As per the discussions with Andreas, I am filing this bug.

After LU-7129 is landed,

• merge the multi-fd support (-I) into the upstream fsx (in xfstests)
• look at the commit history of fsx.c to see what we've changed since the original version, so that the various compiler/coverity fixes are not missed.
• check if O_DIRECT could be enabled on e.g. 1/2 of fds (or maybe some 1/N ratio that is optionally specified with the -Z option) to compete with buffered I/O on the same system.

Andreas,
please correct me if wrong OR
update, if I have missed anything.
Thanks.