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[23.128.96.18]) by mx.google.com with ESMTP id l16si1120112ion.65.2021.06.15.22.47.12; Tue, 15 Jun 2021 22:47:36 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-nfs-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-nfs-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-nfs-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229614AbhFPFtQ (ORCPT + 99 others); Wed, 16 Jun 2021 01:49:16 -0400 Received: from out20-97.mail.aliyun.com ([115.124.20.97]:35886 "EHLO out20-97.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229681AbhFPFtO (ORCPT ); Wed, 16 Jun 2021 01:49:14 -0400 X-Alimail-AntiSpam: AC=CONTINUE;BC=0.04508309|-1;CH=green;DM=|CONTINUE|false|;DS=CONTINUE|ham_regular_dialog|0.433153-0.00164647-0.5652;FP=0|0|0|0|0|-1|-1|-1;HT=ay29a033018047213;MF=wangyugui@e16-tech.com;NM=1;PH=DS;RN=2;RT=2;SR=0;TI=SMTPD_---.KT0hfmF_1623822422; Received: from 192.168.2.112(mailfrom:wangyugui@e16-tech.com fp:SMTPD_---.KT0hfmF_1623822422) by smtp.aliyun-inc.com(10.147.41.187); Wed, 16 Jun 2021 13:47:02 +0800 Date: Wed, 16 Jun 2021 13:47:02 +0800 From: Wang Yugui To: "NeilBrown" , linux-nfs@vger.kernel.org Subject: Re: any idea about auto export multiple btrfs snapshots? In-Reply-To: <20210615231318.F40F.409509F4@e16-tech.com> References: <162371103543.23575.13662722966178222587@noble.neil.brown.name> <20210615231318.F40F.409509F4@e16-tech.com> Message-Id: <20210616134702.A114.409509F4@e16-tech.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.75.04 [en] Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org Hi, > Hi, NeilBrown > > > On Sun, 13 Jun 2021, Wang Yugui wrote: > > > Hi, > > > > > > Any idea about auto export multiple btrfs snapshots? > > > > > > One related patch is yet not merged to nfs-utils 2.5.3. > > > From: "NeilBrown" > > > Subject: [PATCH/RFC v2 nfs-utils] Fix NFSv4 export of tmpfs filesystems. > > > > > > In this patch, an UUID is auto generated when a tmpfs have no UUID. > > > > > > for btrfs, multiple subvolume snapshot have the same filesystem UUID. > > > Could we generate an UUID for btrfs subvol with 'filesystem UUID' + 'subvol ID'? > > > > You really need to ask this question of btrfs developers. 'mountd' > > already has a special-case exception for btrfs, to prefer the uuid > > provided by statfs64() rather than the uuid extracted from the block > > device. It would be quite easy to add another exception. > > But it would only be reasonable to do that if the btrfs team told us how > > that wanted us to generate a UUID for a given mount point, and promised > > that would always provide a unique stable result. > > This is completely separate from the tmpfs patch you identified. > > Thanks a lot for the replay. > > Now btrfs statfs64() return 8 byte unique/stable result. > > It is based on two parts. > 1) 16 byte blkid of file system. this is uniq/stable between btrfs filesystems. > 2) 8 byte of btrfs sub volume objectid. this is uniq/stable inside a > btrfs filesystem. > > the code of linux/fs/btrfs > static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf) > > /* We treat it as constant endianness (it doesn't matter _which_) > because we want the fsid to come out the same whether mounted > on a big-endian or little-endian host */ > buf->f_fsid.val[0] = be32_to_cpu(fsid[0]) ^ be32_to_cpu(fsid[2]); > buf->f_fsid.val[1] = be32_to_cpu(fsid[1]) ^ be32_to_cpu(fsid[3]); > /* Mask in the root object ID too, to disambiguate subvols */ > buf->f_fsid.val[0] ^= > BTRFS_I(d_inode(dentry))->root->root_key.objectid >> 32; > buf->f_fsid.val[1] ^= > BTRFS_I(d_inode(dentry))->root->root_key.objectid; > > > for nfs, we need a 16 byte UUID now. > > The best way I though: > 16 byte blkid , math add 8 byte btrfs sub volume objectid. > but there is yet no a simple/easy way to get the raw value of 'btrfs sub > volume objectid'. The btrfs subvol objectid (8byte) can be extracted from the statfs.f_fsid(8 byte) with the help of blkid(16btye) of the btrfs file system just do a revert cacl in btrfs_statfs(). if we need 8 byte id for btrfs subvol, just use statfs.f_fsid. if we need 16 byte id for btrfs subvol, use the blkid(16btye) of the btrfs filesystem, plus the btrfs subvol objectid (8byte) , and keep the result in 16 byte. Best Regards Wang Yugui (wangyugui@e16-tech.com) 2021/06/16 > A simple but good enough way: > 1) first 8 byte copy from blkid > 2) second 8 byte copy from btrfs_statfs() > the uniq/stable of multiple subvolume inside a btrfs filesystem is kept. > > Best Regards > Wang Yugui (wangyugui@e16-tech.com) > 2021/06/15