GNU bug report logs - #52835
[PATCH 0/2] Fix spawning a child not setting standard fds properly

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From: Josselin Poiret <dev <at> jpoiret.xyz>
To: Ludovic Courtès <ludo <at> gnu.org>
Cc: 52835 <at> debbugs.gnu.org, Timothy Sample <samplet <at> ngyro.com>, Josselin Poiret <dev <at> jpoiret.xyz>
Subject: bug#52835: [PATCH v6 1/3] Add spawn*.
Date: Thu, 22 Dec 2022 13:49:08 +0100

* libguile/posix.c: Include spawn.h from Gnulib.
(do_spawn, scm_spawn_process): New functions.
---
 libguile/posix.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++
 libguile/posix.h |  2 ++
 2 files changed, 83 insertions(+)

diff --git a/libguile/posix.c b/libguile/posix.c
index b5352c2c4..e92625483 100644
--- a/libguile/posix.c
+++ b/libguile/posix.c
@@ -33,6 +33,7 @@
 #include <sys/types.h>
 #include <uniconv.h>
 #include <unistd.h>
+#include <spawn.h>
 
 #ifdef HAVE_SCHED_H
 # include <sched.h>
@@ -1426,6 +1427,86 @@ start_child (const char *exec_file, char **exec_argv,
 }
 #endif
 
+static int
+do_spawn (char *exec_file, char **exec_argv, char **exec_env, int in, int out, int err)
+{
+  int pid = -1;
+
+  posix_spawn_file_actions_t actions;
+  posix_spawnattr_t *attrp = NULL;
+
+  int max_fd = 1024;
+
+#if defined (HAVE_GETRLIMIT) && defined (RLIMIT_NOFILE)
+  {
+    struct rlimit lim = { 0, 0 };
+    if (getrlimit (RLIMIT_NOFILE, &lim) == 0)
+      max_fd = lim.rlim_cur;
+  }
+#endif
+
+  posix_spawn_file_actions_init (&actions);
+
+  int free_fd_slots = 0;
+  int fd_slot[3];
+
+  for (int fdnum = 3;free_fd_slots < 3 && fdnum < max_fd;fdnum++)
+    {
+      if (fdnum != in && fdnum != out && fdnum != err)
+        {
+          fd_slot[free_fd_slots] = fdnum;
+          free_fd_slots++;
+        }
+    }
+
+  /* Move the fds out of the way, so that duplicate fds or fds equal
+     to 0, 1, 2 don't trample each other */
+
+  posix_spawn_file_actions_adddup2 (&actions, in, fd_slot[0]);
+  posix_spawn_file_actions_adddup2 (&actions, out, fd_slot[1]);
+  posix_spawn_file_actions_adddup2 (&actions, err, fd_slot[2]);
+  posix_spawn_file_actions_adddup2 (&actions, fd_slot[0], 0);
+  posix_spawn_file_actions_adddup2 (&actions, fd_slot[1], 1);
+  posix_spawn_file_actions_adddup2 (&actions, fd_slot[2], 2);
+
+  while (--max_fd > 2)
+    posix_spawn_file_actions_addclose (&actions, max_fd);
+
+  if (posix_spawnp (&pid, exec_file, &actions, attrp, exec_argv, environ) != 0)
+      return -1;
+
+  return pid;
+}
+
+SCM_DEFINE (scm_spawn_process, "spawn*", 5, 0, 0,
+           (SCM prog, SCM args, SCM in, SCM out, SCM err),
+"Spawns a new child process executing @var{prog} with arguments\n"
+"@var{args}, with its standard input, output and error file descriptors\n"
+"set to @var{in}, @var{out}, @var{err}.")
+#define FUNC_NAME s_scm_spawn_process
+{
+  int pid;
+  char *exec_file;
+  char **exec_argv;
+  char **exec_env = environ;
+
+  exec_file = scm_to_locale_string (prog);
+  exec_argv = scm_i_allocate_string_pointers (args);
+
+  pid = do_spawn (exec_file, exec_argv, exec_env,
+                  scm_to_int (in),
+                  scm_to_int (out),
+                  scm_to_int (err));
+
+  free (exec_file);
+
+  if (pid == -1)
+      SCM_SYSERROR;
+
+  return scm_from_int (pid);
+}
+#undef FUNC_NAME
+
 #ifdef HAVE_START_CHILD
 static SCM
 scm_piped_process (SCM prog, SCM args, SCM from, SCM to)
diff --git a/libguile/posix.h b/libguile/posix.h
index 6504eaea8..c2703f9ab 100644
--- a/libguile/posix.h
+++ b/libguile/posix.h
@@ -69,6 +69,8 @@ SCM_API SCM scm_tmpnam (void);
 SCM_API SCM scm_tmpfile (void);
 SCM_API SCM scm_open_pipe (SCM pipestr, SCM modes);
 SCM_API SCM scm_close_pipe (SCM port);
+SCM_API SCM scm_spawn_process (SCM prog, SCM args,
+                               SCM in, SCM out, SCM err);
 SCM_API SCM scm_system_star (SCM cmds);
 SCM_API SCM scm_utime (SCM object, SCM actime, SCM modtime,
                        SCM actimens, SCM modtimens, SCM flags);
-- 
2.38.1

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