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, 4 insertions, 2 deletions

diff --git a/tests/py/inet/fib.t b/tests/py/inet/fib.t
index dbe45d95..f9c03b3a 100644
--- a/tests/py/inet/fib.t
+++ b/tests/py/inet/fib.t
@@ -13,5 +13,7 @@ fib daddr . iif type local;ok
 fib daddr . iif type vmap { blackhole : drop, prohibit : drop, unicast : accept };ok
 fib daddr . oif type local;fail
 
-fib daddr oif exists;ok
-fib daddr oif missing;ok
+fib daddr check missing;ok
+fib daddr oif exists;ok;fib daddr check exists
+
+fib daddr check vmap { missing : drop, exists : accept };ok