"file_append" parameter not working.

[darryleg]

Every time I used the "file_append" parameter in fio with "sync" ioengine and "loops", I get the following error:
"No I/O performed by sync, perhaps try --debug=io option for details?"
What I am trying to do is to emulate writes being appended to a single file. I want the writes to be buffered until they are flushed every 500th I/O. I have included the job file that fails. If I remove the "file_append" parameter, it works fine.

[global]
[test]
filename=/data/128mb
bs=4k
size=128m
rw=write
file_append=1
ioengine=sync
fsync=500
loops=100

[sitsofe]

There is a problem interaction between file_append and loops e.g.

./fio --name=test --bs=4k --size=16k --rw=write --file_append=1 --filename=/tmp/fio.tmp --loops=2

demonstrates the problem - the first loop iteration was fine but the second goes on to fail.

In a manner of speaking this is actually related to #453 because there's a general question as to whether fio should actually repeat file layout operations (e.g. extending a file, recreating a file) each time a loop is restarted. If in this case layout really should only be done once then perhaps file_append and loops > 1 should be banned or the offset from the first loop should be kept through all other iterations.