rtnl: add callback support

sd_rtnl_add_match allows you to add a callback function for when given types of
messages are received.

src/libsystemd-rtnl/rtnl-internal.h

@@ -25,6 +25,7 @@
 
 #include "refcnt.h"
 #include "prioq.h"
+#include "list.h"
 
 #include "sd-rtnl.h"
 
@@ -36,6 +37,14 @@ struct reply_callback {
         unsigned prioq_idx;
 };
 
+struct match_callback {
+        sd_rtnl_message_handler_t callback;
+        uint16_t types;
+        void *userdata;
+
+        LIST_FIELDS(struct match_callback, match_callbacks);
+};
+
 struct sd_rtnl {
         RefCount n_ref;
 
@@ -59,6 +68,8 @@ struct sd_rtnl {
         struct Prioq *reply_callbacks_prioq;
         Hashmap *reply_callbacks;
 
+        LIST_HEAD(struct match_callback, match_callbacks);
+
         pid_t original_pid;
 
         sd_event_source *io_event_source;

src/libsystemd-rtnl/sd-rtnl.c

@@ -47,6 +47,8 @@ static int sd_rtnl_new(sd_rtnl **ret) {
 
         rtnl->original_pid = getpid();
 
+        LIST_HEAD_INIT(rtnl->match_callbacks);
+
         /* We guarantee that wqueue always has space for at least
          * one entry */
         rtnl->wqueue = new(sd_rtnl_message*, 1);
@@ -109,6 +111,7 @@ sd_rtnl *sd_rtnl_ref(sd_rtnl *rtnl) {
 sd_rtnl *sd_rtnl_unref(sd_rtnl *rtnl) {
 
         if (rtnl && REFCNT_DEC(rtnl->n_ref) <= 0) {
+                struct match_callback *f;
                 unsigned i;
 
                 for (i = 0; i < rtnl->rqueue_size; i++)
@@ -122,6 +125,11 @@ sd_rtnl *sd_rtnl_unref(sd_rtnl *rtnl) {
                 hashmap_free_free(rtnl->reply_callbacks);
                 prioq_free(rtnl->reply_callbacks_prioq);
 
+                while ((f = rtnl->match_callbacks)) {
+                        LIST_REMOVE(match_callbacks, rtnl->match_callbacks, f);
+                        free(f);
+                }
+
                 if (rtnl->fd >= 0)
                         close_nointr_nofail(rtnl->fd);
 
@@ -281,6 +289,29 @@ static int process_reply(sd_rtnl *rtnl, sd_rtnl_message *m) {
         return r;
 }
 
+static int process_match(sd_rtnl *rtnl, sd_rtnl_message *m) {
+        struct match_callback *c;
+        uint16_t type;
+        int r;
+
+        assert(rtnl);
+        assert(m);
+
+        r = sd_rtnl_message_get_type(m, &type);
+        if (r < 0)
+                return r;
+
+        LIST_FOREACH(match_callbacks, c, rtnl->match_callbacks) {
+                if (type & c->types) {
+                        r = c->callback(rtnl, m, c->userdata);
+                        if (r != 0)
+                                return r;
+                }
+        }
+
+        return 0;
+}
+
 static int process_running(sd_rtnl *rtnl, sd_rtnl_message **ret) {
         _cleanup_sd_rtnl_message_unref_ sd_rtnl_message *m = NULL;
         int r;
@@ -303,6 +334,10 @@ static int process_running(sd_rtnl *rtnl, sd_rtnl_message **ret) {
         if (r != 0)
                 goto null_message;
 
+        r = process_match(rtnl, m);
+        if (r != 0)
+                goto null_message;
+
         if (ret) {
                 *ret = m;
                 m = NULL;
@@ -784,3 +819,48 @@ int sd_rtnl_detach_event(sd_rtnl *rtnl) {
 
         return 0;
 }
+
+int sd_rtnl_add_match(sd_rtnl *rtnl,
+                      uint16_t types,
+                      sd_rtnl_message_handler_t callback,
+                      void *userdata) {
+        struct match_callback *c;
+
+        assert_return(rtnl, -EINVAL);
+        assert_return(callback, -EINVAL);
+        assert_return(types, -EINVAL);
+        assert_return(!rtnl_pid_changed(rtnl), -ECHILD);
+
+        c = new0(struct match_callback, 1);
+        if (!c)
+                return -ENOMEM;
+
+        c->callback = callback;
+        c->types = types;
+        c->userdata = userdata;
+
+        LIST_PREPEND(match_callbacks, rtnl->match_callbacks, c);
+
+        return 0;
+}
+
+int sd_rtnl_remove_match(sd_rtnl *rtnl,
+                         uint16_t types,
+                         sd_rtnl_message_handler_t callback,
+                         void *userdata) {
+        struct match_callback *c;
+
+        assert_return(rtnl, -EINVAL);
+        assert_return(callback, -EINVAL);
+        assert_return(!rtnl_pid_changed(rtnl), -ECHILD);
+
+        LIST_FOREACH(match_callbacks, c, rtnl->match_callbacks)
+                if (c->callback == callback && c->types == types && c->userdata == userdata) {
+                        LIST_REMOVE(match_callbacks, rtnl->match_callbacks, c);
+                        free(c);
+
+                        return 1;
+                }
+
+        return 0;
+}

src/libsystemd-rtnl/test-rtnl.c

@@ -230,6 +230,21 @@ static void test_container(void) {
 */
 }
 
+static void test_match(void) {
+        _cleanup_sd_rtnl_unref_ sd_rtnl *rtnl = NULL;
+
+        assert(sd_rtnl_open(0, &rtnl) >= 0);
+
+        assert(sd_rtnl_add_match(rtnl, 0, &link_handler, NULL) == -EINVAL);
+
+        assert(sd_rtnl_add_match(rtnl, RTMGRP_LINK, &link_handler, NULL) >= 0);
+        assert(sd_rtnl_add_match(rtnl, RTMGRP_LINK, &link_handler, NULL) >= 0);
+
+        assert(sd_rtnl_remove_match(rtnl, RTMGRP_LINK, &link_handler, NULL) == 1);
+        assert(sd_rtnl_remove_match(rtnl, RTMGRP_LINK, &link_handler, NULL) == 1);
+        assert(sd_rtnl_remove_match(rtnl, RTMGRP_LINK, &link_handler, NULL) == 0);
+}
+
 int main(void) {
         sd_rtnl *rtnl;
         sd_rtnl_message *m;
@@ -240,6 +255,8 @@ int main(void) {
         unsigned int mtu = 0;
         unsigned int *mtu_reply;
 
+        test_match();
+
         test_multiple();
 
         test_route();

src/systemd/sd-rtnl.h

@@ -57,6 +57,9 @@ int sd_rtnl_process(sd_rtnl *nl, sd_rtnl_message **ret);
 int sd_rtnl_wait(sd_rtnl *nl, uint64_t timeout);
 int sd_rtnl_flush(sd_rtnl *nl);
 
+int sd_rtnl_add_match(sd_rtnl *nl, uint16_t match, sd_rtnl_message_handler_t c, void *userdata);
+int sd_rtnl_remove_match(sd_rtnl *nl, uint16_t match, sd_rtnl_message_handler_t c, void *userdata);
+
 int sd_rtnl_attach_event(sd_rtnl *nl, sd_event *e, int priority);
 int sd_rtnl_detach_event(sd_rtnl *nl);