bcachefs: bucket_gens btree

To improve mount times, add a btree for just bucket gens, 256 of them
per key: this means we'll have to scan drastically less metadata at
startup.

This adds
 - trigger for keeping it in sync with the all btree
 - initialization code, for filesystems from previous versions
 - new path for reading bucket gens
 - new fsck code

And a new on disk format version.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/bcachefs/bcachefs.h b/fs/bcachefs/bcachefs.h
index 74632105fb45..acd4adaf475a 100644
--- a/fs/bcachefs/bcachefs.h
+++ b/fs/bcachefs/bcachefs.h
@@ -441,6 +441,7 @@ enum gc_phase {
 	GC_PHASE_BTREE_freespace,
 	GC_PHASE_BTREE_need_discard,
 	GC_PHASE_BTREE_backpointers,
+	GC_PHASE_BTREE_bucket_gens,
 
 	GC_PHASE_PENDING_DELETE,
 };