Re: [PATCH 0/4] btrfs: cleanups and preparation for the incoming RAID56J features

[David Sterba <dsterba@suse.cz>]

On Fri, May 13, 2022 at 04:34:27PM +0800, Qu Wenruo wrote:
> Since I'm going to introduce two new chunk profiles, RAID5J and RAID6J
> (J for journal), if we're relying on ad-hoc if () else if () branches to
> calculate thing like number of p/q stripes, it will cause a lot of
> problems.
> 
> In fact, during my development, I have hit tons of bugs related to this.
> 
> One example is alloc_rbio(), it will assign rbio->nr_data, if we forgot
> to update the check for RAID5 and RAID6 profiles, we will got a bad
> nr_data == num_stripes, and screw up later writeback.
> 
> 90% of my suffering comes from such ad-hoc usage doing manual checks on
> RAID56.
> 
> Another example is, scrub_stripe() which due to the extra per-device
> reservation, @dev_extent_len is no longer the same the data stripe
> length calculated from extent_map.
> 
> So this patchset will do the following cleanups preparing for the
> incoming RAID56J (already finished coding, functionality and on-disk
> format are fine, although no journal yet):
> 
> - Calculate device stripe length in-house inside scrub_stripe()
>   This removes one of the nasty mismatch which is less obvious.
> 
> - Use btrfs_raid_array[] based calculation instead of ad-hoc check
>   The only exception is scrub_nr_raid_mirrors(), which has several
>   difference against btrfs_num_copies():
> 
>   * No iteration on all RAID6 combinations
>     No sure if it's planned or not.
> 
>   * Use bioc->num_stripes directly
>     In that context, bioc is already all the mirrors for the same
>     stripe, thus no need to lookup using btrfs_raid_array[].
> 
> With all these cleanups, the RAID56J will be much easier to implement.
> 
> Qu Wenruo (4):
>   btrfs: remove @dev_extent_len argument from scrub_stripe() function
>   btrfs: use btrfs_chunk_max_errors() to replace weird tolerance
>     calculation
>   btrfs: use btrfs_raid_array[] to calculate the number of parity
>     stripes
>   btrfs: use btrfs_raid_array[].ncopies in btrfs_num_copies()

Added to misc-next, thanks.