man/print-unit-path.c

   1 /* SPDX-License-Identifier: MIT-0 */
   2
   3 /* This is equivalent to:
   4  * busctl call org.freedesktop.systemd1 /org/freedesktop/systemd1 \
   5  *       org.freedesktop.systemd1.Manager GetUnitByPID $$
   6  *
   7  * Compile with 'cc print-unit-path.c -lsystemd'
   8  */
   9
  10 #include <errno.h>
  11 #include <stdio.h>
  12 #include <sys/types.h>
  13 #include <unistd.h>
  14
  15 #include <systemd/sd-bus.h>
  16
  17 #define _cleanup_(f) __attribute__((cleanup(f)))
  18 #define DESTINATION "org.freedesktop.systemd1"
  19 #define PATH        "/org/freedesktop/systemd1"
  20 #define INTERFACE   "org.freedesktop.systemd1.Manager"
  21 #define MEMBER      "GetUnitByPID"
  22
  23 static int log_error(int error, const char *message) {
  24   errno = -error;
  25   fprintf(stderr, "%s: %m\n", message);
  26   return error;
  27 }
  28
  29 int main(int argc, char **argv) {
  30   _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
  31   _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
  32   _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL, *m = NULL;
  33   int r;
  34
  35   r = sd_bus_open_system(&bus);
  36   if (r < 0)
  37     return log_error(r, "Failed to acquire bus");
  38
  39   r = sd_bus_message_new_method_call(bus, &m,
  40                                      DESTINATION, PATH, INTERFACE, MEMBER);
  41   if (r < 0)
  42     return log_error(r, "Failed to create bus message");
  43
  44   r = sd_bus_message_append(m, "u", (unsigned) getpid());
  45   if (r < 0)
  46     return log_error(r, "Failed to append to bus message");
  47
  48   r = sd_bus_call(bus, m, -1, &error, &reply);
  49   if (r < 0)
  50     return log_error(r, MEMBER " call failed");
  51
  52   const char *ans;
  53   r = sd_bus_message_read(reply, "o", &ans);
  54   if (r < 0)
  55     return log_error(r, "Failed to read reply");
  56
  57   printf("Unit path is \"%s\".\n", ans);
  58
  59   return 0;
  60 }