Subject: Re: [net-next PATCH v2 2/3] net: set and query VEB/VEPA bridge mode via PF_BRIDGE

From: John Fastabend <[email-masked]>
Date: Fri, 02 Nov 2012 15:48:32 -0700

On 11/2/2012 3:38 PM, Ben Hutchings wrote:
> On Wed, 2012-10-24 at 11:13 -0700, John Fastabend wrote:
>> Hardware switches may support enabling and disabling the
>> loopback switch which puts the device in a VEPA mode defined
>> in the IEEE 802.1Qbg specification. In this mode frames are
>> not switched in the hardware but sent directly to the switch.
>> SR-IOV capable NICs will likely support this mode I am
>> aware of at least two such devices. Also I am told (but don't
>> have any of this hardware available) that there are devices
>> that only support VEPA modes. In these cases it is important
>> at a minimum to be able to query these attributes.
>>
>> This patch adds an additional IFLA_BRIDGE_MODE attribute that can be
>> set and dumped via the PF_BRIDGE:{SET|GET}LINK operations. Also
>> anticipating bridge attributes that may be common for both embedded
>> bridges and software bridges this adds a flags attribute
>> IFLA_BRIDGE_FLAGS currently used to determine if the command or event
>> is being generated to/from an embedded bridge or software bridge.
>> Finally, the event generation is pulled out of the bridge module and
>> into rtnetlink proper.
> [...]
>> --- a/net/core/rtnetlink.c
>> +++ b/net/core/rtnetlink.c
> [...]
>> +static int rtnl_bridge_notify(struct net_device *dev, u16 flags)
>> +{
>> +	struct net *net = dev_net(dev);
>> +	struct net_device *master = dev->master;
>> +	struct sk_buff *skb;
>> +	int err = -EOPNOTSUPP;
>> +
>> +	skb = nlmsg_new(bridge_nlmsg_size(), GFP_ATOMIC);
>> +	if (!skb) {
>> +		err = -ENOMEM;
>> +		goto errout;
>> +	}
>> +
>> +	if (!flags && master && master->netdev_ops->ndo_bridge_getlink)
>> +		err = master->netdev_ops->ndo_bridge_getlink(skb, 0, 0, dev);
>> +	else if (dev->netdev_ops->ndo_bridge_getlink)
>> +		err = dev->netdev_ops->ndo_bridge_getlink(skb, 0, 0, dev);
>
> This doesn't make sense.  If flags == BRIDGE_FLAGS_MASTER then we only
> send the 'self' information.  If flags == BRIDGE_FLAGS_MASTER |
> BRIDGE_FLAGS_SELF then we only send the master information.
>

agh. I screwed this up when I made this handle setting both master
and self flags. I'll fix it. Thanks.

> [...]
>>   static int rtnl_bridge_setlink(struct sk_buff *skb, struct nlmsghdr *nlh,
>>   			       void *arg)
>>   {
>>   	struct net *net = sock_net(skb->sk);
>>   	struct ifinfomsg *ifm;
>>   	struct net_device *dev;
>> -	int err = -EINVAL;
>> +	struct nlattr *br_spec, *attr = NULL;
>> +	int rem, err = -EOPNOTSUPP;
>> +	u16 flags = 0;
>>
>>   	if (nlmsg_len(nlh) < sizeof(*ifm))
>>   		return -EINVAL;
>> @@ -2316,15 +2363,45 @@ static int rtnl_bridge_setlink(struct sk_buff *skb, struct nlmsghdr *nlh,
>>   		return -ENODEV;
>>   	}
>>
>> -	if (dev->master && dev->master->netdev_ops->ndo_bridge_setlink) {
>> +	br_spec = nlmsg_find_attr(nlh, sizeof(struct ifinfomsg), IFLA_AF_SPEC);
>> +	if (br_spec) {
>> +		nla_for_each_nested(attr, br_spec, rem) {
>> +			if (nla_type(attr) == IFLA_BRIDGE_FLAGS) {
>> +				flags = nla_get_u16(attr);
>> +				break;
>> +			}
>> +		}
>> +	}
>> +
>> +	if (!flags || (flags & BRIDGE_FLAGS_MASTER)) {
>> +		if (!dev->master ||
>> +		    !dev->master->netdev_ops->ndo_bridge_setlink) {
>> +			err = -EOPNOTSUPP;
>> +			goto out;
>> +		}
>> +
>>   		err = dev->master->netdev_ops->ndo_bridge_setlink(dev, nlh);
>>   		if (err)
>>   			goto out;
>> +
>> +		flags &= ~BRIDGE_FLAGS_MASTER;
>>   	}
>>
>> -	if (dev->netdev_ops->ndo_bridge_setlink)
>> -		err = dev->netdev_ops->ndo_bridge_setlink(dev, nlh);
>> +	if ((flags & BRIDGE_FLAGS_SELF)) {
>> +		if (!dev->netdev_ops->ndo_bridge_setlink)
>> +			err = -EOPNOTSUPP;
>> +		else
>> +			err = dev->netdev_ops->ndo_bridge_setlink(dev, nlh);
>> +
>> +		if (!err)
>> +			flags &= ~BRIDGE_FLAGS_SELF;
>> +	}
>>
>> +	if (attr && nla_type(attr) == IFLA_BRIDGE_FLAGS)
>
> This condition is wrong; attr will *not* be NULL if the
> nla_for_each_nested() loop terminates without finding an
> IFLA_BRIDGE_FLAGS attribute.

It might be NULL if the nlmsg has no IFLA_AF_SPEC attr. In this case
we still need to send the PROTINFO attribute to the master which
could be the linux bridge.

>
>> +		memcpy(nla_data(attr), &flags, sizeof(flags));
>> +	/* Generate event to notify upper layer of bridge change */
>> +	if (!err)
>> +		err = rtnl_bridge_notify(dev, flags);
>
> flags has been modified above; surely we want to use the original value
> here?

Yes. Thanks Ben. I'll have a patch shortly.

> Ben.
>>   out:
>>   	return err;
>>   }