Re: [PATCH 5/5] qmp: Added qemu-ebpf-rss-path command.

[Markus Armbruster]

Andrew Melnichenko <andrew@daynix.com> writes:

> Hi,
> Yes, the stamp check was added.
> So the qemu emulator should return a suitable RSS BPF helper or nothing.
> Each qemu emulator may have a different helper that suits it.
> So, the idea is to ask for the helper from qemu.

Please answer the question below.

>
> On Tue, Aug 24, 2021 at 9:41 AM Markus Armbruster <armbru@redhat.com> wrote:
>
>> Andrew Melnichenko <andrew@daynix.com> writes:
>>
>> > Hi,
>> >
>> >> The helper may or may not be installed at the path compiled into QEMU.
>> >>
>> > Yes, so the helper will not be called - QEMU will try to initiate eBPF
>> RSS
>> > or use "in-qemu" RSS.
>>
>> My point is: the proposed command's mission is to help the management
>> application run the right helper.  However, its advice is *unreliable*.
>> It may point to the wrong helper, or to nothing at all.  The right
>> helper may still exist elsewhere.
>>
>> I suspect you're trying to address the problem at the wrong level.
>>
>> Similar versioning issues exist with other helpers.  We've been doing
>> fine without QEMU providing unreliable advice on where they might sit in
>> the file system.  What makes this one different?

This one.

>> >> What happens when you use the wrong helper?
>> >>
>> > UB - in most cases, eBPF program will work with wrong configurations.
>> > That's why the stamp was added.
>> >
>> > query-helper-paths checks the stamp only for RSS helper.
>>
>> I have no idea what you're talking about :)
>>
>> My best guess is that you're trying to tell me that attempting to work
>> with the wrong helper will fail cleanly due to some stamp check.  That
>> would be nice.
>>
>>