scoutfs: add scoutfs_lock_protected()

The item code had a manual comparison of lock modes when testing if a
given access was protected by a held lock.  Let's offer a proper
interface from the lock code.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/lock.c

@@ -1288,6 +1288,25 @@ void scoutfs_lock_del_coverage(struct super_block *sb,
 	spin_unlock(&cov->cov_lock);
 }
 
+/*
+ * Returns true if the given lock protects the given access of the given
+ * key.  The lock must have a current granted mode that is compatible
+ * with the access mode and the access key must be in the lock's key
+ * range.
+ *
+ * This is called by lock holders who's use of the lock must be preventing
+ * the mode and keys from changing.
+ */
+bool scoutfs_lock_protected(struct scoutfs_lock *lock, struct scoutfs_key *key,
+			    int mode)
+{
+	signed char lock_mode = ACCESS_ONCE(lock->mode);
+
+	return lock_modes_match(lock_mode, mode) &&
+	       scoutfs_key_compare_ranges(key, key,
+					  &lock->start, &lock->end) == 0;
+}
+
 /*
  * The shrink callback got the lock, marked it request_pending, and
  * handed it off to us.  We kick off a null request and the lock will

kmod/src/lock.h

@@ -83,6 +83,8 @@ bool scoutfs_lock_is_covered(struct super_block *sb,
 			     struct scoutfs_lock_coverage *cov);
 void scoutfs_lock_del_coverage(struct super_block *sb,
 			       struct scoutfs_lock_coverage *cov);
+bool scoutfs_lock_protected(struct scoutfs_lock *lock, struct scoutfs_key *key,
+			    int mode);
 
 void scoutfs_free_unused_locks(struct super_block *sb, unsigned long nr);