systemd-id128: a new tool to print machine/boot/invocation/app-specific ids

The raison d'etre for this program is printing machine-app-specific IDs. We
provide a library function for that, but not a convenient API. We can hardly
ask people to quickly hack their own C programs or call libsystemd through CFFI
in python or another scripting language if they just want to print an ID.

Verb 'new' was already available as 'journalctl --new-id128', but this makes
it more discoverable.

v2:
- rename binary to systemd-id128
- make --app-specific= into a switch that applies to boot-id and machine-id

src/shared/id128-print.c

@@ -7,14 +7,14 @@
 #include "id128-print.h"
 #include "log.h"
 
-int id128_generate_new(void) {
-        sd_id128_t id;
-        int r;
+int id128_pretty_print(sd_id128_t id, bool pretty) {
         unsigned i;
 
-        r = sd_id128_randomize(&id);
-        if (r < 0)
-                return log_error_errno(r, "Failed to generate ID: %m");
+        if (!pretty) {
+                printf(SD_ID128_FORMAT_STR "\n",
+                       SD_ID128_FORMAT_VAL(id));
+                return 0;
+        }
 
         printf("As string:\n"
                SD_ID128_FORMAT_STR "\n\n"
@@ -35,3 +35,14 @@ int id128_generate_new(void) {
 
         return 0;
 }
+
+int id128_print_new(bool pretty) {
+        sd_id128_t id;
+        int r;
+
+        r = sd_id128_randomize(&id);
+        if (r < 0)
+                return log_error_errno(r, "Failed to generate ID: %m");
+
+        return id128_pretty_print(id, pretty);
+}

src/shared/id128-print.h

@@ -2,4 +2,9 @@
 
 #pragma once
 
-int id128_generate_new(void);
+#include <stdbool.h>
+
+#include "sd-id128.h"
+
+int id128_pretty_print(sd_id128_t id, bool pretty);
+int id128_print_new(bool pretty);