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Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 Subject: Re: [PATCH 1/2] btrfs: remove MIXED_BACKREF sysfs file Content-Language: en-US To: dsterba@suse.cz, Qu Wenruo , Nikolay Borisov , linux-btrfs@vger.kernel.org References: <20220624080123.1521917-1-nborisov@suse.com> <20220624080123.1521917-2-nborisov@suse.com> <21f7eb10-09d7-826c-48c3-ded892984d50@gmx.com> <3e01475c-8296-4cf1-14cd-5774d780b6e2@suse.com> <27f72ec4-a365-20ba-03f1-8d603a66e011@gmx.com> <20220624134706.GV20633@twin.jikos.cz> From: Qu Wenruo In-Reply-To: <20220624134706.GV20633@twin.jikos.cz> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: BY3PR10CA0018.namprd10.prod.outlook.com (2603:10b6:a03:255::23) To AM9PR04MB8472.eurprd04.prod.outlook.com (2603:10a6:20b:417::15) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: c58103d7-b732-46aa-e49c-08da55ea3c34 X-MS-TrafficTypeDiagnostic: PA4PR04MB7936:EE_ X-LD-Processed: f7a17af6-1c5c-4a36-aa8b-f5be247aa4ba,ExtFwd X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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Also the commit for >>> the backrefs states: >>> >>> >>> This commit introduces a new kind of back reference for btrfs metadata. >>> Once a filesystem has been mounted with this commit, IT WILL NO LONGER >>> BE MOUNTABLE BY OLDER KERNELS. >> >> That means we're hiding incompat features from the user. >> >> Even if it's not tunable and should always be enabled, we still need to >> add that. > > I think the mixed_backref is an exception because it's been part of the > default format for so long that we don't even remember there was > something else. For users it does not mean anything today, moreover it > could be confused with mixed block groups. Then after some time, there will be some "smart" users find that we have one incompat bit without any explanation. Thanks, Qu