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

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Date:   Wed, 29 Apr 2020 19:33:42 +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,
        Roopa Prabhu <roopa@...ulusnetworks.com>
Subject: Re: [PATCH net-next 1/4] bridge: Allow enslaving DSA master network
 devices

+CC Roopa

On 29/04/2020 19:27, Nikolay Aleksandrov wrote:
> 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
> 
> 
> 
>