Re: [PATCH 0/3] btrfs-progs: detect and fix orphan roots without orphan items

[Qu Wenruo <wqu@suse.com>]

Hi David,

Any idea why the patchest is not merged yet?

In fact we got a newer report on the same problem, which this patchset 
is definitely going to help:

https://lore.kernel.org/linux-btrfs/c75599fa-3b4e-5a5a-c695-75c99b315a06@gmail.com/

It has two subvolumes which has 0 refs, but no ORPHAN item for it.

Thanks,
Qu

On 2021/6/25 15:13, Qu Wenruo wrote:
> There is bug report from Zhenyu Wu <wuzy001@gmail.com>, where even there
> is only one subvolume, his filesystem still consumes way more space than
> expected.
> 
> The problem is, there are 58 snapshots, but all of them have no
> ROOT_REF/ROOT_BACKREF, and all their root refs is 0.
> 
> But strangely there is no orphan items for them.
> 
> This means, btrfs kernel module won't detect them as orphan nor queue
> them to be removed.
> 
> "btrfs subvolume delete -i" do no helps, as it still requires
> ROOT_BACKREF to resolve the dentry.
> 
> For now, we should teach btrfs check to detect and repair the case by
> adding new orphan items for them.
> 
> The root cause I guess is some strange behavior for orphan item insert
> and subvolume unlink.
> As the report mentioned that he had one forced power off.
> 
> Qu Wenruo (3):
>    btrfs-progs: check/lowmem: add the ability to detect and repair orphan
>      subvolume trees which doesn't have orphan item
>    btrfs-progs: check/original: detect and repair orphan subvolume
>      without orphan item
>    btrfs-progs: fsck-tests: add test image for orphan roots without an
>      orphan item
> 
>   check/main.c                                  |  37 ++++--------
>   check/mode-common.c                           |  56 ++++++++++++++++++
>   check/mode-common.h                           |   3 +
>   check/mode-lowmem.c                           |  42 +++++++------
>   .../048-orphan-roots/.lowmem_repairable       |   0
>   .../048-orphan-roots/default.img.xz           | Bin 0 -> 2584 bytes
>   6 files changed, 93 insertions(+), 45 deletions(-)
>   create mode 100644 tests/fsck-tests/048-orphan-roots/.lowmem_repairable
>   create mode 100644 tests/fsck-tests/048-orphan-roots/default.img.xz
>