On Mon, Mar 23, 2020 at 4:24 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: > > Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes: > > > On Fri, Mar 20, 2020 at 11:31 AM John Fastabend > > <john.fastabend@xxxxxxxxx> wrote: > >> > >> Jakub Kicinski wrote: > >> > On Fri, 20 Mar 2020 09:48:10 +0100 Toke Høiland-Jørgensen wrote: > >> > > Jakub Kicinski <kuba@xxxxxxxxxx> writes: > >> > > > On Thu, 19 Mar 2020 14:13:13 +0100 Toke Høiland-Jørgensen wrote: > >> > > >> From: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> > >> > > >> > >> > > >> While it is currently possible for userspace to specify that an existing > >> > > >> XDP program should not be replaced when attaching to an interface, there is > >> > > >> no mechanism to safely replace a specific XDP program with another. > >> > > >> > >> > > >> This patch adds a new netlink attribute, IFLA_XDP_EXPECTED_FD, which can be > >> > > >> set along with IFLA_XDP_FD. If set, the kernel will check that the program > >> > > >> currently loaded on the interface matches the expected one, and fail the > >> > > >> operation if it does not. This corresponds to a 'cmpxchg' memory operation. > >> > > >> > >> > > >> A new companion flag, XDP_FLAGS_EXPECT_FD, is also added to explicitly > >> > > >> request checking of the EXPECTED_FD attribute. This is needed for userspace > >> > > >> to discover whether the kernel supports the new attribute. > >> > > >> > >> > > >> Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> > >> > > > > >> > > > I didn't know we wanted to go ahead with this... > >> > > > >> > > Well, I'm aware of the bpf_link discussion, obviously. Not sure what's > >> > > happening with that, though. So since this is a straight-forward > >> > > extension of the existing API, that doesn't carry a high implementation > >> > > cost, I figured I'd just go ahead with this. Doesn't mean we can't have > >> > > something similar in bpf_link as well, of course. > >> > > >> > I'm not really in the loop, but from what I overheard - I think the > >> > bpf_link may be targeting something non-networking first. > >> > >> My preference is to avoid building two different APIs one for XDP and another > >> for everything else. If we have userlands that already understand links and > >> pinning support is on the way imo lets use these APIs for networking as well. > > > > I agree here. And yes, I've been working on extending bpf_link into > > cgroup and then to XDP. We are still discussing some cgroup-specific > > details, but the patch is ready. I'm going to post it as an RFC to get > > the discussion started, before we do this for XDP. > > Well, my reason for being skeptic about bpf_link and proposing the > netlink-based API is actually exactly this, but in reverse: With > bpf_link we will be in the situation that everything related to a netdev > is configured over netlink *except* XDP. One can argue that everything related to use of BPF is going to be uniform and done through BPF syscall? Given variety of possible BPF hooks/targets, using custom ways to attach for all those many cases is really bad as well, so having a unifying concept and single entry to do this is good, no? > > Other than that, I don't see any reason why the bpf_link API won't work. > So I guess that if no one else has any problem with BPF insisting on > being a special snowflake, I guess I can live with it as well... *shrugs* :) Apart from derogatory remark, BPF is a bit special here, because it requires every potential BPF hook (be it cgroups, xdp, perf_event, etc) to be aware of BPF program(s) and execute them with special macro. So like it or not, it is special and each driver supporting BPF needs to implement this BPF wiring. > > -Toke >
