[dpdk-dev] [RFC PATCH] mbuf: move headers not fragmented check to checksum

[Ananyev, Konstantin]

Hi Andrew,
 
> rte_validate_tx_offload() is used in Tx prepare callbacks
> (RTE_LIBRTE_ETHDEV_DEBUG only) to check Tx offloads consistency.
> Requirement that packet headers should not be fragmented is not
> documented and unclear where it comes from except
> rte_net_intel_cksum_prepare() functions which relies on it.
> 
> It could be NIC vendor specific driver or hardware limitation, but,
> if so, it should be documented and checked in corresponding Tx
> prepare callbacks.
> 
> Signed-off-by: Andrew Rybchenko <arybchenko at solarflare.com>
> ---
> May be the check should be done in rte_net_intel_cksum_prepare()
> under RTE_LIBRTE_ETHDEV_DEBUG only. Mainly I'd like to get feedback
> on where the limitation comes from and idea to remove it from
> rte_validate_tx_offload().
> 
>  lib/librte_mbuf/rte_mbuf.h | 12 ------------
>  lib/librte_net/rte_net.h   | 17 +++++++++++++++++
>  2 files changed, 17 insertions(+), 12 deletions(-)
> 
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index a7f67023a..14a3b472b 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -2257,23 +2257,11 @@ static inline int
>  rte_validate_tx_offload(const struct rte_mbuf *m)
>  {
>  	uint64_t ol_flags = m->ol_flags;
> -	uint64_t inner_l3_offset = m->l2_len;
> 
>  	/* Does packet set any of available offloads? */
>  	if (!(ol_flags & PKT_TX_OFFLOAD_MASK))
>  		return 0;
> 
> -	if (ol_flags & PKT_TX_OUTER_IP_CKSUM)
> -		/* NB: elaborating the addition like this instead of using
> -		 *     += gives the result uint64_t type instead of int,
> -		 *     avoiding compiler warnings on gcc 8.1 at least */
> -		inner_l3_offset = inner_l3_offset + m->outer_l2_len +
> -				  m->outer_l3_len;
> -
> -	/* Headers are fragmented */
> -	if (rte_pktmbuf_data_len(m) < inner_l3_offset + m->l3_len + m->l4_len)
> -		return -ENOTSUP;
> -
>  	/* IP checksum can be counted only for IPv4 packet */
>  	if ((ol_flags & PKT_TX_IP_CKSUM) && (ol_flags & PKT_TX_IPV6))
>  		return -EINVAL;
> diff --git a/lib/librte_net/rte_net.h b/lib/librte_net/rte_net.h
> index e59760a0a..bd75aea8e 100644
> --- a/lib/librte_net/rte_net.h
> +++ b/lib/librte_net/rte_net.h
> @@ -118,10 +118,27 @@ rte_net_intel_cksum_flags_prepare(struct rte_mbuf *m, uint64_t ol_flags)
>  	struct udp_hdr *udp_hdr;
>  	uint64_t inner_l3_offset = m->l2_len;
> 
> +	/*
> +	 * Does packet set any of available offloads?
> +	 * Mainly it is required to avoid fragmented headers check if
> +	 * no offloads are requested.
> +	 */
> +	if (!(ol_flags & PKT_TX_OFFLOAD_MASK))
> +		return 0;
> +
>  	if ((ol_flags & PKT_TX_OUTER_IP_CKSUM) ||
>  		(ol_flags & PKT_TX_OUTER_IPV6))
>  		inner_l3_offset += m->outer_l2_len + m->outer_l3_len;
> 
> +	/*
> +	 * Check if headers are fragmented.
> +	 * The check could be less strict depending on which offloads are
> +	 * requested and headers to be used, but let's keep it simple.
> +	 */
> +	if (unlikely(rte_pktmbuf_data_len(m) <
> +		     inner_l3_offset + m->l3_len + m->l4_len))
> +		return -ENOTSUP;
> +
>  	if (ol_flags & PKT_TX_IPV4) {
>  		ipv4_hdr = rte_pktmbuf_mtod_offset(m, struct ipv4_hdr *,
>  				inner_l3_offset);
> --

Looks good to me, though extra-testing would be needed.
Acked-by: Konstantin Ananyev <konstantin.ananyev at intel.com>

> 2.17.1