Re: [PATCH 2/8] RDMA/siw: remove unused loopback_enabled = true

["yanjun.zhu" <yanjun.zhu@linux.dev>]

On 7/3/25 10:26 AM, Stefan Metzmacher wrote:
> Devices are created explicitly by the administrator using
> 'rdma link add siw_lo type siw netdev lo'.

In the file drivers/infiniband/core/addr.c:

496 static int rdma_set_src_addr_rcu(struct rdma_dev_addr *dev_addr,
497                                  unsigned int *ndev_flags,
498                                  const struct sockaddr *dst_in,
499                                  const struct dst_entry *dst)
500 {
501         struct net_device *ndev = READ_ONCE(dst->dev);
502
503         *ndev_flags = ndev->flags;
504         /* A physical device must be the RDMA device to use */
505         if (ndev->flags & IFF_LOOPBACK) {
506                 /*
507                  * RDMA (IB/RoCE, iWarp) doesn't run on lo interface or
508                  * loopback IP address. So if route is resolved to 
loopback
509                  * interface, translate that to a real ndev based on non
510                  * loopback IP address.
511                  */
512                 ndev = rdma_find_ndev_for_src_ip_rcu(dev_net(ndev), 
dst_in);
513                 if (IS_ERR(ndev))
514                         return -ENODEV;
515         }
516
517         return copy_src_l2_addr(dev_addr, dst_in, dst, ndev);
518 }

I am not sure whether the above comments are correct or not because you 
are creating a siw device on lo netdev.

Yanjun.Zhu

> 
> Cc: Bernard Metzler <bmt@zurich.ibm.com>
> Cc: linux-rdma@vger.kernel.org
> Signed-off-by: Stefan Metzmacher <metze@samba.org>
> ---
>   drivers/infiniband/sw/siw/siw.h      | 1 -
>   drivers/infiniband/sw/siw/siw_main.c | 5 +----
>   2 files changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/drivers/infiniband/sw/siw/siw.h b/drivers/infiniband/sw/siw/siw.h
> index 3e04357ab197..3bdc17eedbe7 100644
> --- a/drivers/infiniband/sw/siw/siw.h
> +++ b/drivers/infiniband/sw/siw/siw.h
> @@ -490,7 +490,6 @@ struct siw_user_mmap_entry {
>   /* Global siw parameters. Currently set in siw_main.c */
>   extern const bool zcopy_tx;
>   extern const bool try_gso;
> -extern const bool loopback_enabled;
>   extern const bool mpa_crc_required;
>   extern const bool mpa_crc_strict;
>   extern const bool siw_tcp_nagle;
> diff --git a/drivers/infiniband/sw/siw/siw_main.c b/drivers/infiniband/sw/siw/siw_main.c
> index 4e1d29832ac8..ba238b0b43a3 100644
> --- a/drivers/infiniband/sw/siw/siw_main.c
> +++ b/drivers/infiniband/sw/siw/siw_main.c
> @@ -38,8 +38,6 @@ const bool zcopy_tx = true;
>    */
>   const bool try_gso;
>   
> -/* Attach siw also with loopback devices */
> -const bool loopback_enabled = true;
>   
>   /* We try to negotiate CRC on, if true */
>   const bool mpa_crc_required;
> @@ -94,8 +92,7 @@ static int siw_dev_qualified(struct net_device *netdev)
>   	 * <linux/if_arp.h> for type identifiers.
>   	 */
>   	if (netdev->type == ARPHRD_ETHER || netdev->type == ARPHRD_IEEE802 ||
> -	    netdev->type == ARPHRD_NONE ||
> -	    (netdev->type == ARPHRD_LOOPBACK && loopback_enabled))
> +	    netdev->type == ARPHRD_NONE || netdev->type == ARPHRD_LOOPBACK)
>   		return 1;
>   
>   	return 0;