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

["Chen, Tiejun" <tiejun.chen@intel.com>]

On 2015/2/3 18:19, Wei Liu wrote:
> 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@intel.com>
>>>> ---
>>>> 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@intel.com>
>>
>
> 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.

I have to provide this exact info after those qemu stuffs are merged, 
but now at lease you guys agree this option named as 'igd-passthrough', 
its enough to first continue working all qemu patches out. Once its 
finished I will go back.

>
>> 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.
>

Sure.

@@ -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 = GCSPRINTF("%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]);


Thanks
Tiejun