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[83.57.175.68]) by smtp.gmail.com with ESMTPSA id b6sm9539848ejb.8.2021.03.10.04.29.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 10 Mar 2021 04:29:36 -0800 (PST) Subject: Re: [PATCH 0/3] block: Introduce the 'zeroes-co' driver to help security reports To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= References: <20210310114314.1068957-1-philmd@redhat.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: <69ac819a-2e16-de72-780b-1cd6edadf5b3@redhat.com> Date: Wed, 10 Mar 2021 13:29:34 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.243, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: Fam Zheng , Kevin Wolf , Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org, qemu-devel@nongnu.org, Markus Armbruster , Prasad J Pandit , Bandan Das , Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 3/10/21 12:55 PM, Daniel P. Berrangé wrote: > On Wed, Mar 10, 2021 at 12:43:11PM +0100, Philippe Mathieu-Daudé wrote: >> Hi, >> >> This is an alternative approach to changing null-co driver >> default 'read-zeroes' option to true: >> https://www.mail-archive.com/qemu-block@nongnu.org/msg80873.html >> >> Instead we introduce yet another block driver with an explicit >> name: 'zeroes-co'. We then clarify in secure-coding-practices.rst >> that security reports have to be sent using this new driver. > > IMHO introducing a new block driver, when this can be solved by > simply adding a property to the existing driver, just feels mad > Your previous series made much more sense, and despite the long > thread, I didn't see anyone suggest a real world blocker with > making it read zeros by default. > > I think Max's last mail sums it up pretty well > > https://lists.gnu.org/archive/html/qemu-devel/2021-02/msg07173.html > > [quote] > In cases where we have a test that just wants a simple block node that > doesn’t use disk space, the memset() can’t be noticeable. But it’s just > a test, so do we even need the memset()? Strictly speaking, perhaps not, > but if someone is to run it via Valgrind or something, they may get > false positives, so just doing the memset() is the right thing to do. > > For performance tests, it must be possible to set read-zeroes=off, > because even though “that memset() isn’t noticeable in a functional > test”, in a hard-core performance test, it will be. > > So we need a switch. It should default to memset(), because (1) making > tools like Valgrind happy seems like a reasonable objective to me, and > (2) in the majority of cases, the memset() cannot have a noticeable > impact. > [/quote] Yes I totally agree with Max, but Fam is the maintainer. I'll keep looking for alternatives. Maybe simply documentation. Thanks, Phil.