netdev - Re: [PATCH net-next 1/4] bridge: Allow enslaving DSA master network devices

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Date:   Wed, 29 Apr 2020 19:27:09 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Vladimir Oltean <olteanv@...il.com>, andrew@...n.ch,
        f.fainelli@...il.com, vivien.didelot@...il.com, davem@...emloft.net
Cc:     jiri@...nulli.us, idosch@...sch.org, kuba@...nel.org,
        netdev@...r.kernel.org, leoyang.li@....com
Subject: Re: [PATCH net-next 1/4] bridge: Allow enslaving DSA master network
 devices

On 29/04/2020 19:19, Vladimir Oltean wrote:
> From: Florian Fainelli <f.fainelli@...il.com>
> 
> Commit 8db0a2ee2c63 ("net: bridge: reject DSA-enabled master netdevices
> as bridge members") added a special check in br_if.c in order to check
> for a DSA master network device with a tagging protocol configured. This
> was done because back then, such devices, once enslaved in a bridge
> would become inoperative and would not pass DSA tagged traffic anymore
> due to br_handle_frame returning RX_HANDLER_CONSUMED.
> 
> But right now we have valid use cases which do require bridging of DSA
> masters. One such example is when the DSA master ports are DSA switch
> ports themselves (in a disjoint tree setup). This should be completely
> equivalent, functionally speaking, from having multiple DSA switches
> hanging off of the ports of a switchdev driver. So we should allow the
> enslaving of DSA tagged master network devices.
> 
> Make br_handle_frame() return RX_HANDLER_PASS in order to call into the
> DSA specific tagging protocol handlers, and lift the restriction from
> br_add_if.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---
>  net/bridge/br_if.c    | 4 +---
>  net/bridge/br_input.c | 4 +++-
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
> index ca685c0cdf95..e0fbdb855664 100644
> --- a/net/bridge/br_if.c
> +++ b/net/bridge/br_if.c
> @@ -18,7 +18,6 @@
>  #include <linux/rtnetlink.h>
>  #include <linux/if_ether.h>
>  #include <linux/slab.h>
> -#include <net/dsa.h>
>  #include <net/sock.h>
>  #include <linux/if_vlan.h>
>  #include <net/switchdev.h>
> @@ -571,8 +570,7 @@ int br_add_if(struct net_bridge *br, struct net_device *dev,
>  	 */
>  	if ((dev->flags & IFF_LOOPBACK) ||
>  	    dev->type != ARPHRD_ETHER || dev->addr_len != ETH_ALEN ||
> -	    !is_valid_ether_addr(dev->dev_addr) ||
> -	    netdev_uses_dsa(dev))
> +	    !is_valid_ether_addr(dev->dev_addr))
>  		return -EINVAL;
>  
>  	/* No bridging of bridges */
> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
> index d5c34f36f0f4..396bc0c18cb5 100644
> --- a/net/bridge/br_input.c
> +++ b/net/bridge/br_input.c
> @@ -17,6 +17,7 @@
>  #endif
>  #include <linux/neighbour.h>
>  #include <net/arp.h>
> +#include <net/dsa.h>
>  #include <linux/export.h>
>  #include <linux/rculist.h>
>  #include "br_private.h"
> @@ -263,7 +264,8 @@ rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
>  	struct sk_buff *skb = *pskb;
>  	const unsigned char *dest = eth_hdr(skb)->h_dest;
>  
> -	if (unlikely(skb->pkt_type == PACKET_LOOPBACK))
> +	if (unlikely(skb->pkt_type == PACKET_LOOPBACK) ||
> +	    netdev_uses_dsa(skb->dev))
>  		return RX_HANDLER_PASS;
>  
>  	if (!is_valid_ether_addr(eth_hdr(skb)->h_source))
> 

Yet another test in fast-path for all packets.
Since br_handle_frame will not be executed at all for such devices I'd suggest
to look into a scheme that avoid installing rx_handler and thus prevents br_handle_frame
to be called in the frist place. In case that is not possible then we can discuss adding
one more test in fast-path.

Actually you can just add a dummy rx_handler that simply returns RX_HANDLER_PASS for
these devices and keep rx_handler_data so all br_port_get_* will continue working.

Thanks,
 Nik