Re: Upgraded from Buster to Bullseye, unmountable Btrfs filesystem

[Qu Wenruo <wqu@suse.com>]

On 2021/11/11 08:18, S. wrote:
> On 11/10/21 18:46, Qu Wenruo wrote:
>> So it means, we still need btrfs-progs to repair it.
>>
>> Thus I believe you still need to prepare a build environment for it.
>>
>> For the worst case, I could try to build a static btrfs-progs for you if
>> you could provide the "uname -a" output.
> 
> Thanks for your time and patience. If you have time for a static build 
> of btrfs-progs I would be very grateful.
> # uname -a
> Linux OpenMediaVault 5.10.0-9-marvell #1 Debian 5.10.70-1 (2021-09-30) 
> armv5tel GNU/Linux
> 

Oh, I was expecting something like aarch64...

I don't have the toolchain for armv5 at hand.

But there is still another way.

Don't mount the fs with older kernel yet, make sure the newer kernel 
still fails with the same dmesg output, especially the same line like:

[  115.428780] BTRFS error (device sda3): block=170459136 read time tree 
block corruption detected

Then use the following command to grab the physical position of the 
corrupted tree block:

# btrfs-map-logical -l 170459136 /dev/sda3

It would show something like:

mirror 1 logical 170459136 physical 178847744 device /dev/test/test
mirror 2 logical 170459136 physical 447283200 device /dev/test/test

Then use the physical values to read the tree block out:

# dd if=/dev/sda3 of=/tmp/mirror1 bs=1 count=16k skip=178847744
# dd if=/dev/sda3 of=/tmp/mirror2 bs=1 count=16k skip=447283200

Then send the file mirror1 and mirror2 to me, so I can modify the tree 
block manually.

NOTE: 178847744 and 447283200 should be from your btrfs-map-logical 
output, the numbers I used are just some examples.
And 16k should be your node size, which you can verify by "btrfs ins 
dump-super /dev/sda3 | grep nodesize".
16K should have been the default value for a long long time.

Thanks,
Qu