Cannot set-default back to ID 0

Hi,

a recent Ubuntu upgrade killed my system. Luckily I had done a btrfs snapshot before, so I set the particular subvolume as default using

# btrfs subvolume set-default 261 /mnt

from a rescue system and was back up in no time. I then mounted the original volume with subvolid=0 and repaired it. So far so good. However, I fail to set the default volume back to the original.

# btrfs subvolume set-default 0 /

apparently does nothing, I don't get an error but I'm still on the snapshot after reboot. Currently I'm working around this adding rootflag=subvolid=0 on the kernel command line, but that is kind of inconvenient.

Is this expected?

Ubuntu natty amd64, Kernel 2.6.38-rc5, btrfs-tools 0.19+20100601

Thanks
Bernhard

I was asking a similar question in IRC, and the answer I got was:
"The "0" alias for the top-level subvol is implemented in the kernel, not the userspace tools."

I was however able to do this using:

# btrfs subvolume set-default 5 /
Using 5 for "the _real_ subvolid"

Or alternatively:

# mount -o defaults,subvolid=0 /mnt
# btrfsctl -m /mnt/

It's a bit odd, agreed, and the people I spoke to seemed to agree as well =)

- arand