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At btrfs_cow_block() we can use round_down() to align the extent buffer's
logical offset to the start offset of a metadata block group, instead of
the less easy to read set of bitwise operations (two plus one subtraction).
So replace the bitwise operations with a round_down() call.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>