Re: [PATCH v9 bpf-next 10/14] bpf: add multi-buffer support to xdp copy helpers

Lorenzo Bianconi
2021-06-29T13:23:35Z

[-- Attachment #1: Type: text/plain, Size: 1904 bytes --]

> >
> >
> > On 23 Jun 2021, at 1:49, John Fastabend wrote:
> >
> > > Lorenzo Bianconi wrote:
> > >> From: Eelco Chaudron <echaudro@redhat.com>
> > >>
> > >> This patch adds support for multi-buffer for the following helpers:
> > >> - bpf_xdp_output()
> > >> - bpf_perf_event_output()
> > >>
> > >> Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
> > >> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> > >> ---
> > >
> > > Ah ok so at least xdp_output will work with all bytes. But this is
> > > getting close to having access into the frags so I think doing
> > > the last bit shouldn't be too hard?
> >
> >
> > Guess you are talking about multi-buffer access in the XDP program?
> >
> > I did suggest an API a while back, https://lore.kernel.org/bpf/FD3E6E08-DE78-4FBA-96F6-646C93E88631@redhat.com/ but I had/have not time to work on it. Guess the difficult part is to convince the verifier to allow the data to be accessed.
>
> Ah great I think we had the same idea I called it xdp_pull_data()
> though.
>
> Whats the complication though it looks like it can be done by simply
> moving the data and data_end pointers around then marking them
> invalidated. This way the verifier knows the program needs to
> rewrite them. I can probably look more into next week.
>
> From my first glance it looks relatively straight forward to do
> now. I really would like to avoid yet another iteration of
> programs features I have to discover and somehow work around
> if we can get the helper into this series. If you really don't
> have time I can probably take a look early next week on an
> RFC for something like above helper.

cool, thx :)
What about discussing APIs during the BPF mtg upstream on Thursday (probably
not next one since most of the people will be in PTO)? I will work on some docs.

Regards,
Lorenzo

>
>
> .John
>

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]