1 files changed, 63 insertions, 0 deletions
diff --git a/src/shared/common-signal.h b/src/shared/common-signal.h
new file mode 100644
index 0000000..1fe7b76
--- /dev/null
+++ b/src/shared/common-signal.h
@@ -0,0 +1,63 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include <syslog.h>
+
+#include <sd-event.h>
+
+/* All our long-running services should implement a SIGRTMIN+18 handler that can be used to trigger certain
+ * actions that affect service runtime. The specific action is indicated via the "value integer" you can pass
+ * along realtime signals. This is mostly intended for debugging purposes and is entirely asynchronous in
+ * nature. Specifically, these are the commands:
+ *
+ * Currently available operations:
+ *
+ *         • Change maximum log level
+ *         • Change log target
+ *         • Invoke memory trimming, like under memory pressure
+ *         • Write glibc malloc() allocation info to logs
+ *
+ * How to use this? Via a command like the following:
+ *
+ *         /usr/bin/kill -s RTMIN+18 -q 768 1
+ *
+ *         (This will tell PID 1 to trim its memory use.)
+ *
+ * or:
+ *
+ *         systemctl kill --kill-value=0x300 -s RTMIN+18 systemd-journald
+ *
+ *         (This will tell journald to trim its memory use.)
+ */
+
+enum {
+        _COMMON_SIGNAL_COMMAND_LOG_LEVEL_BASE = 0x100,
+        COMMON_SIGNAL_COMMAND_LOG_EMERG       = _COMMON_SIGNAL_COMMAND_LOG_LEVEL_BASE + LOG_EMERG,
+        COMMON_SIGNAL_COMMAND_LOG_ALERT       = _COMMON_SIGNAL_COMMAND_LOG_LEVEL_BASE + LOG_ALERT,
+        COMMON_SIGNAL_COMMAND_LOG_CRIT        = _COMMON_SIGNAL_COMMAND_LOG_LEVEL_BASE + LOG_CRIT,
+        COMMON_SIGNAL_COMMAND_LOG_ERR         = _COMMON_SIGNAL_COMMAND_LOG_LEVEL_BASE + LOG_ERR,
+        COMMON_SIGNAL_COMMAND_LOG_WARNING     = _COMMON_SIGNAL_COMMAND_LOG_LEVEL_BASE + LOG_WARNING,
+        COMMON_SIGNAL_COMMAND_LOG_NOTICE      = _COMMON_SIGNAL_COMMAND_LOG_LEVEL_BASE + LOG_NOTICE,
+        COMMON_SIGNAL_COMMAND_LOG_INFO        = _COMMON_SIGNAL_COMMAND_LOG_LEVEL_BASE + LOG_INFO,
+        COMMON_SIGNAL_COMMAND_LOG_DEBUG       = _COMMON_SIGNAL_COMMAND_LOG_LEVEL_BASE + LOG_DEBUG,
+        _COMMON_SIGNAL_COMMAND_LOG_LEVEL_END  = COMMON_SIGNAL_COMMAND_LOG_DEBUG,
+
+        COMMON_SIGNAL_COMMAND_CONSOLE         = 0x200,
+        COMMON_SIGNAL_COMMAND_JOURNAL,
+        COMMON_SIGNAL_COMMAND_KMSG,
+        COMMON_SIGNAL_COMMAND_NULL,
+
+        COMMON_SIGNAL_COMMAND_MEMORY_PRESSURE = 0x300,
+        COMMON_SIGNAL_COMMAND_MALLOC_INFO,
+
+        /* Private signals start at 0x500 */
+        _COMMON_SIGNAL_COMMAND_PRIVATE_BASE = 0x500,
+        _COMMON_SIGNAL_COMMAND_PRIVATE_END = 0xfff,
+};
+
+struct sigrtmin18_info {
+        sd_event_handler_t memory_pressure_handler;
+        void *memory_pressure_userdata;
+};
+
+int sigrtmin18_handler(sd_event_source *s, const struct signalfd_siginfo *si, void *userdata);