On Fri, Oct 9, 2020 at 12:51 PM Xie He <xie.he.0...@gmail.com> wrote: > > On Fri, Oct 9, 2020 at 12:41 PM Xie He <xie.he.0...@gmail.com> wrote: > > > > Thanks. But there is still something that I don't understand. What is > > needed_headroom used for? If we are requesting space for t->encap_hlen > > and t->tun_hlen in hard_header_len. Do we still need to use > > needed_headroom? > > It seems to me that the original code includes t->encap_hlen, > t->tun_hlen, and the IP header length in needed_headroom. (Right?) If > we are including these in hard_header_len, we need to move them out of > needed_headroom.
Interesting point. I think needed_headroom is 0 until we call ipgre_changelink(), but needed_headroom is already being used in multiple places for skb_cow_head() in the same file, I guess they should be replaced with hard_head_len because for GRE tunnel those are its link-layer header. What makes it more complicated is that header_ops is actually set conditionally, so should be hard_header_len/needed_head_room accordingly. Thanks.
