David Ahern wrote:
> On 11/2/20 2:28 AM, Jesper Dangaard Brouer wrote:
> >>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> >>> index e6ceac3f7d62..01b2b17c645a 100644
> >>> --- a/include/uapi/linux/bpf.h
> >>> +++ b/include/uapi/linux/bpf.h
> >>> @@ -2219,6 +2219,9 @@ union bpf_attr {
> >>> * * > 0 one of **BPF_FIB_LKUP_RET_** codes explaining why
> >>> the
> >>> * packet is not forwarded or needs assist from full
> >>> stack
> >>> *
> >>> + * If lookup fails with BPF_FIB_LKUP_RET_FRAG_NEEDED, then
> >>> the MTU
> >>> + * was exceeded and result params->mtu contains the MTU.
> >>> + *
> >>
> >> Do we need to hide this behind a flag? It seems otherwise you might confuse
> >> users. I imagine on error we could reuse the params arg, but now we changed
> >> the tot_len value underneath them?
> >
> > The principle behind this bpf_fib_lookup helper, is that params (struct
> > bpf_fib_lookup) is used for both input and output (results). Almost
> > every field is change after the lookup. (For performance reasons this
> > is kept at 64 bytes (cache-line)) Thus, users of this helper already
> > expect/knows the contents of params have changed.
> >
>
> yes, that was done on purpose.
OK sounds good then. Thanks.
>
> Jesper: you should remove the '(if requested check_mtu)' comment in the
> documentation. That is an internal flag only -- xdp is true, tc is false.
