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From: Ian Campbell <ian.campbell@citrix.com>
Date: Mon, 16 Mar 2015 12:20:00 +0000
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Subject: Re: [Qemu-devel] [v2][PATCH 2/2] libxl: introduce gfx_passthru_kind
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To: "Chen, Tiejun" <tiejun.chen@intel.com>
Cc: Ian.Jackson@eu.citrix.com, wei.liu2@citrix.com, qemu-devel@nongnu.org, stefano.stabellini@citrix.com, xen-devel@lists.xen.org

On Mon, 2015-03-16 at 09:07 +0800, Chen, Tiejun wrote:
> On 2015/3/13 18:11, Ian Campbell wrote:
> > On Fri, 2015-03-13 at 09:39 +0800, Chen, Tiejun wrote:
> >>> I don't think you can abort here, since a user can set
> >>> b_info->u.hvm.gfx_passthru_kind to default. You would need to
> >>> return an error.
> >>
> >> Then, looks I should do this,
> >>
> >> LOG(ERROR, "No supported IGD to passthru," " or please force set
> >> gfx_passthru=\"igd\".\n"); return NULL;
> >
> > If I remember the context correctly this is in the autodetect case,
> > so I think shouldn't mention IGD. Something like "Unable to detect
> > graphics passthru kind, please set gfx_passthru_kind. See xl.cfg(5)
> > for more
> 
> s/gfx_passthru_kind/gfx_passthru, right? Because actually we always get
> 'gfx_passthru_kind' from 'gfx_passthru'.

I think you have it backwards.

In the case here gfx_passthru=1 has been set by the user, but
gfx_passthru_kind=DEFAULT. So libxl has tried to autodetect but it has
failed.

So if the user wants to make progress they should set gfx_passthru_kind
to whatever type of passthrough they were trying to do.

Alternatively I suppose you could recommend removing gfx_passthru=1 (or
changing to=0), but given they've set =1 that doesn't seem to be the
most productive suggestion.

Ian.