[PATCH net-next v3 4/4] ipv4: replace obsolete routing comment

[liamsmith827 <liamsmith827@grapheneos.org>]

From: Liam Smith <liamsmith827@proton.me>

Replace an existing comment which describes obsolete fib_lookup(),
MSG_DONTROUTE and IPv6 behavior.

Signed-off-by: Liam Smith <liamsmith827@proton.me>
---
 net/ipv4/route.c | 27 +++++++++++----------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 03db105303b4..d862b5ecad71 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2856,24 +2856,19 @@ struct rtable *ip_route_output_key_hash_rcu(struct net *net, struct flowi4 *fl4,
 		if (fl4->flowi4_oif &&
 		    (ipv4_is_multicast(fl4->daddr) ||
 		     (!fl4->flowi4_l3mdev && err == -ESRCH))) {
-			/* Apparently, routing tables are wrong. Assume,
-			 * that the destination is on link.
+			/* When oif is specified, fib_lookup() is called
+			 * primarily to determine if the destination is
+			 * accessible directly or through a gateway. It also
+			 * checks whether there are any traffic restrictions
+			 * (blackhole, prohibit, unreachable), or if there's a
+			 * routing lookup miss.
 			 *
-			 * WHY? DW.
-			 * Because we are allowed to send to iface
-			 * even if it has NO routes and NO assigned
-			 * addresses. When oif is specified, routing
-			 * tables are looked up with only one purpose:
-			 * to catch if destination is gatewayed, rather than
-			 * direct. Moreover, if MSG_DONTROUTE is set,
-			 * we send packet, ignoring both routing tables
-			 * and ifaddr state. --ANK
-			 *
-			 *
-			 * We could make it even if oif is unknown,
-			 * likely IPv6, but we do not.
+			 * This fallback path is always taken for multicast,
+			 * regardless of any restrictions or misses. Non-vrf
+			 * unicast does honor restrictions, but falls back if
+			 * there's a miss. The destination is assumed on-link
+			 * for both.
 			 */
-
 			if (fl4->saddr == 0)
 				fl4->saddr = inet_select_addr(dev_out, 0,
 							      RT_SCOPE_LINK);
-- 
2.47.3