Re: [Xen-devel] [PATCH v2] libxl: Implement basic video device selection

[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

On 04.04.2014 12:31, Stefan Bader wrote:
> On 04.04.2014 11:48, Ian Campbell wrote:
>> On Fri, 2014-04-04 at 11:36 +0200, Stefan Bader wrote:
>>> +    /*
>>> +     * Take the first defined video device (graphics card) to display
>>> +     * on the first graphics device (display).
>>> +     * Right now only type and vram info is used and anything beside
>>> +     * type xen and vga is mapped to cirrus.
>>> +     */
>>> +    if (def->nvideos) {
>>> +        unsigned int min_vram = 8 * 1024;
>>> +
>>> +        switch (def->videos[0]->type) {
>>> +            case VIR_DOMAIN_VIDEO_TYPE_VGA:
>>> +            case VIR_DOMAIN_VIDEO_TYPE_XEN:
>>> +                b_info->u.hvm.vga.kind = LIBXL_VGA_INTERFACE_TYPE_STD;
>>> +                /*
>>> +                 * Libxl enforces a minimal VRAM size of 8M when using
>>> +                 * LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL or
>>> +                 * 16M for LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN.
>>> +                 * Avoid build failures and go with the minimum if less
>>> +                 * is specified.
>>
>> Build failures? Do you mean "domain build" rather than "libvirt build"?
>>
>> I'm not sure about this fixing up the GIGO from the user side, but
>> that's a libvirt policy decision I suppose? If it were me I would just
>> let libxl provide the error and expect people to fix their domain config
>> rather than silently giving them something other than what they asked
>> for. What if increasing the VRAM causes a cascading failure due e.g. to
>> lack of memory? That's going to be tricky to debug I think!
> 
> In the end its a start a domain with such a config. Which seems to be what I

*sigh* That wasn't much better English. Yes, I meant a domain build or a failure
to start a domain...

> would end up with in my testing with an admittedly older version of 
> virt-manager
> connecting to a libvirtd running an initial version of this patch without 
> that part.
> The error seen on the front-end was something along the lines of "failed to 
> get
> enough memory to start the guest" (the libxl log on the other side had the
> better error message). And the gui always reduces the memory below the minimum
> for both the options (VGA and "Xen").
> That is the reason I went for "meh, go for the minimum anyways".
> 
> And btw, it is already confusing enough as with cirrus, I get a 9M by default
> which is passed on to qemu on the command line and then ignored by it and one
> gets 32M in any way...
> 
> -Stefan
> 
>>
>>
> 
> 
> 
> 
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