tcp: Add num_closed_socks to struct sock_reuseport.
As noted in the following commit, a closed listener has to hold the
reference to the reuseport group for socket migration. This patch adds a
field (num_closed_socks) to struct sock_reuseport to manage closed sockets
within the same reuseport group. Moreover, this and the following commits
introduce some helper functions to split socks[] into two sections and keep
TCP_LISTEN and TCP_CLOSE sockets in each section. Like a double-ended
queue, we will place TCP_LISTEN sockets from the front and TCP_CLOSE
sockets from the end.
TCP_LISTEN----------> <-------TCP_CLOSE
+---+---+ --- +---+ --- +---+ --- +---+
| 0 | 1 | ... | i | ... | j | ... | k |
+---+---+ --- +---+ --- +---+ --- +---+
i = num_socks - 1
j = max_socks - num_closed_socks
k = max_socks - 1
This patch also extends reuseport_add_sock() and reuseport_grow() to
support num_closed_socks.
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20210612123224.12525-3-kuniyu@amazon.co.jp