posix: Add terminal control setting support for posix_spawn

Currently there is no proper way to set the controlling terminal through
posix_spawn() in race free manner [1].  This forces shell implementations
to keep using fork()+exec() when launching background process groups,
even when using posix_spawn() yields better performance.

This patch adds a new GNU extension so the creating process can
configure the creating process terminal group.  This is done with a new
flag, POSIX_SPAWN_TCSETPGROUP, along with two new attribute functions,
posix_spawnattr_tcsetpgrp_np(), and posix_spawnattr_tcgetpgrp_np().
The function sets a new attribute, spawn-tcgroupfd, that references to
the controlling terminal.

The controlling terminal is set after the spawn-pgroup attribute, and
uses the spawn-tcgroupfd along with current creating process group
(so it is composable with POSIX_SPAWN_SETPGROUP).

To create a process and set the controlling terminal, one can use the
following sequence:

    posix_spawnattr_t attr;
    posix_spawnattr_init (&attr);
    posix_spawnattr_setflags (&attr, POSIX_SPAWN_TCSETPGROUP);
    posix_spawnattr_tcsetpgrp_np (&attr, tcfd);

If the idea is also to create a new process groups:

    posix_spawnattr_t attr;
    posix_spawnattr_init (&attr);
    posix_spawnattr_setflags (&attr, POSIX_SPAWN_TCSETPGROUP
				     | POSIX_SPAWN_SETPGROUP);
    posix_spawnattr_tcsetpgrp_np (&attr, tcfd);
    posix_spawnattr_setpgroup (&attr, 0);

The controlling terminal file descriptor is ignored if the new flag is
not set.

This interface is slight different than the one provided by QNX [2],
which it only provides the POSIX_SPAWN_TCSETPGROUP flag.  The QNX
documentation is not on how the controlling terminal is obtained
not how it iteracts with POSIX_SPAWN_SETPGROUP.  Since a glibc
implementation is library based, I moving the controlling terminal
open to the caller should be more straighforward since it mimics the
tcsetpgrp(), and allow less error handling by posix_spawn().

Checked on x86_64-linux-gnu and i686-linux-gnu.

[1] ksh93/ksh#79
[2] https://www.qnx.com/developers/docs/7.0.0/index.html#com.qnx.doc.neutrino.lib_ref/topic/p/posix_spawn.html

NEWS

@@ -60,6 +60,11 @@ Major new features:
   to call async-signal-safe functions (such as raise or execve).  This function
   is currently a GNU extension.
 
+* The functions posix_spawnattr_tcsetpgrp_np and posix_spawnattr_tcgetpgrp_np
+  have benn added, enabling posix_spawn and posix_spawnp to set the
+  controlling terminal in the new process in a non race manner.  These
+  functions are GNU extensions.
+
 Deprecated and removed features, and other changes affecting compatibility:
 
 * The function pthread_mutex_consistent_np has been deprecated; programs

include/unistd.h

@@ -171,7 +171,10 @@ extern int __ftruncate64 (int __fd, __off64_t __length) attribute_hidden;
 extern int __truncate (const char *path, __off_t __length);
 extern void *__sbrk (intptr_t __delta);
 libc_hidden_proto (__sbrk)
-
+extern int __tcsetpgrp (int fd, __pid_t pgrp);
+libc_hidden_proto (__tcsetpgrp)
+extern pid_t __getpgrp (void);
+libc_hidden_proto (__getpgrp);
 
 /* This variable is set nonzero at startup if the process's effective
    IDs differ from its real IDs, or it is otherwise indicated that

posix/Makefile

@@ -63,6 +63,7 @@ routines :=								      \
 	spawnattr_getpgroup spawnattr_setpgroup spawn spawnp spawni	      \
 	spawnattr_getsigmask spawnattr_getschedpolicy spawnattr_getschedparam \
 	spawnattr_setsigmask spawnattr_setschedpolicy spawnattr_setschedparam \
+	spawnattr_tcgetpgrp spawnattr_tcsetpgrp				      \
 	posix_madvise							      \
 	get_child_max sched_cpucount sched_cpualloc sched_cpufree \
 	streams-compat \
@@ -106,7 +107,7 @@ tests		:= test-errno tstgetopt testfnm runtests runptests \
 		   tst-sysconf-empty-chroot tst-glob_symlinks tst-fexecve \
 		   tst-glob-tilde test-ssize-max tst-spawn4 bug-regex37 \
 		   bug-regex38 tst-regcomp-truncated tst-spawn-chdir \
-		   tst-wordexp-nocmd tst-execveat
+		   tst-wordexp-nocmd tst-execveat tst-spawn5
 
 # Test for the glob symbol version that was replaced in glibc 2.27.
 ifeq ($(have-GLIBC_2.26)$(build-shared),yesyes)
@@ -275,6 +276,7 @@ tst-exec-ARGS = -- $(host-test-program-cmd)
 tst-exec-static-ARGS = $(tst-exec-ARGS)
 tst-execvpe5-ARGS = -- $(host-test-program-cmd)
 tst-spawn-ARGS = -- $(host-test-program-cmd)
+tst-spawn5-ARGS = -- $(host-test-program-cmd)
 tst-spawn-static-ARGS = $(tst-spawn-ARGS)
 tst-dir-ARGS = `pwd` `cd $(common-objdir)/$(subdir); pwd` `cd $(common-objdir); pwd` $(objpfx)tst-dir
 tst-chmod-ARGS = $(objdir)

posix/Versions

@@ -154,6 +154,8 @@ libc {
   GLIBC_2.34 {
     _Fork;
     execveat;
+    posix_spawnattr_tcgetpgrp_np;
+    posix_spawnattr_tcsetpgrp_np;
   }
   GLIBC_PRIVATE {
     __libc_fork; __libc_pread; __libc_pwrite;

posix/spawn.h

@@ -34,7 +34,8 @@ typedef struct
   sigset_t __ss;
   struct sched_param __sp;
   int __policy;
-  int __pad[16];
+  int __ctty_fd;
+  int __pad[15];
 } posix_spawnattr_t;
 
 
@@ -59,6 +60,7 @@ typedef struct
 #ifdef __USE_GNU
 # define POSIX_SPAWN_USEVFORK		0x40
 # define POSIX_SPAWN_SETSID		0x80
+# define POSIX_SPAWN_TCSETPGROUP	0x100
 #endif
 
 
@@ -166,6 +168,18 @@ extern int posix_spawnattr_setschedparam (posix_spawnattr_t *__restrict __attr,
 					  __restrict __schedparam)
      __THROW __nonnull ((1, 2));
 
+#ifdef __USE_GNU
+/* Make the spawned process the foreground process group on the terminal
+   associated with FD (which must be a controlling terminal, and still be
+   associated with its session).  */
+extern int posix_spawnattr_tcsetpgrp_np (posix_spawnattr_t *__attr, int fd)
+     __THROW __nonnull ((1));
+
+/* Return the associated terminal FD in the attribute structure.  */
+extern int posix_spawnattr_tcgetpgrp_np (const posix_spawnattr_t *
+					 __restrict __attr, int *fd)
+     __THROW __nonnull ((1, 2));
+#endif
 
 /* Initialize data structure for file attribute for `spawn' call.  */
 extern int posix_spawn_file_actions_init (posix_spawn_file_actions_t *

posix/spawnattr_setflags.c

@@ -26,7 +26,8 @@
 		   | POSIX_SPAWN_SETSCHEDPARAM				      \
 		   | POSIX_SPAWN_SETSCHEDULER				      \
 		   | POSIX_SPAWN_SETSID					      \
-		   | POSIX_SPAWN_USEVFORK)
+		   | POSIX_SPAWN_USEVFORK				      \
+		   | POSIX_SPAWN_TCSETPGROUP)
 
 /* Store flags in the attribute structure.  */
 int

posix/spawnattr_tcgetpgrp.c

@@ -0,0 +1,26 @@
+/* Get the controlling terminal option.
+   Copyright (C) 2000-2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <spawn.h>
+
+int
+posix_spawnattr_tcgetpgrp_np (const posix_spawnattr_t *attr, int *fd)
+{
+  *fd = attr->__ctty_fd;
+  return 0;
+}

posix/spawnattr_tcsetpgrp.c

@@ -0,0 +1,26 @@
+/* Set the controlling terminal option.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <spawn.h>
+
+int
+posix_spawnattr_tcsetpgrp_np (posix_spawnattr_t *attr, int fd)
+{
+  attr->__ctty_fd = fd;
+  return 0;
+}

posix/tst-spawn5.c

@@ -0,0 +1,167 @@
+/* Check posix_spawn set controlling terminal extension.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <getopt.h>
+#include <intprops.h>
+#include <paths.h>
+#include <spawn.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/xunistd.h>
+#include <sys/wait.h>
+
+static int
+handle_restart (const char *argv1)
+{
+  bool setpgrp = strcmp (argv1, "setgrpr") == 0;
+  int fd = xopen (_PATH_TTY, O_RDONLY, 0600);
+
+  /* If process group is not changed (POSIX_SPAWN_SETPGROUP), then check
+     the creating process one, otherwise check against the process group
+     itself.  */
+  pid_t pgrp;
+  if (!setpgrp)
+    TEST_COMPARE (sscanf (argv1, "%d", &pgrp), 1);
+  else
+    pgrp = getpgrp ();
+  TEST_COMPARE (tcgetpgrp (fd), pgrp);
+
+  xclose (fd);
+  return 0;
+}
+
+static int restart;
+#define CMDLINE_OPTIONS \
+  { "restart", no_argument, &restart, 1 },
+
+static void
+run_subprogram (int argc, char *argv[], const posix_spawnattr_t *attr,
+		int exp_err)
+{
+  short int flags;
+  TEST_COMPARE (posix_spawnattr_getflags (attr, &flags), 0);
+  bool setpgrp = flags & POSIX_SPAWN_SETPGROUP;
+
+  char *spargv[9];
+  char pgrp[INT_STRLEN_BOUND (pid_t)];
+
+  int i = 0;
+  for (; i < argc - 1; i++)
+    spargv[i] = argv[i + 1];
+  spargv[i++] = (char *) "--direct";
+  spargv[i++] = (char *) "--restart";
+  if (setpgrp)
+    spargv[i++] = (char *) "setgrpr";
+  else
+    {
+      snprintf (pgrp, sizeof pgrp, "%d", getpgrp ());
+      spargv[i++] = pgrp;
+    }
+  spargv[i] = NULL;
+
+  pid_t pid;
+  TEST_COMPARE (posix_spawn (&pid, argv[1], NULL, attr, spargv, environ),
+		exp_err);
+  if (exp_err != 0)
+    return;
+
+  int status;
+  TEST_COMPARE (xwaitpid (pid, &status, WUNTRACED), pid);
+  TEST_VERIFY (WIFEXITED (status));
+  TEST_VERIFY (!WIFSTOPPED (status));
+  TEST_VERIFY (!WIFSIGNALED (status));
+  TEST_COMPARE (WEXITSTATUS (status), 0);
+}
+
+static int
+do_test (int argc, char *argv[])
+{
+  /* We must have either:
+     - One our fource parameters left if called initially:
+       + path to ld.so         optional
+       + "--library-path"      optional
+       + the library path      optional
+       + the application name
+     - six parameters left if called through re-execution:
+       + --setgrpr             optional
+   */
+
+  if (restart)
+    return handle_restart (argv[1]);
+
+  int tcfd = xopen (_PATH_TTY, O_RDONLY, 0600);
+
+  /* Check getters and setters.  */
+  {
+    posix_spawnattr_t attr;
+    TEST_COMPARE (posix_spawnattr_init (&attr), 0);
+    TEST_COMPARE (posix_spawnattr_tcsetpgrp_np (&attr, tcfd), 0);
+
+    int fd;
+    TEST_COMPARE (posix_spawnattr_tcgetpgrp_np (&attr, &fd), 0);
+    TEST_COMPARE (tcfd, fd);
+  }
+
+  /* Check setting the controlling terminal without changing the group.  */
+  {
+    posix_spawnattr_t attr;
+    TEST_COMPARE (posix_spawnattr_init (&attr), 0);
+    TEST_COMPARE (posix_spawnattr_setflags (&attr, POSIX_SPAWN_TCSETPGROUP),
+		  0);
+    TEST_COMPARE (posix_spawnattr_tcsetpgrp_np (&attr, tcfd), 0);
+
+    run_subprogram (argc, argv, &attr, 0);
+  }
+
+  /* Check setting both the controlling terminal and the create a new process
+     group.  */
+  {
+    posix_spawnattr_t attr;
+    TEST_COMPARE (posix_spawnattr_init (&attr), 0);
+    TEST_COMPARE (posix_spawnattr_setflags (&attr, POSIX_SPAWN_TCSETPGROUP
+						   | POSIX_SPAWN_SETPGROUP),
+		  0);
+    TEST_COMPARE (posix_spawnattr_setpgroup (&attr, 0), 0);
+    TEST_COMPARE (posix_spawnattr_tcsetpgrp_np (&attr, tcfd), 0);
+
+    run_subprogram (argc, argv, &attr, 0);
+  }
+
+  /* Trying to set the controlling terminal after a setsid() incurs in a ENOTTY
+     from tcsetpgrp.  */
+  {
+    posix_spawnattr_t attr;
+    TEST_COMPARE (posix_spawnattr_init (&attr), 0);
+    TEST_COMPARE (posix_spawnattr_setflags (&attr, POSIX_SPAWN_TCSETPGROUP
+						   | POSIX_SPAWN_SETSID), 0);
+    TEST_COMPARE (posix_spawnattr_tcsetpgrp_np (&attr, tcfd), 0);
+
+    run_subprogram (argc, argv, &attr, ENOTTY);
+  }
+
+  xclose (tcfd);
+
+  return 0;
+}
+
+#define TEST_FUNCTION_ARGV do_test
+#include <support/test-driver.c>

sysdeps/generic/libc.abilist

@@ -0,0 +1,2 @@
+GLIBC_2.34 posix_spawnattr_tcgetpgrp_np F
+GLIBC_2.34 posix_spawnattr_tcsetpgrp_np F

sysdeps/mach/hurd/i386/libc.abilist

@@ -2229,6 +2229,8 @@ GLIBC_2.34 dlopen F
 GLIBC_2.34 dlsym F
 GLIBC_2.34 dlvsym F
 GLIBC_2.34 execveat F
+GLIBC_2.34 posix_spawnattr_tcgetpgrp_np F
+GLIBC_2.34 posix_spawnattr_tcsetpgrp_np F
 GLIBC_2.34 shm_open F
 GLIBC_2.34 shm_unlink F
 GLIBC_2.34 timespec_getres F

sysdeps/mach/hurd/spawni.c

@@ -390,6 +390,19 @@ __spawni (pid_t *pid, const char *file,
   if (!err && (flags & POSIX_SPAWN_SETPGROUP) != 0)
     err = __proc_setpgrp (proc, new_pid, attrp->__pgrp);
 
+  /* Set the controlling terminal.  */
+  if (!err && (flags & POSIX_SPAWN_TCSETPGROUP) != 0)
+    {
+      pid_t pgrp;
+      /* Check if it is possible to avoid an extra syscall.  */
+      if ((attrp->__flags & POSIX_SPAWN_SETPGROUP) != 0 && attrp->__pgrp != 0)
+	pgrp = attrp->__pgrp;
+      else
+	err = __proc_getpgrp (proc, new_pid, &pgrp);
+      if (!err)
+        err = __tcsetpgrp (attrp->__tcpgrp, pgrp);
+    }
+
   /* Set the effective user and group IDs.  */
   if (!err && (flags & POSIX_SPAWN_RESETIDS) != 0)
     {

sysdeps/unix/bsd/tcsetpgrp.c

@@ -22,7 +22,9 @@
 
 /* Set the foreground process group ID of FD set PGRP_ID.  */
 int
-tcsetpgrp (int fd, pid_t pgrp_id)
+__tcsetpgrp (int fd, pid_t pgrp_id)
 {
   return __ioctl (fd, TIOCSPGRP, &pgrp_id);
 }
+weak_alias (__tcsetpgrp, tcsetpgrp)
+libc_hidden_def (__tcsetpgrp)

sysdeps/unix/sysv/linux/aarch64/libc.abilist

@@ -2433,6 +2433,8 @@ GLIBC_2.34 mtx_lock F
 GLIBC_2.34 mtx_timedlock F
 GLIBC_2.34 mtx_trylock F
 GLIBC_2.34 mtx_unlock F
+GLIBC_2.34 posix_spawnattr_tcgetpgrp_np F
+GLIBC_2.34 posix_spawnattr_tcsetpgrp_np F
 GLIBC_2.34 pthread_attr_getaffinity_np F
 GLIBC_2.34 pthread_attr_getguardsize F
 GLIBC_2.34 pthread_attr_getstack F

sysdeps/unix/sysv/linux/alpha/libc.abilist

@@ -2532,6 +2532,8 @@ GLIBC_2.34 mtx_lock F
 GLIBC_2.34 mtx_timedlock F
 GLIBC_2.34 mtx_trylock F
 GLIBC_2.34 mtx_unlock F
+GLIBC_2.34 posix_spawnattr_tcgetpgrp_np F
+GLIBC_2.34 posix_spawnattr_tcsetpgrp_np F
 GLIBC_2.34 pthread_attr_getaffinity_np F
 GLIBC_2.34 pthread_attr_getguardsize F
 GLIBC_2.34 pthread_attr_getstack F

sysdeps/unix/sysv/linux/arc/libc.abilist

@@ -2192,6 +2192,8 @@ GLIBC_2.34 mtx_lock F
 GLIBC_2.34 mtx_timedlock F
 GLIBC_2.34 mtx_trylock F
 GLIBC_2.34 mtx_unlock F
+GLIBC_2.34 posix_spawnattr_tcgetpgrp_np F
+GLIBC_2.34 posix_spawnattr_tcsetpgrp_np F
 GLIBC_2.34 pthread_attr_getaffinity_np F
 GLIBC_2.34 pthread_attr_getguardsize F
 GLIBC_2.34 pthread_attr_getstack F