1 files changed, 136 insertions, 0 deletions
diff --git a/libbcachefs/six.h b/libbcachefs/six.h
new file mode 100644
index 00000000..01ed3385
--- /dev/null
+++ b/libbcachefs/six.h
@@ -0,0 +1,136 @@
+
+#ifndef _BCACHE_SIX_H
+#define _BCACHE_SIX_H
+
+#include <linux/lockdep.h>
+#include <linux/osq_lock.h>
+#include <linux/sched.h>
+#include <linux/types.h>
+
+#include "util.h"
+
+/*
+ * LOCK STATES:
+ *
+ * read, intent, write (i.e. shared/intent/exclusive, hence the name)
+ *
+ * read and write work as with normal read/write locks - a lock can have
+ * multiple readers, but write excludes reads and other write locks.
+ *
+ * Intent does not block read, but it does block other intent locks. The idea is
+ * by taking an intent lock, you can then later upgrade to a write lock without
+ * dropping your read lock and without deadlocking - because no other thread has
+ * the intent lock and thus no other thread could be trying to take the write
+ * lock.
+ */
+
+union six_lock_state {
+	struct {
+		atomic64_t	counter;
+	};
+
+	struct {
+		u64		v;
+	};
+
+	struct {
+		/* for waitlist_bitnr() */
+		unsigned long	l;
+	};
+
+	struct {
+		unsigned	read_lock:26;
+		unsigned	intent_lock:3;
+		unsigned	waiters:3;
+		/*
+		 * seq works much like in seqlocks: it's incremented every time
+		 * we lock and unlock for write.
+		 *
+		 * If it's odd write lock is held, even unlocked.
+		 *
+		 * Thus readers can unlock, and then lock again later iff it
+		 * hasn't been modified in the meantime.
+		 */
+		u32		seq;
+	};
+};
+
+#define SIX_LOCK_MAX_RECURSE	((1 << 3) - 1)
+
+enum six_lock_type {
+	SIX_LOCK_read,
+	SIX_LOCK_intent,
+	SIX_LOCK_write,
+};
+
+struct six_lock {
+	union six_lock_state	state;
+	struct task_struct	*owner;
+	struct optimistic_spin_queue osq;
+
+	raw_spinlock_t		wait_lock;
+	struct list_head	wait_list[3];
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	struct lockdep_map	dep_map;
+#endif
+};
+
+static __always_inline void __six_lock_init(struct six_lock *lock,
+					    const char *name,
+					    struct lock_class_key *key)
+{
+	atomic64_set(&lock->state.counter, 0);
+	raw_spin_lock_init(&lock->wait_lock);
+	INIT_LIST_HEAD(&lock->wait_list[SIX_LOCK_read]);
+	INIT_LIST_HEAD(&lock->wait_list[SIX_LOCK_intent]);
+	INIT_LIST_HEAD(&lock->wait_list[SIX_LOCK_write]);
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	debug_check_no_locks_freed((void *) lock, sizeof(*lock));
+	lockdep_init_map(&lock->dep_map, name, key, 0);
+#endif
+}
+
+#define six_lock_init(lock)						\
+do {									\
+	static struct lock_class_key __key;				\
+									\
+	__six_lock_init((lock), #lock, &__key);				\
+} while (0)
+
+bool six_trylock_type(struct six_lock *, enum six_lock_type);
+bool six_relock_type(struct six_lock *, enum six_lock_type, unsigned);
+void six_lock_type(struct six_lock *, enum six_lock_type);
+void six_unlock_type(struct six_lock *, enum six_lock_type);
+bool six_trylock_convert(struct six_lock *, enum six_lock_type,
+			 enum six_lock_type);
+void six_lock_increment(struct six_lock *, enum six_lock_type);
+void six_lock_downgrade(struct six_lock *);
+
+#define __SIX_VAL(field, _v)	(((union six_lock_state) { .field = _v }).v)
+
+#define __SIX_LOCK(type)						\
+static __always_inline bool six_trylock_##type(struct six_lock *lock)	\
+{									\
+	return six_trylock_type(lock, SIX_LOCK_##type);			\
+}									\
+									\
+static __always_inline bool six_relock_##type(struct six_lock *lock, u32 seq)\
+{									\
+	return six_relock_type(lock, SIX_LOCK_##type, seq);		\
+}									\
+									\
+static __always_inline void six_lock_##type(struct six_lock *lock)	\
+{									\
+	six_lock_type(lock, SIX_LOCK_##type);				\
+}									\
+									\
+static __always_inline void six_unlock_##type(struct six_lock *lock)	\
+{									\
+	six_unlock_type(lock, SIX_LOCK_##type);				\
+}
+
+__SIX_LOCK(read)
+__SIX_LOCK(intent)
+__SIX_LOCK(write)
+
+#endif /* _BCACHE_SIX_H */