xfs: regresion test for fsmap problems with realtime

xfs: regresion test for fsmap problems with realtime

This is a regression test for:

c02f6529864a ("xfs: make xfs_rtalloc_query_range input parameters const")
9ab72f222774 ("xfs: fix off-by-one error when the last rt extent is in use")
7e1826e05ba6 ("xfs: make fsmap backend function key parameters const")

In which we synthesize an XFS with a realtime volume and a special
realtime volume to trip the bugs fixed by all three patches that
resulted in incomplete fsmap output.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>