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

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Date:	Fri, 2 Nov 2012 23:01:01 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	John Fastabend <john.r.fastabend@...el.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 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.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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