Ceph » rbd

Hi, I found that block_name_prefix is not crated rondomly.

test env:
ceph --version
ceph version 12.2.5 (cad919881333ac92274171586c827e01f554a70a) luminous (stable)

1. create rbd images
   $ for i in `seq 1 5`;do rbd create rbd$i -p volumes --image-format 2 --image-feature layering --size 1G;done

1. show block_name_prefix
   $ for i in `seq 1 5`;do rbd info volumes/rbd$i|grep block_name_prefix;done
   block_name_prefix: rbd_data.2378974b0dc51
   block_name_prefix: rbd_data.2378b643c9869
   block_name_prefix: rbd_data.2378c74b0dc51
   block_name_prefix: rbd_data.2378d74b0dc51
   block_name_prefix: rbd_data.2378e74b0dc51

I've checked the source code ceph/src/librbd/Utils.cc.

std::string generate_image_id(librados::IoCtx &ioctx) {
librados::Rados rados(ioctx);

uint64_t bid = rados.get_instance_id();
  uint32_t extra = rand() % 0xFFFFFFFF;   -----> here

ostringstream bid_ss;
  bid_ss << std::hex << bid << std::hex << extra;
  std::string id = bid_ss.str();

// ensure the image id won't overflow the fixed block name size
  if (id.length() > RBD_MAX_IMAGE_ID_LENGTH) {
    id = id.substr(id.length() - RBD_MAX_IMAGE_ID_LENGTH);
  }

return id;
}

I think if we want to make the value of extra random, we need "srand(time(NULL));" in the source code.
Thanks.