Ceph

The

iterator(list *l, unsigned o, std::list<ptr>::iterator ip, unsigned po)

(github) constructor is used by the bufferlist end() method . It can only be properly initialized if given non const access to the _buffers data member.
It can only be initialized with inconsistent arguments when called outside of the bufferlist class.
To make it clear that this constructor is for internal use only, it could be made private. The bufferlist class could be made a friend of the bufferlist::iterator class.

diff --git a/src/include/buffer.h b/src/include/buffer.h
index 4f87ed7..55a5e5b 100644
--- a/src/include/buffer.h
+++ b/src/include/buffer.h
@@ -231,6 +231,10 @@ public:
       unsigned off;  // in bl
       std::list<ptr>::iterator p;
       unsigned p_off; // in *p
+
+      iterator(list *l, unsigned o, std::list<ptr>::iterator ip, unsigned po) : 
+    bl(l), ls(&bl->_buffers), off(o), p(ip), p_off(po) { }
+
     public:
       // constructor.  position.
       iterator() :
@@ -239,8 +243,6 @@ public:
     bl(l), ls(&bl->_buffers), off(0), p(ls->begin()), p_off(0) {
     advance(o);
       }
-      iterator(list *l, unsigned o, std::list<ptr>::iterator ip, unsigned po) : 
-    bl(l), ls(&bl->_buffers), off(o), p(ip), p_off(po) { }

       iterator(const iterator& other) : bl(other.bl),
                     ls(other.ls),
@@ -289,6 +291,7 @@ public:
       void copy_in(unsigned len, const char *src);
       void copy_in(unsigned len, const list& otherl);

+      friend class list;
     };

   private: