bcachefs: Add open_buckets to sysfs

This is to help debug a rare shutdown deadlock in the allocator code -
the btree code is leaking open_buckets.

Signed-off-by: Kent Overstreet <[e-mail]>

fs/bcachefs/alloc_background.c

···
 {
 	spin_lock_init(&c->freelist_lock);
 }
+
+void bch2_open_buckets_to_text(struct printbuf *out, struct bch_fs *c)
+{
+	struct open_bucket *ob;
+
+	for (ob = c->open_buckets;
+	     ob < c->open_buckets + ARRAY_SIZE(c->open_buckets);
+	     ob++) {
+		spin_lock(&ob->lock);
+		if (ob->valid && !ob->on_partial_list) {
+			pr_buf(out, "%zu ref %u type %s\n",
+			       ob - c->open_buckets,
+			       atomic_read(&ob->pin),
+			       bch2_data_types[ob->type]);
+		}
+		spin_unlock(&ob->lock);
+	}
+
+}

fs/bcachefs/alloc_background.h

···
 int bch2_alloc_write(struct bch_fs *, unsigned);
 void bch2_fs_allocator_background_init(struct bch_fs *);
 
+void bch2_open_buckets_to_text(struct printbuf *, struct bch_fs *);
+
 #endif /* _BCACHEFS_ALLOC_BACKGROUND_H */

fs/bcachefs/sysfs.c

···
 read_attribute(btree_key_cache);
 read_attribute(btree_transactions);
 read_attribute(stripes_heap);
+read_attribute(open_buckets);
 
 read_attribute(internal_uuid);
 
···
 		return out.pos - buf;
 	}
 
+	if (attr == &sysfs_open_buckets) {
+		bch2_open_buckets_to_text(&out, c);
+		return out.pos - buf;
+	}
+
 	if (attr == &sysfs_compression_stats) {
 		bch2_compression_stats_to_text(&out, c);
 		return out.pos - buf;
···
 	&sysfs_btree_key_cache,
 	&sysfs_btree_transactions,
 	&sysfs_stripes_heap,
+	&sysfs_open_buckets,
 
 	&sysfs_read_realloc_races,
 	&sysfs_extent_migrate_done,