man/logcontrol-example.c

   1 /* SPDX-License-Identifier: MIT-0 */
   2
   3 /* Implements the LogControl1 interface as per specification:
   4  * https://www.freedesktop.org/software/systemd/man/org.freedesktop.LogControl1.html
   5  *
   6  * Compile with 'cc logcontrol-example.c $(pkg-config --libs --cflags libsystemd)'
   7  *
   8  * To get and set properties via busctl:
   9  *
  10  * $ busctl --user get-property org.freedesktop.Example \
  11  *                              /org/freedesktop/LogControl1 \
  12  *                              org.freedesktop.LogControl1 \
  13  *                              SyslogIdentifier
  14  *   s "example"
  15  * $ busctl --user get-property org.freedesktop.Example \
  16  *                              /org/freedesktop/LogControl1 \
  17  *                              org.freedesktop.LogControl1 \
  18  *                              LogTarget
  19  *   s "journal"
  20  * $ busctl --user get-property org.freedesktop.Example \
  21  *                              /org/freedesktop/LogControl1 \
  22  *                              org.freedesktop.LogControl1 \
  23  *                              LogLevel
  24  *   s "info"
  25  * $ busctl --user set-property org.freedesktop.Example \
  26  *                              /org/freedesktop/LogControl1 \
  27  *                              org.freedesktop.LogControl1 \
  28  *                              LogLevel \
  29  *                              "s" debug
  30  * $ busctl --user get-property org.freedesktop.Example \
  31  *                              /org/freedesktop/LogControl1 \
  32  *                              org.freedesktop.LogControl1 \
  33  *                              LogLevel
  34  *   s "debug"
  35  */
  36
  37 #include <errno.h>
  38 #include <stdlib.h>
  39 #include <stdio.h>
  40 #include <syslog.h>
  41 #include <systemd/sd-bus.h>
  42 #include <systemd/sd-journal.h>
  43
  44 #define _cleanup_(f) __attribute__((cleanup(f)))
  45
  46 static int log_error(int log_level, int error, const char *str) {
  47   sd_journal_print(log_level, "%s failed: %s", str, strerror(-error));
  48   return error;
  49 }
  50
  51 typedef enum LogTarget {
  52   LOG_TARGET_JOURNAL,
  53   LOG_TARGET_KMSG,
  54   LOG_TARGET_SYSLOG,
  55   LOG_TARGET_CONSOLE,
  56   _LOG_TARGET_MAX,
  57 } LogTarget;
  58
  59 static const char* const log_target_table[_LOG_TARGET_MAX] = {
  60   [LOG_TARGET_JOURNAL] = "journal",
  61   [LOG_TARGET_KMSG]    = "kmsg",
  62   [LOG_TARGET_SYSLOG]  = "syslog",
  63   [LOG_TARGET_CONSOLE] = "console",
  64 };
  65
  66 static const char* const log_level_table[LOG_DEBUG + 1] = {
  67   [LOG_EMERG]   = "emerg",
  68   [LOG_ALERT]   = "alert",
  69   [LOG_CRIT]    = "crit",
  70   [LOG_ERR]     = "err",
  71   [LOG_WARNING] = "warning",
  72   [LOG_NOTICE]  = "notice",
  73   [LOG_INFO]    = "info",
  74   [LOG_DEBUG]   = "debug",
  75 };
  76
  77 typedef struct object {
  78   const char *syslog_identifier;
  79   LogTarget log_target;
  80   int log_level;
  81 } object;
  82
  83 static int property_get(
  84                 sd_bus *bus,
  85                 const char *path,
  86                 const char *interface,
  87                 const char *property,
  88                 sd_bus_message *reply,
  89                 void *userdata,
  90                 sd_bus_error *error) {
  91
  92   object *o = userdata;
  93
  94   if (strcmp(property, "LogLevel") == 0)
  95     return sd_bus_message_append(reply, "s", log_level_table[o->log_level]);
  96
  97   if (strcmp(property, "LogTarget") == 0)
  98     return sd_bus_message_append(reply, "s", log_target_table[o->log_target]);
  99
 100   if (strcmp(property, "SyslogIdentifier") == 0)
 101     return sd_bus_message_append(reply, "s", o->syslog_identifier);
 102
 103   return sd_bus_error_setf(error,
 104                            SD_BUS_ERROR_UNKNOWN_PROPERTY,
 105                            "Unknown property '%s'",
 106                            property);
 107 }
 108
 109 static int property_set(
 110                 sd_bus *bus,
 111                 const char *path,
 112                 const char *interface,
 113                 const char *property,
 114                 sd_bus_message *message,
 115                 void *userdata,
 116                 sd_bus_error *error) {
 117
 118   object *o = userdata;
 119   const char *value;
 120   int r;
 121
 122   r = sd_bus_message_read(message, "s", &value);
 123   if (r < 0)
 124     return r;
 125
 126   if (strcmp(property, "LogLevel") == 0) {
 127     int i;
 128     for (i = 0; i < LOG_DEBUG + 1; i++)
 129       if (strcmp(value, log_level_table[i]) == 0) {
 130         o->log_level = i;
 131         setlogmask(LOG_UPTO(i));
 132         return 0;
 133       }
 134
 135     return sd_bus_error_setf(error,
 136                              SD_BUS_ERROR_INVALID_ARGS,
 137                              "Invalid value for LogLevel: '%s'",
 138                              value);
 139   }
 140
 141   if (strcmp(property, "LogTarget") == 0) {
 142     LogTarget i;
 143     for (i = 0; i < _LOG_TARGET_MAX; i++)
 144       if (strcmp(value, log_target_table[i]) == 0) {
 145         o->log_target = i;
 146         return 0;
 147       }
 148
 149     return sd_bus_error_setf(error,
 150                              SD_BUS_ERROR_INVALID_ARGS,
 151                              "Invalid value for LogTarget: '%s'",
 152                              value);
 153   }
 154
 155   return sd_bus_error_setf(error,
 156                            SD_BUS_ERROR_UNKNOWN_PROPERTY,
 157                            "Unknown property '%s'",
 158                            property);
 159 }
 160
 161 /* https://www.freedesktop.org/software/systemd/man/sd_bus_add_object.html
 162  */
 163 static const sd_bus_vtable vtable[] = {
 164   SD_BUS_VTABLE_START(0),
 165   SD_BUS_WRITABLE_PROPERTY(
 166     "LogLevel", "s",
 167     property_get, property_set,
 168     0,
 169     0),
 170   SD_BUS_WRITABLE_PROPERTY(
 171     "LogTarget", "s",
 172     property_get, property_set,
 173     0,
 174     0),
 175   SD_BUS_PROPERTY(
 176     "SyslogIdentifier", "s",
 177     property_get,
 178     0,
 179     SD_BUS_VTABLE_PROPERTY_CONST),
 180   SD_BUS_VTABLE_END
 181 };
 182
 183 int main(int argc, char **argv) {
 184   /* The bus should be relinquished before the program terminates. The cleanup
 185    * attribute allows us to do it nicely and cleanly whenever we exit the
 186    * block.
 187    */
 188   _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
 189
 190   object o = {
 191     .log_level = LOG_INFO,
 192     .log_target = LOG_TARGET_JOURNAL,
 193     .syslog_identifier = "example",
 194   };
 195   int r;
 196
 197   /* https://man7.org/linux/man-pages/man3/setlogmask.3.html
 198    * Programs using syslog() instead of sd_journal can use this API to cut logs
 199    * emission at the source.
 200    */
 201   setlogmask(LOG_UPTO(o.log_level));
 202
 203   /* Acquire a connection to the bus, letting the library work out the details.
 204    * https://www.freedesktop.org/software/systemd/man/sd_bus_default.html
 205    */
 206   r = sd_bus_default(&bus);
 207   if (r < 0)
 208     return log_error(o.log_level, r, "sd_bus_default()");
 209
 210   /* Publish an interface on the bus, specifying our well-known object access
 211    * path and public interface name.
 212    * https://www.freedesktop.org/software/systemd/man/sd_bus_add_object.html
 213    * https://dbus.freedesktop.org/doc/dbus-tutorial.html
 214    */
 215   r = sd_bus_add_object_vtable(bus, NULL,
 216                                "/org/freedesktop/LogControl1",
 217                                "org.freedesktop.LogControl1",
 218                                vtable,
 219                                &o);
 220   if (r < 0)
 221     return log_error(o.log_level, r, "sd_bus_add_object_vtable()");
 222
 223   /* By default the service is assigned an ephemeral name. Also add a fixed
 224    * one, so that clients know whom to call.
 225    * https://www.freedesktop.org/software/systemd/man/sd_bus_request_name.html
 226    */
 227   r = sd_bus_request_name(bus, "org.freedesktop.Example", 0);
 228   if (r < 0)
 229     return log_error(o.log_level, r, "sd_bus_request_name()");
 230
 231   for (;;) {
 232     /* https://www.freedesktop.org/software/systemd/man/sd_bus_wait.html
 233      */
 234     r = sd_bus_wait(bus, UINT64_MAX);
 235     if (r < 0)
 236       return log_error(o.log_level, r, "sd_bus_wait()");
 237     /* https://www.freedesktop.org/software/systemd/man/sd_bus_process.html
 238      */
 239     r = sd_bus_process(bus, NULL);
 240     if (r < 0)
 241       return log_error(o.log_level, r, "sd_bus_process()");
 242   }
 243
 244   /* https://www.freedesktop.org/software/systemd/man/sd_bus_release_name.html
 245    */
 246   r = sd_bus_release_name(bus, "org.freedesktop.Example");
 247   if (r < 0)
 248     return log_error(o.log_level, r, "sd_bus_release_name()");
 249
 250   return 0;
 251 }