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([2a01:4b00:bd21:4f00:7cc6:d3ca:494:116c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42cb7f2e432sm27351895f8f.9.2025.11.24.03.30.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 Nov 2025 03:30:06 -0800 (PST) Message-ID: <905ff009-0e02-4a5b-aa8d-236bfc1a404e@gmail.com> Date: Mon, 24 Nov 2025 11:30:01 +0000 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC v2 00/11] Add dmabuf read/write via io_uring To: =?UTF-8?Q?Christian_K=C3=B6nig?= , linux-block@vger.kernel.org, io-uring@vger.kernel.org Cc: Vishal Verma , tushar.gohad@intel.com, Keith Busch , Jens Axboe , Christoph Hellwig , Sagi Grimberg , Alexander Viro , Christian Brauner , Andrew Morton , Sumit Semwal , linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org References: Content-Language: en-US From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 11/24/25 10:33, Christian König wrote: > On 11/23/25 23:51, Pavel Begunkov wrote: >> Picking up the work on supporting dmabuf in the read/write path. > > IIRC that work was completely stopped because it violated core dma_fence and DMA-buf rules and after some private discussion was considered not doable in general. > > Or am I mixing something up here? The time gap is purely due to me being busy. I wasn't CC'ed to those private discussions you mentioned, but the v1 feedback was to use dynamic attachments and avoid passing dma address arrays directly. https://lore.kernel.org/all/cover.1751035820.git.asml.silence@gmail.com/ I'm lost on what part is not doable. Can you elaborate on the core dma-fence dma-buf rules? > Since I don't see any dma_fence implementation at all that might actually be the case. See Patch 5, struct blk_mq_dma_fence. It's used in the move_notify callback and is signaled when all inflight IO using the current mapping are complete. All new IO requests will try to recreate the mapping, and hence potentially wait with dma_resv_wait_timeout(). > On the other hand we have direct I/O from DMA-buf working for quite a while, just not upstream and without io_uring support. Have any reference? -- Pavel Begunkov