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

[Ilya Maximets]

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.