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

[Ian Campbell <Ian.Campbell@citrix.com>]

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!