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-rw-r--r--man/logcontrol-example.c239
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diff --git a/man/logcontrol-example.c b/man/logcontrol-example.c
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+/* SPDX-License-Identifier: MIT-0 */
+
+/* Implements the LogControl1 interface as per specification:
+ * https://www.freedesktop.org/software/systemd/man/org.freedesktop.LogControl1.html
+ *
+ * Compile with 'cc logcontrol-example.c $(pkg-config --libs --cflags libsystemd)'
+ *
+ * To get and set properties via busctl:
+ *
+ * $ busctl --user get-property org.freedesktop.Example \
+ * /org/freedesktop/LogControl1 \
+ * org.freedesktop.LogControl1 \
+ * SyslogIdentifier
+ * s "example"
+ * $ busctl --user get-property org.freedesktop.Example \
+ * /org/freedesktop/LogControl1 \
+ * org.freedesktop.LogControl1 \
+ * LogTarget
+ * s "journal"
+ * $ busctl --user get-property org.freedesktop.Example \
+ * /org/freedesktop/LogControl1 \
+ * org.freedesktop.LogControl1 \
+ * LogLevel
+ * s "info"
+ * $ busctl --user set-property org.freedesktop.Example \
+ * /org/freedesktop/LogControl1 \
+ * org.freedesktop.LogControl1 \
+ * LogLevel \
+ * "s" debug
+ * $ busctl --user get-property org.freedesktop.Example \
+ * /org/freedesktop/LogControl1 \
+ * org.freedesktop.LogControl1 \
+ * LogLevel
+ * s "debug"
+ */
+
+#include <errno.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <syslog.h>
+#include <systemd/sd-bus.h>
+#include <systemd/sd-journal.h>
+
+#define _cleanup_(f) __attribute__((cleanup(f)))
+
+#define check(log_level, x) ({ \
+ int _r = (x); \
+ errno = _r < 0 ? -_r : 0; \
+ sd_journal_print((log_level), #x ": %m"); \
+ if (_r < 0) \
+ return EXIT_FAILURE; \
+ })
+
+typedef enum LogTarget {
+ LOG_TARGET_JOURNAL,
+ LOG_TARGET_KMSG,
+ LOG_TARGET_SYSLOG,
+ LOG_TARGET_CONSOLE,
+ _LOG_TARGET_MAX,
+} LogTarget;
+
+static const char* const log_target_table[_LOG_TARGET_MAX] = {
+ [LOG_TARGET_JOURNAL] = "journal",
+ [LOG_TARGET_KMSG] = "kmsg",
+ [LOG_TARGET_SYSLOG] = "syslog",
+ [LOG_TARGET_CONSOLE] = "console",
+};
+
+static const char* const log_level_table[LOG_DEBUG + 1] = {
+ [LOG_EMERG] = "emerg",
+ [LOG_ALERT] = "alert",
+ [LOG_CRIT] = "crit",
+ [LOG_ERR] = "err",
+ [LOG_WARNING] = "warning",
+ [LOG_NOTICE] = "notice",
+ [LOG_INFO] = "info",
+ [LOG_DEBUG] = "debug",
+};
+
+typedef struct object {
+ const char *syslog_identifier;
+ LogTarget log_target;
+ int log_level;
+} object;
+
+static int property_get(
+ sd_bus *bus,
+ const char *path,
+ const char *interface,
+ const char *property,
+ sd_bus_message *reply,
+ void *userdata,
+ sd_bus_error *error) {
+
+ object *o = userdata;
+
+ if (strcmp(property, "LogLevel") == 0)
+ return sd_bus_message_append(reply, "s", log_level_table[o->log_level]);
+
+ if (strcmp(property, "LogTarget") == 0)
+ return sd_bus_message_append(reply, "s", log_target_table[o->log_target]);
+
+ if (strcmp(property, "SyslogIdentifier") == 0)
+ return sd_bus_message_append(reply, "s", o->syslog_identifier);
+
+ return sd_bus_error_setf(error,
+ SD_BUS_ERROR_UNKNOWN_PROPERTY,
+ "Unknown property '%s'",
+ property);
+}
+
+static int property_set(
+ sd_bus *bus,
+ const char *path,
+ const char *interface,
+ const char *property,
+ sd_bus_message *message,
+ void *userdata,
+ sd_bus_error *error) {
+
+ object *o = userdata;
+ const char *value;
+ int r;
+
+ r = sd_bus_message_read(message, "s", &value);
+ if (r < 0)
+ return r;
+
+ if (strcmp(property, "LogLevel") == 0) {
+ for (int i = 0; i < LOG_DEBUG + 1; i++)
+ if (strcmp(value, log_level_table[i]) == 0) {
+ o->log_level = i;
+ setlogmask(LOG_UPTO(i));
+ return 0;
+ }
+
+ return sd_bus_error_setf(error,
+ SD_BUS_ERROR_INVALID_ARGS,
+ "Invalid value for LogLevel: '%s'",
+ value);
+ }
+
+ if (strcmp(property, "LogTarget") == 0) {
+ for (LogTarget i = 0; i < _LOG_TARGET_MAX; i++)
+ if (strcmp(value, log_target_table[i]) == 0) {
+ o->log_target = i;
+ return 0;
+ }
+
+ return sd_bus_error_setf(error,
+ SD_BUS_ERROR_INVALID_ARGS,
+ "Invalid value for LogTarget: '%s'",
+ value);
+ }
+
+ return sd_bus_error_setf(error,
+ SD_BUS_ERROR_UNKNOWN_PROPERTY,
+ "Unknown property '%s'",
+ property);
+}
+
+/* https://www.freedesktop.org/software/systemd/man/sd_bus_add_object.html
+ */
+static const sd_bus_vtable vtable[] = {
+ SD_BUS_VTABLE_START(0),
+ SD_BUS_WRITABLE_PROPERTY(
+ "LogLevel", "s",
+ property_get, property_set,
+ 0,
+ 0),
+ SD_BUS_WRITABLE_PROPERTY(
+ "LogTarget", "s",
+ property_get, property_set,
+ 0,
+ 0),
+ SD_BUS_PROPERTY(
+ "SyslogIdentifier", "s",
+ property_get,
+ 0,
+ SD_BUS_VTABLE_PROPERTY_CONST),
+ SD_BUS_VTABLE_END
+};
+
+int main(int argc, char **argv) {
+ /* The bus should be relinquished before the program terminates. The cleanup
+ * attribute allows us to do it nicely and cleanly whenever we exit the
+ * block.
+ */
+ _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+
+ object o = {
+ .log_level = LOG_INFO,
+ .log_target = LOG_TARGET_JOURNAL,
+ .syslog_identifier = "example",
+ };
+
+ /* https://man7.org/linux/man-pages/man3/setlogmask.3.html
+ * Programs using syslog() instead of sd_journal can use this API to cut logs
+ * emission at the source.
+ */
+ setlogmask(LOG_UPTO(o.log_level));
+
+ /* Acquire a connection to the bus, letting the library work out the details.
+ * https://www.freedesktop.org/software/systemd/man/sd_bus_default.html
+ */
+ check(o.log_level, sd_bus_default(&bus));
+
+ /* Publish an interface on the bus, specifying our well-known object access
+ * path and public interface name.
+ * https://www.freedesktop.org/software/systemd/man/sd_bus_add_object.html
+ * https://dbus.freedesktop.org/doc/dbus-tutorial.html
+ */
+ check(o.log_level, sd_bus_add_object_vtable(bus, NULL,
+ "/org/freedesktop/LogControl1",
+ "org.freedesktop.LogControl1",
+ vtable,
+ &o));
+
+ /* By default the service is assigned an ephemeral name. Also add a fixed
+ * one, so that clients know whom to call.
+ * https://www.freedesktop.org/software/systemd/man/sd_bus_request_name.html
+ */
+ check(o.log_level, sd_bus_request_name(bus, "org.freedesktop.Example", 0));
+
+ for (;;) {
+ /* https://www.freedesktop.org/software/systemd/man/sd_bus_wait.html
+ */
+ check(o.log_level, sd_bus_wait(bus, UINT64_MAX));
+ /* https://www.freedesktop.org/software/systemd/man/sd_bus_process.html
+ */
+ check(o.log_level, sd_bus_process(bus, NULL));
+ }
+
+ /* https://www.freedesktop.org/software/systemd/man/sd_bus_release_name.html
+ */
+ check(o.log_level, sd_bus_release_name(bus, "org.freedesktop.Example"));
+
+ return 0;
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-15 15:03:56 +0000