passt: Spare some syscalls, add some optimisations from profiling

Avoid a bunch of syscalls on forwarding paths by:

- storing minimum and maximum file descriptor numbers for each
  protocol, fall back to SO_PROTOCOL query only on overlaps

- allocating a larger receive buffer -- this can result in more
  coalesced packets than sendmmsg() can take (UIO_MAXIOV, i.e. 1024),
  so make sure we don't exceed that within a single call to protocol
  tap handlers

- nesting the handling loop in tap_handler() in the receive loop,
  so that we have better chances of filling our receive buffer in
  fewer calls

- skipping the recvfrom() in the UDP handler on EPOLLERR -- there's
  nothing to be done in that case

and while at it:

- restore the 20ms timer interval for periodic (TCP) events, I
  accidentally changed that to 100ms in an earlier commit

- attempt using SO_ZEROCOPY for UDP -- if it's not available,
  sendmmsg() will succeed anyway

- fix the handling of the status code from sendmmsg(), if it fails,
  we'll try to discard the first message, hence return 1 from the
  UDP handler

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/icmp.c b/icmp.c
index 9a3c740..dd4e3a4 100644
--- a/icmp.c
+++ b/icmp.c
@@ -135,6 +135,9 @@ int icmp_tap_handler(struct ctx *c, int af, void *addr,
  */
 int icmp_sock_init(struct ctx *c)
 {
+	c->icmp.fd_min = INT_MAX;
+	c->icmp.fd_max = 0;
+
 	if (c->v4 && (c->icmp.s4 = sock_l4_add(c, 4, IPPROTO_ICMP, 0)) < 0)
 		return -1;