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

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Message-ID: <e35ddece-3fd2-4252-6786-af507ba819d2@nutanix.com>
Date:   Mon, 14 Jun 2021 10:32:22 +0100
From:   Jonathan Davies <jonathan.davies@...anix.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Oliver Neukum <oneukum@...e.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: usbnet: allow overriding of default USB interface
 naming

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@...anix.com>
>> Suggested-by: Prashanth Sreenivasa <prashanth.sreenivasa@...anix.com>
>> ---
>>   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