system/nxinit: add a per-service "console" option

Services started by nxinit (e.g. "sh") do not open a console device on
their own, unlike nsh_main, which explicitly does so via
nsh_consolemain()/nsh_waitusbready() for USB gadget consoles
(CDC-ACM/PL2303). When such a board switches its top-level init from
nsh_main to nxinit, no code path ever registers/connects the USB
console gadget, and a service that just execs a plain "sh" inherits
whatever (invalid, for a USB gadget console not yet opened at the time
the idle task file descriptors are set up) stdio nxinit itself has.

Add a "console [<device>]" service option: a service declared with it
gets the given device (CONFIG_SYSTEM_NXINIT_CONSOLE_DEV, "/dev/console"
by default, if no device is given) opened and dup'd onto its stdin,
stdout and stderr via posix_spawn_file_actions before it is spawned.
This does not depend on nsh being enabled at all.

For a USB gadget console, the device does not exist until the gadget
is actually registered; boards using one are expected to bring it up
themselves before any service using "console" is started (e.g. via an
"exec -- sercon" action in their init.rc, since apps/system/cdcacm
already implements exactly that registration step and does not depend
on nxinit or nsh either).

console_file_actions() runs after the previous commit's time_started
update, so a failure to build the console's file actions is covered by
the same up to date timestamp - no separate clock_gettime() call is
needed on this failure path.

Covered by a new unit test, test_nxinit_service_console_option, that
exercises the option with and without an explicit device, and confirms
services without the option are left untouched.

Assisted-by: Kiro:claude-sonnet-5
Signed-off-by: wangjianyu3 <wangjianyu3@xiaomi.com>

system/nxinit/Kconfig

@@ -111,6 +111,20 @@ config SYSTEM_NXINIT_SERVICE_RESTART_PERIOD
 	int "Service restart period in ms"
 	default 5000
 
+config SYSTEM_NXINIT_CONSOLE_DEV
+	string "Default console device of a service"
+	default "/dev/console"
+	---help---
+		The device used as stdin/stdout/stderr of a service declared with the
+		option "console" and no explicit device, i.e. "console" rather than
+		"console <device>".
+
+		This is needed by services which expect a controlling terminal but do
+		not open one themselves (e.g. plain "sh"), and is the only way to get
+		a console when the console device is not available at the time the
+		file descriptors of the idle task are set up, as is the case for a USB
+		gadget console.
+
 comment "NXInit Testing"
 
 config SYSTEM_NXINIT_TEST

system/nxinit/service.c

@@ -29,12 +29,14 @@
 
 #include <assert.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <string.h>
 #include <stdlib.h>
 #include <time.h>
 #include <signal.h>
 #include <spawn.h>
 #include <sys/param.h>
+#include <unistd.h>
 
 #include "init.h"
 #include "parser.h"
@@ -100,6 +102,8 @@ static int option_override(FAR struct service_manager_s *sm,
                            int argc, FAR char **argv);
 static int option_oneshot(FAR struct service_manager_s *sm,
                           int argc, FAR char **argv);
+static int option_console(FAR struct service_manager_s *sm,
+                          int argc, FAR char **argv);
 #ifdef CONFIG_BOARDCTL_RESET
 static int option_reboot_on_failure(FAR struct service_manager_s *sm,
                                     int argc, FAR char **argv);
@@ -116,6 +120,7 @@ static const struct cmd_map_s g_option[] =
   {"restart_period", 2, 2, option_restart_period},
   {"override", 1, 1, option_override},
   {"oneshot", 1, 1, option_oneshot},
+  {"console", 1, 2, option_console},
 #ifdef CONFIG_BOARDCTL_RESET
   {"reboot_on_failure", 2, 2, option_reboot_on_failure},
 #endif
@@ -128,6 +133,7 @@ static const struct flag_str_s g_flag_str[] =
   {SVC_ONESHOT, "oneshot"},
   {SVC_RUNNING, "running"},
   {SVC_RESTARTING, "restarting"},
+  {SVC_CONSOLE, "console"},
   {SVC_GENTLE_KILL, "gentle_kill"},
   {SVC_REMOVE, "remove"},
   {SVC_SIGKILL, "sigkill"},
@@ -197,6 +203,7 @@ static void remove_service(FAR struct service_s *service)
       free(service->argv[i]);
     }
 
+  free(service->console);
   list_delete(&service->node);
   free(service);
 }
@@ -273,6 +280,43 @@ static int option_oneshot(FAR struct service_manager_s *sm,
   return 0;
 }
 
+/****************************************************************************
+ * Name: option_console
+ *
+ * Description:
+ *   Handle the service option "console [<device>]".  The service is given
+ *   'device' (CONFIG_SYSTEM_NXINIT_CONSOLE_DEV if omitted) as its stdin,
+ *   stdout and stderr, so that a service which does not open a console
+ *   device on its own still gets a working console.
+ *
+ ****************************************************************************/
+
+static int option_console(FAR struct service_manager_s *sm,
+                          int argc, FAR char **argv)
+{
+  FAR struct service_s *s = list_last_entry(&sm->services, struct service_s,
+                                            node);
+
+  add_flags(s, SVC_CONSOLE);
+
+  if (argc > 1)
+    {
+      /* 'argv' points into the parser line buffer, which is reused for the
+       * next line, so the device name must be duplicated here.
+       */
+
+      free(s->console);
+      s->console = strdup(argv[1]);
+      if (s->console == NULL)
+        {
+          init_err("Alloc console device");
+          return -ENOMEM;
+        }
+    }
+
+  return 0;
+}
+
 #ifdef CONFIG_BOARDCTL_RESET
 static int option_reboot_on_failure(FAR struct service_manager_s *sm,
                                     int argc, FAR char **argv)
@@ -430,8 +474,59 @@ void init_service_reap(FAR struct service_s *service, int status)
     }
 }
 
+/****************************************************************************
+ * Name: console_file_actions
+ *
+ * Description:
+ *   Build the spawn file actions which redirect the stdio of a service
+ *   flagged SVC_CONSOLE to its console device.  The actions are performed
+ *   in the context of the new task, so the stdio of NxInit itself is left
+ *   untouched.
+ *
+ ****************************************************************************/
+
+static int console_file_actions(FAR posix_spawn_file_actions_t *actions,
+                               FAR struct service_s *service)
+{
+  FAR const char *dev = service->console ?
+                        service->console : CONFIG_SYSTEM_NXINIT_CONSOLE_DEV;
+  int ret;
+
+  ret = posix_spawn_file_actions_init(actions);
+  if (ret != 0)
+    {
+      init_err("posix_spawn_file_actions_init %d", ret);
+      return -ret;
+    }
+
+  ret = posix_spawn_file_actions_addopen(actions, STDIN_FILENO, dev,
+                                        O_RDWR, 0);
+  if (ret == 0)
+    {
+      ret = posix_spawn_file_actions_adddup2(actions, STDIN_FILENO,
+                                             STDOUT_FILENO);
+    }
+
+  if (ret == 0)
+    {
+      ret = posix_spawn_file_actions_adddup2(actions, STDIN_FILENO,
+                                             STDERR_FILENO);
+    }
+
+  if (ret != 0)
+    {
+      init_err("Add console '%s' file action %d", dev, ret);
+      posix_spawn_file_actions_destroy(actions);
+      return -ret;
+    }
+
+  return 0;
+}
+
 int init_service_start(FAR struct service_s *service)
 {
+  FAR posix_spawn_file_actions_t *pactions = NULL;
+  posix_spawn_file_actions_t actions;
   posix_spawnattr_t attr;
   sigset_t mask;
   int ret;
@@ -472,9 +567,27 @@ int init_service_start(FAR struct service_s *service)
 
   clock_gettime(CLOCK_MONOTONIC, &service->time_started);
 
-  ret = posix_spawnp(&pid, service->argv[2], NULL, &attr, &service->argv[2],
-                     environ);
+  if (check_flags(service, SVC_CONSOLE))
+    {
+      ret = console_file_actions(&actions, service);
+      if (ret < 0)
+        {
+          posix_spawnattr_destroy(&attr);
+          init_service_reap(service, -ret);
+          return ret;
+        }
+
+      pactions = &actions;
+    }
+
+  ret = posix_spawnp(&pid, service->argv[2], pactions, &attr,
+                     &service->argv[2], environ);
   posix_spawnattr_destroy(&attr);
+  if (pactions != NULL)
+    {
+      posix_spawn_file_actions_destroy(pactions);
+    }
+
   if (ret != 0)
     {
       init_err("Starting service '%s': %d", service->argv[1], ret);

system/nxinit/service.h

@@ -44,6 +44,7 @@
 #define SVC_ONESHOT     (1 << 1)  /* do not restart on exit */
 #define SVC_RUNNING     (1 << 2)  /* currently active */
 #define SVC_RESTARTING  (1 << 3)  /* waiting to restart */
+#define SVC_CONSOLE     (1 << 4)  /* requires a console as its stdio */
 
 /* This service should be stopped with SIGTERM instead of SIGKILL.
  * Will still be SIGKILLed after timeout period of 200 ms.
@@ -105,6 +106,12 @@ struct service_s
   int restart_period;
   pid_t pid;
 
+  /* The device given by the service option "console".  NULL means that the
+   * default console device is used.  Only meaningful with SVC_CONSOLE.
+   */
+
+  FAR char *console;
+
   /* The "target" of service option "reboot_on_failure" */
 
 #ifdef CONFIG_BOARDCTL_RESET

system/nxinit/test/test_nxinit.c

@@ -58,6 +58,7 @@ int main(int argc, FAR char *argv[])
       cmocka_unit_test(test_nxinit_service_duplicate_conflict),
       cmocka_unit_test(test_nxinit_service_override_replaces_duplicate),
       cmocka_unit_test(test_nxinit_service_args_max_boundary),
+      cmocka_unit_test(test_nxinit_service_console_option),
     };
 
   return cmocka_run_group_tests(nxinit_tests, test_nxinit_group_setup,

system/nxinit/test/test_nxinit.h

@@ -77,5 +77,6 @@ void test_nxinit_action_event_and_semantics(FAR void **state);
 void test_nxinit_service_duplicate_conflict(FAR void **state);
 void test_nxinit_service_override_replaces_duplicate(FAR void **state);
 void test_nxinit_service_args_max_boundary(FAR void **state);
+void test_nxinit_service_console_option(FAR void **state);
 
 #endif /* __APPS_SYSTEM_NXINIT_TEST_TEST_NXINIT_H */

system/nxinit/test/test_nxinit_service.c

@@ -80,6 +80,7 @@ static void service_manager_free_all(FAR struct service_manager_s *sm)
           free(s->argv[i]);
         }
 
+      free(s->console);
       list_delete(&s->node);
       free(s);
     }
@@ -249,3 +250,65 @@ void test_nxinit_service_args_max_boundary(FAR void **state)
 
 #undef NARGS_AT_LIMIT
 }
+
+/****************************************************************************
+ * Name: test_nxinit_service_console_option
+ *
+ * Description:
+ *   The "console" option flags the service with SVC_CONSOLE.  Without an
+ *   argument the default console device is used (console == NULL); with an
+ *   argument the device name is duplicated into the service, since the
+ *   parser reuses its line buffer for the next line.
+ ****************************************************************************/
+
+void test_nxinit_service_console_option(FAR void **state)
+{
+  struct service_manager_s sm;
+  struct parser_s parser =
+    {
+      "service", init_service_parse, init_service_check, &sm
+    };
+
+  char decl1[] = "service console1 /bin/sh";
+  char opt_default[] = "  console";
+  char decl2[] = "service console2 /bin/sh";
+  char opt_device[] = "  console /dev/ttyACM0";
+  char decl3[] = "service plain /bin/sh";
+  FAR struct service_s *s;
+
+  service_manager_init(&sm);
+
+  /* "console" without an argument: flagged, default device. */
+
+  assert_int_equal(init_service_parse(&parser, true, decl1), 0);
+  assert_int_equal(init_service_parse(&parser, false, opt_default), 0);
+
+  s = list_last_entry(&sm.services, struct service_s, node);
+  assert_int_equal(s->flags & SVC_CONSOLE, SVC_CONSOLE);
+  assert_null(s->console);
+
+  /* "console <device>": flagged, device duplicated (not aliased into the
+   * caller's line buffer, which is reused for the next line).
+   */
+
+  assert_int_equal(init_service_parse(&parser, true, decl2), 0);
+  assert_int_equal(init_service_parse(&parser, false, opt_device), 0);
+
+  s = list_last_entry(&sm.services, struct service_s, node);
+  assert_int_equal(s->flags & SVC_CONSOLE, SVC_CONSOLE);
+  assert_non_null(s->console);
+  assert_string_equal(s->console, "/dev/ttyACM0");
+  assert_ptr_not_equal(s->console, opt_device + 10);
+
+  /* A service without the option keeps its stdio untouched. */
+
+  assert_int_equal(init_service_parse(&parser, true, decl3), 0);
+
+  s = list_last_entry(&sm.services, struct service_s, node);
+  assert_int_equal(s->flags & SVC_CONSOLE, 0);
+  assert_null(s->console);
+
+  assert_int_equal(init_service_check(&parser), 0);
+
+  service_manager_free_all(&sm);
+}