netdev - Re: [PATCH 2/2] cdc_ncm: Admit multicast traffic

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Date:   Sat, 30 Jun 2018 13:26:57 +0200
From:   Miguel Rodríguez Pérez <miguel@....uvigo.gal>
To:     linux-usb@...r.kernel.org
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] cdc_ncm: Admit multicast traffic

Some CDC_NCM devices are used as docks for laptops. In this case, it
makes sense to accept multicast Ethernet traffic, as these devices
can reside in a proper LAN. Without this, mDNS or IPv6 simply do not
work.

Signed-off-by: Miguel Rodríguez Pérez <miguel@....uvigo.gal>
---
 drivers/net/usb/cdc_ncm.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index d6b51e2b9495..50af1d9d0102 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -132,6 +132,33 @@ static void cdc_ncm_get_strings(struct net_device
__always_unused *netdev, u32 s

 static void cdc_ncm_update_rxtx_max(struct usbnet *dev, u32 new_rx, u32
new_tx);

+static void cdc_ncm_update_filter(struct usbnet *dev)
+{
+       struct cdc_ncm_ctx *ctx = (struct cdc_ncm_ctx *)dev->data[0];
+	u8 iface_no = ctx->control->cur_altsetting->desc.bInterfaceNumber;
+	struct net_device *net = dev->net;
+
+	u16 cdc_filter = USB_CDC_PACKET_TYPE_DIRECTED
+			| USB_CDC_PACKET_TYPE_BROADCAST;
+
+	/* filtering on the device is an optional feature and not worth
+	 * the hassle so we just roughly care about snooping and if any
+	 * multicast is requested, we take every multicast
+	 */
+	if (net->flags & IFF_PROMISC)
+		cdc_filter |= USB_CDC_PACKET_TYPE_PROMISCUOUS;
+	if (!netdev_mc_empty(net) || (net->flags & IFF_ALLMULTI))
+		cdc_filter |= USB_CDC_PACKET_TYPE_ALL_MULTICAST;
+
+	usbnet_write_cmd(dev,
+			USB_CDC_SET_ETHERNET_PACKET_FILTER,
+			USB_TYPE_CLASS | USB_DIR_OUT | USB_RECIP_INTERFACE,
+			cdc_filter,
+			iface_no,
+			NULL,
+			0);
+}
+
 static const struct ethtool_ops cdc_ncm_ethtool_ops = {
 	.get_link          = usbnet_get_link,
 	.nway_reset        = usbnet_nway_reset,
@@ -1652,6 +1679,7 @@ static const struct driver_info cdc_ncm_info = {
 	.status = cdc_ncm_status,
 	.rx_fixup = cdc_ncm_rx_fixup,
 	.tx_fixup = cdc_ncm_tx_fixup,
+	.set_rx_mode = cdc_ncm_update_filter,
 };

 /* Same as cdc_ncm_info, but with FLAG_WWAN */
-- 
2.17.1


On 30/06/18 13:21, Miguel Rodríguez Pérez wrote:
> Sending again, as the previous try had the wrong subjects. Sorry about that.
> 
> Dell D6000 dock (and I guess other docks too) exposes a CDC_NCM device
> for Ethernet traffic. However, multicast Ethernet traffic is not
> processed making IPv6 not functional. Other services, like mDNS used for
> LAN service discovery are also hindered.
> 
> The actual reason is that CDC_NCM driver was not processing requests to
> filter (admit) multicast traffic. I provide two patches to the linux
> kernel that admit all Ethernet multicast traffic whenever a multicast
> group is being joined.
> 
> The solution is not optimal, as it makes the system receive more traffic
> than that strictly needed, but otherwise this only happens when the
> computer is connected to a dock and thus is running on AC power. I
> believe it is not worth the hassle to join only the requested groups.
> This is the same that is done in the CDN_ETHER driver.
> 
> Best regards,
> 

-- 
Miguel Rodríguez Pérez
Laboratorio de Redes
EE Telecomunicación – Universidade de Vigo