From: Pierre Ossman <drzeus@xxxxxxxxx> Date: Mon, 22 Oct 2007 19:05:32 +0200 > + /* > + * The IP stack is littered with silly assumptions on alignment, > + * so we need to do a bit of layering violation here and make > + * assumptions about the size of the headers between us and the > + * IP stack. > + */ > + skb_reserve(skb, NET_IP_ALIGN); > + Please remove this comment. Where else could we possibly ensure that post-link-level headers are aligned properly, taking into account DMA engine restrictions and whatnot, other than in the driver itself? It's not about IP, even though the macro has "IP" in it's name. It's meant to ensure reasonable alignment after the link-level header, regardless of upper-level protocol. So your layering violation commentary is simply rediculious and frankly starting to annoy the crap out of me. As you were also shown, all of THIS is fully documented in a huge comment above the definition of NET_IP_ALIGN. The irony in all of this is that NET_IP_ALIGN is in fact fully documented even in books such as O'Reilly's Understanding Linux Network Internals. See chapter 10, sub-section 4. The skb_reserve() sequence that was so terribly difficult for you to discover is used in just about every network driver, and even used in the drivers/net/pci-skeleton.c, a skeleton PCI ethernet driver that is there exactly to show people how to do things properly. It uses the constant '2' instead of NET_IP_ALIGN, which should obviously be corrected. All of your complaining is simply because you didn't put much effort into looking around to see what the existing practice was and therefore you got surprising results. We have nearly a hundred ethernet drivers you could have studied to see how things are supposed to be done. I'm sorry for flaming you so much, but you are showing zero respect for existing practice in the kernel networking and you behave as if you're the only person in the world who has to deal with these issues. You accuse us openly of mis-architecting the Linux networking with these so-called "layering violations" and having maintained the stack for more than 10 years I start to take things like that quite personally. - To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
