system/popen: support no-shell mode via posix_spawnp

When NSH_LIBRARY is not available, dpopen()/popen() can still execute
commands by splitting the command string by whitespace and calling
posix_spawnp() directly.  Shell syntax (pipes, redirects, globbing)
is not supported in this mode.

Add CONFIG_SYSTEM_POPEN_MAXARGUMENTS (default 7) to control the
argv array size for the no-shell path.

Remove the hard dependency on NSH_LIBRARY from SYSTEM_POPEN so the
feature can be used in minimal configurations without a shell.

Signed-off-by: cuiziwei <cuiziwei@xiaomi.com>

Author: cuiziweizw

system/popen/Kconfig

@@ -7,7 +7,7 @@ config SYSTEM_POPEN
 	bool "popen()/pclose()/dpopen()/dpclose() Functions"
 	default n
 	select SCHED_WAITPID
-	depends on NSH_LIBRARY && PIPES
+	depends on PIPES
 	---help---
 		Enable support for the popen(), pclose(), dpopen(), and
 		dpclose() interfaces.
@@ -20,16 +20,20 @@ config SYSTEM_POPEN
 		popen()/pclose() are thin wrappers around dpopen()/dpclose()
 		that additionally wrap the fd in a FILE stream.
 
-		Commands are executed through the NSH shell (sh -c command),
-		supporting full shell syntax including pipes, redirects,
-		and globbing.
+		When NSH is available (NSH_LIBRARY), commands are executed
+		through the shell (sh -c command), supporting full shell
+		syntax including pipes, redirects, and globbing.
+
+		When NSH is not available, commands are executed directly
+		via posix_spawnp(). The command string must be a simple
+		"program arg1 arg2" form without shell syntax.
 
 if SYSTEM_POPEN
 
 config SYSTEM_POPEN_SHPATH
 	string "Path to shell command"
 	default "/bin/sh"
-	depends on SYSTEM_NSH=m || BUILD_KERNEL
+	depends on (SYSTEM_NSH=m || BUILD_KERNEL) && NSH_LIBRARY
 	---help---
 		This is the full path to the program in a mounted file system that
 		implements the system() command.  That is, a program that starts the
@@ -53,4 +57,17 @@ config SYSTEM_POPEN_PRIORITY
 	---help---
 		The priority of the shell.
 
+config SYSTEM_POPEN_MAXARGUMENTS
+	int "Maximum number of command arguments (no-shell mode)"
+	default 7
+	depends on !NSH_LIBRARY
+	---help---
+		When NSH is not available, dpopen()/popen() splits the command
+		string by whitespace into an argv array.  This sets the maximum
+		number of arguments (excluding the program name and the
+		terminating NULL).
+
+		This is analogous to CONFIG_NSH_MAXARGUMENTS but applies
+		only to the no-shell path.
+
 endif

system/popen/dpopen.c

@@ -27,6 +27,7 @@
 #include <sys/wait.h>
 #include <sys/ioctl.h>
 #include <unistd.h>
+#include <string.h>
 #include <sched.h>
 #include <spawn.h>
 #include <debug.h>
@@ -37,7 +38,17 @@
 #  include <sys/socket.h>
 #endif
 
-#include "nshlib/nshlib.h"
+#ifdef CONFIG_NSH_LIBRARY
+#  include "nshlib/nshlib.h"
+#endif
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+#ifndef CONFIG_NSH_LIBRARY
+#  define DPOPEN_MAX_ARGV (CONFIG_SYSTEM_POPEN_MAXARGUMENTS + 1)
+#endif
 
 /****************************************************************************
  * Public Functions
@@ -58,6 +69,10 @@
  *   When NSH is available, commands are executed through the shell
  *   (sh -c command), supporting full shell syntax.
  *
+ *   When NSH is not available, the command is split by whitespace and
+ *   executed directly via posix_spawnp().  Shell syntax (pipes, redirects,
+ *   globbing) is not supported in this mode.
+ *
  * Input Parameters:
  *   command - The command string to execute
  *   oflag   - O_RDONLY to read child stdout, O_WRONLY to write child stdin,
@@ -74,7 +89,14 @@ int dpopen(FAR const char *command, int oflag, FAR pid_t *pid)
   struct sched_param param;
   posix_spawnattr_t attr;
   posix_spawn_file_actions_t file_actions;
+#ifdef CONFIG_NSH_LIBRARY
   FAR char *argv[4];
+#else
+  char cmdbuf[PATH_MAX];
+  FAR char *argv[DPOPEN_MAX_ARGV];
+  FAR char *saveptr;
+  int argc = 0;
+#endif
   int fd[2];
   int childfd;
   int parentfd;
@@ -224,21 +246,52 @@ int dpopen(FAR const char *command, int oflag, FAR pid_t *pid)
    * appropriately.
    */
 
+#ifdef CONFIG_NSH_LIBRARY
+  /* Shell mode: execute command through sh -c */
+
   argv[1] = "-c";
   argv[2] = (FAR char *)command;
   argv[3] = NULL;
 
-#ifdef CONFIG_SYSTEM_POPEN_SHPATH
+#  ifdef CONFIG_SYSTEM_POPEN_SHPATH
   argv[0] = CONFIG_SYSTEM_POPEN_SHPATH;
   errcode = posix_spawn(pid, argv[0], &file_actions,
                         &attr, argv, NULL);
-#else
+#  else
   *pid = task_spawn("dpopen", nsh_system, &file_actions,
                     &attr, argv + 1, NULL);
   if (*pid < 0)
     {
       errcode = -*pid;
     }
+#  endif
+#else
+  /* No-shell mode: split command and execute directly via posix_spawnp.
+   * The command must be in "program arg1 arg2" form -- no shell syntax.
+   */
+
+  if (strlcpy(cmdbuf, command, sizeof(cmdbuf)) >= sizeof(cmdbuf))
+    {
+      errcode = ENAMETOOLONG;
+      goto errout_with_actions;
+    }
+
+  do
+    {
+      argv[argc] = strtok_r(argc ? NULL : cmdbuf, " \t", &saveptr);
+    }
+  while (argv[argc] != NULL && ++argc < DPOPEN_MAX_ARGV - 1);
+
+  argv[argc] = NULL;
+
+  if (argc == 0)
+    {
+      errcode = EINVAL;
+      goto errout_with_actions;
+    }
+
+  errcode = posix_spawnp(pid, argv[0], &file_actions,
+                         &attr, argv, NULL);
 #endif
 
   if (errcode != 0)