firstboot: add new systemd.firstboot=headless mode

This adds a new systemd.firstboot=headless mode. It differs from the
existing systemd.firstboot=no mode in that it still performs the
non-interactive auto-configuration that requires no user input (such
as selecting the only installed locale, or applying settings provided
via credentials), and only skips the prompts that would otherwise
block waiting for user input. In contrast, =no disables that
auto-configuration along with the prompts.

The option is also honoured by homectls firstboot logic and
systemd-cryptenroll, where headless behaves the same as no
(because the is no auto-configuration).

src/firstboot/firstboot.c

@@ -24,6 +24,7 @@
 #include "errno-util.h"
 #include "fd-util.h"
 #include "fileio.h"
+#include "firstboot-util.h"
 #include "format-table.h"
 #include "fs-util.h"
 #include "glyph-util.h"
@@ -47,7 +48,6 @@
 #include "password-quality-util.h"
 #include "path-util.h"
 #include "plymouth-util.h"
-#include "proc-cmdline.h"
 #include "prompt-util.h"
 #include "runtime-scope.h"
 #include "smack-util.h"
@@ -79,6 +79,7 @@ static bool arg_prompt_timezone = false;
 static bool arg_prompt_hostname = false;
 static bool arg_prompt_root_password = false;
 static bool arg_prompt_root_shell = false;
+static bool arg_headless = false;
 static bool arg_copy_locale = false;
 static bool arg_copy_keymap = false;
 static bool arg_copy_timezone = false;
@@ -244,6 +245,16 @@ static int locale_is_ok(const char *name, void *userdata) {
         return r != 0 ? locale_is_installed(name) > 0 : locale_is_valid(name);
 }
 
+static bool headless_skips_prompt_for(const char *what) {
+        assert(what);
+
+        if (!arg_headless)
+                return false;
+
+        log_debug("Running headless, not prompting for %s.", what);
+        return true;
+}
+
 static int prompt_locale(int rfd, sd_varlink **mute_console_link) {
         _cleanup_strv_free_ char **locales = NULL;
         bool acquired_from_creds = false;
@@ -296,6 +307,9 @@ static int prompt_locale(int rfd, sd_varlink **mute_console_link) {
                         /* Not setting arg_locale_message here, since it defaults to LANG anyway */
                 }
         } else {
+                if (headless_skips_prompt_for("locale"))
+                        return 0;
+
                 print_welcome(rfd, mute_console_link);
 
                 _cleanup_free_ char *prefill = NULL;
@@ -456,6 +470,9 @@ static int prompt_keymap(int rfd, sd_varlink **mute_console_link) {
                 return 0;
         }
 
+        if (headless_skips_prompt_for("keymap"))
+                return 0;
+
         r = get_keymaps(&kmaps);
         if (r == -ENOENT) /* no keymaps installed */
                 return log_debug_errno(r, "No keymaps are installed.");
@@ -578,6 +595,9 @@ static int prompt_timezone(int rfd, sd_varlink **mute_console_link) {
                 return 0;
         }
 
+        if (headless_skips_prompt_for("timezone"))
+                return 0;
+
         r = get_timezones(&zones);
         if (r < 0)
                 return log_error_errno(r, "Cannot query timezone list: %m");
@@ -691,6 +711,9 @@ static int prompt_hostname(int rfd, sd_varlink **mute_console_link) {
                 return 0;
         }
 
+        if (headless_skips_prompt_for("hostname"))
+                return 0;
+
         print_welcome(rfd, mute_console_link);
 
         r = prompt_loop("Please enter the new hostname",
@@ -879,6 +902,9 @@ static int prompt_root_password(int rfd, sd_varlink **mute_console_link) {
                 return 0;
         }
 
+        if (headless_skips_prompt_for("root password"))
+                return 0;
+
         print_welcome(rfd, mute_console_link);
 
         msg1 = "Please enter the new root password (empty to skip):";
@@ -980,6 +1006,9 @@ static int prompt_root_shell(int rfd, sd_varlink **mute_console_link) {
                 return 0;
         }
 
+        if (headless_skips_prompt_for("root shell"))
+                return 0;
+
         print_welcome(rfd, mute_console_link);
 
         return prompt_loop(
@@ -1688,13 +1717,18 @@ static int run(int argc, char *argv[]) {
                  * command line option, because we are called to provision the host with basic settings (as
                  * opposed to some other file system tree/image) */
 
-                bool enabled;
-                r = proc_cmdline_get_bool("systemd.firstboot", /* flags= */ 0, &enabled);
+                FirstBootMode mode;
+                _cleanup_free_ char *bad = NULL;
+                r = firstboot_mode_from_cmdline(&mode, &bad);
                 if (r < 0)
-                        return log_error_errno(r, "Failed to parse systemd.firstboot= kernel command line argument, ignoring: %m");
-                if (r > 0 && !enabled) {
+                        return log_error_errno(r, "Failed to parse systemd.firstboot= kernel command line argument%s: %m",
+                                               bad ? strjoina(" (invalid value '", bad, "')") : "");
+                if (mode == FIRSTBOOT_NO) {
                         log_debug("Found systemd.firstboot=no kernel command line argument, turning off all prompts.");
                         arg_prompt_locale = arg_prompt_keymap = arg_prompt_keymap_auto = arg_prompt_timezone = arg_prompt_hostname = arg_prompt_root_password = arg_prompt_root_shell = false;
+                } else if (mode == FIRSTBOOT_HEADLESS) {
+                        log_debug("Found systemd.firstboot=headless kernel command line argument, skipping interactive prompts but keeping non-interactive auto-configuration.");
+                        arg_headless = true;
                 }
         }