[RFC bpf-next 0/5] Extend SOCKMAP to store listening sockets

[Jakub Sitnicki <jakub@cloudflare.com>]

This patch set is a follow up on a suggestion from LPC '19 discussions to
make SOCKMAP (or a new map type derived from it) a generic type for storing
established as well as listening sockets.

We found ourselves in need of a map type that keeps references to listening
sockets when working on making the socket lookup programmable, aka BPF
inet_lookup [1].  Initially we repurposed REUSEPORT_SOCKARRAY but found it
problematic to extend due to being tightly coupled with reuseport
logic (see slides [2]). So we've turned our attention to SOCKMAP instead.

As it turns out the changes needed to make SOCKMAP suitable for storing
listening sockets are self-contained and have use outside of programming
the socket lookup. Hence this patch set.

With these patches SOCKMAP can be used in SK_REUSEPORT BPF programs as a
drop-in replacement for REUSEPORT_SOCKARRAY for TCP. This can hopefully
lead to code consolidation between the two map types in the future.

Having said that, the main intention here is to lay groundwork for using
SOCKMAP in the next iteration of programmable socket lookup patches.

I'm looking for feedback if there's anything fundamentally wrong with
extending SOCKMAP map type like this that I might have missed.

Thanks,
Jakub

[1] https://lore.kernel.org/bpf/20190828072250.29828-1-jakub@cloudflare.com/
[2] https://linuxplumbersconf.org/event/4/contributions/487/attachments/238/417/Programmable_socket_lookup_LPC_19.pdf


Jakub Sitnicki (5):
  bpf, sockmap: Let BPF helpers use lookup operation on SOCKMAP
  bpf, sockmap: Allow inserting listening TCP sockets into SOCKMAP
  bpf, sockmap: Don't let child socket inherit psock or its ops on copy
  bpf: Allow selecting reuseport socket from a SOCKMAP
  selftests/bpf: Extend SK_REUSEPORT tests to cover SOCKMAP

 kernel/bpf/verifier.c                         |   6 +-
 net/core/sock_map.c                           |  11 +-
 net/ipv4/tcp_bpf.c                            |  30 ++++
 tools/testing/selftests/bpf/Makefile          |   7 +-
 .../selftests/bpf/test_select_reuseport.c     | 141 ++++++++++++++----
 .../selftests/bpf/test_select_reuseport.sh    |  14 ++
 6 files changed, 173 insertions(+), 36 deletions(-)
 create mode 100755 tools/testing/selftests/bpf/test_select_reuseport.sh

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2.20.1