Re: strange btrfs sub list output

[Stephane Chazelas <stephane_chazelas@yahoo.fr>]

2011-05-26 22:22:03 +0100, Stephane Chazelas:
[...]
> I get a btrfs sub list output that I don't understand:
> 
> # btrfs sub list /backup/
> ID 257 top level 5 path u1/linux/lvm+btrfs/storage/data/data
> ID 260 top level 5 path u2/linux/lvm/linux/var/data
> ID 262 top level 5 path u1/linux/lvm+btrfs/storage/data/snapshots/2010-10-11
> ID 263 top level 5 path u2/linux/lvm/linux/home/snapshots/2011-04-07
> ID 264 top level 5 path u2/linux/lvm/linux/root/snapshots/2011-04-07
> ID 265 top level 5 path u2/linux/lvm/linux/var/snapshots/2011-04-07
> ID 266 top level 5 path u1/linux/lvm+btrfs/storage/data/snapshots/2010-10-26
> ID 267 top level 5 path u1/linux/lvm+btrfs/storage/data/snapshots/2010-11-08
> ID 268 top level 5 path u1/linux/lvm+btrfs/storage/data/snapshots/2010-11-22
> ID 269 top level 5 path u1/linux/lvm+btrfs/storage/data/snapshots/2010-12-15
> ID 270 top level 5 path u2/linux/lvm/linux/home/snapshots/2011-04-14
> ID 271 top level 5 path u2/linux/lvm/linux/root/snapshots/2011-04-14
> ID 272 top level 5 path u2/linux/lvm/linux/var/snapshots/2011-04-14
> ID 273 top level 5 path u1/linux/lvm+btrfs/storage/data/snapshots/2010-12-29
> ID 274 top level 5 path u1/linux/lvm+btrfs/storage/data/snapshots/2011-01-26
> ID 275 top level 5 path u1/linux/lvm+btrfs/storage/data/snapshots/2011-03-07
> ID 276 top level 5 path u1/linux/lvm+btrfs/storage/data/snapshots/2011-04-01
> ID 277 top level 5 path u2/linux/lvm/linux/home/data
> ID 278 top level 5 path u2/linux/lvm/linux/home/snapshots/2011-04-27
> ID 279 top level 5 path u2/linux/lvm/linux/root/snapshots/2011-04-27
> ID 280 top level 5 path u2/linux/lvm/linux/var/snapshots/2011-04-27
> ID 281 top level 5 path u3:10022/vm+xfs@u9/xvda1/g1/v4/data
> ID 282 top level 5 path u3:10022/vm+xfs@u9/xvda1/g1/v4/snapshots/2011-05-19
> ID 283 top level 5 path u5/vm+xfs@u9/xvda1/g1/v5/data
> ID 284 top level 5 path u6:10022/vm+xfs@u8/xvda1/g8/v3/data
> ID 286 top level 5 path u5/vm+xfs@u9/xvda1/g1/v5/snapshots/2011-05-24
> ID 287 top level 285 path data
> ID 288 top level 5 path u4/vm+xfs@u9/xvda1/g1/v1/data
> ID 289 top level 5 path u4/vm+xfs@u9/xvda1/g1/v1/snapshots/2011-03-11
> ID 290 top level 5 path u4/vm+xfs@u9/xvda1/g1/v2/data
> ID 291 top level 5 path u4/vm+xfs@u9/xvda1/g1/v2/snapshots/2011-05-11
> ID 292 top level 5 path u4/vm+xfs@u9/xvda1/g1/v1/snapshots/2011-05-11
[...]
> There is no "/backup/data" directory. There is however a
> /backup/u6:10022/vm+xfs@u8/xvda1/g8/v3/snapshots/2011-03-30 that
> contains the same thing as what I get if I mount the fs with
> subvolid=287. And I did do a btrfs sub snap data
> snapshots/2011-03/30 there.
> 
> What could be the cause of that? How to fix it?
> 
> In case that matters, there used to be more components in the
> path of u6:10022/vm+xfs@u8/xvda1/g8/v3/data.
[...]

I tried deleting the
/backup/u6:10022/vm+xfs@u8/xvda1/g8/v3/snapshots/2011-03-30
subvolume (what seems to be id 287) and I get:

# btrfs sub delete snapshots/2011-03-30
Delete subvolume '/backup/u6:10022/vm+xfs@u8/xvda1/g8/v3/snapshots/2011-03-30'
ERROR: cannot delete '/backup/u6:10022/vm+xfs@u8/xvda1/g8/v3/snapshots/2011-03-30'

With a strace, it tells me:

ioctl(3, 0x5000940f, 0x7fffc7841a80)    = -1 ENOTEMPTY (Directory not empty)

Then I realised that there was a "data" directory in there and
that snapshots/2011-03-30 was actually id 285 (which doesn't
appear in the btrfs sub list) and "snapshots/2011-03-30/data" is
id 287.

What do those top-level IDs mean by the way?

Then I was able to delete snapshots/2011-03-30/data, but
snapshots/2011-03-30 still didn't appear in the list.

Then I was able to delete snapshots/2011-03-30 and recreate it,
and this time it was fine.

Still don't know what happened there.

-- 
Stephane