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[164.138.29.33]) by smtp.gmail.com with ESMTPSA id og50-20020a1709071df200b00a51ba0be887sm2047386ejc.192.2024.04.12.10.22.37 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 12 Apr 2024 10:22:37 -0700 (PDT) Date: Fri, 12 Apr 2024 19:22:00 +0200 From: Stefano Brivio To: Jakub Kicinski Cc: David Ahern , davem@davemloft.net, netdev@vger.kernel.org, edumazet@google.com, pabeni@redhat.com, Ilya Maximets , donald.hunter@gmail.com Subject: Re: [PATCH net] inet: bring NLM_DONE out to a separate recv() again Message-ID: <20240412192200.662d92ae@elisabeth> In-Reply-To: <20240411140154.2acd3d0a@kernel.org> References: <20240411180202.399246-1-kuba@kernel.org> <20240411140154.2acd3d0a@kernel.org> Organization: Red Hat X-Mailer: Claws Mail 4.2.0 (GTK 3.24.36; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 11 Apr 2024 14:01:54 -0700 Jakub Kicinski wrote: > On Thu, 11 Apr 2024 13:45:42 -0600 David Ahern wrote: > > > + /* Don't let NLM_DONE coalesce into a message, even if it could. > > > + * Some user space expects NLM_DONE in a separate recv(). > > > > that's unfortunate > > Do you have an opinion on the sysfs/opt-in question? > Feels to me like there shouldn't be that much user space doing raw > netlink, without a library. Old crufty code usually does ioctls, right? I think so too -- if there were more (maintained) applications with this issue, we would have noticed by now. > So maybe we can periodically reintroduce this bug to shake out all > the bad apps? :D Actually, I had half a mind of proposing something on these lines: add a TODO comment here and revisit in, say, two years. I guess it's definitely more painful for libreswan, but for passt, I think it's quite unlikely that distribution users could get the "breaking" kernel change without a fixed version of the application: we made a new release relatively close to the NLM_DONE change. There might be substantial value in keeping this type of short netlink exchanges fast, for example for container engines that need to be able to spawn a bazillion containers per second. -- Stefano