1 files changed, 27 insertions, 0 deletions
diff --git a/libbcachefs/buckets_types.h b/libbcachefs/buckets_types.h
index 7174047b..900b8680 100644
--- a/libbcachefs/buckets_types.h
+++ b/libbcachefs/buckets_types.h
@@ -7,6 +7,33 @@
 
 #define BUCKET_JOURNAL_SEQ_BITS		16
 
+/*
+ * Ugly hack alert:
+ *
+ * We need to cram a spinlock in a single byte, because that's what we have left
+ * in struct bucket, and we care about the size of these - during fsck, we need
+ * in memory state for every single bucket on every device.
+ *
+ * We used to do
+ *   while (xchg(&b->lock, 1) cpu_relax();
+ * but, it turns out not all architectures support xchg on a single byte.
+ *
+ * So now we use bit_spin_lock(), with fun games since we can't burn a whole
+ * ulong for this - we just need to make sure the lock bit always ends up in the
+ * first byte.
+ */
+
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#define BUCKET_LOCK_BITNR	0
+#else
+#define BUCKET_LOCK_BITNR	(BITS_PER_LONG - 1)
+#endif
+
+union ulong_byte_assert {
+	ulong	ulong;
+	u8	byte;
+};
+
 struct bucket {
 	u8			lock;
 	u8			gen_valid:1;