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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Feb 03, 2015 at 09:01:53AM +0800, Chen, Tiejun wrote:
> 
> On 2015/2/2 20:19, Wei Liu wrote:
> >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.
> 
> Understood.
> 
> >
> >>  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.
> 
> Yeah.
> 
> >
> >>              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?
> 
> Right. So what about this?
> 
>     libxl: add one machine property to support IGD GFX passthrough
> 
>     When we're working to support IGD GFX passthrough with qemu
>     upstream, we'd like to introduce a machine option,
>     "-machine xxx,igd-passthru=on", to enable/disable that feature.
>     And we also remove that old option, "-gfx_passthru", just from
>     the case of LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN since actually
>     no any qemu stream version really need or use that.
> 
>     Signed-off-by: Tiejun Chen <tiejun.chen@xxxxxxxxx>
> 

Yes. I think a patch like this reflects the reality.

It would be nice, as Ian J suggested, to state which version of QEMU
upstream introduces that new option in commit message.

> diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
> index c2b0487..b888f19 100644
> --- a/tools/libxl/libxl_dm.c
> +++ b/tools/libxl/libxl_dm.c
> @@ -701,9 +701,6 @@ static char **
> libxl__build_device_model_args_new(libxl__gc *gc,
>              flexarray_append(dm_args, "-net");
>              flexarray_append(dm_args, "none");
>          }
> -        if (libxl_defbool_val(b_info->u.hvm.gfx_passthru)) {
> -            flexarray_append(dm_args, "-gfx_passthru");
> -        }
>      } else {
>          if (!sdl && !vnc) {
>              flexarray_append(dm_args, "-nographic");
> @@ -748,6 +745,11 @@ 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);
> +        }
> +

Please use GCSPRINTF macro.

Wei.

>          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]);
> 

> Thanks
> Tiejun
> 
> >
> >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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