networkd: netdev - reduce chance of race when receiving netdev's ifindex

When creating a new link, the kernel will not inform us about the new ifindex
in its ack. We have to listen for newly created devices and deduce the new
ifindex by matching on the ifname.

We used to do this by waiting for a new device from libudev, but that is asking
for trouble, as udev will happily rename the device before handing it to us.
Listen on rtnl instead, the chance of the name being changed before reaching us
is much smaller (if not nil).

Kernel patch in the works to make this unneccessary.

1 files changed, 18 insertions, 1 deletions

diff --git a/src/network/networkd-manager.c b/src/network/networkd-manager.c
index 7b93c5b5e8..a007b0485f 100644
--- a/src/network/networkd-manager.c
+++ b/src/network/networkd-manager.c
@@ -25,6 +25,7 @@
 #include "networkd.h"
 #include "libudev-private.h"
 #include "udev-util.h"
+#include "rtnl-util.h"
 #include "mkdir.h"
 
 const char* const network_dirs[] = {
@@ -244,15 +245,31 @@ int manager_udev_listen(Manager *m) {
 static int manager_rtnl_process_link(sd_rtnl *rtnl, sd_rtnl_message *message, void *userdata) {
         Manager *m = userdata;
         Link *link;
+        const char *name;
         uint64_t ifindex_64;
         int r, ifindex;
 
         r = sd_rtnl_message_link_get_ifindex(message, &ifindex);
-        if (r < 0) {
+        if (r < 0 || ifindex <= 0) {
                 log_debug("received RTM_NEWLINK message without valid ifindex");
                 return 0;
         }
 
+        r = rtnl_message_link_get_ifname(message, &name);
+        if (r < 0)
+                log_debug("received RTM_NEWLINK message without valid IFLA_IFNAME");
+        else {
+                Netdev *netdev;
+
+                r = netdev_get(m, name, &netdev);
+                if (r >= 0) {
+                        r = netdev_set_ifindex(netdev, ifindex);
+                        if (r < 0)
+                                log_debug("could not set ifindex of netdev '%s' to %d: %s",
+                                          name, ifindex, strerror(-r));
+                }
+        }
+
         ifindex_64 = ifindex;
         link = hashmap_get(m->links, &ifindex_64);
         if (!link) {