Re: [RFC PATCH 0/2] Btrfs partial csum support

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

Ping

Any comments?

Thanks,
Qu

Qu Wenruo wrote on 2015/07/10 12:09 +0800:
> This patchset will add partial csum support for btrfs.
>
> Partial csum will take full advantage of the 32 bytes csum space inside
> the tree block, while still maintain backward compatibility on old
> kernels.
>
> The overall idea is like the following on 16K leaf:
> [Old tree block csum]
> 0     4     8    12    16    20    24    28    32
> -------------------------------------------------
> |csum |   unused, all 0				|
> -------------------------------------------------
> Csum is the crc32 of the whole tree block data.
>
> [New tree block csum]
> -------------------------------------------------
> |csum0|csum1|csum2|csum3|csum4|csum5|csum6|csum7|
> -------------------------------------------------
> Where csum0 is the same as the old one, crc32 of the whole tree block
> data.
>
> And csum1~csum7 will restore crc32 of each eighth part.
> Take example of 16K leafsize, then:
> csum1: crc32 of BTRFS_CSUM_SIZE~4K
> csum2: crc32 of 4K~6K
> ...
> csum7: crc32 of 14K~16K
>
>
> When nodesize is small, like 4K, partial csum is completely useless.
> But when nodesize grows up, like 32K, each partial csum will just covers
> a page, making scrub able to judge which page is OK even without reading
> out the whole tree block.
>
> And add the possibility to fix case like corruption happens at all
> mirror but in different part.
> Such case should be more possible if nodesize goes up beyond 16K.
>
> Qu Wenruo (1):
>    btrfs: csum: Introduce partial csum for tree block.
>
> Zhao Lei (1):
>    btrfs: scrub: Add support partial csum
>
>   fs/btrfs/disk-io.c |  74 ++++++++++++-------
>   fs/btrfs/scrub.c   | 207 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
>   2 files changed, 255 insertions(+), 26 deletions(-)
>