Re: [Xen-devel] [v2][PATCH] libxl: add one machine property to support IGD GFX passthrough

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Feb 02, 2015 at 09:17:23AM +0800, Tiejun Chen wrote:
> When we're working to support IGD GFX passthrough with qemu
> upstream, instead of "-gfx_passthru" we'd like to make that
> a machine option, "-machine xxx,-igd-passthru=on". This need
> to bring a change on tool side.
> 
> Signed-off-by: Tiejun Chen <tiejun.chen@xxxxxxxxx>
> ---
> v2:
>  
> * Based on some discussions with Wei we'd like to keep both old
>   option, -gfx_passthru, and new machine property option,
>   "-machine xxx,-igd-passthru=on" at the same time but deprecate
>   the old one. Then finally we remove the old one at that point
>   that to give downstream (in this case, Xen) time to cope with the
>   change.
> 

My suggestion has one premise -- if upstream QEMU has already released
that -gfx_passthru option. If there is no "old one" (in upstream QEMU)
at all, then there is nothing to keep and deprecate.

>  tools/libxl/libxl_dm.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
> index c2b0487..8405f0b 100644
> --- a/tools/libxl/libxl_dm.c
> +++ b/tools/libxl/libxl_dm.c
> @@ -701,6 +701,11 @@ static char ** 
> libxl__build_device_model_args_new(libxl__gc *gc,

Note this function is upstream QEMU specfic.

>              flexarray_append(dm_args, "-net");
>              flexarray_append(dm_args, "none");
>          }
> +        /*
> +         * Although we already introduce 'igd-passthru', but we'd like
> +         * to remove this until we give downstream time to cope with
> +         * the change.
> +         */
>          if (libxl_defbool_val(b_info->u.hvm.gfx_passthru)) {
>              flexarray_append(dm_args, "-gfx_passthru");
>          }

The comment contradicts what I know (or what I think I know). In our
last email exchange you said there was no "-gfx_passthru" in any version
of upstream QEMU.

So, shouldn't you just remove this `if' statement?

Wei.

> @@ -748,6 +753,11 @@ static char ** 
> libxl__build_device_model_args_new(libxl__gc *gc,
>                                              machinearg, max_ram_below_4g);
>              }
>          }
> +
> +        if (libxl_defbool_val(b_info->u.hvm.gfx_passthru)) {
> +            machinearg = libxl__sprintf(gc, "%s,igd-passthru=on", 
> machinearg);
> +        }
> +
>          flexarray_append(dm_args, machinearg);
>          for (i = 0; b_info->extra_hvm && b_info->extra_hvm[i] != NULL; i++)
>              flexarray_append(dm_args, b_info->extra_hvm[i]);
> -- 
> 1.9.1

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