Re: [PATCH] btrfs-progs: mkfs: set super_cache_generation to 0 if we're using free space tree

[David Sterba <dsterba@suse.cz>]

On Sat, Jul 31, 2021 at 03:42:40PM +0800, Qu Wenruo wrote:
> [HICCUP]
> There is a bug report that mkfs.btrfs -R free-space-tree still makes
> kernel to try to cleanup the v1 space cache:
> 
>   # mkfs.btrfs -R free-space-tree -f /dev/test/scratch1
>   # mount /dev/test/scratch1 /mnt/btrfs
>   # dmesg | grep cleaning
>   BTRFS info (device dm-6): cleaning free space cache v1
> 
> [CAUSE]
> By default, mkfs.btrfs will set super cache generation to (u64)-1, which
> will inform kernel that the v1 space cache is invalid, needs to
> regenerate it.
> 
> But for free space cache tree, kernel will set super cache generation to
> 0, to indicate v1 space cache is not in use.
> 
> This means, even we enabled free space tree with all the RO compatible
> bits and new tree, as long as super cache generation is not 0, kernel
> still consider the fs has some invalid v1 space cache, and will try to
> remove them.
> 
> [FIX]
> This is not a big deal, but to make the "-R free-space-tree" to really
> work as kernel, we also need to set super cache generation to 0.
> 
> Reported-by: Chris Murphy <lists@colorremedies.com>
> Link: https://lore.kernel.org/linux-btrfs/CAJCQCtSvgzyOnxtrqQZZirSycEHp+g0eDH5c+Kw9mW=PgxuXmw@mail.gmail.com/
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Added to devel, thanks.