netdev - [PATCH] net: cdc_ncm: switch to eth%d interface naming

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Message-Id: <20210615080549.3362337-1-zenczykowski@gmail.com>
Date:   Tue, 15 Jun 2021 01:05:49 -0700
From:   Maciej Żenczykowski <zenczykowski@...il.com>
To:     Maciej Żenczykowski <maze@...gle.com>
Cc:     Linux Network Development Mailing List <netdev@...r.kernel.org>,
        Lorenzo Colitti <lorenzo@...gle.com>
Subject: [PATCH] net: cdc_ncm: switch to eth%d interface naming

From: Maciej Żenczykowski <maze@...gle.com>

This is meant to make the host side cdc_ncm interface consistently
named just like the older CDC protocols: cdc_ether & cdc_ecm
(and even rndis_host), which all use 'FLAG_ETHER | FLAG_POINTTOPOINT'.

include/linux/usb/usbnet.h:
  #define FLAG_ETHER	0x0020		/* maybe use "eth%d" names */
  #define FLAG_WLAN	0x0080		/* use "wlan%d" names */
  #define FLAG_WWAN	0x0400		/* use "wwan%d" names */
  #define FLAG_POINTTOPOINT 0x1000	/* possibly use "usb%d" names */

drivers/net/usb/usbnet.c @ line 1711:
  strcpy (net->name, "usb%d");
  ...
  // heuristic:  "usb%d" for links we know are two-host,
  // else "eth%d" when there's reasonable doubt.  userspace
  // can rename the link if it knows better.
  if ((dev->driver_info->flags & FLAG_ETHER) != 0 &&
      ((dev->driver_info->flags & FLAG_POINTTOPOINT) == 0 ||
       (net->dev_addr [0] & 0x02) == 0))
          strcpy (net->name, "eth%d");
  /* WLAN devices should always be named "wlan%d" */
  if ((dev->driver_info->flags & FLAG_WLAN) != 0)
          strcpy(net->name, "wlan%d");
  /* WWAN devices should always be named "wwan%d" */
  if ((dev->driver_info->flags & FLAG_WWAN) != 0)
          strcpy(net->name, "wwan%d");

So by using ETHER | POINTTOPOINT the interface naming is
either usb%d or eth%d based on the global uniqueness of the
mac address of the device.

Without this 2.5gbps ethernet dongles which all seem to use the cdc_ncm
driver end up being called usb%d instead of eth%d even though they're
definitely not two-host.  (All 1gbps & 5gbps ethernet usb dongles I've
tested don't hit this problem due to use of different drivers, primarily
r8152 and aqc111)

Fixes tag is based purely on git blame, and is really just here to make
sure this hits LTS branches newer than v4.5.

Cc: Lorenzo Colitti <lorenzo@...gle.com>
Fixes: 4d06dd537f95 ("cdc_ncm: do not call usbnet_link_change from cdc_ncm_bind")
Signed-off-by: Maciej Żenczykowski <maze@...gle.com>
---
 drivers/net/usb/cdc_ncm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index c67f11e0e9a7..24753a4da7e6 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -1892,7 +1892,7 @@ static void cdc_ncm_status(struct usbnet *dev, struct urb *urb)
 static const struct driver_info cdc_ncm_info = {
 	.description = "CDC NCM",
 	.flags = FLAG_POINTTOPOINT | FLAG_NO_SETINT | FLAG_MULTI_PACKET
-			| FLAG_LINK_INTR,
+			| FLAG_LINK_INTR | FLAG_ETHER,
 	.bind = cdc_ncm_bind,
 	.unbind = cdc_ncm_unbind,
 	.manage_power = usbnet_manage_power,
-- 
2.32.0.272.g935e593368-goog