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Merge pull request #27357 from bluca/example_logcontrol
man: add working example to LogControl1 manpage
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
GitHub
commit
3539b3a9f1
232
man/logcontrol-example.c
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232
man/logcontrol-example.c
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/* SPDX-License-Identifier: MIT-0 */
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/* Implements the LogControl1 interface as per specification:
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* https://www.freedesktop.org/software/systemd/man/org.freedesktop.LogControl1.html
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*
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* Compile with 'cc logcontrol-example.c $(pkg-config --libs --cflags libsystemd)'
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*
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* To get and set properties via busctl:
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*
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* $ busctl --user get-property org.freedesktop.Example \
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* /org/freedesktop/LogControl1 \
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* org.freedesktop.LogControl1 \
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* SyslogIdentifier
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* s "example"
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* $ busctl --user get-property org.freedesktop.Example \
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* /org/freedesktop/LogControl1 \
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* org.freedesktop.LogControl1 \
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* LogTarget
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* s "journal"
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* $ busctl --user get-property org.freedesktop.Example \
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* /org/freedesktop/LogControl1 \
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* org.freedesktop.LogControl1 \
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* LogLevel
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* s "info"
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* $ busctl --user set-property org.freedesktop.Example \
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* /org/freedesktop/LogControl1 \
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* org.freedesktop.LogControl1 \
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* LogLevel \
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* "s" debug
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* $ busctl --user get-property org.freedesktop.Example \
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* /org/freedesktop/LogControl1 \
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* org.freedesktop.LogControl1 \
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* LogLevel
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* s "debug"
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*/
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#include <errno.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <syslog.h>
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#include <systemd/sd-bus.h>
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#include <systemd/sd-journal.h>
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#define _cleanup_(f) __attribute__((cleanup(f)))
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#define check(log_level, x) ({ \
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int _r = (x); \
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errno = _r < 0 ? -_r : 0; \
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sd_journal_print((log_level), #x ": %m"); \
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if (_r < 0) \
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return EXIT_FAILURE; \
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})
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typedef enum LogTarget {
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LOG_TARGET_JOURNAL,
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LOG_TARGET_KMSG,
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LOG_TARGET_SYSLOG,
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LOG_TARGET_CONSOLE,
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_LOG_TARGET_MAX,
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} LogTarget;
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static const char* const log_target_table[_LOG_TARGET_MAX] = {
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[LOG_TARGET_JOURNAL] = "journal",
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[LOG_TARGET_KMSG] = "kmsg",
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[LOG_TARGET_SYSLOG] = "syslog",
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[LOG_TARGET_CONSOLE] = "console",
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};
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static const char* const log_level_table[LOG_DEBUG + 1] = {
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[LOG_EMERG] = "emerg",
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[LOG_ALERT] = "alert",
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[LOG_CRIT] = "crit",
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[LOG_ERR] = "err",
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[LOG_WARNING] = "warning",
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[LOG_NOTICE] = "notice",
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[LOG_INFO] = "info",
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[LOG_DEBUG] = "debug",
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};
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typedef struct object {
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const char *syslog_identifier;
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LogTarget log_target;
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int log_level;
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} object;
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static int property_get(
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sd_bus *bus,
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const char *path,
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const char *interface,
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const char *property,
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sd_bus_message *reply,
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void *userdata,
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sd_bus_error *error) {
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object *o = userdata;
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if (strcmp(property, "LogLevel") == 0)
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return sd_bus_message_append(reply, "s", log_level_table[o->log_level]);
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if (strcmp(property, "LogTarget") == 0)
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return sd_bus_message_append(reply, "s", log_target_table[o->log_target]);
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if (strcmp(property, "SyslogIdentifier") == 0)
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return sd_bus_message_append(reply, "s", o->syslog_identifier);
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return sd_bus_error_setf(error,
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SD_BUS_ERROR_INVALID_ARGS,
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"Unknown property '%s'",
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property);
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}
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static int property_set(
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sd_bus *bus,
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const char *path,
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const char *interface,
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const char *property,
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sd_bus_message *message,
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void *userdata,
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sd_bus_error *error) {
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object *o = userdata;
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const char *value;
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int r;
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r = sd_bus_message_read(message, "s", &value);
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if (r < 0)
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return r;
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if (strcmp(property, "LogLevel") == 0) {
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for (int i = 0; i < LOG_DEBUG + 1; i++)
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if (strcmp(value, log_level_table[i]) == 0) {
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o->log_level = i;
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return 0;
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}
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return sd_bus_error_setf(error,
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SD_BUS_ERROR_INVALID_ARGS,
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"Invalid value for LogLevel: '%s'",
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value);
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}
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if (strcmp(value, "LogTarget") == 0) {
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for (LogTarget i = 0; i < _LOG_TARGET_MAX; i++)
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if (strcmp(value, log_target_table[i]) == 0) {
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o->log_target = i;
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return 0;
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}
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return sd_bus_error_setf(error,
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SD_BUS_ERROR_INVALID_ARGS,
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"Invalid value for LogTarget: '%s'",
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value);
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}
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return sd_bus_error_setf(error,
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SD_BUS_ERROR_INVALID_ARGS,
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"Unknown property '%s'",
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property);
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}
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/* https://www.freedesktop.org/software/systemd/man/sd_bus_add_object.html
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*/
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static const sd_bus_vtable vtable[] = {
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SD_BUS_VTABLE_START(0),
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SD_BUS_WRITABLE_PROPERTY(
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"LogLevel", "s",
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property_get, property_set,
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0,
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0),
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SD_BUS_WRITABLE_PROPERTY(
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"LogTarget", "s",
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property_get, property_set,
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0,
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0),
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SD_BUS_PROPERTY(
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"SyslogIdentifier", "s",
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property_get,
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0,
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SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_VTABLE_END
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};
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int main(int argc, char **argv) {
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/* The bus should be relinquished before the program terminates. The cleanup
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* attribute allows us to do it nicely and cleanly whenever we exit the
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* block.
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*/
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_cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
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/* Acquire a connection to the bus, letting the library work out the details.
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* https://www.freedesktop.org/software/systemd/man/sd_bus_default.html
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*/
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sd_bus_default(&bus);
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object o = {
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.log_level = LOG_INFO,
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.log_target = LOG_TARGET_JOURNAL,
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.syslog_identifier = "example",
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};
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/* Publish an interface on the bus, specifying our well-known object access
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* path and public interface name.
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* https://www.freedesktop.org/software/systemd/man/sd_bus_add_object.html
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* https://dbus.freedesktop.org/doc/dbus-tutorial.html
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*/
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check(o.log_level, sd_bus_add_object_vtable(bus, NULL,
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"/org/freedesktop/LogControl1",
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"org.freedesktop.LogControl1",
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vtable,
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&o));
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/* By default the service is assigned an ephemeral name. Also add a fixed
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* one, so that clients know whom to call.
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* https://www.freedesktop.org/software/systemd/man/sd_bus_request_name.html
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*/
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check(o.log_level, sd_bus_request_name(bus, "org.freedesktop.Example", 0));
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for (;;) {
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/* https://www.freedesktop.org/software/systemd/man/sd_bus_wait.html
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*/
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check(o.log_level, sd_bus_wait(bus, UINT64_MAX));
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/* https://www.freedesktop.org/software/systemd/man/sd_bus_process.html
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*/
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check(o.log_level, sd_bus_process(bus, NULL));
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}
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/* https://www.freedesktop.org/software/systemd/man/sd_bus_release_name.html
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*/
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check(o.log_level, sd_bus_release_name(bus, "org.freedesktop.Example"));
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return 0;
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}
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@ -116,6 +116,20 @@ node /org/freedesktop/LogControl1 {
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for details about <varname>BusName=</varname>.)</para>
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</refsect1>
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<refsect1>
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<title>Example</title>
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<example>
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<title>Create a simple listener on the bus that implements LogControl1</title>
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<programlisting><xi:include href="logcontrol-example.c" parse="text"/></programlisting>
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<para>This creates a simple server on the bus. It implements the LogControl1 interface by providing
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the required properties and allowing to set the writable ones. It logs at the configured log level using
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<citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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</example>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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@ -110,13 +110,14 @@
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<title>Description</title>
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<para><function>sd_bus_default()</function> acquires a bus
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connection object to the user bus when invoked in user context, or
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to the system bus otherwise. The connection object is associated
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with the calling thread. Each time the function is invoked from
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the same thread, the same object is returned, but its reference
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count is increased by one, as long as at least one reference is
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kept. When the last reference to the connection is dropped (using
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the
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connection object to the user bus when invoked from within a user
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slice (any session under <literal>user-*.slice</literal>, e.g.:
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<literal>user@1000.service</literal>), or to the system bus
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otherwise. The connection object is associated with the calling
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thread. Each time the function is invoked from the same thread,
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the same object is returned, but its reference count is increased
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by one, as long as at least one reference is kept. When the last
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reference to the connection is dropped (using the
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<citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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call), the connection is terminated. Note that the connection is
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not automatically terminated when the associated thread ends. It
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