ceph: support ceph_pagelist for message payload

The ceph_pagelist is a simple list of whole pages, strung together via
their lru list_head.  It facilitates encoding to a "buffer" of unknown
size.  Allow its use in place of the ceph_msg page vector.

This will be used to fix the huge buffer preallocation woes of MDS
reconnection.

Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/fs/ceph/Makefile b/fs/ceph/Makefile
index 827629c8..47caf2f 100644
--- a/fs/ceph/Makefile
+++ b/fs/ceph/Makefile
@@ -8,7 +8,7 @@
 
 ceph-objs := super.o inode.o dir.o file.o addr.o ioctl.o \
 	export.o caps.o snap.o xattr.o \
-	messenger.o msgpool.o buffer.o \
+	messenger.o msgpool.o buffer.o pagelist.o \
 	mds_client.o mdsmap.o \
 	mon_client.o \
 	osd_client.o osdmap.o crush/crush.o crush/mapper.o crush/hash.o \