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().
