Re: [PATCH bpf-next V5 2/5] bpf: bpf_fib_lookup return MTU value as output when looked up

[David Ahern <dsahern@gmail.com>]

On 10/30/20 10:50 AM, Jesper Dangaard Brouer wrote:
> The BPF-helpers for FIB lookup (bpf_xdp_fib_lookup and bpf_skb_fib_lookup)
> can perform MTU check and return BPF_FIB_LKUP_RET_FRAG_NEEDED.  The BPF-prog
> don't know the MTU value that caused this rejection.
> 
> If the BPF-prog wants to implement PMTU (Path MTU Discovery) (rfc1191) it
> need to know this MTU value for the ICMP packet.
> 
> Patch change lookup and result struct bpf_fib_lookup, to contain this MTU
> value as output via a union with 'tot_len' as this is the value used for
> the MTU lookup.
> 
> V5:
>  - Fixed uninit value spotted by Dan Carpenter.
>  - Name struct output member mtu_result
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> ---
>  include/uapi/linux/bpf.h       |   11 +++++++++--
>  net/core/filter.c              |   22 +++++++++++++++-------
>  tools/include/uapi/linux/bpf.h |   11 +++++++++--
>  3 files changed, 33 insertions(+), 11 deletions(-)
> 

Reviewed-by: David Ahern <dsahern@kernel.org>