libceph: activate message data assignment checks

The mds client no longer tries to assign zero-length message data,
and the osd client no longer sets its data info more than once.
This allows us to activate assertions in the messenger to verify
these things never happen.

This resolves both of these:
    http://tracker.ceph.com/issues/4263
    http://tracker.ceph.com/issues/4284Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Greg Farnum <greg@inktank.com>

net/ceph/messenger.c

@@ -2690,10 +2690,10 @@ 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->length); */
+	BUG_ON(!pages);
+	BUG_ON(!length);
+	BUG_ON(msg->pages);
+	BUG_ON(msg->length);
 
 	msg->pages = pages;
 	msg->length = length;
@@ -2704,9 +2704,9 @@ EXPORT_SYMBOL(ceph_msg_data_set_pages);
 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); */
+	BUG_ON(!pagelist);
+	BUG_ON(!pagelist->length);
+	BUG_ON(msg->pagelist);
 
 	msg->pagelist = pagelist;
 }
@@ -2714,8 +2714,8 @@ EXPORT_SYMBOL(ceph_msg_data_set_pagelist);
 
 void ceph_msg_data_set_bio(struct ceph_msg *msg, struct bio *bio)
 {
-	/* BUG_ON(!bio); */
-	/* BUG_ON(msg->bio); */
+	BUG_ON(!bio);
+	BUG_ON(msg->bio);
 
 	msg->bio = bio;
 }
@@ -2723,9 +2723,9 @@ 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); */
+	BUG_ON(!trail);
+	BUG_ON(!trail->length);
+	BUG_ON(msg->trail);
 
 	msg->trail = trail;
 }