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References: <20210713153758.323614-1-andrew@daynix.com> <20210713153758.323614-6-andrew@daynix.com> <87y29dct4m.fsf@dusky.pond.sub.org> <877dgbpco1.fsf@dusky.pond.sub.org> Date: Mon, 30 Aug 2021 08:10:28 +0200 In-Reply-To: (Yuri Benditovich's message of "Sun, 29 Aug 2021 23:13:42 +0300") Message-ID: <87v93n8nu3.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=216.205.24.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.393, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Andrew Melnichenko , "Daniel P. =?utf-8?Q?Berrang=C3=A9?=" , "Michael S. Tsirkin" , Jason Wang , qemu-devel@nongnu.org, Yan Vugenfirer , Eric Blake Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Yuri Benditovich writes: > On Tue, Aug 24, 2021 at 9:41 AM Markus Armbruster wrote: >> >> Andrew Melnichenko 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. >>