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Sun, 23 Aug 2020 15:05:35 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 07NF00v5088638; Sun, 23 Aug 2020 15:05:34 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserp3020.oracle.com with ESMTP id 333ru2exng-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sun, 23 Aug 2020 15:05:34 +0000 Received: from abhmp0018.oracle.com (abhmp0018.oracle.com [141.146.116.24]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 07NF5XOe028064; Sun, 23 Aug 2020 15:05:33 GMT Received: from [192.168.1.102] (/39.109.231.106) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Sun, 23 Aug 2020 08:05:33 -0700 Subject: Re: [PATCH RFC 2/2] btrfs: fix replace of seed device To: Josef Bacik , linux-btrfs@vger.kernel.org Cc: boris@bur.io References: <2c7ca821f53d71d6c1a4e1f1c969c1d8e686021a.1598012410.git.anand.jain@oracle.com> <56431875-619d-fb49-efb2-9fcd265a8a69@toxicpanda.com> From: Anand Jain Message-ID: <0f7add45-911f-825a-965e-7cd76bb3ee22@oracle.com> Date: Sun, 23 Aug 2020 23:05:30 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.1.1 MIME-Version: 1.0 In-Reply-To: <56431875-619d-fb49-efb2-9fcd265a8a69@toxicpanda.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9722 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 phishscore=0 bulkscore=0 suspectscore=0 spamscore=0 mlxscore=0 adultscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2008230168 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9722 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 phishscore=0 impostorscore=0 bulkscore=0 adultscore=0 spamscore=0 suspectscore=0 lowpriorityscore=0 mlxlogscore=999 clxscore=1011 priorityscore=1501 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2008230169 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 21/8/20 10:38 pm, Josef Bacik wrote: > On 8/21/20 9:15 AM, Anand Jain wrote: >> If you replace a seed device in a sprouted fs, it appears to have >> successfully replaced the seed device, but if you look closely, it >> didn't. >> >> Here is an example. >> >> mkfs.btrfs -fq /dev/sda >> btrfstune -S1 /dev/sda >> mount /dev/sda /btrfs >> btrfs dev add /dev/sdb /btrfs >> umount /btrfs; btrfs dev scan --forget >> mount -o device=/dev/sda /dev/sdb /btrfs >> btrfs rep start -f /dev/sda /dev/sdc /btrfs; echo $? >> 0 >> >>    BTRFS info (device sdb): dev_replace from /dev/sda (devid 1) to >> /dev/sdc started >>    BTRFS info (device sdb): dev_replace from /dev/sda (devid 1) to >> /dev/sdc finished >> >> btrfs fi show >> Label: none  uuid: ab2c88b7-be81-4a7e-9849-c3666e7f9f4f >>     Total devices 2 FS bytes used 256.00KiB >>     devid    1 size 3.00GiB used 520.00MiB path /dev/sdc >>     devid    2 size 3.00GiB used 896.00MiB path /dev/sdb >> >> Label: none  uuid: 10bd3202-0415-43af-96a8-d5409f310a7e >>     Total devices 1 FS bytes used 128.00KiB >>     devid    1 size 3.00GiB used 536.00MiB path /dev/sda >> >> So as per the replace start command and kernel log replace was >> successful. >> >> Now let's try to clean mount. >> >> umount /btrfs;  btrfs dev scan --forget >> >> mount -o device=/dev/sdc /dev/sdb /btrfs >> mount: /btrfs: wrong fs type, bad option, bad superblock on /dev/sdb, >> missing codepage or helper program, or other error. >> >> [  636.157517] BTRFS error (device sdc): failed to read chunk tree: -2 >> [  636.180177] BTRFS error (device sdc): open_ctree failed >> >> That's because per dev items it is still looking for the original seed >> device. >> >> btrfs in dump-tree -d /dev/sdb >> >>     item 0 key (DEV_ITEMS DEV_ITEM 1) itemoff 16185 itemsize 98 >>         devid 1 total_bytes 3221225472 bytes_used 545259520 >>         io_align 4096 io_width 4096 sector_size 4096 type 0 >>         generation 6 start_offset 0 dev_group 0 >>         seek_speed 0 bandwidth 0 >>         uuid 59368f50-9af2-4b17-91da-8a783cc418d4  <--- seed uuid >>         fsid 10bd3202-0415-43af-96a8-d5409f310a7e  <--- seed fsid >>     item 1 key (DEV_ITEMS DEV_ITEM 2) itemoff 16087 itemsize 98 >>         devid 2 total_bytes 3221225472 bytes_used 939524096 >>         io_align 4096 io_width 4096 sector_size 4096 type 0 >>         generation 0 start_offset 0 dev_group 0 >>         seek_speed 0 bandwidth 0 >>         uuid 56a0a6bc-4630-4998-8daf-3c3030c4256a  <- sprout uuid >>         fsid ab2c88b7-be81-4a7e-9849-c3666e7f9f4f <- sprout fsid >> >> But the replaced target has the following uuid+fsid in its superblock >> which doesn't match with the expected uuid+fsid in its devitem. >> >> btrfs in dump-super /dev/sdc | egrep >> '^generation|dev_item.uuid|dev_item.fsid|devid' >> generation    20 >> dev_item.uuid    59368f50-9af2-4b17-91da-8a783cc418d4 >> dev_item.fsid    ab2c88b7-be81-4a7e-9849-c3666e7f9f4f [match] >> dev_item.devid    1 >> >> So if you provide the original seed device the mount shall be successful. >> Which so long happening in the test case btrfs/163. >> >> btrfs dev scan --forget >> mount -o device=/dev/sda /dev/sdb /btrfs >> >> Fix in this patch: >> Make it as you can't replace a seed device, you can only add a new device >> and then delete the seed device. If replace is attempted then returns >> -EINVAL. >> As in the below changes. >> >> Another possible fix: >> If we want to keep the ability to replace for seed-device, then we could >> update the fsid of the replace-target blocks. And after replacement, you >> have seed device but with sprout fsid. But then I don't know what is the >> point and if there is any such use case. >> >> Signed-off-by: Anand Jain >> --- > > This is something Boris dug into until I told him to drop it.  I _think_ > I'm ok with this, but really what I'd rather do is restripe the whole fs > with the new UUID for this case.  Where did that redo the UUID work go? Redo the UUID part is not yet implemented. Perhaps restripe the whole fs- is another approach, both of these approaches have the same question unanswered what use case does the replace of seed device solve and would it be a redundant operation to device add and delete ops. Thanks, Anand > Thanks, > > Josef