Re: [PATCH v1 1/7] xen-block: Do not write frontend nodes

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 11/11/2023 10:55 am, David Woodhouse wrote:
> On Fri, 2023-11-10 at 20:42 +0000, Volodymyr Babchuk wrote:
>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
>>
>> The PV backend running in other than Dom0 domain (non toolstack domain)
>> is not allowed to write frontend nodes. The more, the backend does not
>> need to do that at all, this is purely toolstack/xl devd business.
>>
>> I do not know for what reason the backend does that here, this is not really
>> needed, probably it is just a leftover and all xen_device_frontend_printf()
>> instances should go away completely.
> No, this is what allows qemu to create PV devices, as opposed to just
> handle the ones which are created for it by the toolstack.
>
> Perhaps we should only create the frontend nodes (and likewise, only
> destroy those and the backend nodes on destruction) in the case where
> the device was instantiated directly by the QEMU command line, and
> refrain from doing so for the devices which were created by the
> toolstack and merely 'discovered' by xen_block_device_create()?
>
> (Note that we need to look at net and console devices too, now they've
> finally been converted to the 'new' XenBus framework in QEMU 8.2.)
>
>

Furthermore, the control domain doesn't always have the domid of 0.

If qemu wants/needs to make changes like this, the control domain has to
arrange for qemu's domain to have appropriate permissions on the nodes.

~Andrew