bcachefs: Allow for unknown btree IDs

We need to allow filesystems with metadata from newer versions to be
mountable and usable by older versions.

This patch enables us to roll out new btrees without a new major version
number; we can now handle btree roots for unknown btree types.

The unknown btree roots will be retained, and fsck (including
backpointers) will check them, the same as other btree types.

We add a dynamic array for the extra, unknown btree roots, in addition
to the fixed size btree root array, and add new helpers for looking up
btree roots.

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

1 files changed, 9 insertions, 9 deletions

diff --git a/fs/bcachefs/btree_update_interior.c b/fs/bcachefs/btree_update_interior.c
index 4c8effa4b8d9..490c41e8f8fe 100644
--- a/fs/bcachefs/btree_update_interior.c
+++ b/fs/bcachefs/btree_update_interior.c
@@ -1199,7 +1199,7 @@ static void bch2_btree_set_root_inmem(struct bch_fs *c, struct btree *b)
 	       (b->c.level < btree_node_root(c, b)->c.level ||
 		!btree_node_dying(btree_node_root(c, b))));
 
-	btree_node_root(c, b) = b;
+	bch2_btree_id_root(c, b->c.btree_id)->b = b;
 	mutex_unlock(&c->btree_root_lock);
 
 	bch2_recalc_btree_reserve(c);
@@ -2402,7 +2402,7 @@ bool bch2_btree_interior_updates_flush(struct bch_fs *c)
 
 void bch2_journal_entry_to_btree_root(struct bch_fs *c, struct jset_entry *entry)
 {
-	struct btree_root *r = &c->btree_roots[entry->btree_id];
+	struct btree_root *r = bch2_btree_id_root(c, entry->btree_id);
 
 	mutex_lock(&c->btree_root_lock);
 
@@ -2428,15 +2428,15 @@ bch2_btree_roots_to_journal_entries(struct bch_fs *c,
 
 	mutex_lock(&c->btree_root_lock);
 
-	for (i = 0; i < BTREE_ID_NR; i++)
-		if (c->btree_roots[i].alive && !test_bit(i, &have)) {
-			journal_entry_set(end,
-					  BCH_JSET_ENTRY_btree_root,
-					  i, c->btree_roots[i].level,
-					  &c->btree_roots[i].key,
-					  c->btree_roots[i].key.k.u64s);
+	for (i = 0; i < btree_id_nr_alive(c); i++) {
+		struct btree_root *r = bch2_btree_id_root(c, i);
+
+		if (r->alive && !test_bit(i, &have)) {
+			journal_entry_set(end, BCH_JSET_ENTRY_btree_root,
+					  i, r->level, &r->key, r->key.k.u64s);
 			end = vstruct_next(end);
 		}
+	}
 
 	mutex_unlock(&c->btree_root_lock);