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

[Ilya Maximets <i.maximets@samsung.com>]

On 11.12.2018 13:53, Daniel P. Berrangé wrote:
> On Tue, Nov 27, 2018 at 04:50:27PM +0300, Ilya Maximets wrote:
>> If seals are not supported, memfd_create() will fail.
>> Furthermore, there is no way to disable it in this case because
>> '.seal' property is not registered.
> 
> Isn't the real problem here that memfd_backend_instance_init() has
> unconditionally set  "m->seal = true"
> 
> Surely, if we don't register the '.seal' property, we should default
> that flag to false.
> 
>>
>> This issue leads to vhost-user-test failures on RHEL 7.2:
>>
>>   qemu-system-x86_64: -object memory-backend-memfd,id=mem,size=2M,: \
>>                       failed to create memfd: Invalid argument
>>
>> and actually breaks the feature on such systems.
>>
>> 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?

> 
>> Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
> 
> 
> Regards,
> Daniel
>