defrag: loosen input file requirements

We don't have perfect control of file allocation for these tests;
in some cases we may fail to adequately fragment a file prior to
defragmentation testing, and today that will fail the test.

Attack this on 2 fronts:

1) Explicitly allow fewer extents on one of the input files in
   generic/018 where the allocator has discretion.
2) _notrun rather than _fail if we don't create enough extents;
   this is a defrag test, not an allocator/fragmentation test,
   so just skip the test if we can't create an acceptable file
   for defrag testing.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Acked-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Dave Chinner <david@fromorbit.com>

tests/generic/018

@@ -77,7 +77,9 @@ for i in `seq 9 -1 0`; do
 	$XFS_IO_PROG -fs -c "pwrite -b $bsize $((i * bsize)) $bsize" $fragfile \
 					> /dev/null
 done
-_defrag --before 10 --after 1 $fragfile
+
+# Accept fewer fragments than we might expect; we don't have perfect control.
+_defrag --max_before 10 --min_before 5 --after 1 $fragfile
 
 echo "Write backwards sync leaving holes - defrag should do nothing" | tee -a $seqres.full
 for i in `seq 31 -2 0`; do

tests/generic/018.out

@@ -9,7 +9,7 @@ Contiguous file:
 Before: 1
 After: 1
 Write backwards sync, but contiguous - should defrag to 1 extent
-Before: 10
+Before: in_range(5, 10)
 After: 1
 Write backwards sync leaving holes - defrag should do nothing
 Before: 16