netdev - Re: [PATCH v4] hv_netvsc: add support for vlans in AF

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Date:   Tue, 21 Jul 2020 09:05:28 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Sriram Krishnan <srirakr2@...co.com>
Cc:     "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, mbumgard@...co.com,
        ugm@...co.com, nimm@...co.com, xe-linux-external@...co.com,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-hyperv@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] hv_netvsc: add support for vlans in AF_PACKET mode

On Tue, 21 Jul 2020 12:44:03 +0530
Sriram Krishnan <srirakr2@...co.com> wrote:

> +	/* When using AF_PACKET we need to drop VLAN header from
> +	 * the frame and update the SKB to allow the HOST OS
> +	 * to transmit the 802.1Q packet
> +	 */
> +	if (skb->protocol == htons(ETH_P_8021Q)) {
> +		u16 vlan_tci = 0;
Unnecessary initialization.

> +		skb_reset_mac_header(skb);
> +		if (eth_type_vlan(eth_hdr(skb)->h_proto)) {
> +			int pop_err;
> +			pop_err = __skb_vlan_pop(skb, &vlan_tci);
> +			if (likely(pop_err == 0)) {
> +				__vlan_hwaccel_put_tag(skb, htons(ETH_P_8021Q), vlan_tci);
> +				/* Update the NDIS header pkt lengths */
> +				packet->total_data_buflen -= VLAN_HLEN;
> +				rndis_msg->msg_len = packet->total_data_buflen;
> +				rndis_msg->msg.pkt.data_len = packet->total_data_buflen;
> +			} else {
> +				netdev_err(net, "Pop vlan err %x\n", pop_err);
> +				goto drop;
> +			}
> +		}
> +	}

Printing error messages is good for debugging but bad IRL.
Users ignore it, or it overflows the log buffer.

A better alternative would be to add a counter to netvsc_ethtool_stats.
Something like:

diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_net.h
index abda736e7c7d..2181d4538ab7 100644
--- a/drivers/net/hyperv/hyperv_net.h
+++ b/drivers/net/hyperv/hyperv_net.h
@@ -897,6 +897,7 @@ struct netvsc_ethtool_stats {
 	unsigned long rx_no_memory;
 	unsigned long stop_queue;
 	unsigned long wake_queue;
+	unsigned long vlan_error;
 };
 
 struct netvsc_ethtool_pcpu_stats {
diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index 6267f706e8ee..89568276e653 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -605,6 +605,28 @@ static int netvsc_xmit(struct sk_buff *skb, struct net_device *net, bool xdp_tx)
 		*hash_info = hash;
 	}
 
+	/* When using AF_PACKET we need to drop VLAN header from
+	 * the frame and update the SKB to allow the HOST OS
+	 * to transmit the 802.1Q packet
+	 */
+	if (skb->protocol == htons(ETH_P_8021Q)) {
+		skb_reset_mac_header(skb);
+		if (eth_type_vlan(eth_hdr(skb)->h_proto)) {
+			u16 vlan_tci;
+
+			if (unlikely(__skb_vlan_pop(skb, &vlan_tci) != 0)) {
+				++net_device_ctx->eth_stats.vlan_error;
+				goto drop;
+			}
+
+			__vlan_hwaccel_put_tag(skb, htons(ETH_P_8021Q), vlan_tci);
+			/* Update the NDIS header pkt lengths */
+			packet->total_data_buflen -= VLAN_HLEN;
+			rndis_msg->msg_len = packet->total_data_buflen;
+			rndis_msg->msg.pkt.data_len = packet->total_data_buflen;
+		}
+	}
+
 	if (skb_vlan_tag_present(skb)) {
 		struct ndis_pkt_8021q_info *vlan;
 
@@ -1427,6 +1449,7 @@ static const struct {
 	{ "rx_no_memory", offsetof(struct netvsc_ethtool_stats, rx_no_memory) },
 	{ "stop_queue", offsetof(struct netvsc_ethtool_stats, stop_queue) },
 	{ "wake_queue", offsetof(struct netvsc_ethtool_stats, wake_queue) },
+	{ "vlan_error", offsetof(struct netvsc_ethtool_stats, vlan_error) },
 }, pcpu_stats[] = {
 	{ "cpu%u_rx_packets",
 		offsetof(struct netvsc_ethtool_pcpu_stats, rx_packets) },