logind: update empty and "infinity" handling for [User]TasksMax (#3835)

The parsing functions for [User]TasksMax were inconsistent.  Empty string and
"infinity" were interpreted as no limit for TasksMax but not accepted for
UserTasksMax.  Update them so that they're consistent with other knobs.

* Empty string indicates the default value.
* "infinity" indicates no limit.

While at it, replace opencoded (uint64_t) -1 with CGROUP_LIMIT_MAX in TasksMax
handling.

v2: Update empty string to indicate the default value as suggested by Zbigniew
    Jędrzejewski-Szmek.

v3: Fixed empty UserTasksMax handling.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/core/main.c b/src/core/main.c
index 02324d325e..c7c6df3447 100644
--- a/src/core/main.c
+++ b/src/core/main.c
@@ -1559,7 +1559,7 @@ int main(int argc, char *argv[]) {
         (void) reset_all_signal_handlers();
         (void) ignore_signals(SIGNALS_IGNORE, -1);
 
-        arg_default_tasks_max = system_tasks_max_scale(15U, 100U); /* 15% the system PIDs equals 4915 by default. */
+        arg_default_tasks_max = system_tasks_max_scale(DEFAULT_TASKS_MAX_PERCENTAGE, 100U);
 
         if (parse_config_file() < 0) {
                 error_message = "Failed to parse config file";