On Wed, Feb 18, 2015 at 10:16:56AM +0100, Olivier MATZ wrote: > Hi Sergio, > > On 02/16/2015 05:08 PM, Sergio Gonzalez Monroy wrote: > >This patch removes all references to RTE_MBUF_REFCNT, setting the refcnt > >field in the mbuf struct permanently. > > > >Signed-off-by: Sergio Gonzalez Monroy <sergio.gonzalez.monroy at intel.com> > > I think removing the refcount compile option goes in the right > direction. However, activating the refcount will break the applications > that reserve a private zone in mbufs. This is due to the macros > RTE_MBUF_TO_BADDR() and RTE_MBUF_FROM_BADDR() that suppose that > the beginning of the mbuf is 128 bytes (sizeof mbuf) before the > data buffer. >
While I understand how the macros make certain assumptions, how does activating the refcnt specifically lead to the problems you describe? Could you explain that part in a bit more detail? Thanks, /Bruce > For RTE_MBUF_TO_BADDR(), it's relatively easy to replace it. The > mbuf pool could store the size of the private size like it's done > for mbp_priv->mbuf_data_room_size. Using rte_mempool_from_obj(m) > or m->pool, we can retrieve the mbuf pool and this value, then > compute the buffer address. > > For RTE_MBUF_FROM_BADDR(), it's more complex. We could ensure that > a backpointer to the mbuf is always located before the data buffer, > but it looks difficult to do. > > Another idea would be to add a field in indirect mbufs that stores > the pointer to the "parent" mbuf. > > Regards, > Olivier >
