rule: change API for setting/getting l3mdev rule property

- for rtnl_rule_set_l3mdev(), also allow unsetting the l3mdev field.
  In practice, kernel only allows for two options: either omit
  tb[FRA_L3MDEV] or set it to 1. As such, rtnl_rule_set_l3mdev()
  allows for both of these. In principle the setter could get
  extended to set other values. Such values are reserved.

- for rtnl_rule_get_l3mdev() also return an error code. I think it
  is appropriate to mix value and negative error code, as long as
  the range of values cannot overlap with error codes.
  Arguably, the outcome is a bit awkward, as the function now is
  expected to return -NLE_MISSING_ATTR or 1. So, the best check
  is probably

      if (rtnl_rule_get_l3mdev(r) > 0) { ... }

The reason for this change is that libnl should expose the netlink
API without coercing uint8 to boolean. That way, future changes
in kernel don't require update to libnl3.

Signed-off-by: Thomas Haller <thaller@redhat.com>

1 files changed, 31 insertions, 4 deletions

diff --git a/lib/route/rule.c b/lib/route/rule.c
index 76d9fe8..e257349 100644
--- a/lib/route/rule.c
+++ b/lib/route/rule.c
@@ -706,14 +706,41 @@ uint8_t rtnl_rule_get_action(struct rtnl_rule *rule)
 	return rule->r_action;
 }
 
-void rtnl_rule_set_l3mdev(struct rtnl_rule *rule)
+/**
+ * Set l3mdev value of the rule (FRA_L3MDEV)
+ * @arg rule		rule
+ * @arg value		value to set
+ *
+ * Set the l3mdev value to value. Currently supported values
+ * are only 1 (set it) and -1 (unset it). All other values
+ * are reserved.
+ */
+void rtnl_rule_set_l3mdev(struct rtnl_rule *rule, int value)
 {
-	rule->r_l3mdev = 1;
-	rule->ce_mask |= RULE_ATTR_L3MDEV;
+	if (value >= 0) {
+		rule->r_l3mdev = (uint8_t) value;
+		rule->ce_mask |= RULE_ATTR_L3MDEV;
+	} else {
+		rule->r_l3mdev = 0;
+		rule->ce_mask &= ~((uint32_t) RULE_ATTR_L3MDEV);
+	}
 }
 
-uint8_t rtnl_rule_get_l3mdev(struct rtnl_rule *rule)
+/**
+ * Get l3mdev value of the rule (FRA_L3MDEV)
+ * @arg rule		rule
+ *
+ * @return a negative error code, including -NLE_MISSING_ATTR
+ *   if the property is unset. Otherwise returns a non-negative
+ *   value. As FRA_L3MDEV is a boolean, the only expected
+ *   value at the moment is 1.
+ */
+int rtnl_rule_get_l3mdev(struct rtnl_rule *rule)
 {
+	if (!rule)
+		return -NLE_INVAL;
+	if (!(rule->ce_mask & RULE_ATTR_L3MDEV))
+		return -NLE_MISSING_ATTR;
 	return rule->r_l3mdev;
 }