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   fprintf(stderr, "%s: %s\n", message, strerror(-error));
  25   return error;
  26 }
  27
  28 int main(int argc, char **argv) {
  29   _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
  30   _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
  31   _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL, *m = NULL;
  32   int r;
  33
  34   r = sd_bus_open_system(&bus);
  35   if (r < 0)
  36     return log_error(r, "Failed to acquire bus");
  37
  38   r = sd_bus_message_new_method_call(bus, &m,
  39                                      DESTINATION, PATH, INTERFACE, MEMBER);
  40   if (r < 0)
  41     return log_error(r, "Failed to create bus message");
  42
  43   r = sd_bus_message_append(m, "u", (unsigned) getpid());
  44   if (r < 0)
  45     return log_error(r, "Failed to append to bus message");
  46
  47   r = sd_bus_call(bus, m, -1, &error, &reply);
  48   if (r < 0)
  49     return log_error(r, MEMBER " call failed");
  50
  51   const char *ans;
  52   r = sd_bus_message_read(reply, "o", &ans);
  53   if (r < 0)
  54     return log_error(r, "Failed to read reply");
  55
  56   printf("Unit path is \"%s\".\n", ans);
  57
  58   return 0;
  59 }