netdev - Re: [PATCH] usbnet: modern method to get random MAC

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Date:   Thu, 07 Jul 2022 15:38:58 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Oliver Neukum <oneukum@...e.com>, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, netdev@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH] usbnet: modern method to get random MAC

On Wed, 2022-07-06 at 11:15 +0200, Oliver Neukum wrote:
> The old method had the bug of issuing the same
> random MAC over and over even to two devices at the
> same time. Instead of fixing that, this does as
> Jakub suggested and moves to the modern method.
> 
> This bug is as old as the driver.
> 
> Signed-off-by: Oliver Neukum <oneukum@...e.com>
> ---
>  drivers/net/usb/usbnet.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
> index c70def1a87ca..715cc8b66776 100644
> --- a/drivers/net/usb/usbnet.c
> +++ b/drivers/net/usb/usbnet.c
> @@ -61,9 +61,6 @@
>  
>  /*-------------------------------------------------------------------------*/
>  
> -// randomly generated ethernet address
> -static u8	node_id [ETH_ALEN];
> -
>  /* use ethtool to change the level for any given device */
>  static int msg_level = -1;
>  module_param (msg_level, int, 0);
> @@ -1725,7 +1722,6 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
>  
>  	dev->net = net;
>  	strscpy(net->name, "usb%d", sizeof(net->name));
> -	eth_hw_addr_set(net, node_id);
>  
>  	/* rx and tx sides can use different message sizes;
>  	 * bind() should set rx_urb_size in that case.
> @@ -1793,9 +1789,13 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
>  		goto out4;
>  	}
>  
> -	/* let userspace know we have a random address */
> -	if (ether_addr_equal(net->dev_addr, node_id))
> -		net->addr_assign_type = NET_ADDR_RANDOM;
> +	/*
> +	 * if the device does not come with a MAC
> +	 * we ask the network core to generate us one
> +	 * and flag the device accordingly
> +	 */

Minir nit: even if usbnet uses a mixed style for comments, I think it's
better to stick to netdev format for new code.

	/* if the device does not come with a MAC
...
	 */

Thanks!

/P

> +	if (!is_valid_ether_addr(net->dev_addr))
> +		eth_hw_addr_random(net);
>  
>  	if ((dev->driver_info->flags & FLAG_WLAN) != 0)
>  		SET_NETDEV_DEVTYPE(net, &wlan_type);
> @@ -2205,7 +2205,6 @@ static int __init usbnet_init(void)
>  	BUILD_BUG_ON(
>  		sizeof_field(struct sk_buff, cb) < sizeof(struct skb_data));
>  
> -	eth_random_addr(node_id);
>  	return 0;
>  }
>  module_init(usbnet_init);