Message-ID: <3631ae6c-6780-50ae-ba42-462d8155ed4e@mellanox.com>
Date:   Sun, 8 Oct 2017 13:30:08 +0300
From:   Yotam Gigi <yotamg@...lanox.com>
To:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, idosch@...lanox.com, nogahf@...lanox.com,
        mlxsw@...lanox.com, ivecera@...hat.com, andrew@...n.ch,
        stephen@...workplumber.org, nbd@....name, roopa@...ulusnetworks.com
Subject: Re: [patch net-next 1/6] net: bridge: Use the MDB_RTR_TYPE_TEMP on
 bridge device too

On 10/08/2017 12:42 PM, Nikolay Aleksandrov wrote:
> On 08/10/17 12:39, Nikolay Aleksandrov wrote:
>> On 08/10/17 08:23, Yotam Gigi wrote:
>>> On 10/05/2017 03:09 PM, Nikolay Aleksandrov wrote:
>>>> On 05/10/17 13:36, Jiri Pirko wrote:
>>>>> From: Yotam Gigi <yotamg@...lanox.com>
>>>>>
>>>>> Every bridge port is in one of four mcast router port states:
>>>>>  - MDB_RTR_TYPE_PERM - the port is set by the user to be an mrouter port
>>>>>    regardless of IGMP queries.
>>>>>  - MDB_RTR_TYPE_DISABLED - the port is set by the user to not be an mrouter
>>>>>    port regardless of IGMP queries.
>>>>>  - MDB_RTR_TYPE_TEMP - the port is set by the user to be in mcast router
>>>>>    learning state, but currently it is not an mrouter port as no IGMP query
>>>>>    has been received by it for the last multicast_querier_interval.
>>>>>  - MDB_RTR_TYPE_TEMP_QUERY - the port is set by the user to be in mcast
>>>>>    router learning state, and currently it is an mrouter port due to an
>>>>>    IGMP query that has been received by it during the passed
>>>>>    multicast_querier_interval.
>>>> I think you got the last two partially mixed up, MDB_RTR_TYPE_TEMP marks the port as a router
>>>> regardless if there were any igmp queries, while TYPE_TEMP_QUERY means it's in learning
>>>> state. It is the timer (armed vs not) that defines if currently the port is a router
>>>> when one of the TEMP/TEMP_QUERY are set. In the _TEMP case it is always armed as it
>>>> is refreshed by user or igmp queries which was the point of that mode.
>>>> So this means in br_multicast_router() just check for the timer_pending or perm mode.
>>>
>>> As much as I tried to make this clear, it seems like I failed :)
>>>
>>> The 4 states I described are currently the "bridged port" states, not the
>>> "bridge device" state. A bridged port has these 4 states, all can be set by the
>>> user, while the bridge device only uses 3 of these states. This patch makes the
>>> bridge device use the 4 states too. I thought it makes sense.
>> (disclaimer: this is all about bridge ports, not bridge device)
>> Right, I'll try to explain again: _TEMP always marks the port as a mcast router,
>> it does not put it into just learning state waiting for an igmp query and it can
>> be refreshed by either a query or the user again setting the port in _TEMP.
>> While _TEMP_QUERY puts the port in learning state waiting for a query to become
>> a router, and _TEMP downgrades to _TEMP_QUERY if it expires.
>>
>> Does that make it clearer ?
>>
>> so for _TEMP you say:
>>>>>  - MDB_RTR_TYPE_TEMP - the port is set by the user to be in mcast router
>>>>>    learning state, but currently it is not an mrouter port as no IGMP query
>>>>>    has been received by it for the last multicast_querier_interval.
>> which is not the case, it is always a router when that mode is set on a port.
>> Same for _TEMP_QUERY.
> Err, sorry by same I meant it is not correct, not that the _TEMP definition is the same.
> Need to get coffee :-)

Ho, I see  that I was clear but not right :)

I had a look at the code and seems like you are right - for some reason I
thought that _TEMP is learning-active and _TEMP_QUERY is learning-inactive, and
the ports change states when according to IGMP queries.


>
>>> The first paragraph describes the current states of a bridged port, and the
>>> second one explains the difference between bridged port and bridge device. I
>>> will (try to) make it clearer if we agree on resending this patch.
>>>
>>> Is it clearer now?


Yes it is.

>>>
>>>
>>>> In the port code you have the following transitions:
>>>>  _TEMP -> TEMP_QUERY (on timer fire or user-set val, port becomes learning only)
>>>>  _TEMP -> _TEMP (noop on user refresh or igmp query, timer refreshes)
>>>>  _TEMP_QUERY -> _TEMP_QUERY (on igmp query the timer is armed, port becomes router)
>>>>
>>>> you never have _TEMP_QUERY -> _TEMP, which you're using here to denote the timer
>>>> getting armed and the bridge becoming a router.
>>>
>>> I am not sure I got this one. I do address that: when an IGMP query is recieved
>>> and the current state is _TEMP_QUERY, I arm the timer and set the state to
>>> _TEMP. I marked that place on the patch, so you can see below.
>>>
>> Exactly, there is no such transition for the ports. I tried to say that you're using
>> the router type to distinguish between when a query is received and it is just learning.
>> I get that you need to do so, but that deviates from how ports are handled, thus I
>> suggested to use the timer state instead and drop the _TEMP for bridge device altogether.
>> If it's possible then the patch will be much simpler and you will not need the hacks
>> to hide the state from user-space which is the part I really don't like.


Yeah, I agree. Thanks for the feedback and sorry for the late answer :)

>>
>>>>> The bridge device (brX) itself can also be configured by the user to be
>>>>> either fixed, disabled or learning mrouter port states, but currently there
>>>>> is no distinction between the MDB_RTR_TYPE_TEMP_QUERY and MDB_RTR_TYPE_TEMP
>>>>> in the bridge internal state. Due to that, when an IGMP query is received,
>>>>> it is not straightforward to tell whether it changes the bridge device
>>>>> mrouter port status or not.
>>>> But before this patch the bridge device could not get that set.
>>>>
>>>>> Further patches in this patch-set will introduce notifications upon the
>>>>> bridge device mrouter port state. In order to prevent resending bridge
>>>>> mrouter notification when it is not needed, such distinction is necessary.
>>>>>
>>>> Granted the bridge device hasn't got a way to clearly distinguish the transitions
>>>> without the chance for a race and if using the timer one could get an unnecessary
>>> Is there a race condition?
>>>
>> With this state - no, if you try to use the timer state though there might be
>> an extra notification as I've explained below, that's why I asked if it would be
>> a problem. I think it is worth looking into using the timer state because it will
>> remove a lot of the hacks for hiding the state needed in this patch.
>>
>>>> notification but that seems like a corner case when the timer fires exactly at the
>>>> same time as the igmp query is received. Can't it be handled by just checking if
>>>> the new state is different in the notification receiver ?
>>>> If it can't and is a problem then I'd prefer to add a new boolean to denote that
>>>> router on/off transition rather than doing this.
>>>>
>>>>> Hence, add the distinction between MDB_RTR_TYPE_TEMP and
>>>>> MDB_RTR_TYPE_TEMP_QUERY states for the bridge device, similarly to any
>>>>> other bridge port.
>>>>>
>>>> This does not add proper MDB_RTR_TYPE_TEMP support for the bridge device
>>>> but seems to abuse it to distinguish the timer state, and changes
>>>> the meaning of MDB_RTR_TYPE_TEMP. Can't you just use the timer instead ?
>>>> I think it will simplify the set and avoid all of this.
>>>>
>>>>> In order to not break the current kernel-user API, don't propagate the new
>>>>> state to the user and use it only in the bridge internal state. Thus, if
>>>>> the user reads (either via sysfs or netlink) the bridge device mrouter
>>>>> state, he will get the MDB_RTR_TYPE_TEMP_QUERY state even if the current
>>>>> bridge state is MDB_RTR_TYPE_TEMP.
>>>>>
>>>>> Signed-off-by: Yotam Gigi <yotamg@...lanox.com>
>>>>> Reviewed-by: Nogah Frankel <nogahf@...lanox.com>
>>>>> Signed-off-by: Jiri Pirko <jiri@...lanox.com>
>>>>> ---
>>>>>  net/bridge/br_multicast.c | 25 +++++++++++++++++++++----
>>>>>  net/bridge/br_netlink.c   |  3 ++-
>>>>>  net/bridge/br_private.h   | 13 ++++++++++---
>>>>>  net/bridge/br_sysfs_br.c  |  3 ++-
>>>>>  4 files changed, 35 insertions(+), 9 deletions(-)
>>>>>
>>>>> diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
>>>>> index 8dc5c8d..b86307b 100644
>>>>> --- a/net/bridge/br_multicast.c
>>>>> +++ b/net/bridge/br_multicast.c
>>>>> @@ -861,6 +861,17 @@ static void br_multicast_router_expired(unsigned long data)
>>>>>  
>>>>>  static void br_multicast_local_router_expired(unsigned long data)
>>>>>  {
>>>>> +	struct net_bridge *br = (struct net_bridge *) data;
>>>>> +
>>>>> +	spin_lock(&br->multicast_lock);
>>>>> +	if (br->multicast_router == MDB_RTR_TYPE_DISABLED ||
>>>>> +	    br->multicast_router == MDB_RTR_TYPE_PERM ||
>>>>> +	    timer_pending(&br->multicast_router_timer))
>>>>> +		goto out;
>>>>> +
>>>>> +	br->multicast_router = MDB_RTR_TYPE_TEMP_QUERY;
>>>>> +out:
>>>>> +	spin_unlock(&br->multicast_lock);
>>>>>  }
>>>>>  
>>>>>  static void br_multicast_querier_expired(struct net_bridge *br,
>>>>> @@ -1364,9 +1375,12 @@ static void br_multicast_mark_router(struct net_bridge *br,
>>>>>  	unsigned long now = jiffies;
>>>>>  
>>>>>  	if (!port) {
>>>>> -		if (br->multicast_router == MDB_RTR_TYPE_TEMP_QUERY)
>>>>> +		if (br->multicast_router == MDB_RTR_TYPE_TEMP_QUERY ||
>>>>> +		    br->multicast_router == MDB_RTR_TYPE_TEMP) {
>>>>>  			mod_timer(&br->multicast_router_timer,
>>>>>  				  now + br->multicast_querier_interval);
>>>>> +			br->multicast_router = MDB_RTR_TYPE_TEMP;
>>>>> +		}
>>>
>>> These are the transitions:
>>> _TEMP -> _TEMP_QUERY
>>> _TEMP_QUERY -> _TEMP_QUERY
>> You clearly always set multicast_router to _TEMP, where did you see a transition
>> _TEMP_QUERY -> _TEMP_QUERY or _TEMP -> _TEMP_QUERY ?
>> All transitions are -> _TEMP, because you use it to differentiate between learning
>> state and when a query was received. Maybe we have different definition for 
>> a transition :-)
>>
>>> In both transitions the timer is armed.
>>>
>>>
>>>>>  		return;
>>>>>  	}
>>>>>  
>>>>> @@ -1952,7 +1966,7 @@ void br_multicast_init(struct net_bridge *br)
>>>>>  
>>>>>  	spin_lock_init(&br->multicast_lock);
>>>>>  	setup_timer(&br->multicast_router_timer,
>>>>> -		    br_multicast_local_router_expired, 0);
>>>>> +		    br_multicast_local_router_expired, (unsigned long)br);
>>>>>  	setup_timer(&br->ip4_other_query.timer,
>>>>>  		    br_ip4_multicast_querier_expired, (unsigned long)br);
>>>>>  	setup_timer(&br->ip4_own_query.timer, br_ip4_multicast_query_expired,
>>>>> @@ -2043,11 +2057,14 @@ int br_multicast_set_router(struct net_bridge *br, unsigned long val)
>>>>>  	case MDB_RTR_TYPE_DISABLED:
>>>>>  	case MDB_RTR_TYPE_PERM:
>>>>>  		del_timer(&br->multicast_router_timer);
>>>>> -		/* fall through */
>>>>> -	case MDB_RTR_TYPE_TEMP_QUERY:
>>>>>  		br->multicast_router = val;
>>>>>  		err = 0;
>>>>>  		break;
>>>>> +	case MDB_RTR_TYPE_TEMP_QUERY:
>>>>> +		if (br->multicast_router != MDB_RTR_TYPE_TEMP)
>>>>> +			br->multicast_router = val;
>>>>> +		err = 0;
>>>>> +		break;
>>>>>  	}
>>>>>  
>>>>>  	spin_unlock_bh(&br->multicast_lock);
>>>>> diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
>>>>> index dea88a2..cee5016 100644
>>>>> --- a/net/bridge/br_netlink.c
>>>>> +++ b/net/bridge/br_netlink.c
>>>>> @@ -1357,7 +1357,8 @@ static int br_fill_info(struct sk_buff *skb, const struct net_device *brdev)
>>>>>  		return -EMSGSIZE;
>>>>>  #endif
>>>>>  #ifdef CONFIG_BRIDGE_IGMP_SNOOPING
>>>>> -	if (nla_put_u8(skb, IFLA_BR_MCAST_ROUTER, br->multicast_router) ||
>>>>> +	if (nla_put_u8(skb, IFLA_BR_MCAST_ROUTER,
>>>>> +		       br_multicast_router_translate(br->multicast_router)) ||
>>>>>  	    nla_put_u8(skb, IFLA_BR_MCAST_SNOOPING, !br->multicast_disabled) ||
>>>>>  	    nla_put_u8(skb, IFLA_BR_MCAST_QUERY_USE_IFADDR,
>>>>>  		       br->multicast_query_use_ifaddr) ||
>>>>> diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
>>>>> index ab4df24..e6e3fec 100644
>>>>> --- a/net/bridge/br_private.h
>>>>> +++ b/net/bridge/br_private.h
>>>>> @@ -649,9 +649,8 @@ void br_multicast_get_stats(const struct net_bridge *br,
>>>>>  
>>>>>  static inline bool br_multicast_is_router(struct net_bridge *br)
>>>>>  {
>>>>> -	return br->multicast_router == 2 ||
>>>>> -	       (br->multicast_router == 1 &&
>>>>> -		timer_pending(&br->multicast_router_timer));
>>>>> +	return br->multicast_router == MDB_RTR_TYPE_PERM ||
>>>>> +	       br->multicast_router == MDB_RTR_TYPE_TEMP;
>>>>>  }
>>>>>  
>>>>>  static inline bool
>>>>> @@ -790,6 +789,14 @@ static inline int br_multicast_igmp_type(const struct sk_buff *skb)
>>>>>  }
>>>>>  #endif
>>>>>  
>>>>> +static inline unsigned char
>>>> u8
>>>>
>>>>> +br_multicast_router_translate(unsigned char multicast_router)
>>>> u8, if need be change the type of the struct member
>>>
>>> Sorry, didn't quite get that. Currently, both the bridge_port and bridge have
>>> the multicast_router field, and in both cases it is of type unsigned char. Do
>>> you suggest to change both to be "u8"?
>>>
>> Right, and this is unnecessarily long and requires to be broken ugly like that with
>> the type above and name below. So I suggested to use u8 to avoid that.
>>
>>>>> +{
>>>>> +	if (multicast_router == MDB_RTR_TYPE_TEMP)
>>>>> +		return MDB_RTR_TYPE_TEMP_QUERY;
>>>>> +	return multicast_router;
>>>>> +}
>>>>> +
>>>>>  /* br_vlan.c */
>>>>>  #ifdef CONFIG_BRIDGE_VLAN_FILTERING
>>>>>  bool br_allowed_ingress(const struct net_bridge *br,
>>>>> diff --git a/net/bridge/br_sysfs_br.c b/net/bridge/br_sysfs_br.c
>>>>> index 723f25e..9b9c597 100644
>>>>> --- a/net/bridge/br_sysfs_br.c
>>>>> +++ b/net/bridge/br_sysfs_br.c
>>>>> @@ -340,7 +340,8 @@ static ssize_t multicast_router_show(struct device *d,
>>>>>  				     struct device_attribute *attr, char *buf)
>>>>>  {
>>>>>  	struct net_bridge *br = to_bridge(d);
>>>>> -	return sprintf(buf, "%d\n", br->multicast_router);
>>>>> +	return sprintf(buf, "%d\n",
>>>>> +		       br_multicast_router_translate(br->multicast_router));
>>>>>  }
>>>>>  
>>>>>  static ssize_t multicast_router_store(struct device *d,
>>>>>

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