Re: [PATCH] net: usbnet: allow overriding of default USB interface naming

From: Jonathan Davies
Date: Mon Jun 14 2021 - 05:32:41 EST


On 11/06/2021 18:16, Andrew Lunn wrote:
On Fri, Jun 11, 2021 at 03:23:39PM +0000, Jonathan Davies wrote:
When the predictable device naming scheme for NICs is not in use, it is
common for there to be udev rules to rename interfaces to names with
prefix "eth".

Since the timing at which USB NICs are discovered is unpredictable, it
can be interfere with udev's attempt to rename another interface to
"eth0" if a freshly discovered USB interface is initially given the name
"eth0".

Hence it is useful to be able to override the default name. A new usbnet
module parameter allows this to be configured.

Signed-off-by: Jonathan Davies <jonathan.davies@xxxxxxxxxxx>
Suggested-by: Prashanth Sreenivasa <prashanth.sreenivasa@xxxxxxxxxxx>
---
drivers/net/usb/usbnet.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index ecf6284..55f6230 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -72,6 +72,13 @@ static int msg_level = -1;
module_param (msg_level, int, 0);
MODULE_PARM_DESC (msg_level, "Override default message level");
+#define DEFAULT_ETH_DEV_NAME "eth%d"
+
+static char *eth_device_name = DEFAULT_ETH_DEV_NAME;
+module_param(eth_device_name, charp, 0644);
+MODULE_PARM_DESC(eth_device_name, "Device name pattern for Ethernet devices"
+ " (default: \"" DEFAULT_ETH_DEV_NAME "\")");

Module parameter are not liked in the network stack.

Thanks, I wasn't aware. Please help me understand: is that in an effort to avoid configurability altogether, or because there's some preferred mechanism for performing configuration?

It actually seems like a udev problem, and you need to solve it
there. It is also not specific to USB. Any sort of interface can pop
up at an time, especially with parallel probing of busses.

Yes, this is also applicable to the naming done for all ethernet devices. But I've seen the problem multiple times for USB NICs, which is why I proposed a fix here first.

So you need
udev to detect there has been a race condition and try again with the
rename.

(See reply to similar question in sibling thread.)

Thanks,
Jonathan