame buffer size
>> 1 GiB).
> 
> Google says you can already get graphics cards that can do 15360x8640,
> which is really quite close to that 16384 limit...

Then we can do 32767 * 16384 * 4, but I'm a bit afraid of off-by-ones.

Paolo