+.BI lockfile \fR=\fPstr
+Fio defaults to not locking any files before it does IO to them. If a file or
+file descriptor is shared, fio can serialize IO to that file to make the end
+result consistent. This is usual for emulating real workloads that share files.
+The lock modes are:
+.RS
+.RS
+.TP
+.B none
+No locking. This is the default.
+.TP
+.B exclusive
+Only one thread or process may do IO at the time, excluding all others.
+.TP
+.B readwrite
+Read-write locking on the file. Many readers may access the file at the same
+time, but writes get exclusive access.
+.RE
+.P
+The option may be post-fixed with a lock batch number. If set, then each
+thread/process may do that amount of IOs to the file before giving up the lock.
+Since lock acquisition is expensive, batching the lock/unlocks will speed up IO.
+.RE
+.P