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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: <20230913224402.3940543-1-gpiccoli@igalia.com> <20230913224402.3940543-3-gpiccoli@igalia.com> <20230918215250.GQ2747@twin.jikos.cz> <9ee57635-81bf-3307-27ac-8cb7a4fa02f6@igalia.com> <20230920183756.GG2268@twin.jikos.cz> From: Anand Jain In-Reply-To: <20230920183756.GG2268@twin.jikos.cz> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SGXP274CA0001.SGPP274.PROD.OUTLOOK.COM (2603:1096:4:b8::13) To PH0PR10MB5706.namprd10.prod.outlook.com (2603:10b6:510:148::10) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH0PR10MB5706:EE_|BLAPR10MB5028:EE_ 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4GZAVudGyOYm8Mc2s/Pcq91YX6WlvrgMGqh8q2xYdeaJ5uexr0ThKl09S4x+g75xH9LhbBjAcHJZfpP68VbBGA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BLAPR10MB5028 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.980,Hydra:6.0.601,FMLib:17.11.176.26 definitions=2023-09-20_13,2023-09-20_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 mlxscore=0 malwarescore=0 adultscore=0 suspectscore=0 spamscore=0 mlxlogscore=999 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2308100000 definitions=main-2309210000 X-Proofpoint-ORIG-GUID: tbp7borWmC8XUFwUQbCXi8O2p-miGYDM X-Proofpoint-GUID: tbp7borWmC8XUFwUQbCXi8O2p-miGYDM Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 21/09/2023 02:37, David Sterba wrote: > On Wed, Sep 20, 2023 at 09:16:02AM -0300, Guilherme G. Piccoli wrote: >> On 19/09/2023 02:01, Anand Jain wrote: >>> [...] >>> This must successfully pass the remaining Btrfs fstests test cases with >>> the MKFS_OPTION="-O temp-fsid" configuration option, or it should call >>> not run for the incompatible feature. >> >> I kinda disagree here - this feature is not compatible with anything >> else, so I don't think it's fair to expect mounting with temp-fsid will >> just pass all other tests, specially for things like (the real) >> metadata_uuid or extra devices, like device removal... > > Yeah, fstests are not in general ready for enabling some feature from > the outside (mkfs, or mount options). Some of them work as long as > they're orthogonal but some tests need to detect that and skip. In this > case all multidevice tests would fail. > > For test coverage there should be at lest one test that verifies known > set of compatible features or usecases we care about in comibnation with > the temp-fsid. > If this patch had undergone verification using fstests for a single device, it might have already resolved the data corruption issue I recently reported. While it could be an isolated bug, having fstests confirm that 'yes, everything else is verified except for multi-device support' would be helpful. The MKFS_OPTION="-O temp_fsid" config would help create temp_fsid in fstests, it may not be too difficult to verify. Also, as commented in v3, btrfs-progs needs to support listing single devices with conflicting fsids while they are unmounted. Thanks, Anand >>> I have observed that the following test case is failing with this patch: >>> >>> $ mkfs.btrfs -fq /dev/sdb1 :0 >>> $ btrfstune --convert-to-temp-fsid /dev/sdb1 :0 >>> $ mount /dev/sdb1 /btrfs :0 >>> >>> Mount /dev/sdb1 again at a different mount point and look for the copied >>> file 'messages': >>> >>> $ cp /var/log/messages /btrfs :0 >>> >>> $ mount /dev/sdb1 /btrfs1 :0 >>> $ ls -l /btrfs1 :0 >>> total 0 <-- empty >>> >>> The copied file is missing because we consider each mount as a new fsid. >>> This means subvolume mounts are also not working. Some operating systems >>> mount $HOME as a subvolume, so those won't work either. >>> >>> To resolve this, we can use devt to match in the device list and find >>> the matching fs_devices or NULL. >> >> Ugh, this one is ugly. Thanks for noticing that, I think this needs >> fixing indeed. >> >> I've tried here, mounted the same temp-fsid btrfs device in 2 different >> mount points, and wrote two different files on each. The mount A can >> only see the file A, mount B can only see file B. Then after unmouting >> both, I cannot mount anymore with errors in ctree, so it got corrupted. >> >> The way I think we could resolve this is by forbidding mounting a >> temp-fsid twice - after the random uuid generation, we could check for >> all fs_devices present and if any of it has the same metadata_uuid, we >> check if it's the same dev_t and bail. >> >> The purpose of the feature is for having the same filesystem in >> different devices able to mount at the same time, but on different mount >> points. WDYT? > > The subvolume mount is a common use case and I hope it continues to > work. Currently it does not seem so as said above, for correctness we > may need to prevent it. We might find more and this should be known or > fixed before final release.