libceph: allow ceph_osdc_new_request to accept a multi-op read

Currently we have some special-casing for multi-op writes, but in the
case of a read, we can't really handle it. All of the current multi-op
callers call it with CEPH_OSD_FLAG_WRITE set.

Have ceph_osdc_new_request check for CEPH_OSD_FLAG_READ and if it's set,
allocate multiple reply ops instead of multiple request ops. If neither
flag is set, return -EINVAL.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Reviewed-and-tested-by: Luís Henriques <lhenriques@suse.de>
Reviewed-by: Milind Changire <mchangir@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

net/ceph/osd_client.c

@@ -1136,15 +1136,30 @@ struct ceph_osd_request *ceph_osdc_new_request(struct ceph_osd_client *osdc,
 	if (flags & CEPH_OSD_FLAG_WRITE)
 		req->r_data_offset = off;
 
-	if (num_ops > 1)
+	if (num_ops > 1) {
+		int num_req_ops, num_rep_ops;
+
 		/*
-		 * This is a special case for ceph_writepages_start(), but it
-		 * also covers ceph_uninline_data().  If more multi-op request
-		 * use cases emerge, we will need a separate helper.
+		 * If this is a multi-op write request, assume that we'll need
+		 * request ops. If it's a multi-op read then assume we'll need
+		 * reply ops. Anything else and call it -EINVAL.
 		 */
-		r = __ceph_osdc_alloc_messages(req, GFP_NOFS, num_ops, 0);
-	else
+		if (flags & CEPH_OSD_FLAG_WRITE) {
+			num_req_ops = num_ops;
+			num_rep_ops = 0;
+		} else if (flags & CEPH_OSD_FLAG_READ) {
+			num_req_ops = 0;
+			num_rep_ops = num_ops;
+		} else {
+			r = -EINVAL;
+			goto fail;
+		}
+
+		r = __ceph_osdc_alloc_messages(req, GFP_NOFS, num_req_ops,
+					       num_rep_ops);
+	} else {
 		r = ceph_osdc_alloc_messages(req, GFP_NOFS);
+	}
 	if (r)
 		goto fail;