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, 8 insertions, 8 deletions

diff --git a/fs/bcachefs/recovery.c b/fs/bcachefs/recovery.c
index b86442c7c912..268fae9e7bf9 100644
--- a/fs/bcachefs/recovery.c
+++ b/fs/bcachefs/recovery.c
@@ -702,13 +702,13 @@ static int journal_replay_entry_early(struct bch_fs *c,
 	case BCH_JSET_ENTRY_btree_root: {
 		struct btree_root *r;
 
-		if (entry->btree_id >= BTREE_ID_NR) {
-			bch_err(c, "filesystem has unknown btree type %u",
-				entry->btree_id);
-			return -EINVAL;
+		while (entry->btree_id >= c->btree_roots_extra.nr + BTREE_ID_NR) {
+			ret = darray_push(&c->btree_roots_extra, (struct btree_root) { NULL });
+			if (ret)
+				return ret;
 		}
 
-		r = &c->btree_roots[entry->btree_id];
+		r = bch2_btree_id_root(c, entry->btree_id);
 
 		if (entry->u64s) {
 			r->level = entry->level;
@@ -980,8 +980,8 @@ static int read_btree_roots(struct bch_fs *c)
 	unsigned i;
 	int ret = 0;
 
-	for (i = 0; i < BTREE_ID_NR; i++) {
-		struct btree_root *r = &c->btree_roots[i];
+	for (i = 0; i < btree_id_nr_alive(c); i++) {
+		struct btree_root *r = bch2_btree_id_root(c, i);
 
 		if (!r->alive)
 			continue;
@@ -1014,7 +1014,7 @@ static int read_btree_roots(struct bch_fs *c)
 	}
 
 	for (i = 0; i < BTREE_ID_NR; i++) {
-		struct btree_root *r = &c->btree_roots[i];
+		struct btree_root *r = bch2_btree_id_root(c, i);
 
 		if (!r->b) {
 			r->alive = false;