man: add sd_bus_message_new_call(3)

1 files changed, 64 insertions, 0 deletions

diff --git a/man/print-unit-path.c b/man/print-unit-path.c
new file mode 100644
index 0000000000..23b58a26e2
--- /dev/null
+++ b/man/print-unit-path.c
@@ -0,0 +1,64 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+
+#include <systemd/sd-bus.h>
+#define _cleanup_(f) __attribute__((cleanup(f)))
+
+/* This is equivalent to:
+ * busctl call org.freedesktop.systemd1 /org/freedesktop/systemd1 \
+ *       org.freedesktop.systemd1.Manager GetUnitByPID $$
+ *
+ * Compile with 'cc -lsystemd print-unit-path.c'
+ */
+
+#define DESTINATION "org.freedesktop.systemd1"
+#define PATH        "/org/freedesktop/systemd1"
+#define INTERFACE   "org.freedesktop.systemd1.Manager"
+#define MEMBER      "GetUnitByPID"
+
+static int log_error(int error, const char *message) {
+  fprintf(stderr, "%s: %s\n", message, strerror(-error));
+  return error;
+}
+
+static int print_unit_path(sd_bus *bus) {
+  _cleanup_(sd_bus_message_unrefp) sd_bus_message *m = NULL;
+  _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+  _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
+  int r;
+
+  r = sd_bus_message_new_method_call(bus, &m,
+                                     DESTINATION, PATH, INTERFACE, MEMBER);
+  if (r < 0)
+    return log_error(r, "Failed to create bus message");
+
+  r = sd_bus_message_append(m, "u", (unsigned) getpid());
+  if (r < 0)
+    return log_error(r, "Failed to append to bus message");
+
+  r = sd_bus_call(bus, m, -1, &error, &reply);
+  if (r < 0)
+    return log_error(r, "Call failed");
+
+  const char *ans;
+  r = sd_bus_message_read(reply, "o", &ans);
+  if (r < 0)
+    return log_error(r, "Failed to read reply");
+
+  printf("Unit path is \"%s\".\n", ans);
+
+  return 0;
+}
+
+int main(int argc, char **argv) {
+  _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+  int r;
+
+  r = sd_bus_open_system(&bus);
+  if (r < 0)
+    return log_error(r, "Failed to acquire bus");
+
+  print_unit_path(bus);
+}