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h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=B4jBFIdFiNtDsmQMyWWPd+1DnLb23kwsj3MeQY91MXI=; b=oSkzNAr/27e92aKNerb+qZa44Z+sXt2zjnAe8/cVBq6IRDAtWKDeS3YSG5QeN9uTKVl1yhTAvRyvpxMavXVXKU220fKkSaWt4WMbC4LZ4x6mdnQuzfD6WVWvQWCD0WweXJAbGwUQGGaGqjzoMx8HKgmMTmjWN38FnJ5EQmMbEsI= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R191e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033037026112;MF=hsiangkao@linux.alibaba.com;NM=1;PH=DS;RN=17;SR=0;TI=SMTPD_---0X5.qxzD_1781627749; Received: from 30.120.66.214(mailfrom:hsiangkao@linux.alibaba.com fp:SMTPD_---0X5.qxzD_1781627749 cluster:ay36) by smtp.aliyun-inc.com; Wed, 17 Jun 2026 00:35:50 +0800 Message-ID: <8f1c032b-b951-4d0d-93fa-229248993f2c@linux.alibaba.com> Date: Wed, 17 Jun 2026 00:35:48 +0800 X-Mailing-List: linux-erofs@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 2/8] fs: add a global device to super block hash table To: Christoph Hellwig , Christian Brauner Cc: Jan Kara , Jens Axboe , Alexander Viro , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Carlos Maiolino , linux-xfs@vger.kernel.org, Chris Mason , David Sterba , linux-btrfs@vger.kernel.org, Theodore Ts'o , linux-ext4@vger.kernel.org, Gao Xiang , linux-erofs@lists.ozlabs.org References: <20260602-work-super-bdev_holder_global-v1-0-bb0fd82f3861@kernel.org> <20260602-work-super-bdev_holder_global-v1-2-bb0fd82f3861@kernel.org> <20260616123443.GA21024@lst.de> From: Gao Xiang In-Reply-To: <20260616123443.GA21024@lst.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2026/6/16 20:34, Christoph Hellwig wrote: > IMHO sharing devices between superblocks is a bad idea, but that ship > has sailed, but please keep it contained inside of erofs. I'm not sure why it's a bad idea, for example, the immutable layer model is already applied to layered virtual block formats (such as qcow2) and layered fs like overlayfs. and I think device mappers may have some similar immutable approaches as shared layers but works in a slight different way. The principle is that each instance uses shared blobs in a read-only way, and that is almost a simple and safest way to share data among filesystem instances. Yet I don't want to argue with that since it's pretty common for years and I've seen no practical risk using this model. Thanks, Gao Xiang