Re: [dpdk-dev] [PATCH] mbuf: outer offsets must be zero for non-tunnel packets

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

Hi Ivan,

> 
> Make sure that outer L2 and L3 header length fields are
> equal to zero for non-tunnel packets in order to ensure
> consistent and predictable behaviour in network drivers.
> Explain this expectation in comments to help developers.
> 
> Signed-off-by: Ivan Malov <ivan.malov@oktetlabs.ru>
> Reviewed-by: Andrew Rybchenko <arybchenko@solarflare.com>
> ---

Not sure it is a good idea:
1) it is a change in public API behavior (requirements).
2) why these 2 particular tx_offload fields only?
If we'll follow that logic we should enforce same rule for other
tx_offload fileds (tso, l4_len, l3_len, etc.)

Personally I don't think there will be much gain from it.
Might be better and easier just to fix offending drivers that make wrong assumptions.

If we'll still decide to go that way, then I think at least it needs
to be explained in RN, and probably deprecation process has to be followed here.
 
Konstantin

> 
> Notes:
>     At the time of writing a couple of network drivers rely on
>     the statement (i40e, ice) whilst more drivers have runtime
>     conditional checks to guard all references to these fields.
>     This patch is likely to relieve datapath checks in drivers.
> 
>  lib/librte_mbuf/rte_mbuf.h | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index 0d9fef0..cb8b34e 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -702,7 +702,12 @@ struct rte_mbuf {
>  			uint64_t tso_segsz:RTE_MBUF_TSO_SEGSZ_BITS;
>  			/**< TCP TSO segment size */
> 
> -			/* fields for TX offloading of tunnels */
> +			/*
> +			 * Fields for Tx offloading of tunnels.
> +			 * These fields must be equal to zero in the case
> +			 * when (ol_flags & PKT_TX_TUNNEL_MASK) == 0,
> +			 * i.e. for all non-tunnel packets.
> +			 */
>  			uint64_t outer_l3_len:RTE_MBUF_OUTL3_LEN_BITS;
>  			/**< Outer L3 (IP) Hdr Length. */
>  			uint64_t outer_l2_len:RTE_MBUF_OUTL2_LEN_BITS;
> @@ -2376,6 +2381,11 @@ static inline int rte_pktmbuf_chain(struct rte_mbuf *head, struct rte_mbuf *tail
>  			!(ol_flags & PKT_TX_OUTER_IPV4))
>  		return -EINVAL;
> 
> +	/* Outer L2/L3 offsets must be equal to zero for non-tunnel packets. */
> +	if ((ol_flags & PKT_TX_TUNNEL_MASK) == 0 &&
> +	    m->outer_l2_len + m->outer_l3_len != 0)
> +		return -EINVAL;
> +
>  	return 0;
>  }
> 
> --
> 1.8.3.1