Add two new function pointers 'lc_lock' and 'lc_unlock' to lock classes.

These functions are intended to be used to drop a lock and then reacquire
it when doing an sleep such as msleep(9).  Both functions accept a
'struct lock_object *' as their first parameter.  The 'lc_unlock' function
returns an integer that is then passed as the second paramter to the
subsequent 'lc_lock' function.  This can be used to communicate state.
For example, sx locks and rwlocks use this to indicate if the lock was
share/read locked vs exclusive/write locked.

Currently, spin mutexes and lockmgr locks do not provide working lc_lock
and lc_unlock functions.

1 files changed, 9 insertions, 0 deletions

diff --git a/sys/sys/lock.h b/sys/sys/lock.h
index a30a595f03c6..3a3b4d28a3b8 100644
--- a/sys/sys/lock.h
+++ b/sys/sys/lock.h
@@ -45,12 +45,21 @@ struct thread;
  * an error to perform any type of context switch while holding a spin lock.
  * Also, for an individual lock to be recursable, its class must allow
  * recursion and the lock itself must explicitly allow recursion.
+ *
+ * The 'lc_ddb_show' function pointer is used to dump class-specific
+ * data for the 'show lock' DDB command.  The 'lc_lock' and
+ * 'lc_unlock' function pointers are used in sleep(9) and cv_wait(9)
+ * to lock and unlock locks while blocking on a sleep queue.  The
+ * return value of 'lc_unlock' will be passed to 'lc_lock' on resume
+ * to allow communication of state between the two routines.
  */
 
 struct lock_class {
 	const	char *lc_name;
 	u_int	lc_flags;
 	void	(*lc_ddb_show)(struct lock_object *lock);
+	void	(*lc_lock)(struct lock_object *lock, int how);
+	int	(*lc_unlock)(struct lock_object *lock);
 };
 
 #define	LC_SLEEPLOCK	0x00000001	/* Sleep lock. */