bcachefs: Scan for old btree nodes if necessary on mount

We dropped support for !BTREE_NODE_NEW_EXTENT_OVERWRITE but it turned
out there were people who still had filesystems with btree nodes in that
format in the wild. This adds a new compat feature that indicates we've
scanned for and rewritten nodes in the old format, and does that scan at
mount time if the option isn't set.

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

fs/bcachefs/bcachefs_format.h

@@ -1373,6 +1373,7 @@ enum bch_sb_feature {
 enum bch_sb_compat {
 	BCH_COMPAT_FEAT_ALLOC_INFO	= 0,
 	BCH_COMPAT_FEAT_ALLOC_METADATA	= 1,
+	BCH_COMPAT_FEAT_EXTENTS_ABOVE_BTREE_UPDATES_DONE = 2,
 };
 
 /* options: */

fs/bcachefs/btree_gc.c

@@ -1618,7 +1618,8 @@ int bch2_gc_thread_start(struct bch_fs *c)
 {
 	struct task_struct *p;
 
-	BUG_ON(c->gc_thread);
+	if (c->gc_thread)
+		return 0;
 
 	p = kthread_create(bch2_gc_thread, c, "bch-gc/%s", c->name);
 	if (IS_ERR(p)) {

fs/bcachefs/move.c

@@ -845,6 +845,25 @@ static enum data_cmd rewrite_old_nodes_pred(struct bch_fs *c, void *arg,
 	return DATA_SKIP;
 }
 
+int bch2_scan_old_btree_nodes(struct bch_fs *c, struct bch_move_stats *stats)
+{
+	int ret;
+
+	ret = bch2_move_btree(c,
+			      0,		POS_MIN,
+			      BTREE_ID_NR,	POS_MAX,
+			      rewrite_old_nodes_pred, c, stats);
+	if (!ret) {
+		mutex_lock(&c->sb_lock);
+		c->disk_sb.sb->compat[0] |= 1ULL << BCH_COMPAT_FEAT_EXTENTS_ABOVE_BTREE_UPDATES_DONE;
+		c->disk_sb.sb->version_min = c->disk_sb.sb->version;
+		bch2_write_super(c);
+		mutex_unlock(&c->sb_lock);
+	}
+
+	return ret;
+}
+
 int bch2_data_job(struct bch_fs *c,
 		  struct bch_move_stats *stats,
 		  struct bch_ioctl_data op)
@@ -894,17 +913,7 @@ int bch2_data_job(struct bch_fs *c,
 		ret = bch2_replicas_gc2(c) ?: ret;
 		break;
 	case BCH_DATA_OP_REWRITE_OLD_NODES:
-		ret = bch2_move_btree(c,
-				      op.start_btree,	op.start_pos,
-				      op.end_btree,	op.end_pos,
-				      rewrite_old_nodes_pred, &op, stats) ?: ret;
-
-		if (!ret) {
-			mutex_lock(&c->sb_lock);
-			c->disk_sb.sb->version_min = c->disk_sb.sb->version;
-			bch2_write_super(c);
-			mutex_unlock(&c->sb_lock);
-		}
+		ret = bch2_scan_old_btree_nodes(c, stats);
 		break;
 	default:
 		ret = -EINVAL;

fs/bcachefs/move.h

@@ -52,6 +52,8 @@ typedef enum data_cmd (*move_pred_fn)(struct bch_fs *, void *,
 				struct bkey_s_c,
 				struct bch_io_opts *, struct data_opts *);
 
+int bch2_scan_old_btree_nodes(struct bch_fs *, struct bch_move_stats *);
+
 int bch2_move_data(struct bch_fs *,
 		   enum btree_id, struct bpos,
 		   enum btree_id, struct bpos,

fs/bcachefs/rebalance.c

@@ -312,6 +312,9 @@ int bch2_rebalance_start(struct bch_fs *c)
 {
 	struct task_struct *p;
 
+	if (c->rebalance.thread)
+		return 0;
+
 	if (c->opts.nochanges)
 		return 0;
 

fs/bcachefs/recovery.c

@@ -16,6 +16,7 @@
 #include "journal_io.h"
 #include "journal_reclaim.h"
 #include "journal_seq_blacklist.h"
+#include "move.h"
 #include "quota.h"
 #include "recovery.h"
 #include "replicas.h"
@@ -1200,6 +1201,20 @@ use_clean:
 		bch_verbose(c, "quotas done");
 	}
 
+	if (!(c->sb.compat & (1ULL << BCH_COMPAT_FEAT_EXTENTS_ABOVE_BTREE_UPDATES_DONE))) {
+		struct bch_move_stats stats = { 0 };
+
+		bch_verbose(c, "scanning for old btree nodes");
+		ret = bch2_fs_read_write(c);
+		if (ret)
+			goto err;
+
+		ret = bch2_scan_old_btree_nodes(c, &stats);
+		if (ret)
+			goto err;
+		bch_verbose(c, "scanning for old btree nodes done");
+	}
+
 	mutex_lock(&c->sb_lock);
 	if (c->opts.version_upgrade) {
 		if (c->sb.version < bcachefs_metadata_version_new_versioning)
@@ -1271,6 +1286,7 @@ int bch2_fs_initialize(struct bch_fs *c)
 		le16_to_cpu(bcachefs_metadata_version_current);
 	c->disk_sb.sb->features[0] |= 1ULL << BCH_FEATURE_atomic_nlink;
 	c->disk_sb.sb->features[0] |= BCH_SB_FEATURES_ALL;
+	c->disk_sb.sb->compat[0] |= 1ULL << BCH_COMPAT_FEAT_EXTENTS_ABOVE_BTREE_UPDATES_DONE;
 
 	bch2_write_super(c);
 	mutex_unlock(&c->sb_lock);