[PATCH v6 04/18] fwd_rule: Move conflict checking back within fwd_rule_add()

[Stefano Brivio <sbrivio@redhat.com>]

From: David Gibson <david@gibson.dropbear.id.au>

2bffb631d31e ("fwd_rule: Move rule conflict checking from fwd_rule_add()
to caller") moved rule conflict checking out of fwd_rule_add().  This
seemed like a good idea at the time, but turns out to be kind of awkward:
it means we're now checking for conflicts *before* we've checked the rule
for internal consistency (including first <= last), which leaves an awkward
assert() which might fire in unexpected places.

While it's true that it's not really necessary to include this in order to
safely add a rule, the benefits from skipping it are pretty marginal.  So,
for simplicity, fold this check back into fwd_rule_add(), making it
non-fatal.  If we ever have cases with enough rules that the O(n^2) nature
of the check matters, we might need to revisit.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 fwd_rule.c | 38 +++++++++++++-------------------------
 1 file changed, 13 insertions(+), 25 deletions(-)

diff --git a/fwd_rule.c b/fwd_rule.c
index cd3dec0..1413584 100644
--- a/fwd_rule.c
+++ b/fwd_rule.c
@@ -195,29 +195,6 @@ static bool fwd_rule_conflicts(const struct fwd_rule *a, const struct fwd_rule *
 	return true;
 }
 
-/**
- * fwd_rule_conflict_check() - Die if given rule conflicts with any in list
- * @new:	New rule
- * @rules:	Existing rules against which to test
- * @count:	Number of rules in @rules
- */
-static void fwd_rule_conflict_check(const struct fwd_rule *new,
-				    const struct fwd_rule *rules, size_t count)
-{
-	unsigned i;
-
-	for (i = 0; i < count; i++) {
-		char newstr[FWD_RULE_STRLEN], rulestr[FWD_RULE_STRLEN];
-
-		if (!fwd_rule_conflicts(new, &rules[i]))
-			continue;
-
-		die("Forwarding configuration conflict: %s versus %s",
-		    fwd_rule_fmt(new, newstr, sizeof(newstr)),
-		    fwd_rule_fmt(&rules[i], rulestr, sizeof(rulestr)));
-	}
-}
-
 /**
  * fwd_rule_add() - Validate and add a rule to a forwarding table
  * @fwd:	Table to add to
@@ -230,7 +207,7 @@ static int fwd_rule_add(struct fwd_table *fwd, const struct fwd_rule *new)
 	/* Flags which can be set from the caller */
 	const uint8_t allowed_flags = FWD_WEAK | FWD_SCAN | FWD_DUAL_STACK_ANY;
 	unsigned num = (unsigned)new->last - new->first + 1;
-	unsigned port;
+	unsigned port, i;
 
 	if (new->first > new->last) {
 		warn("Rule has invalid port range %u-%u",
@@ -293,6 +270,18 @@ static int fwd_rule_add(struct fwd_table *fwd, const struct fwd_rule *new)
 		return -EINVAL;
 	}
 
+	for (i = 0; i < fwd->count; i++) {
+		char newstr[FWD_RULE_STRLEN], rulestr[FWD_RULE_STRLEN];
+
+		if (!fwd_rule_conflicts(new, &fwd->rules[i]))
+			continue;
+
+		warn("Forwarding configuration conflict: %s versus %s",
+		     fwd_rule_fmt(new, newstr, sizeof(newstr)),
+		     fwd_rule_fmt(&fwd->rules[i], rulestr, sizeof(rulestr)));
+		return -EEXIST;
+	}
+
 	if (fwd->count >= ARRAY_SIZE(fwd->rules)) {
 		warn("Too many rules (maximum %u)", ARRAY_SIZE(fwd->rules));
 		return -ENOSPC;
@@ -435,7 +424,6 @@ static void fwd_rule_range_except(struct fwd_table *fwd, uint8_t proto,
 		rule.last = i - 1;
 		rule.to = base + delta;
 
-		fwd_rule_conflict_check(&rule, fwd->rules, fwd->count);
 		if (fwd_rule_add(fwd, &rule) < 0)
 			goto fail;
 
-- 
2.43.0