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

[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

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
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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