-If set, fio will fill the IO buffers with this pattern. If not set, the contents
-of IO buffers is defined by the other options related to buffer contents. The
-setting can be any pattern of bytes, and can be prefixed with 0x for hex
-values. It may also be a string, where the string must then be wrapped with
-"", e.g.:
+If set, fio will fill the I/O buffers with this pattern or with the contents
+of a file. If not set, the contents of I/O buffers are defined by the other
+options related to buffer contents. The setting can be any pattern of bytes,
+and can be prefixed with 0x for hex values. It may also be a string, where
+the string must then be wrapped with ``""``. Or it may also be a filename,
+where the filename must be wrapped with ``''`` in which case the file is
+opened and read. Note that not all the file contents will be read if that
+would cause the buffers to overflow. So, for example: