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 #define check(log_level, x) ({                  \
  47   int _r = (x);                                 \
  48   errno = _r < 0 ? -_r : 0;                     \
  49   sd_journal_print((log_level), #x ": %m");     \
  50   if (_r < 0)                                   \
  51     return EXIT_FAILURE;                        \
  52   })
  53
  54 typedef enum LogTarget {
  55   LOG_TARGET_JOURNAL,
  56   LOG_TARGET_KMSG,
  57   LOG_TARGET_SYSLOG,
  58   LOG_TARGET_CONSOLE,
  59   _LOG_TARGET_MAX,
  60 } LogTarget;
  61
  62 static const char* const log_target_table[_LOG_TARGET_MAX] = {
  63   [LOG_TARGET_JOURNAL] = "journal",
  64   [LOG_TARGET_KMSG]    = "kmsg",
  65   [LOG_TARGET_SYSLOG]  = "syslog",
  66   [LOG_TARGET_CONSOLE] = "console",
  67 };
  68
  69 static const char* const log_level_table[LOG_DEBUG + 1] = {
  70   [LOG_EMERG]   = "emerg",
  71   [LOG_ALERT]   = "alert",
  72   [LOG_CRIT]    = "crit",
  73   [LOG_ERR]     = "err",
  74   [LOG_WARNING] = "warning",
  75   [LOG_NOTICE]  = "notice",
  76   [LOG_INFO]    = "info",
  77   [LOG_DEBUG]   = "debug",
  78 };
  79
  80 typedef struct object {
  81   const char *syslog_identifier;
  82   LogTarget log_target;
  83   int log_level;
  84 } object;
  85
  86 static int property_get(
  87                 sd_bus *bus,
  88                 const char *path,
  89                 const char *interface,
  90                 const char *property,
  91                 sd_bus_message *reply,
  92                 void *userdata,
  93                 sd_bus_error *error) {
  94
  95   object *o = userdata;
  96
  97   if (strcmp(property, "LogLevel") == 0)
  98     return sd_bus_message_append(reply, "s", log_level_table[o->log_level]);
  99
 100   if (strcmp(property, "LogTarget") == 0)
 101     return sd_bus_message_append(reply, "s", log_target_table[o->log_target]);
 102
 103   if (strcmp(property, "SyslogIdentifier") == 0)
 104     return sd_bus_message_append(reply, "s", o->syslog_identifier);
 105
 106   return sd_bus_error_setf(error,
 107                            SD_BUS_ERROR_UNKNOWN_PROPERTY,
 108                            "Unknown property '%s'",
 109                            property);
 110 }
 111
 112 static int property_set(
 113                 sd_bus *bus,
 114                 const char *path,
 115                 const char *interface,
 116                 const char *property,
 117                 sd_bus_message *message,
 118                 void *userdata,
 119                 sd_bus_error *error) {
 120
 121   object *o = userdata;
 122   const char *value;
 123   int r;
 124
 125   r = sd_bus_message_read(message, "s", &value);
 126   if (r < 0)
 127     return r;
 128
 129   if (strcmp(property, "LogLevel") == 0) {
 130     for (int i = 0; i < LOG_DEBUG + 1; i++)
 131       if (strcmp(value, log_level_table[i]) == 0) {
 132         o->log_level = i;
 133         setlogmask(LOG_UPTO(i));
 134         return 0;
 135       }
 136
 137     return sd_bus_error_setf(error,
 138                              SD_BUS_ERROR_INVALID_ARGS,
 139                              "Invalid value for LogLevel: '%s'",
 140                              value);
 141   }
 142
 143   if (strcmp(property, "LogTarget") == 0) {
 144     for (LogTarget i = 0; i < _LOG_TARGET_MAX; i++)
 145       if (strcmp(value, log_target_table[i]) == 0) {
 146         o->log_target = i;
 147         return 0;
 148       }
 149
 150     return sd_bus_error_setf(error,
 151                              SD_BUS_ERROR_INVALID_ARGS,
 152                              "Invalid value for LogTarget: '%s'",
 153                              value);
 154   }
 155
 156   return sd_bus_error_setf(error,
 157                            SD_BUS_ERROR_UNKNOWN_PROPERTY,
 158                            "Unknown property '%s'",
 159                            property);
 160 }
 161
 162 /* https://www.freedesktop.org/software/systemd/man/sd_bus_add_object.html
 163  */
 164 static const sd_bus_vtable vtable[] = {
 165   SD_BUS_VTABLE_START(0),
 166   SD_BUS_WRITABLE_PROPERTY(
 167     "LogLevel", "s",
 168     property_get, property_set,
 169     0,
 170     0),
 171   SD_BUS_WRITABLE_PROPERTY(
 172     "LogTarget", "s",
 173     property_get, property_set,
 174     0,
 175     0),
 176   SD_BUS_PROPERTY(
 177     "SyslogIdentifier", "s",
 178     property_get,
 179     0,
 180     SD_BUS_VTABLE_PROPERTY_CONST),
 181   SD_BUS_VTABLE_END
 182 };
 183
 184 int main(int argc, char **argv) {
 185   /* The bus should be relinquished before the program terminates. The cleanup
 186    * attribute allows us to do it nicely and cleanly whenever we exit the
 187    * block.
 188    */
 189   _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
 190
 191   object o = {
 192     .log_level = LOG_INFO,
 193     .log_target = LOG_TARGET_JOURNAL,
 194     .syslog_identifier = "example",
 195   };
 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   check(o.log_level, sd_bus_default(&bus));
 207
 208   /* Publish an interface on the bus, specifying our well-known object access
 209    * path and public interface name.
 210    * https://www.freedesktop.org/software/systemd/man/sd_bus_add_object.html
 211    * https://dbus.freedesktop.org/doc/dbus-tutorial.html
 212    */
 213   check(o.log_level, sd_bus_add_object_vtable(bus, NULL,
 214                                               "/org/freedesktop/LogControl1",
 215                                               "org.freedesktop.LogControl1",
 216                                               vtable,
 217                                               &o));
 218
 219   /* By default the service is assigned an ephemeral name. Also add a fixed
 220    * one, so that clients know whom to call.
 221    * https://www.freedesktop.org/software/systemd/man/sd_bus_request_name.html
 222    */
 223   check(o.log_level, sd_bus_request_name(bus, "org.freedesktop.Example", 0));
 224
 225   for (;;) {
 226     /* https://www.freedesktop.org/software/systemd/man/sd_bus_wait.html
 227      */
 228     check(o.log_level, sd_bus_wait(bus, UINT64_MAX));
 229     /* https://www.freedesktop.org/software/systemd/man/sd_bus_process.html
 230      */
 231     check(o.log_level, sd_bus_process(bus, NULL));
 232   }
 233
 234   /* https://www.freedesktop.org/software/systemd/man/sd_bus_release_name.html
 235    */
 236   check(o.log_level, sd_bus_release_name(bus, "org.freedesktop.Example"));
 237
 238   return 0;
 239 }