ceph: fix intra strip unit length calculation

Commit 645a1025 fixes calculation of object
offset for layouts with multiple stripes per object. This updates the
calculation of the length written to take into account multiple stripes per
object.
Signed-off-by: Noah Watkins <noah@noahdesu.com>
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/osdmap.c

@@ -731,7 +731,7 @@ void ceph_calc_file_object_mapping(struct ceph_file_layout *layout,
 	u32 sc = le32_to_cpu(layout->fl_stripe_count);
 	u32 bl, stripeno, stripepos, objsetno;
 	u32 su_per_object;
-	u64 t;
+	u64 t, su_offset;
 
 	dout("mapping %llu~%llu  osize %u fl_su %u\n", off, *plen,
 	     osize, su);
@@ -755,10 +755,15 @@ void ceph_calc_file_object_mapping(struct ceph_file_layout *layout,
 
 	/* *oxoff = *off % layout->fl_stripe_unit;  # offset in su */
 	t = off;
-	*oxoff = do_div(t, su);
-	*oxoff += (stripeno % su_per_object) * su;
+	su_offset = do_div(t, su);
+	*oxoff = su_offset + (stripeno % su_per_object) * su;
 
-	*oxlen = min_t(u64, *plen, su - *oxoff);
+	/*
+	 * Calculate the length of the extent being written to the selected
+	 * object. This is the minimum of the full length requested (plen) or
+	 * the remainder of the current stripe being written to.
+	 */
+	*oxlen = min_t(u64, *plen, su - su_offset);
 	*plen = *oxlen;
 
 	dout(" obj extent %llu~%llu\n", *oxoff, *oxlen);