common: New flags for gnupg_spawn_process

* common/exechelp.h (GNUPG_SPAWN_KEEP_STDIN): New.
(GNUPG_SPAWN_KEEP_STDOUT): New.
(GNUPG_SPAWN_KEEP_STDERR): New.
* common/exechelp-posix.c (do_exec): Add arg flags and implement new
flags.
* common/exechelp-w32.c (gnupg_spawn_process): Implement new flags.

common/exechelp-posix.c

@@ -276,16 +276,21 @@ get_all_open_fds (void)
 static void
 do_exec (const char *pgmname, const char *argv[],
          int fd_in, int fd_out, int fd_err,
-         int *except, void (*preexec)(void) )
+         int *except, void (*preexec)(void), unsigned int flags)
 {
   char **arg_list;
   int i, j;
   int fds[3];
+  int nodevnull[3];
 
   fds[0] = fd_in;
   fds[1] = fd_out;
   fds[2] = fd_err;
 
+  nodevnull[0] = !!(flags & GNUPG_SPAWN_KEEP_STDIN);
+  nodevnull[1] = !!(flags & GNUPG_SPAWN_KEEP_STDOUT);
+  nodevnull[2] = !!(flags & GNUPG_SPAWN_KEEP_STDERR);
+
   /* Create the command line argument array.  */
   i = 0;
   if (argv)
@@ -304,7 +309,9 @@ do_exec (const char *pgmname, const char *argv[],
   /* Assign /dev/null to unused FDs. */
   for (i=0; i <= 2; i++)
     {
-      if (fds[i] == -1 )
+      if (nodevnull[i])
+        continue;
+      if (fds[i] == -1)
         {
           fds[i] = open ("/dev/null", i? O_WRONLY : O_RDONLY);
           if (fds[i] == -1)
@@ -316,6 +323,8 @@ do_exec (const char *pgmname, const char *argv[],
   /* Connect the standard files.  */
   for (i=0; i <= 2; i++)
     {
+      if (nodevnull[i])
+        continue;
       if (fds[i] != i && dup2 (fds[i], i) == -1)
         log_fatal ("dup2 std%s failed: %s\n",
                    i==0?"in":i==1?"out":"err", strerror (errno));
@@ -525,7 +534,7 @@ gnupg_spawn_process (const char *pgmname, const char *argv[],
       es_fclose (outfp);
       es_fclose (errfp);
       do_exec (pgmname, argv, inpipe[0], outpipe[1], errpipe[1],
-               except, preexec);
+               except, preexec, flags);
       /*NOTREACHED*/
     }
 
@@ -575,7 +584,7 @@ gnupg_spawn_process_fd (const char *pgmname, const char *argv[],
     {
       gcry_control (GCRYCTL_TERM_SECMEM);
       /* Run child. */
-      do_exec (pgmname, argv, infd, outfd, errfd, NULL, NULL);
+      do_exec (pgmname, argv, infd, outfd, errfd, NULL, NULL, 0);
       /*NOTREACHED*/
     }
 
@@ -874,7 +883,7 @@ gnupg_spawn_process_detached (const char *pgmname, const char *argv[],
         for (i=0; envp[i]; i++)
           putenv (xstrdup (envp[i]));
 
-      do_exec (pgmname, argv, -1, -1, -1, NULL, NULL);
+      do_exec (pgmname, argv, -1, -1, -1, NULL, NULL, 0);
 
       /*NOTREACHED*/
     }

common/exechelp-w32.c

@@ -544,11 +544,14 @@ gnupg_spawn_process (const char *pgmname, const char *argv[],
     return err;
 
   if (inpipe[0] == INVALID_HANDLE_VALUE)
-    nullhd[0] = w32_open_null (0);
+    nullhd[0] = ((flags & GNUPG_SPAWN_KEEP_STDIN)?
+                 GetStdHandle (STD_INPUT_HANDLE) : w32_open_null (0));
   if (outpipe[1] == INVALID_HANDLE_VALUE)
-    nullhd[1] = w32_open_null (1);
+    nullhd[1] = ((flags & GNUPG_SPAWN_KEEP_STDOUT)?
+                 GetStdHandle (STD_OUTPUT_HANDLE) : w32_open_null (1));
   if (errpipe[1] == INVALID_HANDLE_VALUE)
-    nullhd[2] = w32_open_null (1);
+    nullhd[2] = ((flags & GNUPG_SPAWN_KEEP_STDOUT)?
+                 GetStdHandle (STD_ERROR_HANDLE) : w32_open_null (1));
 
   /* Start the process.  Note that we can't run the PREEXEC function
      because this might change our own environment. */

common/exechelp.h

@@ -71,7 +71,9 @@ gpg_error_t gnupg_create_pipe (int filedes[2]);
 #define GNUPG_SPAWN_NONBLOCK   16
 #define GNUPG_SPAWN_RUN_ASFW   64
 #define GNUPG_SPAWN_DETACHED  128
-
+#define GNUPG_SPAWN_KEEP_STDIN   256
+#define GNUPG_SPAWN_KEEP_STDOUT  512
+#define GNUPG_SPAWN_KEEP_STDERR 1024
 
 /* Fork and exec the program PGMNAME.
 
@@ -117,6 +119,12 @@ gpg_error_t gnupg_create_pipe (int filedes[2]);
           the child.  Note that due to unknown problems this actually
           allows SetForegroundWindow for all children of this process.
 
+   GNUPG_SPAWN_KEEP_STDIN
+   GNUPG_SPAWN_KEEP_STDOUT
+   GNUPG_SPAWN_KEEP_STDERR
+          Do not assign /dev/null to a non-required standard file
+          descriptor.
+
  */
 gpg_error_t
 gnupg_spawn_process (const char *pgmname, const char *argv[],