Re: [PATCH 0/7] Allow btrfsck to reset csum of all tree blocks, AKA dangerous mode.

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

Ping.

No new comment nor merged?

Thanks,
Qu

-------- Original Message  --------
Subject: [PATCH 0/7] Allow btrfsck to reset csum of all tree blocks, AKA 
dangerous mode.
From: Qu Wenruo <quwenruo@cn.fujitsu.com>
To: <linux-btrfs@vger.kernel.org>
Date: 2015年02月04日 15:16

> Btrfs's metadata csum is a good mechanism, keeping bit error away from
> sensitive kernel. But such mechanism will also be too sensitive, like
> bit error in csum bytes or low all zero bits in nodeptr.
> It's a trade using "error tolerance" for stable, and is reasonable for
> most cases since there is DUP/RAID1/5/6/10 duplication level.
>
> But in some case, whatever for development purpose or despair user who
> can't tolerant all his/her inline data lost, or even crazy QA team
> hoping btrfs can survive heavy random bits bombing, there are some guys
> want to get rid of the csum protection and face the crucial raw data no
> matter what disaster may happen.
>
> So, introduce the new '--dangerous' (or "destruction"/"debug" if you like)
> option for btrfsck to reset all csum of tree blocks.
>
> The csum reseting have the following features:
> 1) Top to down level by level
> The csum resetting is done from tree to level 1, and only when all the
> csum of nodes in this level is reset and can pass read_tree_block()
> check, it will continue to next level.
> And all bytenr in nodeptr will be re-aligned, so bit error in the low 12
> bits(4K sector size case) can also be repaired without pain.
> With this behavior, error in nodeptr has a chance not affecting its
> child.
>
> 2) No Copy-on-write
> COW means we needs to have a valid extent tree, if extent tree is
> corrupted COW will only be a BUG_ON blocking us.
> So all the r/w in this dangerous mode will use no-cow write. That's why
> we export and slightly modified write_tree_block() to do no-cow tree
> block write with newly calculated csum.
> Since the write is not cowed, if it fails, it will also destroy the last
> hope for manual inspection.
>
> Qu Wenruo (7):
>    btrfs-progs: Add btrfs_(prev/next)_tree_block() to keep search result
>      in     the same level of path->lowest_level.
>    btrfs-progs: Introduce btrfs_next_slot() function to iterate to next
>        slot in given level.
>    btrfs-progs: Allow btrfs_read_fs_root() to re-read the tree node.
>    btrfs-progs: Export write_tree_block() and allow it to do nocow write.
>    btrfs-progs: Introduce new function reset_tree_block_csum() for later
>         tree block csum reset.
>    btrfs-progs: Introduce new function reset_(one_root/roots)_csum() to
>        reset one/all tree's csum in tree root.
>    btrfs-progs: Introduce "--dangerous" option to reset all tree block
>       csum.
>
>   cmds-check.c | 284 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>   ctree.c      |  18 ++--
>   ctree.h      |  25 +++++-
>   disk-io.c    |  55 +++++++++---
>   disk-io.h    |   3 +
>   5 files changed, 359 insertions(+), 26 deletions(-)
>