Re: [Not TLS] Re: [PATCH 3/4] btrfs: include non-missing as a qualifier for the latest_bdev

[Nikolay Borisov <nborisov@suse.com>]

On 4.10.19 г. 12:08 ч., Graham Cobb wrote:
> On 04/10/2019 09:11, Nikolay Borisov wrote:
>>
>>
>> On 4.10.19 г. 10:50 ч., Anand Jain wrote:
>>> btrfs_free_extra_devids() reorgs fs_devices::latest_bdev
>>> to point to the bdev with greatest device::generation number.
>>> For a typical-missing device the generation number is zero so
>>> fs_devices::latest_bdev will never point to it.
>>>
>>> But if the missing device is due to alienating [1], then
>>> device::generation is not-zero and if it is >= to rest of
>>> device::generation in the list, then fs_devices::latest_bdev
>>> ends up pointing to the missing device and reports the error
>>> like this [2]
>>>
>>> [1]
>>> mkfs.btrfs -fq /dev/sdd && mount /dev/sdd /btrfs
>>> mkfs.btrfs -fq -draid1 -mraid1 /dev/sdb /dev/sdc
>>> sleep 3 # avoid racing with udev's useless scans if needed
>>> btrfs dev add -f /dev/sdb /btrfs
>>
>> Hm, here I think the correct way is to refuse adding /dev/sdb to an
>> existing fs if it's detected to be part of a different one. I.e it
>> should require wipefs to be done.
> 
> I disagree. -f means "force overwrite of existing filesystem on the
> given disk(s)". It shouldn't be any different whether the existing fs is
> btrfs or something else.

You are right, looking at btrfs device add implementation though it
seems that wipefs is being done on the device to be added:

cmd_device_add
 btrfs_prepare_device
  btrfs_wipe_existing_sb

So if the device to be added is formatted and then it goes through
btrfs_init_new_device which commits the transaction which in turns
rewrites the sb then why is the error happening in the first place?


> 
> Graham
>