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Date: Wed, 30 May 2007 20:39:09 +0200 From: Oliver Hartkopp <oliver@...tkopp.net> To: Patrick McHardy <kaber@...sh.net> CC: Urs Thuermann <urs@...ogud.escape.de>, David Miller <davem@...emloft.net>, Thomas Gleixner <tglx@...utronix.de>, Oliver Hartkopp <oliver.hartkopp@...kswagen.de>, Urs Thuermann <urs.thuermann@...kswagen.de>, netdev@...r.kernel.org Subject: Re: [patch 5/7] CAN: Add virtual CAN netdevice driver Patrick McHardy wrote: > I have a set of patches coming up that introduce a rtnetlink API > for adding/modifying/deleting software network devices. I would > prefer if you could switch this driver over instead of doing the > "create N devices during loading" that many current drivers do, > leaving you with 20 unused devices after boot. > Hi Patrick, next Friday? Too late ;-) Ok, your approach is indeed an interesting idea and we would look on it, as we also not interested in creating unused devices and do any double work. > And it allows you have both loopback and non-loopback devices > in case that would be useful. > > (..) > Qdiscs might change skb->cb. Maybe use skb->sk? > > > The loopback functionality in CAN is a bit tricky (maybe you can take a look into the Documentation patch [7/7] at chapter 3.2 and 4.1.4). The problem is, that we need a per socket(!) option that enables the loopback for the sent CAN-Frames or not, so the information about loopback a skb content or not is contained inside the skb sent down to the CAN netdevice. If the CAN networkdevice is not capable to perform a loopback itself (see dev->flags, chapter 6) the CAN core has to do the loopback as a fallback. The use of skb->cb is also needed in the receive path to recognize and trash loopback'ed CAN-frames inside the *originating* socket (see chapter 4.1.4). Please consider the referenced documentation and give me a feedback, if you have a better idea how to deal with variable loopbacks on driver level (with is vital for CAN). Thanks for your feedback, Oliver - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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