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Wed, 17 Nov 2021 03:29:33 +0000 Message-ID: <5f269a90-7145-0991-5da4-5f03fc0937fa@oracle.com> Date: Wed, 17 Nov 2021 11:29:26 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0 Subject: Re: [PATCH v2 2/2] btrfs: sysfs add devinfo/fsid to retrieve fsid from the device Content-Language: en-US To: dsterba@suse.cz, linux-btrfs@vger.kernel.org, Josef Bacik References: <33e179f8b9341c88754df639b77dafaa1ffec0d1.1634829757.git.anand.jain@oracle.com> <20211116171621.GU28560@twin.jikos.cz> From: Anand Jain In-Reply-To: <20211116171621.GU28560@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 MN2PR10MB4128.namprd10.prod.outlook.com (2603:10b6:208:1d2::24) MIME-Version: 1.0 Received: from [192.168.10.100] (39.109.140.76) by SGXP274CA0001.SGPP274.PROD.OUTLOOK.COM (2603:1096:4:b8::13) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4713.19 via Frontend Transport; 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The userland has to read the device superblock to know the >> fsid but, that idea fails if the device is missing. So add a sysfs >> interface devinfo//fsid to show the fsid of the device. >> >> For example: >> $ cd /sys/fs/btrfs/b10b02a5-f9de-4276-b9e8-2bfd09a578a8 >> >> $ cat devinfo/1/fsid >> c44d771f-639d-4df3-99ec-5bc7ad2af93b >> $ cat devinfo/3/fsid >> b10b02a5-f9de-4276-b9e8-2bfd09a578a8 > > From user perspective, it's another fsid, one is in the path, so I'm > wondering if it should be named like read_fsid or sprout_fsid or if the > seed/sprout information should be put into another directory completely. I am viewing it as fsid as per the device's sb. This fsid matches with the blkid(8) output. A path to the device's fsid will help to script. So I am not voting for sprout_fsid because it does not exist in the most common non-sprouted fsid. Now to show whether a device is seed or sprout, the user friendly approach will be like for example: /sys/fs/btrfs//devinfo//device_state to show all that apply, for example: SEED|SPROUT|READ_ONLY|WRITABLE|ZONED|METADATA_ONLY|\ DATA_ONLY|READ_PREFERRED|REPLACE_TGT|REPLACE_SRC|\ SCRUB_RUNNING However, per kernel general rule of thumb one value per sys-fs file, so it should be for example: /sys/fs/btrfs//devinfo//seed 0 /sys/fs/btrfs//devinfo//sprout 1 So based on this my patch "btrfs: introduce new device-state read_preferred" in the mailing list already proposed /sys/fs/btrfs//devinfo//read_preferred So to summarize, I can rename fsid to read_fsid. And, progressively in a separate patch, we can add <>/seed <>/sprout sysfs files as above. What do you think?