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PH0PR10MB5706.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Oct 2023 08:02:09.8615 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: kOBDhsFw1yigTtBD+jcfPXVMw2OYqbDt1UqDIq4Q4nRDjZErkAYHRSPVZ3qwl2xNQ6suq2Jp+hVZLyD1zqPb8Q== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR10MB4751 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.980,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-10-07_05,2023-10-06_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 mlxlogscore=999 mlxscore=0 bulkscore=0 phishscore=0 suspectscore=0 spamscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2309180000 definitions=main-2310070069 X-Proofpoint-GUID: gcVaSf9MFsU97ZDkNyLQQssFXZtdyqx7 X-Proofpoint-ORIG-GUID: gcVaSf9MFsU97ZDkNyLQQssFXZtdyqx7 Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 10/6/23 15:42, Guilherme G. Piccoli wrote: > Hi Anand / David, I was out at a conference and some holidays, so missed > this patch. Is this a replacement of the temp-fsid approach? > > So, to clarify a bit the inner workings of this patch: we don't have the > temp-fsid superblock flag anymore? While btrfs doesn't need this superblock flag internally, we may consider adding it for improved usability with other Btrfs features. > Also, we can mount multiple > partitions holding the same filesystem at the same time, given the > nature of the patch (that generates the random fsid based on devt as per > my superficial understanding) - right? Indeed, devt remains unique to the partition we've utilized for a similar purpose prior to this patch. Are there any devices lacking a distinct devt value? > And we don't use the > metadata_uuid field here anymore, Btrfs has always assigned fs_devices::metadata_uuid to either fsid or metadata_uuid. > i.e., we kinda "lose" the original fsid? How? Have you tested to confirm? > If that approaches is considered better than mine and works fine for the > Steam Deck use case, > I'm glad in having that! As you have a use case to verify, can you indeed confirm whether it works? > But I would like at least > to understand why it was preferred over the temp-fsid one, and what are > the differences we can expect (need a flag to mkfs or can use btrfstune > for that, for example). The in-memory disk-super hack in the original patch is essentially a workaround. This led to the necessity of restricting devices using metadata_uuid from being used as temp-fsid device. A more appropriate approach is to enhance device_list_add() to intelligently manage duplicate disk-super entries by checking devt and permitting them to mount if unique. This solution deviates from the original patch and simultaneously addresses the subvol-mount corruption issue observed in the original implementation. The additional adjustments [1], such as sysfs interface, the constraints on device additions, and the limitations on seed devices, are supplementary patches essential to the comprehensive solution. [1] [PATCH 0/4] btrfs: sysfs and unsupported temp-fsid features for clones However, the superblock temp-fsid flag isn't inherently necessary within btrfs internals. Nevertheless, it can be considered for addition if it makes the usability of other btrfs features with temp-fsid more seamless. Thanks, Anand