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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 18/09/2025 1.17 pm, Filipe Manana wrote: > On Thu, Sep 18, 2025 at 6:10 AM Mark Harmstone wrote: >> >> On 18/09/2025 1.33 am, David Sterba wrote: >>> On Wed, Sep 17, 2025 at 04:41:43PM +0100, Filipe Manana wrote: >>>> With this btrfs-progs release, running 'btrfs check' fails on a >>>> filesystem created by an older mkfs.btrfs. >>> >>>> A bisection points to: >>>> >>>> commit e2cf6a03796b73d446b086022c0dfcf6a6552928 >>>> Author: Mark Harmstone >>>> Date: Fri Jul 18 15:26:27 2025 +0100 >>>> >>>> btrfs-progs: use btrfs_lookup_block_group() in check_free_space_tree() >>> >>> Thanks for the report, I'll do a release with this patch reverted unless >>> there's an updated fix. >> >> The patch is correct: older versions of mkfs were creating spurious >> free-space entries. btrfs-check was supposed to diagnose this but there >> was a bug that meant it only triggered for entries at the end of the tree. > > Sure, but now we have btrfs check failing for every fs created up to > btrfs-progs v16.0 since we have the free space tree feature. > That makes scripts fail since btrfs check returns a non-zero status > now for such fs. > Do we have any code to remove those unnecessary and harmless free space entries? > > This will confuse and potentially scare some users, besides breaking > scripts that verify the result from btrfs check exit status. To be clear, this patch does address an actual issue: it caused me problems while developing btrfs-discard-check. Leo independently ran into it last year too. btrfs rescue clear-space-cache will get rid of the error, though it's obviously a little heavy-handed. I don't know if btrfs check --repair fixes the FST. Maybe the thing to do is to add a compat_flag to say that the FST doesn't contain spurious entries, and to clean these up and set the flag on mount if it's not there - what do you think? Like we have for BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE_VALID already, though compat rather than compat_ro because the kernel won't create these entries itself.