mctp-netlink: Add a facility to store external data on links

For upcoming mctpd changes, we will need a facility for storing
dbus-specific information on each link. This change adds a

  void * userdata

pointer to the links, and accessors for callers to get/set this pointer.
For convenience, we also pass this pointer on change events, allowing
for a quick way to release/update the userdata on link delete/change.

WIP: untested.

Signed-off-by: Jeremy Kerr <[email protected]>

src/mctp-netlink.c

@@ -28,6 +28,8 @@ struct linkmap_entry {
 
 	mctp_eid_t *local_eids;
 	size_t num_local;
+
+	void	*userdata;
 };
 
 struct mctp_nl {
@@ -242,15 +244,15 @@ static void fill_eid_changes(const struct linkmap_entry *oe,
 }
 
 static void fill_link_changes(const struct linkmap_entry *old, size_t old_count,
-	const struct linkmap_entry *new, size_t new_count,
+	struct linkmap_entry *new, size_t new_count,
 	mctp_nl_change **changes, size_t *num_changes) {
 
 	size_t siz = 0;
 
 	// iterate and match old/new interface lists
 	for (size_t o = 0, n = 0; o < old_count || n < new_count; ) {
 		const struct linkmap_entry *oe = &old[o];
-		const struct linkmap_entry *ne = &new[n];
+		struct linkmap_entry *ne = &new[n];
 		mctp_nl_change *ch = NULL;
 
 		if (o >= old_count)
@@ -261,6 +263,7 @@ static void fill_link_changes(const struct linkmap_entry *old, size_t old_count,
 
 		if (oe && ne && oe->ifindex == ne->ifindex) {
 			// Same link.
+			ne->userdata = oe->userdata;
 			if (oe->net == ne->net) {
 				// Same net. Check for eid changes.
 				fill_eid_changes(oe,
@@ -280,13 +283,15 @@ static void fill_link_changes(const struct linkmap_entry *old, size_t old_count,
 				ch->op = MCTP_NL_CHANGE_NET;
 				ch->ifindex = ne->ifindex;
 				ch->old_net = oe->net;
+				ch->link_userdata = oe->userdata;
 			}
 
 			if (oe->up != ne->up) {
 				ch = push_change(changes, &siz);
 				ch->op = MCTP_NL_CHANGE_UP;
 				ch->ifindex = ne->ifindex;
 				ch->old_up = oe->up;
+				ch->link_userdata = oe->userdata;
 			}
 			o++;
 			n++;
@@ -309,6 +314,7 @@ static void fill_link_changes(const struct linkmap_entry *old, size_t old_count,
 			ch->op = MCTP_NL_DEL_LINK;
 			ch->ifindex = oe->ifindex;
 			ch->old_net = oe->net;
+			ch->link_userdata = oe->userdata;
 			o++;
 		}
 	}
@@ -929,6 +935,26 @@ int mctp_nl_net_byindex(const mctp_nl *nl, int index)
 	return 0;
 }
 
+int mctp_nl_set_userdata(mctp_nl *nl, int ifindex, void *userdata)
+{
+	struct linkmap_entry *entry = entry_byindex(nl, ifindex);
+	if (!entry)
+		return -1;
+
+	entry->userdata = userdata;
+	return 0;
+}
+
+int mctp_nl_get_userdata(const mctp_nl *nl, int ifindex, void **userdata)
+{
+	struct linkmap_entry *entry = entry_byindex(nl, ifindex);
+	if (!entry)
+		return -1;
+
+	*userdata = entry->userdata;
+	return 0;
+}
+
 bool mctp_nl_up_byindex(const mctp_nl *nl, int index)
 {
 	struct linkmap_entry *entry = entry_byindex(nl, index);

src/mctp-netlink.h

@@ -31,6 +31,10 @@ struct mctp_nl_change {
 
 	// Filled for CHANGE_UP
 	bool old_up;
+
+	// If userdata is present on the link, it is passed here. Populated for
+	// link change events (DEL_LINK, CHANGE_NET, CHANGE_UP).
+	void *link_userdata;
 };
 typedef struct mctp_nl_change mctp_nl_change;
 
@@ -69,6 +73,16 @@ int *mctp_nl_net_list(const mctp_nl *nl, size_t *ret_num_nets);
 /* Returns an allocated list of ifindex, caller to free */
 int *mctp_nl_if_list(const mctp_nl *nl, size_t *ret_num_if);
 
+/* Get/set userdata for a link. The userdata is attached to a link
+ * with index @ifindex. Userdata will be populated into
+ * struct mctp_nl_change->userdata, and would typically be freed on
+ * MCTP_NL_DEL_LINK events
+ *
+ * Returns non-zero if the link does not exist.
+ */
+int mctp_nl_set_userdata(mctp_nl *nl, int ifindex, void *userdata);
+int mctp_nl_get_userdata(const mctp_nl *nl, int ifindex, void **userdata);
+
 /* MCTP route helper */
 int mctp_nl_route_add(struct mctp_nl *nl, uint8_t eid, const char* ifname,
 		uint32_t mtu);