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

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Date:	Fri, 02 Nov 2012 16:03:01 -0700
From:	John Fastabend <john.r.fastabend@...el.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	shemminger@...tta.com, buytenh@...tstofly.org, davem@...emloft.net,
	vyasevic@...hat.com, jhs@...atatu.com, chrisw@...hat.com,
	krkumar2@...ibm.com, samudrala@...ibm.com,
	peter.p.waskiewicz.jr@...el.com, jeffrey.t.kirsher@...el.com,
	netdev@...r.kernel.org, gregory.v.rose@...el.com,
	eilong@...adcom.com
Subject: Re: [net-next PATCH v2 2/3] net: set and query VEB/VEPA bridge mode
 via PF_BRIDGE

On 11/2/2012 4:01 PM, Ben Hutchings wrote:
> On Fri, 2012-11-02 at 15:48 -0700, John Fastabend wrote:
>> 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.
> [...]
>>>> +	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.
> [...]
>
> I think nla_for_each_nested() can leave attr non-null but also not valid
> for use with nla_type().  And that's a problem.  I think it would be
> better to use an explicit flag for whether we found that attribute,
> rather than trying to re-test here.
>
> Ben.
>

OK. I'll add an explicit flag for this. Thanks.
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