Don't allow pre_read on IO engines that cannot seek
We cannot pre-read files, if we cannot seek back and read the same
data again. So just disable it with a warning to the user.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/HOWTO b/HOWTO
index 3107d3a..708eca0 100644
--- a/HOWTO
+++ b/HOWTO
@@ -741,7 +741,10 @@
pre_read=bool If this is given, files will be pre-read into memory before
starting the given IO operation. This will also clear
the 'invalidate' flag, since it is pointless to pre-read
- and then drop the cache.
+ and then drop the cache. This will only work for IO engines
+ that are seekable, since they allow you to read the same data
+ multiple times. Thus it will not work on eg network or splice
+ IO.
unlink=bool Unlink the job files when done. Not the default, as repeated
runs of that job would then waste time recreating the file