xfstests: generic/315: allow a little tolerance for our used check

So df in btrfs is tricky at best, and relying on it for accurate information is
not great, but it's the best way to verify this test.  To get around btrfs being
inconsistent sometimes just use _within_tolerance to check our new df value to
make sure that our truncate did something.  With this patch I no longer see
transient failures of this test.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Reviewed-by: Jie Liu <jeff.liu@oracle.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

diff --git a/tests/generic/315 b/tests/generic/315
index 7cfc40d775905edf2f8a493272318ab82e2b8bb2..9c01b5efd03468f416f749645128849ac2082471 100644 (file)
--- a/tests/generic/315
+++ b/tests/generic/315
@@ -73,7 +73,8 @@ sync
 
 # Preallocated disk space should be released
 avail_done=`df -P $TEST_DIR | awk 'END {print $4}'`
-[ "$avail_done" -eq "$avail_begin" ] || _fail "Available disk space ($avail_done KiB)"
+_within_tolerance "df" $avail_done $avail_begin 1%
+[ $? -eq 0 ] || _fail "Available disk space ($avail_done KiB) wanted ($avail_begin KiB)"
 
 # success, all done
 exit