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Mercier" , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, opensource.kernel@vivo.com References: <20240711074221.459589-1-link@vivo.com> <20240711074221.459589-2-link@vivo.com> <5ccbe705-883c-4651-9e66-6b452c414c74@amd.com> <99364176-a7f0-4a17-8889-75ff92d5694e@amd.com> <06713006-c5ce-4773-a1b3-ca3bea56ee45@vivo.com> From: Huan Yang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: TY2PR06CA0030.apcprd06.prod.outlook.com (2603:1096:404:2e::18) To PUZPR06MB5676.apcprd06.prod.outlook.com (2603:1096:301:f8::10) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PUZPR06MB5676:EE_|TYUPR06MB6271:EE_ X-MS-Office365-Filtering-Correlation-Id: 79e3dc2a-1239-47a1-4546-08dca6cc2cad X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|52116014|376014|1800799024|366016|38350700014|921020; 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Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ] > > On Wed, Jul 17, 2024 at 05:15:07PM +0200, Daniel Vetter wrote: >> I'm talking about memfd, not dma-buf here. I think copy_file_range to >> dma-buf is as architecturally unsound as allowing O_DIRECT on the dma-buf >> mmap. > copy_file_range only work inside the same file system anyway, so > it is completely irrelevant here. Yes, actually, if dma-buf want's to copy_file_range from a file, it need change something in vfs_copy_file_range: 1. in generic_file_rw_checks, dma-buf file is not a normal file, but inode_out check it.  need bypass 2. file in and out need in the same file system which you point it. So, need bypass it 3. if dma-buf above 2G, need bypass generic_write_check_limits's file O_LARGEFILE check, it only allow copy range below 2G. I feel that the above limitations indicate that copy_file_range is not really suitable for copying between different file systems or unconventional file types.(both shmemfs and other's) Perhaps enabling dma-buf to support copy_file_range is not a good idea? :) > > What should work just fine is using sendfile (or splice if you like it > complicated) to write TO the dma buf. That just iterates over the page OK, I'll research it also. > cache on the source file and calls ->write_iter from the page cache > pages. Of course that requires that you actually implement > ->write_iter, but given that dmabufs support mmaping there I can't > see why you should not be able to write to it. > > Reading FROM the dma buf in that fashion should also work if you provide > a ->read_iter wire up ->splice_read to copy_splice_read so that it > doesn't require any page cache. >