ceph: fix object striping calculation for non-default striping schemes

We were incorrectly calculationing of object offset.  If we have multiple
stripe units per object, we need to shift to the start of the current
su in addition to the offset within the su.

Also rename bno to ono (object number) to avoid some variable naming
confusion.
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/osdmap.c

@@ -723,7 +723,7 @@ struct ceph_osdmap *osdmap_apply_incremental(void **p, void *end,
  */
 void ceph_calc_file_object_mapping(struct ceph_file_layout *layout,
 				   u64 off, u64 *plen,
-				   u64 *bno,
+				   u64 *ono,
 				   u64 *oxoff, u64 *oxlen)
 {
 	u32 osize = le32_to_cpu(layout->fl_object_size);
@@ -750,11 +750,14 @@ void ceph_calc_file_object_mapping(struct ceph_file_layout *layout,
 	stripepos = bl % sc;
 	objsetno = stripeno / su_per_object;
 
-	*bno = objsetno * sc + stripepos;
-	dout("objset %u * sc %u = bno %u\n", objsetno, sc, (unsigned)*bno);
-	/* *oxoff = *off % layout->fl_stripe_unit; */
+	*ono = objsetno * sc + stripepos;
+	dout("objset %u * sc %u = ono %u\n", objsetno, sc, (unsigned)*ono);
+
+	/* *oxoff = *off % layout->fl_stripe_unit;  # offset in su */
 	t = off;
 	*oxoff = do_div(t, su);
+	*oxoff += (stripeno % su_per_object) * su;
+
 	*oxlen = min_t(u64, *plen, su - *oxoff);
 	*plen = *oxlen;