Re: [Qemu-devel] [PATCH v2 1/4] hostmem-memfd: disable for systems wihtout sealing support

[Ilya Maximets]

On 16.01.2019 18:48, Daniel P. Berrangé wrote:
> On Wed, Jan 16, 2019 at 06:46:39PM +0300, Ilya Maximets wrote:
>>
>>
>> On 16.01.2019 18:30, Eduardo Habkost wrote:
>>> On Wed, Dec 12, 2018 at 07:49:36AM +0100, Gerd Hoffmann wrote:
>>>> On Tue, Dec 11, 2018 at 02:09:11PM +0300, Ilya Maximets wrote:
>>>>> On 11.12.2018 13:53, Daniel P. Berrangé wrote:
>>>>>>>
>>>>>>> Let's restrict memfd backend to systems with sealing support.
>>>>>>
>>>>>> I don't think we need todo that - sealing is optional in the QEMU code,
>>>>>> we simply have it set to the wrong default when sealing is not available.
>>>>>
>>>>> That was literally what I've fixed in v1:
>>>>>     https://lists.nongnu.org/archive/html/qemu-devel/2018-11/msg05483.html
>>>>>
>>>>> but 2 people suggested me to disable memfd entirely for this case.
>>>>> Do you think I need to get patch from v1 back ?
>>>>>
>>>>> Gerd, Marc-André, what do you think?
>>>>
>>>> I still think it makes sense to require sealing support.  Sealing is
>>>> very useful, and there are only a few kernel versions with memfd but
>>>> without sealing.  So finding such kernels in the wild will become more
>>>> rare over time.  I wouldn't worry too much about them.
>>>
>>> -object memory-backend-memfd,id=mem,size=2M,seal=off still
>>> works on those systems, doesn't it?  What's the rationale for
>>> breaking a working configuration without following the
>>> deprecation policy?
>>>
>>
>> See the commit message.
>> '.seal' property is not registered if sealing is not supported.
>> So, there is no way to disable sealing on the system that does not support 
>> it.
> 
> As I pointed out a few lines up, this is simply because QEMU has a bug
> setting seal=true as the built-in default value even when it isn't
> supported. 

So, do you think I need to return to the solution from my v1:
  https://lists.nongnu.org/archive/html/qemu-devel/2018-11/msg05483.html

?