[nft PATCH 1/3] src: Improve cache_needs_more() algorithm

[Phil Sutter <phil@nwl.cc>]

The old logic wasn't optimal: If e.g. current command was CMD_RESET and
old command was CMD_LIST, cache was already fully populated but still
refreshed.

Introduce a simple scoring system which reflects how
cache_init_objects() looks at the current command to decide if it is
finished already or not. Then use that in cache_needs_more(): If current
commands score is higher than old command's, cache needs an update.

Signed-off-by: Phil Sutter <phil@nwl.cc>
---
 src/rule.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/src/rule.c b/src/rule.c
index afe37cd90b1da..17bf5bbbe680c 100644
--- a/src/rule.c
+++ b/src/rule.c
@@ -220,13 +220,21 @@ static int cache_init(struct netlink_ctx *ctx, enum cmd_ops cmd)
 	return 0;
 }
 
-static int cache_needs_more(enum cmd_ops old_cmd, enum cmd_ops cmd)
+/* Return a "score" of how complete local cache will be if
+ * cache_init_objects() ran for given cmd. Higher value
+ * means more complete. */
+static int cache_completeness(enum cmd_ops cmd)
 {
-	if (cmd == CMD_LIST && old_cmd != CMD_LIST)
-		return 1;
-	if (cmd == CMD_RESET && old_cmd != CMD_RESET)
-		return 1;
-	return 0;
+	if (cmd == CMD_LIST)
+		return 3;
+	if (cmd != CMD_RESET)
+		return 2;
+	return 1;
+}
+
+static bool cache_needs_more(enum cmd_ops old_cmd, enum cmd_ops cmd)
+{
+	return cache_completeness(old_cmd) < cache_completeness(cmd);
 }
 
 int cache_update(struct nft_ctx *nft, enum cmd_ops cmd, struct list_head *msgs)
-- 
2.21.0