[FIXED] Can't read superblock
Desobediente
Long story of how my SSD drive got corrupted: I went to sleep one day after making sure all torrents were seeding, unaware that the power chord of qubestop-1 (that's how I call the computer) was loose, and therefore it ran from battery for some hours, but when I woke up qubestop-1 was off. I plugged the power cord, tried to boot and after I unencrypted the hard disk, I got a warning that the second partition couldn't mount because of a superblock error. Then I got dropped to an emergency shell.
So I was left with a disk that was mounting only the boot partition and the encrypted swap, but not the qubes root filesystem. I could decrypt it, but not mount the BTRFS filesystem.
I then boot qubestop-1 from a Kali Linux live usb. It didn't have btrfs, so I had to install it:
root@kali:~# apt-get update; apt-get install btrfs-tools
The next step (or could have been the prior) was to mount the qubes SSD drive and decrypt the partition with errors. I used gnome-disks for that. It is important to note that the device that I will use below is not /dev/sdb2. When the partition was unencrypted, gnome-disks "created" a new file which looks like /dev/mapper/luks-01234567-890a-bcde-f012-3456789abcde.
I first made sure that btrfs-check was going to fix the error by running in read only mode. This is the default and normally don't require any further action:
root@kali:~# btrfs check -p /dev/mapper/luks-01234567-890a-bcde-f012-3456789abcde
After I've done saying my prayers and convinced myself that I knew what I was doing, I ran the real deal with the scary --repair option:
root@kali:~# btrfs check -p --repair /dev/mapper/luks-01234567-890a-bcde-f012-3456789abcde
I could then mount the partition normally and resume seeding my torrents.
One thing totally unrelated but which should be noted is that KDE or some other tool at dom0 should have hibernated before the battery finished, and it didn't. I'm not sure if this was my fault.