ceph: only set message data pointers if non-empty

Change it so we only assign outgoing data information for messages
if there is outgoing data to send.

This then allows us to add a few more (currently commented-out)
assertions.

This is related to:
    http://tracker.ceph.com/issues/4284

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Greg Farnum <greg@inktank.com>

fs/ceph/mds_client.c

@@ -1721,7 +1721,11 @@ static struct ceph_msg *create_request_message(struct ceph_mds_client *mdsc,
 	msg->front.iov_len = p - msg->front.iov_base;
 	msg->hdr.front_len = cpu_to_le32(msg->front.iov_len);
 
-	ceph_msg_data_set_pages(msg, req->r_pages, req->r_data_len, 0);
+	if (req->r_data_len) {
+		/* outbound data set only by ceph_sync_setxattr() */
+		BUG_ON(!req->r_pages);
+		ceph_msg_data_set_pages(msg, req->r_pages, req->r_data_len, 0);
+	}
 
 	msg->hdr.data_len = cpu_to_le32(req->r_data_len);
 	msg->hdr.data_off = cpu_to_le16(0);
@@ -2603,10 +2607,13 @@ static void send_mds_reconnect(struct ceph_mds_client *mdsc,
 			goto fail;
 	}
 
-	ceph_msg_data_set_pagelist(reply, pagelist);
 	if (recon_state.flock)
 		reply->hdr.version = cpu_to_le16(2);
-	reply->hdr.data_len = cpu_to_le32(pagelist->length);
+	if (pagelist->length) {
+		/* set up outbound data if we have any */
+		reply->hdr.data_len = cpu_to_le32(pagelist->length);
+		ceph_msg_data_set_pagelist(reply, pagelist);
+	}
 	ceph_con_send(&session->s_con, reply);
 
 	mutex_unlock(&session->s_mutex);

net/ceph/messenger.c

@@ -2692,6 +2692,8 @@ EXPORT_SYMBOL(ceph_con_keepalive);
 void ceph_msg_data_set_pages(struct ceph_msg *msg, struct page **pages,
 		size_t length, size_t alignment)
 {
+	/* BUG_ON(!pages); */
+	/* BUG_ON(!length); */
 	/* BUG_ON(msg->pages); */
 	/* BUG_ON(msg->page_count); */
 
@@ -2705,6 +2707,7 @@ void ceph_msg_data_set_pagelist(struct ceph_msg *msg,
 				struct ceph_pagelist *pagelist)
 {
 	/* BUG_ON(!pagelist); */
+	/* BUG_ON(!pagelist->length); */
 	/* BUG_ON(msg->pagelist); */
 
 	msg->pagelist = pagelist;
@@ -2723,6 +2726,7 @@ EXPORT_SYMBOL(ceph_msg_data_set_bio);
 void ceph_msg_data_set_trail(struct ceph_msg *msg, struct ceph_pagelist *trail)
 {
 	/* BUG_ON(!trail); */
+	/* BUG_ON(!trail->length); */
 	/* BUG_ON(msg->trail); */
 
 	msg->trail = trail;

net/ceph/osd_client.c

@@ -1759,8 +1759,10 @@ int ceph_osdc_start_request(struct ceph_osd_client *osdc,
 	osd_data = &req->r_data_out;
 	if (osd_data->type == CEPH_OSD_DATA_TYPE_PAGES) {
 		BUG_ON(osd_data->length > (u64) SIZE_MAX);
-		ceph_msg_data_set_pages(req->r_request, osd_data->pages,
-			osd_data->length, osd_data->alignment);
+		if (osd_data->length)
+			ceph_msg_data_set_pages(req->r_request,
+				osd_data->pages, osd_data->length,
+				osd_data->alignment);
 #ifdef CONFIG_BLOCK
 	} else if (osd_data->type == CEPH_OSD_DATA_TYPE_BIO) {
 		ceph_msg_data_set_bio(req->r_request, osd_data->bio);
@@ -1768,7 +1770,8 @@ int ceph_osdc_start_request(struct ceph_osd_client *osdc,
 	} else {
 		BUG_ON(osd_data->type != CEPH_OSD_DATA_TYPE_NONE);
 	}
-	ceph_msg_data_set_trail(req->r_request, &req->r_trail);
+	if (req->r_trail.length)
+		ceph_msg_data_set_trail(req->r_request, &req->r_trail);
 
 	register_request(osdc, req);