netdev - Re: [PATCH net-next v7 3/3] net: ethernet: rmnet: Add support for MAPv5 egress packets

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Date:   Fri, 28 May 2021 16:11:31 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Sharath Chandra Vurukala <sharathv@...eaurora.org>
Cc:     davem@...emloft.net, elder@...nel.org, cpratapa@...eaurora.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v7 3/3] net: ethernet: rmnet: Add support for
 MAPv5 egress packets

On Thu, 27 May 2021 14:18:42 +0530 Sharath Chandra Vurukala wrote:
> Adding support for MAPv5 egress packets.
> 
> This involves adding the MAPv5 header and setting the csum_valid_required
> in the checksum header to request HW compute the checksum.
> 
> Corresponding stats are incremented based on whether the checksum is
> computed in software or HW.
> 
> New stat has been added which represents the count of packets whose
> checksum is calculated by the HW.
> 
> Signed-off-by: Sharath Chandra Vurukala <sharathv@...eaurora.org>

> +static void rmnet_map_v5_checksum_uplink_packet(struct sk_buff *skb,
> +						struct rmnet_port *port,
> +						struct net_device *orig_dev)
> +{
> +	struct rmnet_priv *priv = netdev_priv(orig_dev);
> +	struct rmnet_map_v5_csum_header *ul_header;
> +
> +	if (!(port->data_format & RMNET_FLAGS_EGRESS_MAP_CKSUMV5))
> +		return;

how can we get here if this condition is not met? Looks like defensive
programming.

> +	ul_header = skb_push(skb, sizeof(*ul_header));

Are you making sure you can modify head? I only see a check if there is
enough headroom but not if head is writable (skb_cow_head()).

> +	memset(ul_header, 0, sizeof(*ul_header));
> +	ul_header->header_info = u8_encode_bits(RMNET_MAP_HEADER_TYPE_CSUM_OFFLOAD,
> +						MAPV5_HDRINFO_HDR_TYPE_FMASK);

Is prepending the header required even when packet doesn't need
checksuming?

> +	if (skb->ip_summed == CHECKSUM_PARTIAL) {
> +		void *iph = (char *)ul_header + sizeof(*ul_header);

ip_hdr(skb)

> +		__sum16 *check;
> +		void *trans;
> +		u8 proto;
> +
> +		if (skb->protocol == htons(ETH_P_IP)) {
> +			u16 ip_len = ((struct iphdr *)iph)->ihl * 4;
> +
> +			proto = ((struct iphdr *)iph)->protocol;
> +			trans = iph + ip_len;
> +		} else if (skb->protocol == htons(ETH_P_IPV6)) {
> +#if IS_ENABLED(CONFIG_IPV6)
> +			u16 ip_len = sizeof(struct ipv6hdr);
> +
> +			proto = ((struct ipv6hdr *)iph)->nexthdr;
> +			trans = iph + ip_len;
> +#else
> +			priv->stats.csum_err_invalid_ip_version++;
> +			goto sw_csum;
> +#endif /* CONFIG_IPV6 */
> +		} else {
> +			priv->stats.csum_err_invalid_ip_version++;
> +			goto sw_csum;
> +		}
> +
> +		check = rmnet_map_get_csum_field(proto, trans);
> +		if (check) {
> +			skb->ip_summed = CHECKSUM_NONE;
> +			/* Ask for checksum offloading */
> +			ul_header->csum_info |= MAPV5_CSUMINFO_VALID_FLAG;
> +			priv->stats.csum_hw++;
> +			return;

Please try to keep the success path unindented.

> +		}
> +	}
> +
> +sw_csum:
> +	priv->stats.csum_sw++;
> +}