Re: [PATCH bpf-next v2 00/12] Link-based program attachment to network namespaces

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Sun, May 31, 2020 at 1:28 AM Jakub Sitnicki <jakub@cloudflare.com> wrote:
>
> One of the pieces of feedback from recent review of BPF hooks for socket
> lookup [0] was that new program types should use bpf_link-based
> attachment.
>
> This series introduces new bpf_link type for attaching to network
> namespace. All link operations are supported. Errors returned from ops
> follow cgroup example. Patch 4 description goes into error semantics.
>
> The major change in v2 is a switch away from RCU to mutex-only
> synchronization. Andrii pointed out that it is not needed, and it makes
> sense to keep locking straightforward.
>
> Also, there were a couple of bugs in update_prog and fill_info initial
> implementation, one picked up by kbuild. Those are now fixed. Tests have
> been extended to cover them. Full changelog below.
>
> Series is organized as so:
>
> Patches 1-3 prepare a space in struct net to keep state for attached BPF
> programs, and massage the code in flow_dissector to make it attach type
> agnostic, to finally move it under kernel/bpf/.
>
> Patch 4, the most important one, introduces new bpf_link link type for
> attaching to network namespace.
>
> Patch 5 unifies the update error (ENOLINK) between BPF cgroup and netns.
>
> Patches 6-8 make libbpf and bpftool aware of the new link type.
>
> Patches 9-12 Add and extend tests to check that link low- and high-level
> API for operating on links to netns works as intended.
>
> Thanks to Alexei, Andrii, Lorenz, Marek, and Stanislav for feedback.
>
> -jkbs
>
> [0] https://lore.kernel.org/bpf/20200511185218.1422406-1-jakub@cloudflare.com/
>
> Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
> Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
> Cc: Lorenz Bauer <lmb@cloudflare.com>
> Cc: Marek Majkowski <marek@cloudflare.com>
> Cc: Stanislav Fomichev <sdf@google.com>
>
> v1 -> v2:
>
> - Switch to mutex-only synchronization. Don't rely on RCU grace period
>   guarantee when accessing struct net from link release / update /
>   fill_info, and when accessing bpf_link from pernet pre_exit
>   callback. (Andrii)
> - Drop patch 1, no longer needed with mutex-only synchronization.
> - Don't leak uninitialized variable contents from fill_info callback
>   when link is in defunct state. (kbuild)
> - Make fill_info treat the link as defunct (i.e. no attached netns) when
>   struct net refcount is 0, but link has not been yet auto-detached.
> - Add missing BPF_LINK_TYPE define in bpf_types.h for new link type.
> - Fix link update_prog callback to update the prog that will run, and
>   not just the link itself.
> - Return EEXIST on prog attach when link already exists, and on link
>   create when prog is already attached directly. (Andrii)
> - Return EINVAL on prog detach when link is attached. (Andrii)
> - Fold __netns_bpf_link_attach into its only caller. (Stanislav)
> - Get rid of a wrapper around container_of() (Andrii)
> - Use rcu_dereference_protected instead of rcu_access_pointer on
>   update-side. (Stanislav)
> - Make return-on-success from netns_bpf_link_create less
>   confusing. (Andrii)
> - Adapt bpf_link for cgroup to return ENOLINK when updating a defunct
>   link. (Andrii, Alexei)
> - Order new exported symbols in libbpf.map alphabetically (Andrii)
> - Keep libbpf's "failed to attach link" warning message clear as to what
>   we failed to attach to (cgroup vs netns). (Andrii)
> - Extract helpers for printing link attach type. (bpftool, Andrii)
> - Switch flow_dissector tests to BPF skeleton and extend them to
>   exercise link-based flow dissector attachment. (Andrii)
> - Harden flow dissector attachment tests with prog query checks after
>   prog attach/detach, or link create/update/close.
> - Extend flow dissector tests to cover fill_info for defunct links.
> - Rebase onto recent bpf-next

I really like the set. Applied. Thanks!