netdev - [PATCH] net: usb: usbnet: restore usb%d name exception for local mac addresses

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Message-ID: <20241203130457.904325-1-asmadeus@codewreck.org>
Date: Tue,  3 Dec 2024 22:04:55 +0900
From: Dominique Martinet <asmadeus@...ewreck.org>
To: Oliver Neukum <oneukum@...e.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Cc: Dominique Martinet <dominique.martinet@...ark-techno.com>,
	netdev@...r.kernel.org,
	linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] net: usb: usbnet: restore usb%d name exception for local mac addresses

From: Dominique Martinet <dominique.martinet@...ark-techno.com>

The previous commit assumed that local addresses always came from the
kernel, but some devices hand out local mac addresses so we ended up
with point-to-point devices with a mac set by the driver, renaming to
eth%d when they used to be named usb%d.

Userspace should not rely on device name, but for the sake of stability
restore the local mac address check portion of the naming exception:
point to point devices which either have no mac set by the driver or
have a local mac handed out by the driver will keep the usb%d name.

Fixes: 8a7d12d674ac ("net: usb: usbnet: fix name regression")
Signed-off-by: Dominique Martinet <dominique.martinet@...ark-techno.com>
---
 drivers/net/usb/usbnet.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 44179f4e807f..d044dc7b7622 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -178,6 +178,17 @@ int usbnet_get_ethernet_addr(struct usbnet *dev, int iMACAddress)
 }
 EXPORT_SYMBOL_GPL(usbnet_get_ethernet_addr);
 
+static bool usbnet_needs_usb_name_format(struct usbnet *dev, struct net_device *net)
+{
+	/* Point to point devices which don't have a real MAC address
+	 * (or report a fake local one) have historically used the usb%d
+	 * naming. Preserve this..
+	 */
+	return (dev->driver_info->flags & FLAG_POINTTOPOINT) != 0 &&
+		(is_zero_ether_addr(net->dev_addr) ||
+		 is_local_ether_addr(net->dev_addr));
+}
+
 static void intr_complete (struct urb *urb)
 {
 	struct usbnet	*dev = urb->context;
@@ -1762,13 +1773,10 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
 		if (status < 0)
 			goto out1;
 
-		// 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.
+		/* heuristic: rename to "eth%d" if we are not sure this link
+		 * is two-host (these links keep "usb%d") */
 		if ((dev->driver_info->flags & FLAG_ETHER) != 0 &&
-		    ((dev->driver_info->flags & FLAG_POINTTOPOINT) == 0 ||
-		     /* somebody touched it*/
-		     !is_zero_ether_addr(net->dev_addr)))
+		    !usbnet_needs_usb_name_format(dev, net))
 			strscpy(net->name, "eth%d", sizeof(net->name));
 		/* WLAN devices should always be named "wlan%d" */
 		if ((dev->driver_info->flags & FLAG_WLAN) != 0)
-- 
2.47.0