run: fix generated unit name clash after soft-reboot

When sd-run connects to D-Bus rather than the private socket, it will
generate the transient unit name using the bus ID assigned by the D-Bus
broker/daemon. The issue is that this ID is only unique per D-Bus run,
if the broker/daemon restarts it starts again from 1, and it's a simple
incremental counter for each client.
So if a transient unit run-u6.service starts and fails, and it is not
collected (default on failure), and the system soft-reboots, any new
transient unit might conflict as the counter will restart:

Failed to start transient service unit: Unit run-u6.service was already loaded or has a fragment file.

Get the soft-reboot counter, and if it's greater than zero, append it
to the autogenerated unit name to avoid clashes.

1 files changed, 18 insertions, 3 deletions

diff --git a/src/run/run.c b/src/run/run.c
index 7f40ed0076..9349bfafbc 100644
--- a/src/run/run.c
+++ b/src/run/run.c
@@ -1313,6 +1313,7 @@ static int transient_timer_set_properties(sd_bus_message *m) {
 }
 
 static int make_unit_name(sd_bus *bus, UnitType t, char **ret) {
+        unsigned soft_reboots_count = 0;
         const char *unique, *id;
         char *p;
         int r;
@@ -1351,9 +1352,23 @@ static int make_unit_name(sd_bus *bus, UnitType t, char **ret) {
                                        "Unique name %s has unexpected format.",
                                        unique);
 
-        p = strjoin("run-u", id, ".", unit_type_to_string(t));
-        if (!p)
-                return log_oom();
+        /* The unique D-Bus names are actually unique per D-Bus instance, so on soft-reboot they will wrap
+         * and start over since the D-Bus broker is restarted. If there's a failed unit left behind that
+         * hasn't been garbage collected, we'll conflict. Append the soft-reboot counter to avoid clashing. */
+        _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+        r = bus_get_property_trivial(
+                        bus, bus_systemd_mgr, "SoftRebootsCount", &error, 'u', &soft_reboots_count);
+        if (r < 0)
+                log_debug_errno(r, "Failed to get SoftRebootsCount property, ignoring: %s", bus_error_message(&error, r));
+
+        if (soft_reboots_count > 0) {
+                if (asprintf(&p, "run-u%s-s%u.%s", id, soft_reboots_count, unit_type_to_string(t)) < 0)
+                        return log_oom();
+        } else {
+                p = strjoin("run-u", id, ".", unit_type_to_string(t));
+                if (!p)
+                        return log_oom();
+        }
 
         *ret = p;
         return 0;