[v2,bpf-next,0/4] L2 encap support for bpf_skb_adjust_room

Message

Alan Maguire April 8, 2019, 4:57 p.m. UTC

Extend bpf_skb_adjust_room growth to mark inner MAC header so that
L2 encapsulation can be used for tc tunnels.

Patch #1 extends the existing test_tc_tunnel to support UDP
encapsulation; later we want to be able to test MPLS over UDP and
MPLS over GRE encapsulation.

Patch #2 adds the BPF_F_ADJ_ROOM_ENCAP_L2(len) macro, which
allows specification of inner mac length.  Other approaches were
explored prior to taking this approach.  Specifically, I tried
automatically computing the inner mac length on the basis of the
specified flags (so inner maclen for GRE/IPv4 encap is the len_diff
specified to bpf_skb_adjust_room minus GRE + IPv4 header length
for example).  Problem with this is that we don't know for sure
what form of GRE/UDP header we have; is it a full GRE header,
or is it a FOU UDP header or generic UDP encap header? My fear
here was we'd end up with an explosion of flags.  The other approach
tried was to support inner L2 header marking as a separate room
adjustment, i.e. adjust for L3/L4 encap, then call
bpf_skb_adjust_room for L2 encap.  This can be made to work but
because it imposed an order on operations, felt a bit clunky.

Patch #3 syncs tools/ bpf.h.

Patch #4 extends the tests again to support MPLSoverGRE,
MPLSoverUDP, and transparent ethernet bridging (TEB) where
the inner L2 header is an ethernet header.  Testing of BPF
encap against tunnels is done for cases where configuration
of such tunnels is possible (MPLSoverGRE[6], MPLSoverUDP,
gre[6]tap), and skipped otherwise.  Testing of BPF encap/decap
is always carried out.

Changes since v1:
 - fixed formatting of commit references.
 - BPF_F_ADJ_ROOM_FIXED_GSO flag enabled on all variants (patch 1)
 - fixed fou6 options for UDP encap; checksum errors observed were
   due to the fact fou6 tunnel was not set up with correct ipproto
   options (41 -6).  0 checksums work fine (patch 1)
 - added definitions for mask and shift used in setting L2 length
   (patch 2)
 - allow udp encap with fixed GSO (patch 2)
 - changed "elen" to "l2_len" to be more descriptive (patch 4)
 - added support for ethernet L2 encap to tests; testing against
   gre[6]tap tunnels (patch 4).

Alan Maguire (4):
  selftests_bpf: add UDP encap to test_tc_tunnel
  bpf: add layer 2 encap support to bpf_skb_adjust_room
  bpf: sync bpf.h to tools/ for BPF_F_ADJ_ROOM_ENCAP_L2
  selftests_bpf: add L2 encap to test_tc_tunnel

 include/uapi/linux/bpf.h                           |  10 +
 net/core/filter.c                                  |  15 +-
 tools/include/uapi/linux/bpf.h                     |  10 +
 tools/testing/selftests/bpf/progs/test_tc_tunnel.c | 335 +++++++++++++++++----
 tools/testing/selftests/bpf/test_tc_tunnel.sh      | 147 +++++++--
 5 files changed, 427 insertions(+), 90 deletions(-)

Comments

Willem de Bruijn April 8, 2019, 7:07 p.m. UTC | #1

On Mon, Apr 8, 2019 at 12:59 PM Alan Maguire <[e-mail]> wrote:
>
> Extend bpf_skb_adjust_room growth to mark inner MAC header so that
> L2 encapsulation can be used for tc tunnels.
>
> Patch #1 extends the existing test_tc_tunnel to support UDP
> encapsulation; later we want to be able to test MPLS over UDP and
> MPLS over GRE encapsulation.
>
> Patch #2 adds the BPF_F_ADJ_ROOM_ENCAP_L2(len) macro, which
> allows specification of inner mac length.  Other approaches were
> explored prior to taking this approach.  Specifically, I tried
> automatically computing the inner mac length on the basis of the
> specified flags (so inner maclen for GRE/IPv4 encap is the len_diff
> specified to bpf_skb_adjust_room minus GRE + IPv4 header length
> for example).  Problem with this is that we don't know for sure
> what form of GRE/UDP header we have; is it a full GRE header,
> or is it a FOU UDP header or generic UDP encap header? My fear
> here was we'd end up with an explosion of flags.  The other approach
> tried was to support inner L2 header marking as a separate room
> adjustment, i.e. adjust for L3/L4 encap, then call
> bpf_skb_adjust_room for L2 encap.  This can be made to work but
> because it imposed an order on operations, felt a bit clunky.
>
> Patch #3 syncs tools/ bpf.h.
>
> Patch #4 extends the tests again to support MPLSoverGRE,
> MPLSoverUDP, and transparent ethernet bridging (TEB) where
> the inner L2 header is an ethernet header.  Testing of BPF
> encap against tunnels is done for cases where configuration
> of such tunnels is possible (MPLSoverGRE[6], MPLSoverUDP,
> gre[6]tap), and skipped otherwise.  Testing of BPF encap/decap
> is always carried out.
>
> Changes since v1:
>  - fixed formatting of commit references.
>  - BPF_F_ADJ_ROOM_FIXED_GSO flag enabled on all variants (patch 1)
>  - fixed fou6 options for UDP encap; checksum errors observed were
>    due to the fact fou6 tunnel was not set up with correct ipproto
>    options (41 -6).  0 checksums work fine (patch 1)
>  - added definitions for mask and shift used in setting L2 length
>    (patch 2)
>  - allow udp encap with fixed GSO (patch 2)
>  - changed "elen" to "l2_len" to be more descriptive (patch 4)
>  - added support for ethernet L2 encap to tests; testing against
>    gre[6]tap tunnels (patch 4).
>
> Alan Maguire (4):
>   selftests_bpf: add UDP encap to test_tc_tunnel
>   bpf: add layer 2 encap support to bpf_skb_adjust_room
>   bpf: sync bpf.h to tools/ for BPF_F_ADJ_ROOM_ENCAP_L2
>   selftests_bpf: add L2 encap to test_tc_tunnel

A few small nits in the patches, but overall this looks great. Thanks
a lot for adding the detailed tests for UDP, TEB and MPLS!

The only change that may really be needed is adding mpls to the config
to avoid kselftest bot failures. Otherwise, I would not even have
bothered pointing out the nits.

With that change, for the series,

Acked-by: Willem de Bruijn <[e-mail]>