From: Jesper Dangaard Brouer <brouer@redhat.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: David Ahern <dsahern@gmail.com>,
bpf@vger.kernel.org, netdev@vger.kernel.org,
Daniel Borkmann <borkmann@iogearbox.net>,
Andrii Nakryiko <andrii.nakryiko@gmail.com>,
Lorenzo Bianconi <lorenzo@kernel.org>,
David Miller <davem@davemloft.net>,
brouer@redhat.com
Subject: Re: [PATCH bpf-next V1] bpf: devmap dynamic map-value area based on BTF
Date: Fri, 5 Jun 2020 10:23:23 +0200 [thread overview]
Message-ID: <20200605102323.15c2c06c@carbon> (raw)
In-Reply-To: <20200604173341.rvfrjmt433knl3uv@ast-mbp.dhcp.thefacebook.com>
On Thu, 4 Jun 2020 10:33:41 -0700
Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> On Thu, Jun 04, 2020 at 10:40:06AM -0600, David Ahern wrote:
> > On 6/4/20 9:48 AM, Jesper Dangaard Brouer wrote:
> > > I will NOT send a patch that expose this in uapi/bpf.h. As I explained
> > > before, this caused the issues for my userspace application, that
> > > automatically picked-up struct bpf_devmap_val, and started to fail
> > > (with no code changes), because it needed minus-1 as input. I fear
> > > that this will cause more work for me later, when I have to helpout and
> > > support end-users on e.g. xdp-newbies list, as it will not be obvious
> > > to end-users why their programs map-insert start to fail. I have given
> > > up, so I will not NACK anyone sending such a patch.
>
> Jesper,
>
> you gave wrong direction to David during development of the patches and
> now the devmap uapi is suffering the consequences.
>
> > >
> > > Why is it we need to support file-descriptor zero as a valid
> > > file-descriptor for a bpf-prog?
> >
> > That was a nice property of using the id instead of fd. And the init to
> > -1 is not unique to this; adopters of the bpf_set_link_xdp_fd_opts for
> > example have to do the same.
>
> I think it's better to adopt "fd==0 -> invalid" approach.
> It won't be unique here. We're already using it in other places in bpf syscall.
> I agree with Jesper that requiring -1 init of 2nd field is quite ugly
> and inconvenient.
Great. If we can remove this requirement of -1 init (and let zero mean
feature isn't used), then I'm all for exposing expose in uapi/bpf.h.
For future extensions there is still a problem/challenge in
dev_map_can_have_prog() that blocks generic-XDP for using future
extensions. BUT next person extending devmap can deal with that, so
it's not something we need to deal with now.
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
next prev parent reply other threads:[~2020-06-05 8:23 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-03 15:44 [PATCH bpf-next V1] bpf: devmap dynamic map-value area based on BTF Jesper Dangaard Brouer
2020-06-03 16:22 ` Alexei Starovoitov
2020-06-04 15:48 ` Jesper Dangaard Brouer
2020-06-04 16:40 ` David Ahern
2020-06-04 17:33 ` Alexei Starovoitov
2020-06-05 8:23 ` Jesper Dangaard Brouer [this message]
2020-06-05 11:01 ` Toke Høiland-Jørgensen
2020-06-05 17:01 ` Alexei Starovoitov
2020-06-05 16:58 ` Alexei Starovoitov
2020-06-09 12:19 ` Jesper Dangaard Brouer
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