Ceph

This code seems to work in the Ioctx class:

def trunc(self,key,size):
        self.require_ioctx_open()
        if not isinstance(key, str):
            raise TypeError('key must be a string')
        ret = self.librados.rados_trunc(self.io,c_char_p(key),c_size_t(size))
        if ret < 0:
            raise make_ex(ret, "Ioctx.trunc(%s): failed to truncate %s" % (self.name, key))
        return ret