Re: [PATCH RFC 1/3] net/tun: Ensure tun devices have a MAC address

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 05 May 2023 11:42:17 -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/tun.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index d4d0a41a905a..da85abfcd254 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1384,7 +1384,7 @@ static void tun_net_initialize(struct net_device *dev)
>  
>  		/* Point-to-Point TUN Device */
>  		dev->hard_header_len = 0;
> -		dev->addr_len = 0;
> +		dev->addr_len = ETH_ALEN;
>  		dev->mtu = 1500;
>  
>  		/* Zero header length */

This is a bad idea.
TUN devices are L3 devices without any MAC address.
This patch will change the semantics and break users.

If you want an L2 address, you need to use TAP, not TUN device.