Re: [PATCH 0/4] btrfs: DEV_STATS item related minor fixes

[David Sterba <dsterba@suse.cz>]

On Tue, Apr 07, 2026 at 07:03:57PM +0930, Qu Wenruo wrote:
> [BACKGROUND]
> DEV_STATS (objectid, not type) items are storing the error counts for
> each device. It's updated every time an error is hit, including
> the following types:
> 
> - READ errors
> - WRITE errors
> - FLUSH errors
>   Above alls are all errors directly returned from the device.
> 
> - CORRUPTION errors
>   Aka, checksum mismatch.
> 
> - GENERATION errors
>   Metadata generation mismatch.
> 
> [MINOR BUGS]
> Recently when debugging an error reported about rejected dev-replace,
> the device tree dump includes a DEV_STATS item for devid 0.
> 
> I'm wondering if that DEV_STATS item will ever be deleted, but
> unfortunately it will never be deleted.
> 
> Normally it's not a big deal, as the DEV_STATS are normally all zeros.
> 
> But if it's not, and a new dev-replace is started and interrupted, at
> the next mount the replace target device will suddenly inherit all the
> error records, giving end users false alerts about a completely good
> device.
> 
> [FIX]
> The first 2 are manually removing the DEV_STATS items when dev-replace
> and dev-removal finishes.

The device stat item is expected by btrfs-progs even if it's just zeros,
otherwise the 'btrfs device stats' prints just 'no stats found'. This
has a high potential to break any monitoring tools or scripts. So please
don't delete the item, and create it empty in case it does not exist.

For the wrong stats on the replaced device the stats should be zero from
the beginning of the operation.