58dfc900fa
commit 868d523535c2 ("bpf: add bpf_skb_adjust_room encap flags")
introduced support to bpf_skb_adjust_room for GSO-friendly GRE
and UDP encapsulation.
For GSO to work for skbs, the inner headers (mac and network) need to
be marked. For L3 encapsulation using bpf_skb_adjust_room, the mac
and network headers are identical. Here we provide a way of specifying
the inner mac header length for cases where L2 encap is desired. Such
an approach can support encapsulated ethernet headers, MPLS headers etc.
For example to convert from a packet of form [eth][ip][tcp] to
[eth][ip][udp][inner mac][ip][tcp], something like the following could
be done:
headroom = sizeof(iph) + sizeof(struct udphdr) + inner_maclen;
ret = bpf_skb_adjust_room(skb, headroom, BPF_ADJ_ROOM_MAC,
BPF_F_ADJ_ROOM_ENCAP_L4_UDP |
BPF_F_ADJ_ROOM_ENCAP_L3_IPV4 |
BPF_F_ADJ_ROOM_ENCAP_L2(inner_maclen));
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.