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. > > Would a link_swap() API (proposed by Andrii iirc) resolve this use case as > well? If not why? If it can it seems like the more general and consistent > solution. I can imagine swapping links is useful in tracing as well and > likely other cases I haven't thought about. Yes, that's the idea. Right now I have implementation for cgroups, but API itself is generic and should/will be extended to tracing and XDP.
