libceph: add helper that duplicates last extent operation

This helper duplicates last extent operation in OSD request, then
adjusts the new extent operation's offset and length. The helper
is for scatterd page writeback, which adds nonconsecutive dirty
pages to single OSD request.
Signed-off-by: Yan, Zheng <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

include/linux/ceph/osd_client.h

@@ -266,6 +266,8 @@ extern void osd_req_op_extent_init(struct ceph_osd_request *osd_req,
 					u64 truncate_size, u32 truncate_seq);
 extern void osd_req_op_extent_update(struct ceph_osd_request *osd_req,
 					unsigned int which, u64 length);
+extern void osd_req_op_extent_dup_last(struct ceph_osd_request *osd_req,
+				       unsigned int which, u64 offset_inc);
 
 extern struct ceph_osd_data *osd_req_op_extent_osd_data(
 					struct ceph_osd_request *osd_req,

net/ceph/osd_client.c

@@ -534,6 +534,28 @@ void osd_req_op_extent_update(struct ceph_osd_request *osd_req,
 }
 EXPORT_SYMBOL(osd_req_op_extent_update);
 
+void osd_req_op_extent_dup_last(struct ceph_osd_request *osd_req,
+				unsigned int which, u64 offset_inc)
+{
+	struct ceph_osd_req_op *op, *prev_op;
+
+	BUG_ON(which + 1 >= osd_req->r_num_ops);
+
+	prev_op = &osd_req->r_ops[which];
+	op = _osd_req_op_init(osd_req, which + 1, prev_op->op, prev_op->flags);
+	/* dup previous one */
+	op->indata_len = prev_op->indata_len;
+	op->outdata_len = prev_op->outdata_len;
+	op->extent = prev_op->extent;
+	/* adjust offset */
+	op->extent.offset += offset_inc;
+	op->extent.length -= offset_inc;
+
+	if (op->op == CEPH_OSD_OP_WRITE || op->op == CEPH_OSD_OP_WRITEFULL)
+		op->indata_len -= offset_inc;
+}
+EXPORT_SYMBOL(osd_req_op_extent_dup_last);
+
 void osd_req_op_cls_init(struct ceph_osd_request *osd_req, unsigned int which,
 			u16 opcode, const char *class, const char *method)
 {