xfs: test per-inode DAX flag by IO

In a DAX mountpoint, do IO betwen files with and
without DAX per-inode flag. We do mmap, both
O_DIRECT and buffered read/write IO in this case.
Then test again in the same device without dax
mountoption.

Add help _require_scratch_dax to make sure we can
test DAX feature on SCRATCH_DEV.

Add mmap dio test programme to test read/write
between a mmap area of one file and another file
directly or buffered, with different size.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Xiong Zhou <xzhou@redhat.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>
7 files changed