Re: [PATCH RFC 2/3] net/lo: Ensure lo devices have a MAC address

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 05 May 2023 11:42:44 -0400
Chuck Lever <cel@kernel.org> wrote:

> From: Chuck Lever <chuck.lever@oracle.com>
> 
> A non-zero MAC address enables a network device to be assigned as
> the underlying device for a virtual RDMA device. Without a non-
> zero MAC address, cma_acquire_dev_by_src_ip() is unable to find the
> underlying egress device that corresponds to a source IP address,
> and rdma_resolve_address() fails.
> 
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  drivers/net/loopback.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
> index f6d53e63ef4e..1ce4f19d8065 100644
> --- a/drivers/net/loopback.c
> +++ b/drivers/net/loopback.c
> @@ -192,6 +192,8 @@ static void gen_lo_setup(struct net_device *dev,
>  	dev->needs_free_netdev	= true;
>  	dev->priv_destructor	= dev_destructor;
>  
> +	eth_hw_addr_random(dev);
> +
>  	netif_set_tso_max_size(dev, GSO_MAX_SIZE);
>  }
>  
> 
> 
> 

This enough of a change, it will probably break somebody.
If you need dummy endpoint (ie multiple loopback), a common way
is to use dummy devices for that.