run: tweak how we name our transient units

The current logic is a bit complex how systemd-run units are called. It
used to be just the unique ID of the dbus connection. Which was nice,
since its system-widely, uniquely assigned to us. But this didn't work
out well, due to direct connections to PID 1 and due to soft reboots.

We nowadays have a better ID to use though, with nicer properties: the
kernel manages a pidfd ID for every process after all, and it's globally
unique, for any process, and regardless of soft reboots. Hence use that
for naming preferably, and just keep one branch with a randomized name
as fallback.

1 files changed, 22 insertions, 54 deletions

diff --git a/src/run/run.c b/src/run/run.c
index 88fe8a0c8f..42eb756fa9 100644
--- a/src/run/run.c
+++ b/src/run/run.c
@@ -1401,70 +1401,38 @@ static int transient_timer_set_properties(sd_bus_message *m) {
         return 0;
 }
 
-static int make_unit_name(sd_bus *bus, UnitType t, char **ret) {
-        unsigned soft_reboots_count = 0;
-        const char *unique, *id;
-        char *p;
+static int make_unit_name(UnitType t, char **ret) {
         int r;
 
-        assert(bus);
         assert(t >= 0);
         assert(t < _UNIT_TYPE_MAX);
         assert(ret);
 
-        r = sd_bus_get_unique_name(bus, &unique);
-        if (r < 0) {
-                sd_id128_t rnd;
+        /* Preferably use our PID + pidfd ID as identifier, if available. It's a boot time unique identifier
+         * managed by the kernel. Unfortunately only new kernels support this, hence we keep some fallback
+         * logic in place. */
 
-                /* We couldn't get the unique name, which is a pretty
-                 * common case if we are connected to systemd
-                 * directly. In that case, just pick a random uuid as
-                 * name */
+        _cleanup_(pidref_done) PidRef self = PIDREF_NULL;
+        r = pidref_set_self(&self);
+        if (r < 0)
+                return log_error_errno(r, "Failed to get reference to my own process: %m");
+
+        r = pidref_acquire_pidfd_id(&self);
+        if (r < 0) {
+                log_debug_errno(r, "Failed to acquire pidfd ID of myself, defaulting to randomized unit name: %m");
 
+                /* We couldn't get the pidfd id. In that case, just pick a random uuid as name */
+                sd_id128_t rnd;
                 r = sd_id128_randomize(&rnd);
                 if (r < 0)
                         return log_error_errno(r, "Failed to generate random run unit name: %m");
 
-                if (asprintf(ret, "run-r" SD_ID128_FORMAT_STR ".%s", SD_ID128_FORMAT_VAL(rnd), unit_type_to_string(t)) < 0)
-                        return log_oom();
-
-                return 0;
-        }
-
-        /* We managed to get the unique name, then let's use that to name our transient units. */
-
-        id = startswith(unique, ":1."); /* let' strip the usual prefix */
-        if (!id)
-                id = startswith(unique, ":"); /* the spec only requires things to start with a colon, hence
-                                               * let's add a generic fallback for that. */
-        if (!id)
-                return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
-                                       "Unique name %s has unexpected format.",
-                                       unique);
-
-        /* 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. */
-        if (arg_runtime_scope == RUNTIME_SCOPE_SYSTEM) {
-                _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();
-        }
+                r = asprintf(ret, "run-r" SD_ID128_FORMAT_STR ".%s", SD_ID128_FORMAT_VAL(rnd), unit_type_to_string(t));
+        } else
+                r = asprintf(ret, "run-p" PID_FMT "-i%" PRIu64 ".%s", self.pid, self.fd_id, unit_type_to_string(t));
+        if (r < 0)
+                return log_oom();
 
-        *ret = p;
         return 0;
 }
 
@@ -1874,7 +1842,7 @@ static int start_transient_service(sd_bus *bus) {
                 if (r < 0)
                         return log_error_errno(r, "Failed to mangle unit name: %m");
         } else {
-                r = make_unit_name(bus, UNIT_SERVICE, &service);
+                r = make_unit_name(UNIT_SERVICE, &service);
                 if (r < 0)
                         return r;
         }
@@ -2089,7 +2057,7 @@ static int start_transient_scope(sd_bus *bus) {
                 if (r < 0)
                         return log_error_errno(r, "Failed to mangle scope name: %m");
         } else {
-                r = make_unit_name(bus, UNIT_SCOPE, &scope);
+                r = make_unit_name(UNIT_SCOPE, &scope);
                 if (r < 0)
                         return r;
         }
@@ -2388,7 +2356,7 @@ static int start_transient_trigger(sd_bus *bus, const char *suffix) {
                         break;
                 }
         } else {
-                r = make_unit_name(bus, UNIT_SERVICE, &service);
+                r = make_unit_name(UNIT_SERVICE, &service);
                 if (r < 0)
                         return r;