Re: [PATCH v2 0/6] btrfs-progs: introduce "btrfs rescue fix-data-checksum"

[David Sterba <dsterba@suse.cz>]

On Thu, May 15, 2025 at 05:30:15PM +0930, Qu Wenruo wrote:
> [CHANGELOG]
> v2:
> - Rename the subcommand to "fix-data-checksum"
>   It's better to use full name in the command name
> 
> - Remove unused members inside corrupted_block
>   The old @extent_bytenr and @extent_len is no longer needed, even for
>   the future file-deletion action.
> 
> - Fix the bitmap size off-by-1 bug
>   We must use the bit 0 to represent mirror 1, or the bitmap size will
>   exceed num_mirrors.
> 
> - Introduce -i|--interactive mode
>   Will ask the user for the action on the corrupted block, including:
> 
>   * Ignore
>     The default behavior if no command is provided
> 
>   * Use specified mirror to update the data checksum item
>     The user must input a number inside range [1, num_mirrors].
> 
> - Introduce -m|--mirror <num> mode
>   Use specified mirror for all corrupted blocks.
>   The value <num> must be >= 1. And if the value is larger than the
>   actual max mirror number, the real mirror number will be
>   `num % (num_mirror + 1)`.
> 
> We have a long history of data csum mismatch, caused by direct IO and
> buffered being modified during writeback.
> 
> Although the problem is worked around in v6.15 (and being backported),
> for the affected fs there is no good way to fix them, other than complex
> manually find out which files are affected and delete them.
> 
> This series introduce the initial implementation of "btrfs rescue
> fix-data-checksum", which is designed to fix such problem by either:
> 
> - Update the csum items using the data from specified copy
> 
> The subcommand has 3 modes so far:
> 
> - Readonly mode
>   Only report all corrupted blocks and affected files, no repair is
>   done.
> 
> - Interactive mode
>   Ask for what to do, including
> 
>   * Ignore (the default)
>   * Use certain mirror to update the checksum item
> 
> - Mirror mode
>   Use specified mirror to update the checksum item, the batch mode of
>   the interactive one.
> 
> In the future, there will be one more mode:
> 
> - Delete mode
>   Delete all involved files.
> 
>   There are still some points to address before implementing this mode.
> 
> Qu Wenruo (6):
>   btrfs-progs: introduce "btrfs rescue fix-data-checksum"
>   btrfs-progs: fix a bug in btrfs_find_item()
>   btrfs-progs: fix-data-checksum: show affected files
>   btrfs-progs: fix-data-checksum: introduce interactive mode
>   btrfs-progs: fix-data-checksum: update csum items to fix csum mismatch
>   btrfs-progs: fix-data-checksum: introduce -m|--mirror option

Thanks, this is certainly useful and is a reasonable compromise to have
a way to fix the checksums. I did some conding style fixups in the devel
branch, I'll comment under the patches.