Re: [PATCH 0/2] btrfs-progs: btrfstune: fix false alerts on dev-replace when changing csum

[David Sterba <dsterba@suse.cz>]

On Sun, Jun 02, 2024 at 01:15:31PM +0930, Qu Wenruo wrote:
> There is a bug report that if a btrfs has experienced any dev-replace,
> "btrfstune --csum" would always report a running dev-replace and refuse
> to continue.
> 
> It turns out that, DEV_REPLACE item is not a transient one (but not
> created properly as mkfs time either), after a dev-replace the
> DEV_REPLACE item would exist forever, recording the last dev-replace
> timestamp.

I don't think we want to create the item at mkfs time, this would be
confusing and not related to any previous dev-replace operation.

> Although I really hate such behavior (especially when balance item would
> be gone after a balance is finished/canceled), at least fix the problem
> first.

It's handled differently yeah, though the two operations are bit
different, one would run balance more often that dev-replace. But it's
still only for internal tracking, other than that it's not handled the
same way I don't se any problem.

> The first patch enhances the print-tree to properly output the
> contents of the dev-replace item, then the second patch fixes the
> problem.
> 
> I'd like to add test cases for it, but it turns out there is no csum
> change test cases.

I have tests locally from the time I developed it but yeah they should
be in the testsuite.

> My guess is we do not have proper way to skip the test if it's
> experiemental feature?

Currently there's no way to detect it. For some things we can use the
help text, like is done for some features in fstests.

> Maybe it's time to move csum change out of experiemental features?

This depends on creating the separate command group 'tune', this is in
the phase of interface review.

> Qu Wenruo (2):
>   btrfs-progs: print-tree: add support for dev-replace item
>   btrfs-progs: change-csum: handle finished dev-replace correctly

Added to devel, thanks.