Re: [PATCH v3 5/6] btrfs-progs: convert: Switch to new rollback function

[Chandan Rajendra <chandan@linux.vnet.ibm.com>]

On Monday, December 19, 2016 02:56:41 PM Qu Wenruo wrote:
> Since we have the whole facilities needed to rollback, switch to the new
> rollback.
> 
> The new rollback function can handle the following things that old
> rollback either can't handle or just refuse to rollback:
> 
> 1) New converted btrfs which allocates new data chunk
>    This is due to the too restrict may_roll_back() condition, which is
>    never a good friend for new convert behavior.
> 
>    The new rollback behavior fixes it by not checking data chunks, but
>    only to check the file extents of the convert image file.
> 
>    If all file extents except the ones in reserved ranges, then we allow
>    rollback.
> 
> 2) New converted btrfs which enabled NO_HOLES feature
>    Thanks to previous patches, we can convert to real NO_HOLES btrfs.
> 
>    And since old rollback assumes that file extents and holes covers the
>    whole image file, it will fail due to the non-exists holes.
> 
>    Fix it by iterating file extents of convert image, and only compare
>    the size we checked against file size if NO_HOLES is not enabled.
> 
> And makes rollback function simpler:
> 
> 1) Read-n-write vs extra chunk tree relocation
>    Since converted btrfs only has 3 ranges that are not 1:1 mapped, just
>    read this data out, and close btrfs, finally write them into position
>    will be good enough, for both new convert and old convert.
>    (To be more specific, old convert is just a subset of more universal
>     new convert behavior)
> 
>    No extra work is needed any more, and we can even open the btrfs RO.

Thanks for fixing this. The patchset works fine on ppc64 and x86_64.

Tested-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>

-- 
chandan