On 01/22/2016 11:25 PM, Hugo Mills wrote:

On Fri, Jan 22, 2016 at 04:11:53PM +0100, Radek Sprta wrote:

quoted

Hello everybody,

after a recent power outage attempting to mount a my btrfs partition
fails with the following error:

mount: wrong fs type, bad option, bad superblock on /dev/sda8,
        missing codepage or helper program, or other error

This is what dmesg shows:
[ 1035.236081] BTRFS (device sda8): parent transid verify failed on
410124288 wanted 85753 found 85755
[ 1035.240756] BTRFS (device sda8): parent transid verify failed on
410124288 wanted 85753 found 85755
[ 1035.240780] BTRFS: failed to read tree root on sda8
[ 1035.252025] BTRFS: open_ctree failed

    Try mounting with -orecovery. That's the main approach for dealing
with transid failures.

IIRC, current "recovery" will only try to use backup roots.
And that's why I am going to rename the mount option to "usebackuproot" 
in next kernel release.

It's quite strange that current kernel doesn't have mount option to 
ignore transid error any longer.
Just grep "RECOVERY" in btrfs modules sources, and it should be quite 
easy to find this fact.

quoted

Below is the result of btrfs check:
Checking filesystem on /dev/sda8
UUID: b0486700-ff9f-4979-8735-257ff1428a0d
checking extents
checking free space cache
checking fs roots
checking csums
checking root refs
found 311702978854 bytes used err is 0
total csum bytes: 271057636
total tree bytes: 1859862528
total fs tree bytes: 1473953792
total extent tree bytes: 72876032
btree space waste bytes: 377740163
file data blocks allocated: 11278336921600
  referenced 975937630208
btrfs-progs v4.0

    That looks reasonably promising -- nothing seriously damaged that
btrfs check could find, at least.

Quite strange.
IIRC, btrfsck should at least report transid error.
As written in disk-io.c, verify_parent_transid() function.

Since btrfsck reports no error, I think btrfs-image could dump the 
metadata without problem.

So, would you please dump a btrfs-image dump, by the following command?
# btrfs-image -c9 /dev/sda8

Such dump will only contain your metadata(dir/file hierarchy including 
dir/file names), no data will be dump.

And if you think the filename can leak important data, you can use '-ss' 
or '-s' to sanitize them.

Thanks,
Qu

quoted

I tried googling the "open_ctree failed" error, but couldn't find any
definite answers. Here's some additional info:

    "open_ctree failed" is a really generic error message,
unfortunately. Almost every case that leads to a failure to mount will
output that message, so there's no single solution you can find from
just that error. The "parent transid verify failed" is a much better
indication of what's happened here, and the small difference in
transid numbers would indicate that -orecovery might actually have a
chance of working.

    Hugo.

quoted

uname -a:
Linux Computer 4.2.0-22-generic #27-Ubuntu SMP Thu Dec 17 22:57:08 UTC
2015 x86_64 x86_64 x86_64 GNU/Linux

btrfs fi show:
Label: none  uuid: b0486700-ff9f-4979-8735-257ff1428a0d
Total devices 1 FS bytes used 290.37GiB
devid    1 size 301.32GiB used 295.04GiB path /dev/sda8

Thanks in advance for any help,
Radek