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/fio.1 b/fio.1
index aa7b9d6..32993b6 100644
--- a/fio.1
+++ b/fio.1
@@ -544,7 +544,9 @@
.BI pre_read \fR=\fPbool
If this is given, files will be pre-read into memory before starting the given
IO operation. This will also clear the \fR \fBinvalidate\fR flag, since it is
-pointless to pre-read and then drop the cache.
+pointless to pre-read 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.
.TP
.BI unlink \fR=\fPbool
Unlink job files when done. Default: false.