On Tue, 2019-01-01 at 09:53 -0800, David Miller wrote: > From: Radu Rendec <radu.ren...@gmail.com > Date: Sat, 29 Dec 2018 13:26:34 -0500 > > > I'm working on some application-specific NIC driver. On the TX path, it > > must remove a custom tag that sits between the Ethernet type field and > > the actual Ethernet payload; then it must add a different tag in front > > of the Ethernet header (the MAC DA field) before it hands over the frame > > to the hardware for delivery. > > > I'm wondering if skb_cow_head() is enough to safely modify the skb as > > described above, or I should use skb_cow() instead. > > skb_cow_head() should be sufficient. This is what the DSA layer tagging > code uses, and it is doing something similar if not exactly like what you > are doing. > > See net/dsa/tag_dsa.c:dsa_xmit().
David, thank you - this is very helpful! Indeed, my use case is very similar to DSA, but not identical, so unfortunately I can't use DSA. However, my other question is still unanswered: what exactly is the "header"? In the case of a fragmented skb, is it the entire "main" skb (i.e. skb->data, without the fragments) or just a portion of it? Does the "header" concept still apply to linear skb's? Thanks, Radu Rendec
