pid1: preserve current value of log level across re-{load,execution}

To make debugging easier, this patches allows one to change the log level and
do reload/reexec without modifying configuration permanently, which makes
debugging easier.

Indeed if one changed the log max level at runtime (via the bus or via
signals), the change was lost on the next daemon reload/reexecution.

In order to restore the original value back (set via system.conf, environment
variables or any other means), the empty string in the "LogLevel" property is
now supported as well as sending SIGRTMIN+23 signal.

4 files changed, 78 insertions, 13 deletions

diff --git a/src/core/dbus-manager.c b/src/core/dbus-manager.c
index 09daf268b7..d97fe4087c 100644
--- a/src/core/dbus-manager.c
+++ b/src/core/dbus-manager.c
@@ -158,6 +158,7 @@ static int property_set_log_level(
                 void *userdata,
                 sd_bus_error *error) {
 
+        Manager *m = userdata;
         const char *t;
         int r;
 
@@ -168,10 +169,19 @@ static int property_set_log_level(
         if (r < 0)
                 return r;
 
-        r = log_set_max_level_from_string(t);
-        if (r == 0)
-                log_info("Setting log level to %s.", t);
-        return r;
+        if (isempty(t))
+                manager_restore_original_log_level(m);
+        else {
+                int level;
+
+                level = log_level_from_string(t);
+                if (level < 0)
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid log level '%s'", t);
+
+                manager_override_log_level(m, level);
+        }
+
+        return 0;
 }
 
 static int property_get_progress(
diff --git a/src/core/main.c b/src/core/main.c
index 1e75ad7203..d044427d74 100644
--- a/src/core/main.c
+++ b/src/core/main.c
@@ -525,10 +525,10 @@ static int parse_proc_cmdline_item(const char *key, const char *value, void *dat
                 return 0;                                             \
         }
 
-DEFINE_SETTER(config_parse_level2, log_set_max_level_from_string, "log level")
-DEFINE_SETTER(config_parse_target, log_set_target_from_string, "target")
-DEFINE_SETTER(config_parse_color, log_show_color_from_string, "color" )
-DEFINE_SETTER(config_parse_location, log_show_location_from_string, "location")
+DEFINE_SETTER(config_parse_level2, log_set_max_level_from_string, "log level");
+DEFINE_SETTER(config_parse_target, log_set_target_from_string, "target");
+DEFINE_SETTER(config_parse_color, log_show_color_from_string, "color" );
+DEFINE_SETTER(config_parse_location, log_show_location_from_string, "location");
 
 static int config_parse_cpu_affinity2(
                 const char *unit,
@@ -1640,20 +1640,28 @@ static int invoke_main_loop(
 
                 switch (m->exit_code) {
 
-                case MANAGER_RELOAD:
+                case MANAGER_RELOAD: {
+                        int saved_log_level;
+
                         log_info("Reloading.");
 
+                        saved_log_level = m->log_level_overridden ? log_get_max_level() : -1;
+
                         r = parse_config_file();
                         if (r < 0)
                                 log_warning_errno(r, "Failed to parse config file, ignoring: %m");
 
                         set_manager_defaults(m);
 
+                        if (saved_log_level >= 0)
+                                manager_override_log_level(m, saved_log_level);
+
                         r = manager_reload(m);
                         if (r < 0)
                                 log_warning_errno(r, "Failed to reload, ignoring: %m");
 
                         break;
+                }
 
                 case MANAGER_REEXECUTE:
 
diff --git a/src/core/manager.c b/src/core/manager.c
index e1ce9229a3..92d5a0fff6 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -74,6 +74,7 @@
 #include "string-util.h"
 #include "strv.h"
 #include "strxcpyx.h"
+#include "syslog-util.h"
 #include "terminal-util.h"
 #include "time-util.h"
 #include "transaction.h"
@@ -735,6 +736,7 @@ int manager_new(UnitFileScope scope, unsigned test_run_flags, Manager **_m) {
         m->default_timeout_start_usec = DEFAULT_TIMEOUT_USEC;
         m->default_timeout_stop_usec = DEFAULT_TIMEOUT_USEC;
         m->default_restart_usec = DEFAULT_RESTART_USEC;
+        m->original_log_level = -1;
 
 #if ENABLE_EFI
         if (MANAGER_IS_SYSTEM(m) && detect_container() <= 0)
@@ -2626,13 +2628,11 @@ static int manager_dispatch_signal_fd(sd_event_source *source, int fd, uint32_t
                         break;
 
                 case 22:
-                        log_set_max_level(LOG_DEBUG);
-                        log_info("Setting log level to debug.");
+                        manager_override_log_level(m, LOG_DEBUG);
                         break;
 
                 case 23:
-                        log_set_max_level(LOG_INFO);
-                        log_info("Setting log level to info.");
+                        manager_restore_original_log_level(m);
                         break;
 
                 case 24:
@@ -3027,6 +3027,9 @@ int manager_serialize(Manager *m, FILE *f, FDSet *fds, bool switching_root) {
         fprintf(f, "taint-logged=%s\n", yes_no(m->taint_logged));
         fprintf(f, "service-watchdogs=%s\n", yes_no(m->service_watchdogs));
 
+        if (m->log_level_overridden)
+                fprintf(f, "log-level-override=%i\n", log_get_max_level());
+
         for (q = 0; q < _MANAGER_TIMESTAMP_MAX; q++) {
                 /* The userspace and finish timestamps only apply to the host system, hence only serialize them there */
                 if (in_initrd() && IN_SET(q, MANAGER_TIMESTAMP_USERSPACE, MANAGER_TIMESTAMP_FINISH))
@@ -3210,6 +3213,15 @@ int manager_deserialize(Manager *m, FILE *f, FDSet *fds) {
                         else
                                 m->service_watchdogs = b;
 
+                } else if ((val = startswith(l, "log-level-override="))) {
+                        int level;
+
+                        level = log_level_from_string(val);
+                        if (level < 0)
+                                log_notice("Failed to parse log-level-override value '%s', ignoring.", val);
+                        else
+                                manager_override_log_level(m, level);
+
                 } else if (startswith(l, "env=")) {
                         r = deserialize_environment(&m->environment, l);
                         if (r == -ENOMEM)
@@ -4448,6 +4460,35 @@ void manager_unref_console(Manager *m) {
                 m->no_console_output = false; /* unset no_console_output flag, since the console is definitely free now */
 }
 
+void manager_override_log_level(Manager *m, int level) {
+        _cleanup_free_ char *s = NULL;
+        assert(m);
+
+        if (!m->log_level_overridden) {
+                m->original_log_level = log_get_max_level();
+                m->log_level_overridden = true;
+        }
+
+        (void) log_level_to_string_alloc(level, &s);
+        log_info("Setting log level to %s.", strna(s));
+
+        log_set_max_level(level);
+}
+
+void manager_restore_original_log_level(Manager *m) {
+        _cleanup_free_ char *s = NULL;
+        assert(m);
+
+        if (!m->log_level_overridden)
+                return;
+
+        (void) log_level_to_string_alloc(m->original_log_level, &s);
+        log_info("Restoring log level to original (%s).", strna(s));
+
+        log_set_max_level(m->original_log_level);
+        m->log_level_overridden = false;
+}
+
 static const char *const manager_state_table[_MANAGER_STATE_MAX] = {
         [MANAGER_INITIALIZING] = "initializing",
         [MANAGER_STARTING] = "starting",
diff --git a/src/core/manager.h b/src/core/manager.h
index 8868e9c158..fb28316b8e 100644
--- a/src/core/manager.h
+++ b/src/core/manager.h
@@ -302,6 +302,9 @@ struct Manager {
         uint64_t default_tasks_max;
         usec_t default_timer_accuracy_usec;
 
+        int original_log_level;
+        bool log_level_overridden:1;
+
         struct rlimit *rlimit[_RLIMIT_MAX];
 
         /* non-zero if we are reloading or reexecuting, */
@@ -465,6 +468,9 @@ char *manager_taint_string(Manager *m);
 void manager_ref_console(Manager *m);
 void manager_unref_console(Manager *m);
 
+void manager_override_log_level(Manager *m, int level);
+void manager_restore_original_log_level(Manager *m);
+
 const char *manager_state_to_string(ManagerState m) _const_;
 ManagerState manager_state_from_string(const char *s) _pure_;