KRT: Scan routing tables separetely on linux to avoid congestion

Remove compile-time sysdep option CONFIG_ALL_TABLES_AT_ONCE, replace it
with runtime ability to run either separate table scans or shared scan.

On Linux, use separate table scans by default when the netlink socket
option NETLINK_GET_STRICT_CHK is available, but retreat to shared scan
when it fails.

Running separate table scans has advantages where some routing tables are
managed independently, e.g. when multiple routing daemons are running on
the same machine, as kernel routing table modification performance is
significantly reduced when the table is modified while it is being
scanned.

Thanks Daniel Gröber for the original patch and Toke Høiland-Jørgensen
for suggestions.

1 files changed, 37 insertions, 12 deletions

diff --git a/sysdep/linux/netlink.c b/sysdep/linux/netlink.c
index 29b744cb..bc65e0d2 100644
--- a/sysdep/linux/netlink.c
+++ b/sysdep/linux/netlink.c
@@ -161,16 +161,13 @@ nl_open_sock(struct nl_sock *nl)
     }
 }
 
-static void
+static int
 nl_set_strict_dump(struct nl_sock *nl UNUSED, int strict UNUSED)
 {
-  /*
-   * Strict checking is not necessary, it improves behavior on newer kernels.
-   * If it is not available (missing SOL_NETLINK compile-time, or ENOPROTOOPT
-   * run-time), we can just ignore it.
-   */
 #ifdef SOL_NETLINK
-  setsockopt(nl->fd, SOL_NETLINK, NETLINK_GET_STRICT_CHK, &strict, sizeof(strict));
+  return setsockopt(nl->fd, SOL_NETLINK, NETLINK_GET_STRICT_CHK, &strict, sizeof(strict));
+#else
+  return -1;
 #endif
 }
 
@@ -198,10 +195,17 @@ nl_cfg_rx_buffer_size(struct config *cfg)
 static void
 nl_open(void)
 {
+  if ((nl_scan.fd >= 0) && (nl_req.fd >= 0))
+    return;
+
   nl_open_sock(&nl_scan);
   nl_open_sock(&nl_req);
 
-  nl_set_strict_dump(&nl_scan, 1);
+  if (nl_set_strict_dump(&nl_scan, 1) < 0)
+  {
+    log(L_WARN "KRT: Netlink strict checking failed, will scan all tables at once");
+    krt_use_shared_scan();
+  }
 }
 
 static void
@@ -256,11 +260,13 @@ nl_request_dump_addr(int af)
 }
 
 static void
-nl_request_dump_route(int af)
+nl_request_dump_route(int af, int table_id)
 {
   struct {
     struct nlmsghdr nh;
     struct rtmsg rtm;
+    struct rtattr rta;
+    u32 table_id;
   } req = {
     .nh.nlmsg_type = RTM_GETROUTE,
     .nh.nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg)),
@@ -269,7 +275,17 @@ nl_request_dump_route(int af)
     .rtm.rtm_family = af,
   };
 
-  send(nl_scan.fd, &req, sizeof(req), 0);
+  if (table_id < 256)
+    req.rtm.rtm_table = table_id;
+  else
+  {
+    req.rta.rta_type = RTA_TABLE;
+    req.rta.rta_len = RTA_LENGTH(4);
+    req.table_id = table_id;
+    req.nh.nlmsg_len = NLMSG_ALIGN(req.nh.nlmsg_len) + req.rta.rta_len;
+  }
+
+  send(nl_scan.fd, &req, req.nh.nlmsg_len, 0);
   nl_scan.last_hdr = NULL;
 }
 
@@ -1976,18 +1992,27 @@ nl_parse_route(struct nl_parse_state *s, struct nlmsghdr *h)
 }
 
 void
-krt_do_scan(struct krt_proto *p UNUSED)	/* CONFIG_ALL_TABLES_AT_ONCE => p is NULL */
+krt_do_scan(struct krt_proto *p)
 {
   struct nlmsghdr *h;
   struct nl_parse_state s;
 
   nl_parse_begin(&s, 1);
-  nl_request_dump_route(AF_UNSPEC);
+
+  /* Table-specific scan or shared scan */
+  if (p)
+    nl_request_dump_route(p->af, krt_table_id(p));
+  else
+    nl_request_dump_route(AF_UNSPEC, 0);
+
   while (h = nl_get_scan())
+  {
     if (h->nlmsg_type == RTM_NEWROUTE || h->nlmsg_type == RTM_DELROUTE)
       nl_parse_route(&s, h);
     else
       log(L_DEBUG "nl_scan_fire: Unknown packet received (type=%d)", h->nlmsg_type);
+  }
+
   nl_parse_end(&s);
 }