rbd: use helpers to handle discard for layered images correctly

Only allocate two osd ops for discard requests, since the
preallocation hint is only added for regular writes.  Use
rbd_img_obj_request_fill() to recreate the original write or discard
osd operations, isolating that logic to one place, and change the
assert in rbd_osd_req_create_copyup() to accept discard requests as
well.

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index c07cb1d..e1dcd36 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -1934,9 +1934,10 @@
 }
 
 /*
- * Create a copyup osd request based on the information in the
- * object request supplied.  A copyup request has three osd ops,
- * a copyup method call, a hint op, and a write op.
+ * Create a copyup osd request based on the information in the object
+ * request supplied.  A copyup request has two or three osd ops, a
+ * copyup method call, potentially a hint op, and a write or truncate
+ * or zero op.
  */
 static struct ceph_osd_request *
 rbd_osd_req_create_copyup(struct rbd_obj_request *obj_request)
@@ -1946,18 +1947,24 @@
 	struct rbd_device *rbd_dev;
 	struct ceph_osd_client *osdc;
 	struct ceph_osd_request *osd_req;
+	int num_osd_ops = 3;
 
 	rbd_assert(obj_request_img_data_test(obj_request));
 	img_request = obj_request->img_request;
 	rbd_assert(img_request);
-	rbd_assert(img_request_write_test(img_request));
+	rbd_assert(img_request_write_test(img_request) ||
+			img_request_discard_test(img_request));
 
-	/* Allocate and initialize the request, for the three ops */
+	if (img_request_discard_test(img_request))
+		num_osd_ops = 2;
+
+	/* Allocate and initialize the request, for all the ops */
 
 	snapc = img_request->snapc;
 	rbd_dev = img_request->rbd_dev;
 	osdc = &rbd_dev->rbd_client->client->osdc;
-	osd_req = ceph_osdc_alloc_request(osdc, snapc, 3, false, GFP_ATOMIC);
+	osd_req = ceph_osdc_alloc_request(osdc, snapc, num_osd_ops,
+						false, GFP_ATOMIC);
 	if (!osd_req)
 		return NULL;	/* ENOMEM */
 
@@ -2337,10 +2344,9 @@
 	u16 opcode;
 
 	if (op_type == OBJ_OP_DISCARD) {
-		if (!offset && (length == object_size)
-			&& (!img_request_layered_test(img_request) ||
-				(rbd_dev->parent_overlap <=
-					obj_request->img_offset))) {
+		if (!offset && length == object_size &&
+		    (!img_request_layered_test(img_request) ||
+		     !obj_request_overlaps_parent(obj_request))) {
 			opcode = CEPH_OSD_OP_DELETE;
 		} else if ((offset + length == object_size)) {
 			opcode = CEPH_OSD_OP_TRUNCATE;
@@ -2500,7 +2506,8 @@
 	struct page **pages;
 	u32 page_count;
 
-	rbd_assert(obj_request->type == OBJ_REQUEST_BIO);
+	rbd_assert(obj_request->type == OBJ_REQUEST_BIO ||
+		obj_request->type == OBJ_REQUEST_NODATA);
 	rbd_assert(obj_request_img_data_test(obj_request));
 	img_request = obj_request->img_request;
 	rbd_assert(img_request);
@@ -2538,11 +2545,10 @@
 	struct ceph_osd_client *osdc;
 	struct rbd_device *rbd_dev;
 	struct page **pages;
+	enum obj_operation_type op_type;
 	u32 page_count;
 	int img_result;
 	u64 parent_length;
-	u64 offset;
-	u64 length;
 
 	rbd_assert(img_request_child_test(img_request));
 
@@ -2606,26 +2612,10 @@
 	osd_req_op_cls_request_data_pages(osd_req, 0, pages, parent_length, 0,
 						false, false);
 
-	/* Then the hint op */
+	/* Add the other op(s) */
 
-	osd_req_op_alloc_hint_init(osd_req, 1, rbd_obj_bytes(&rbd_dev->header),
-				   rbd_obj_bytes(&rbd_dev->header));
-
-	/* And the original write request op */
-
-	offset = orig_request->offset;
-	length = orig_request->length;
-	osd_req_op_extent_init(osd_req, 2, CEPH_OSD_OP_WRITE,
-					offset, length, 0, 0);
-	if (orig_request->type == OBJ_REQUEST_BIO)
-		osd_req_op_extent_osd_data_bio(osd_req, 2,
-					orig_request->bio_list, length);
-	else
-		osd_req_op_extent_osd_data_pages(osd_req, 2,
-					orig_request->pages, length,
-					offset & ~PAGE_MASK, false, false);
-
-	rbd_osd_req_format_write(orig_request);
+	op_type = rbd_img_request_op_type(orig_request->img_request);
+	rbd_img_obj_request_fill(orig_request, osd_req, op_type, 1);
 
 	/* All set, send it off. */