/* 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)))

static int log_error(int log_level, int error, const char *str) {

sd_journal_print(log_level, "%s failed: %s", str, strerror(-error));

return error;

}

typedef enum LogTarget {

} 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 {

} object;

static int property_get(

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_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) {

int i;

for (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) {

LogTarget i;

for (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",

};

int r;

/* 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

*/

r = sd_bus_default(&bus);

if (r < 0)

return log_error(o.log_level, r, "sd_bus_default()");

/* 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

*/

r = sd_bus_add_object_vtable(bus, NULL,

"/org/freedesktop/LogControl1",

"org.freedesktop.LogControl1",

vtable,

&o);

if (r < 0)

return log_error(o.log_level, r, "sd_bus_add_object_vtable()");

/* 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

*/

r = sd_bus_request_name(bus, "org.freedesktop.Example", 0);

if (r < 0)

return log_error(o.log_level, r, "sd_bus_request_name()");

for (;;) {

/* https://www.freedesktop.org/software/systemd/man/sd_bus_wait.html

*/

r = sd_bus_wait(bus, UINT64_MAX);

if (r < 0)

return log_error(o.log_level, r, "sd_bus_wait()");

/* https://www.freedesktop.org/software/systemd/man/sd_bus_process.html

*/

r = sd_bus_process(bus, NULL);

if (r < 0)

return log_error(o.log_level, r, "sd_bus_process()");

}

/* https://www.freedesktop.org/software/systemd/man/sd_bus_release_name.html

*/

r = sd_bus_release_name(bus, "org.freedesktop.Example");

if (r < 0)

return log_error(o.log_level, r, "sd_bus_release_name()");

return 0;

}