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[68.160.166.30]) by smtp.gmail.com with ESMTPSA id h6-20020a05620a10a600b007246f005d8bsm293223qkk.116.2023.02.02.11.56.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Feb 2023 11:56:35 -0800 (PST) Date: Thu, 2 Feb 2023 14:56:34 -0500 From: Mike Snitzer To: Demi Marie Obenour Cc: Jens Axboe , Roger Pau =?iso-8859-1?Q?Monn=E9?= , Alasdair Kergon , Marek =?iso-8859-1?Q?Marczykowski-G=F3recki?= , Juergen Gross , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, dm-devel@redhat.com Subject: Re: [RFC PATCH 0/7] Allow race-free block device handling Message-ID: References: <20230126033358.1880-1-demi@invisiblethingslab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, Feb 02 2023 at 1:41P -0500, Demi Marie Obenour wrote: > On Thu, Feb 02, 2023 at 11:50:37AM -0500, Mike Snitzer wrote: > > On Wed, Jan 25 2023 at 10:33P -0500, > > Demi Marie Obenour wrote: > > > > > This work aims to allow userspace to create and destroy block devices > > > in a race-free and leak-free way, > > > > "race-free and leak-free way" implies there both races and leaks in > > existing code. You're making claims that are likely very specific to > > your Xen use-case. Please explain more carefully. > > Will do in v2. > > > > and to allow them to be exposed to > > > other Xen VMs via blkback without leaks or races. It’s marked as RFC > > > for a few reasons: > > > > > > - The code has been only lightly tested. It might be unstable or > > > insecure. > > > > > > - The DM_DEV_CREATE ioctl gains a new flag. Unknown flags were > > > previously ignored, so this could theoretically break buggy userspace > > > tools. > > > > Not seeing a reason that type of DM change is needed. If you feel > > strongly about it send a separate patch and we can discuss it. > > Patch 2/7 is the diskseq change. v2 will contain a revised and tested > version with a greatly expanded commit message. I'm aware that 2/7 is where you make the DM change to disallow unknown flags, what I'm saying is I don't see a reason for that change. Certainly doesn't look to be a requirement for everything else in that patch. So send a separate patch, but I'm inclined to _not_ accept it because it does potentially break some userspace. > > > - I have no idea if I got the block device reference counting and > > > locking correct. > > > > Your headers and justifcation for this line of work are really way too > > terse. Please take the time to clearly make the case for your changes > > in both the patch headers and code. > > I will expand the commit message in v2, but I am not sure what you want > me to add to the code comments. Would you mind explaining? Nothing specific about code, was just a general reminder (based on how terse the 2/7 header was). Mike