libceph: primary_temp infrastructure

Add primary_temp mappings infrastructure.  struct ceph_pg_mapping is
overloaded, primary_temp mappings are stored in an rb-tree, rooted at
ceph_osdmap, in a manner similar to pg_temp mappings.

Dump primary_temp mappings to /sys/kernel/debug/ceph/<client>/osdmap,
one 'primary_temp <pgid> <osd>' per line, e.g:

    primary_temp 2.6 4

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Alex Elder <elder@linaro.org>
diff --git a/include/linux/ceph/osdmap.h b/include/linux/ceph/osdmap.h
index 4837e58..db4fb63 100644
--- a/include/linux/ceph/osdmap.h
+++ b/include/linux/ceph/osdmap.h
@@ -66,6 +66,9 @@
 			int len;
 			int osds[];
 		} pg_temp;
+		struct {
+			int osd;
+		} primary_temp;
 	};
 };
 
@@ -83,6 +86,8 @@
 	struct ceph_entity_addr *osd_addr;
 
 	struct rb_root pg_temp;
+	struct rb_root primary_temp;
+
 	struct rb_root pg_pools;
 	u32 pool_max;