fib: allow to check if route exists in maps

f686a17eafa0 ("fib: Support existence check") adds EXPR_F_BOOLEAN as a
workaround to infer from the rhs of the relational expression if the fib
lookup wants to check for a specific output interface or, instead,
simply check for existence. This, however, does not work with maps.

The NFT_FIB_F_PRESENT flag can be used both with NFT_FIB_RESULT_OIF and
NFT_FIB_RESULT_OFINAME, my understanding is that they serve the same
purpose which is to check if a route exists, so they are redundant.

Add a 'check' fib result to check for routes while still keeping the
inference workaround for backward compatibility, but prefer the new
syntax in the listing.

Update man nft(8) and tests/py.

Fixes: f686a17eafa0 ("fib: Support existence check")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/tests/py/inet/fib.t.payload b/tests/py/inet/fib.t.payload
index 050857d9..e09a260c 100644
--- a/tests/py/inet/fib.t.payload
+++ b/tests/py/inet/fib.t.payload
@@ -26,7 +26,13 @@ ip test-ip prerouting
   [ fib daddr oif present => reg 1 ]
   [ cmp eq reg 1 0x00000001 ]
 
-# fib daddr oif missing
+# fib daddr check missing
 ip test-ip prerouting
   [ fib daddr oif present => reg 1 ]
   [ cmp eq reg 1 0x00000000 ]
+
+# fib daddr check vmap { missing : drop, exists : accept }
+        element 00000000  : drop 0 [end]        element 00000001  : accept 0 [end]
+ip test-ip prerouting
+  [ fib daddr oif present => reg 1 ]
+  [ lookup reg 1 set __map%d dreg 0 ]