From: Michael Biebl <biebl@debian.org>
Date: Thu, 18 Jul 2013 01:04:07 +0200
Subject: Revert "udev: network device renaming - immediately give up if the
 target name isn't available"

This reverts commit 97595710b77aa162ca5e20da57d0a1ed7355eaad.

We need to keep supporting systems with 75-persistent-net-generator.rules
generated names for a while after switching to net.ifnames. Re-apply this old
hack to make the renaming less likely to fail.
---
--- systemd-242/src/udev/udev-event.c.orig	2019-04-11 18:28:36.000000000 +0200
+++ systemd-242/src/udev/udev-event.c	2019-04-13 14:19:13.346990771 +0200
@@ -698,6 +698,8 @@
         sd_device *dev = event->dev;
         const char *oldname;
         int ifindex, r;
+        char name[IFNAMSIZ];
+        int loop;
 
         if (!event->name)
                 return 0; /* No new name is requested. */
@@ -719,22 +720,66 @@
                 return log_device_error_errno(dev, r, "Failed to get ifindex: %m");
 
         r = rtnl_set_link_name(&event->rtnl, ifindex, event->name);
+        if (r >= 0) {
+                /* Set ID_RENAMING boolean property here, and drop it in the corresponding move uevent later. */
+                r = device_add_property(dev, "ID_RENAMING", "1");
+                if (r < 0)
+                        log_device_warning_errno(dev, r, "Failed to add 'ID_RENAMING' property: %m");
+
+                r = device_rename(dev, event->name);
+                if (r < 0)
+                        log_device_warning_errno(dev, r, "Failed to update properties with new name '%s': %m", event->name);
+
+                log_device_debug(dev, "Network interface %i is renamed from '%s' to '%s'", ifindex, oldname, event->name);
+                return 1;
+        }
+
+        /* keep trying if the destination interface name already exists */
+        if (r != -EEXIST)
+                goto out;
+
+        /* free our own name, another process may wait for us */
+        snprintf(name, IFNAMSIZ, "rename%u", ifindex);
+        r = rtnl_set_link_name(&event->rtnl, ifindex, name);
         if (r < 0)
-                return log_device_error_errno(dev, r, "Failed to rename network interface %i from '%s' to '%s': %m",
-                                              ifindex, oldname, event->name);
+                goto out;
+ 
+        /* log temporary name */
+        log_device_debug(dev, "Network interface %i is renamed from '%s' to '%s'", ifindex, oldname, event->name);
 
-        /* Set ID_RENAMING boolean property here, and drop it in the corresponding move uevent later. */
-        r = device_add_property(dev, "ID_RENAMING", "1");
-        if (r < 0)
-                log_device_warning_errno(dev, r, "Failed to add 'ID_RENAMING' property: %m");
+        /* wait a maximum of 90 seconds for our target to become available */
+        strscpy(name, IFNAMSIZ, event->name);
+        loop = 90 * 20;
+        while (loop--) {
+                const struct timespec duration = { 0, 1000 * 1000 * 1000 / 20 };
+
+                nanosleep(&duration, NULL);
+
+                r = rtnl_set_link_name(&event->rtnl, ifindex, name);
+                if (r >= 0) {
+                        /* Set ID_RENAMING boolean property here, and drop it in the corresponding move uevent later. */
+                        r = device_add_property(dev, "ID_RENAMING", "1");
+                        if (r < 0)
+                                log_device_warning_errno(dev, r, "Failed to add 'ID_RENAMING' property: %m");
+
+                        r = device_rename(dev, event->name);
+                        if (r < 0)
+                                log_device_warning_errno(dev, r, "Failed to update properties with new name '%s': %m", event->name);
+
+                        log_device_debug(dev, "Network interface %i is renamed from '%s' to '%s'", ifindex, oldname, event->name);
+                        return 1;
+                }
+                if (r != -EEXIST)
+                        goto out;
+        }
 
-        r = device_rename(dev, event->name);
+out:
         if (r < 0)
-                log_device_warning_errno(dev, r, "Failed to update properties with new name '%s': %m", event->name);
+                return log_device_error_errno(dev, r, "Failed to rename network interface %i from '%s' to '%s': %m",
+                                              ifindex, oldname, event->name);
+        return r;
 
-        log_device_debug(dev, "Network interface %i is renamed from '%s' to '%s'", ifindex, oldname, event->name);
 
-        return 1;
 }
 
 static int update_devnode(UdevEvent *event) {