From: Anand Jain <anand.jain@oracle.com>
To: Josef Bacik <josef@toxicpanda.com>, linux-btrfs@vger.kernel.org
Cc: boris@bur.io
Subject: Re: [PATCH RFC 2/2] btrfs: fix replace of seed device
Date: Sun, 23 Aug 2020 23:05:30 +0800 [thread overview]
Message-ID: <0f7add45-911f-825a-965e-7cd76bb3ee22@oracle.com> (raw)
In-Reply-To: <56431875-619d-fb49-efb2-9fcd265a8a69@toxicpanda.com>
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 <anand.jain@oracle.com>
>> ---
>
> 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
next prev parent reply other threads:[~2020-08-23 15:06 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-31 1:38 [PATCH 0/11] btrfs: seed fix null ptr, use only main device_list_mutex, and cleanups Anand Jain
2020-08-21 13:15 ` [PATCH RFC] btrfs/163: replace sprout instead of seed Anand Jain
2020-08-21 13:15 ` [PATCH 1/2] btrfs: initialize sysfs devid and device link for seed device Anand Jain
2020-08-21 13:15 ` [PATCH RFC 2/2] btrfs: fix replace of " Anand Jain
2020-08-21 14:38 ` Josef Bacik
2020-08-23 15:05 ` Anand Jain [this message]
2020-08-21 14:36 ` [PATCH 1/2] btrfs: initialize sysfs devid and device link for " Josef Bacik
2020-08-23 13:05 ` Anand Jain
2020-08-29 11:44 ` Anand Jain
2020-08-30 14:41 ` [PATCH] fstests: btrfs/163: replace sprout instead of seed Anand Jain
2020-08-30 14:40 ` Anand Jain
2020-08-30 14:40 ` [PATCH 01/11] btrfs: initialize sysfs devid and device link for seed device Anand Jain
2020-08-31 9:07 ` Nikolay Borisov
2020-08-31 12:00 ` Anand Jain
2020-08-31 16:21 ` Josef Bacik
2020-09-01 16:16 ` Anand Jain
2020-08-30 14:40 ` [PATCH 02/11] btrfs: refactor btrfs_sysfs_add_devices_dir Anand Jain
2020-08-30 14:40 ` [PATCH 03/11] btrfs: refactor btrfs_sysfs_remove_devices_dir Anand Jain
2020-08-31 8:58 ` Nikolay Borisov
2020-08-31 9:12 ` Anand Jain
2020-08-30 14:40 ` [PATCH 04/11] btrfs: reada: use sprout device_list_mutex Anand Jain
2020-08-31 8:54 ` Nikolay Borisov
2020-08-31 16:08 ` Josef Bacik
2020-09-01 9:02 ` Anand Jain
2020-08-30 14:41 ` [PATCH 05/11] btrfs: btrfs_init_devices_late: " Anand Jain
2020-08-31 8:37 ` Nikolay Borisov
2020-09-01 8:54 ` Anand Jain
2020-08-30 14:41 ` [PATCH 06/11] btrfs: open code list_head pointer in btrfs_init_dev_replace_tgtdev Anand Jain
2020-08-31 8:38 ` Nikolay Borisov
2020-08-30 14:41 ` [PATCH 07/11] btrfs: cleanup btrfs_remove_chunk Anand Jain
2020-08-31 8:43 ` Nikolay Borisov
2020-08-30 14:41 ` [PATCH 08/11] btrfs: cleanup btrfs_assign_next_active_device() Anand Jain
2020-08-31 8:44 ` Nikolay Borisov
2020-08-30 14:41 ` [PATCH 09/11] btrfs: cleanup unnecessary goto in open_seed_device Anand Jain
2020-08-31 8:44 ` Nikolay Borisov
2020-08-30 14:41 ` [PATCH 10/11] btrfs: btrfs_dev_replace_update_device_in_mapping_tree drop file global declare Anand Jain
2020-08-31 8:46 ` Nikolay Borisov
2020-08-30 14:41 ` [PATCH 11/11] btrfs: fix replace of seed device Anand Jain
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