Re: [dpdk-dev] [PATCH 0/2] Removal of RTE_MBUF_REFCNT

[Stephen Hemminger <stephen@networkplumber.org>]

On Mon, 16 Feb 2015 16:08:31 +0000
Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com> wrote:

> This patch tries to remove the RTE_MBUF_REFCNT config options and dependencies
> by introducing a new mbuf flag IND_ATTACHED_MBUF that would indicate when the mbuf
> is an indirect attached mbuf, to differentiate between indirect mbufs and mbufs
> with external memory buffers (ie. vhost zero copy).
> 
> Previous discussion:
> http://dpdk.org/ml/archives/dev/2014-October/007127.html
> 
> Currently for mbufs with refcnt, we cannot free mbufs with external memory
> buffers (ie. vhost zero copy), as they are recognized as indirect
> attached mbufs and therefore we free the direct mbuf it points to,
> resulting in an error in the case of external memory buffers.
> 
> We solve the issue by introducing the IND_ATTACHED_MBUF flag, which indicates
> that the mbuf is an indirect attached mbuf pointing to another mbuf.
> When we free an mbuf, we only free the direct mbuf if the flag is set.
> Freeing an mbuf with external buffer is the same as freeing a non attached mbuf.
> The flag is set during attach and clear on detach.
> 
> So in the case of vhost zero copy where we have mbufs with external
> buffers, by default we just free the mbuf and it is up to the user to deal with
> the external buffer.
> 
> Sergio Gonzalez Monroy (2):
>   mbuf: Introduce IND_ATTACHED_MBUF flag
>   Remove RTE_MBUF_REFCNT references
> 
>  app/test/test_link_bonding.c            | 15 -----------
>  app/test/test_mbuf.c                    | 17 +++----------
>  config/common_bsdapp                    |  1 -
>  config/common_linuxapp                  |  1 -
>  examples/Makefile                       |  4 +--
>  examples/ip_fragmentation/Makefile      |  4 ---
>  examples/ip_pipeline/Makefile           |  3 ---
>  examples/ip_pipeline/main.c             |  5 ----
>  examples/ipv4_multicast/Makefile        |  4 ---
>  examples/vhost/main.c                   | 19 +++-----------
>  lib/librte_ip_frag/Makefile             |  4 ---
>  lib/librte_ip_frag/rte_ip_frag.h        |  4 ---
>  lib/librte_mbuf/rte_mbuf.c              |  2 --
>  lib/librte_mbuf/rte_mbuf.h              | 45 +++++++--------------------------
>  lib/librte_pmd_bond/Makefile            |  4 ---
>  lib/librte_pmd_bond/rte_eth_bond.h      |  2 --
>  lib/librte_pmd_bond/rte_eth_bond_args.c |  2 --
>  lib/librte_pmd_bond/rte_eth_bond_pmd.c  | 10 --------
>  lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c   |  8 ------
>  lib/librte_port/Makefile                |  4 ---
>  20 files changed, 19 insertions(+), 139 deletions(-)
> 

What about supporting a clone operation instead of and in addition
to attach?  The refcnt is also useful when there are two paths for
a packet (going into mulitple rings).