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Piccoli" Cc: linux-btrfs@vger.kernel.org, clm@fb.com, josef@toxicpanda.com, dsterba@suse.com, linux-fsdevel@vger.kernel.org, kernel@gpiccoli.net, kernel-dev@igalia.com, david@fromorbit.com, kreijack@libero.it, johns@valvesoftware.com, ludovico.denittis@collabora.com, quwenruo.btrfs@gmx.com, wqu@suse.com, vivek@collabora.com References: <20230831001544.3379273-1-gpiccoli@igalia.com> <20230831001544.3379273-3-gpiccoli@igalia.com> <20230911182804.GA20408@twin.jikos.cz> From: Anand Jain In-Reply-To: <20230911182804.GA20408@twin.jikos.cz> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SG3P274CA0002.SGPP274.PROD.OUTLOOK.COM (2603:1096:4:be::14) To PH0PR10MB5706.namprd10.prod.outlook.com (2603:10b6:510:148::10) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH0PR10MB5706:EE_|PH0PR10MB4616:EE_ X-MS-Office365-Filtering-Correlation-Id: 7cda2bbc-018f-4228-0194-08dbb3719056 X-MS-Exchange-SenderADCheck: 1 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LYSJG1ksLw8S7PGzJxO49KdHm6/c6rJKpNWJqJ2UfSHXgQ1lF4jN4x0AStB9heD3tjwNBFEuvca3mu//SnFmtw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR10MB4616 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.957,Hydra:6.0.601,FMLib:17.11.176.26 definitions=2023-09-12_06,2023-09-05_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 mlxscore=0 adultscore=0 phishscore=0 spamscore=0 suspectscore=0 malwarescore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2308100000 definitions=main-2309120079 X-Proofpoint-ORIG-GUID: Td6C_eEP7hhZ-ZBr3avVmJhqXNkgdWCd X-Proofpoint-GUID: Td6C_eEP7hhZ-ZBr3avVmJhqXNkgdWCd Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 12/09/2023 02:28, David Sterba wrote: > On Wed, Aug 30, 2023 at 09:12:34PM -0300, Guilherme G. Piccoli wrote: >> Btrfs doesn't currently support to mount 2 different devices holding the >> same filesystem - the fsid is exposed as a unique identifier by the >> driver. This case is supported though in some other common filesystems, >> like ext4. >> >> Supporting the same-fsid mounts has the advantage of allowing btrfs to >> be used in A/B partitioned devices, like mobile phones or the Steam Deck >> for example. Without this support, it's not safe for users to keep the >> same "image version" in both A and B partitions, a setup that is quite >> common for development, for example. Also, as a big bonus, it allows fs >> integrity check based on block devices for RO devices (whereas currently >> it is required that both have different fsid, breaking the block device >> hash comparison). >> >> Such same-fsid mounting is hereby added through the usage of the >> filesystem feature "single-dev" - when such feature is used, btrfs >> generates a random fsid for the filesystem and leverages the long-term >> present metadata_uuid infrastructure to enable the usage of this >> secondary virtual fsid, effectively requiring few non-invasive changes >> to the code and no new potential corner cases. >> >> In order to prevent more code complexity and corner cases, given >> the nature of this mechanism (single devices), the single-dev feature >> is not allowed when the metadata_uuid flag is already present on the >> fs, or if the device is on fsid-change state. Device removal/replace >> is also disabled for devices presenting the single-dev feature. >> >> Suggested-by: John Schoenick >> Suggested-by: Qu Wenruo >> Signed-off-by: Guilherme G. Piccoli > > I've added Anand's patch > https://lore.kernel.org/linux-btrfs/de8d71b1b08f2c6ce75e3c45ee801659ecd4dc43.1694164368.git.anand.jain@oracle.com/ > to misc-next that implements subset of your patch, namely extending > btrfs_scan_one_device() with the 'mounting' parameter. I haven't looked > if the semantics is the same so I let you take a look. > > As there were more comments to V3, please fix that and resend. Thanks. Guliherme, Please also add the newly sent patch to the latest misc-next branch: [PATCH] btrfs: scan forget for no instance of dev The test case btrfs/254 fails without it. Thanks.