log: add new "prohibit_ipc" flag to logging system

If set, we'll avoid logging to any IPC log targets, i.e. syslog or the
journal, but allow stderr, kmsg, console logging.

This is useful as PID 1 wants to turn this off explicitly as long as the
journal is not up.

Previously we'd open/close the log stream to these services whenever
needed but this is incompatible with the "open_when_needed" logic
introduced in #6915, which might open the log streams whenever it likes,
including possibly inside of the child process we fork off that'll
become journald later on. Hence, let's make this all explicit, and
instead of managing when we open/close log streams add a boolean that
clearly prohibits the IPC targets when needed, so that opening can be
done at any time, but will honour this.

See: #7985

2 files changed, 13 insertions, 2 deletions

diff --git a/src/basic/log.c b/src/basic/log.c
index 8a65aa349e..ae0ac72b57 100644
--- a/src/basic/log.c
+++ b/src/basic/log.c
@@ -77,6 +77,7 @@ static bool show_location = false;
 static bool upgrade_syslog_to_journal = false;
 static bool always_reopen_console = false;
 static bool open_when_needed = false;
+static bool prohibit_ipc = false;
 
 /* Akin to glibc's __abort_msg; which is private and we hence cannot
  * use here. */
@@ -254,7 +255,8 @@ int log_open(void) {
             getpid_cached() == 1 ||
             isatty(STDERR_FILENO) <= 0) {
 
-                if (IN_SET(log_target, LOG_TARGET_AUTO,
+                if (!prohibit_ipc &&
+                    IN_SET(log_target, LOG_TARGET_AUTO,
                                        LOG_TARGET_JOURNAL_OR_KMSG,
                                        LOG_TARGET_JOURNAL)) {
                         r = log_open_journal();
@@ -265,7 +267,8 @@ int log_open(void) {
                         }
                 }
 
-                if (IN_SET(log_target, LOG_TARGET_SYSLOG_OR_KMSG,
+                if (!prohibit_ipc &&
+                    IN_SET(log_target, LOG_TARGET_SYSLOG_OR_KMSG,
                                        LOG_TARGET_SYSLOG)) {
                         r = log_open_syslog();
                         if (r >= 0) {
@@ -1332,6 +1335,10 @@ void log_set_open_when_needed(bool b) {
         open_when_needed = b;
 }
 
+void log_set_prohibit_ipc(bool b) {
+        prohibit_ipc = b;
+}
+
 int log_emergency_level(void) {
         /* Returns the log level to use for log_emergency() logging. We use LOG_EMERG only when we are PID 1, as only
          * then the system of the whole system is obviously affected. */
diff --git a/src/basic/log.h b/src/basic/log.h
index 910a89a255..0a8fa22866 100644
--- a/src/basic/log.h
+++ b/src/basic/log.h
@@ -307,6 +307,10 @@ void log_set_upgrade_syslog_to_journal(bool b);
 void log_set_always_reopen_console(bool b);
 void log_set_open_when_needed(bool b);
 
+/* If turned on, then we'll never use IPC-based logging, i.e. never log to syslog or the journal. We'll only log to
+ * stderr, the console or kmsg */
+void log_set_prohibit_ipc(bool b);
+
 int log_syntax_internal(
                 const char *unit,
                 int level,