libceph: hold off building osd request

Defer building the osd request until just before submitting it in
all callers except ceph_writepages_start().  (That caller will be
handed in the next patch.)

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
diff --git a/net/ceph/osd_client.c b/net/ceph/osd_client.c
index 115790a..9ca693d 100644
--- a/net/ceph/osd_client.c
+++ b/net/ceph/osd_client.c
@@ -2056,8 +2056,6 @@
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
-	ceph_osdc_build_request(req, off, 1, &op, NULL, vino.snap, NULL);
-
 	/* it may be a short read due to an object boundary */
 
 	osd_data = &req->r_data_in;
@@ -2069,6 +2067,8 @@
 	dout("readpages  final extent is %llu~%llu (%llu bytes align %d)\n",
 	     off, *plen, osd_data->length, page_align);
 
+	ceph_osdc_build_request(req, off, 1, &op, NULL, vino.snap, NULL);
+
 	rc = ceph_osdc_start_request(osdc, req, false);
 	if (!rc)
 		rc = ceph_osdc_wait_request(osdc, req);
@@ -2105,8 +2105,6 @@
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
-	ceph_osdc_build_request(req, off, 1, &op, snapc, CEPH_NOSNAP, mtime);
-
 	/* it may be a short write due to an object boundary */
 	osd_data = &req->r_data_out;
 	osd_data->type = CEPH_OSD_DATA_TYPE_PAGES;
@@ -2115,6 +2113,8 @@
 	osd_data->alignment = page_align;
 	dout("writepages %llu~%llu (%llu bytes)\n", off, len, osd_data->length);
 
+	ceph_osdc_build_request(req, off, 1, &op, snapc, CEPH_NOSNAP, mtime);
+
 	rc = ceph_osdc_start_request(osdc, req, true);
 	if (!rc)
 		rc = ceph_osdc_wait_request(osdc, req);