Yuri Benditovich <yuri.benditov...@daynix.com> writes: > On Tue, Aug 24, 2021 at 9:41 AM Markus Armbruster <arm...@redhat.com> wrote: >> >> Andrew Melnichenko <and...@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. > > Hi Markus, > Indeed the intention of this command is to return the proper helper. > Especially in the case of RSS helper this is *reliable* advice and it > points to the helper that was built together with QEMU, i.e. with the > same headers. > This was discussed earlier, for example in > https://lists.nongnu.org/archive/html/qemu-devel/2021-06/msg02248.html > >> >> I suspect you're trying to address the problem at the wrong level. > > What is the proper solution for the problem from your point of view?
I'll explain in more detail, but first I'd like you to answer my question below. >> 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 is required to be *fully synchronized* with the existing build of > QEMU. > Other helpers are probably less restrictive and do not have common > structures definitions with the QEMU, otherwise they would face the > same problem. > >> >> >> What happens when you use the wrong helper? > > Our intention is that libvirt should never use the wrong RSS helper. > But it does not have any ability to check which helper is compatible > with the QEMU. > QEMU can easily recognize the correct one. You did not actually answer my question :) So let's try again: if libvirt does use the wrong RSS helper, how does the system behave? >> >> >> > 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. >>
