posix_spawn_file_actions_add[f]chdir_np

[Bruno Haible]

Hi Corinna,

> Actually I had some spare time yesterday so I came up with an
> implementation of posix_spawn_file_actions_addchdir_np and
> posix_spawn_file_actions_addfchdir_np.  It's pretty straightforward:
> 
> https://cygwin.com/cgit/newlib-cygwin/commit/?id=7e03fc35f528

Yes, it's pretty straightforward on Unix-like platforms.

Note that there is a small inconsistency between implementations:
The manual page
https://man.freebsd.org/cgi/man.cgi?query=posix_spawn_file_actions_addfchdir_np&apropos=0&sektion=3&manpath=FreeBSD+13.2-RELEASE+and+Ports&arch=default&format=html
mentions that when the dirfd argument is negative, the
posix_spawn_file_actions_addfchdir function should fail with error EBADF.
musl libc, FreeBSD, macOS do this; glibc doesn't. Test program attached below.
Confirmed by looking at the source code:
- musl libc:
        if (fd < 0) return EBADF;
- FreeBSD:
        if (fildes < 0)
                return (EBADF);

> You can install the just building test release
> cygwin-3.5.0-0.287.g53f7fb20a064 via our installer, if you'd
> like to test it.
> 
> Actually... do you have a testcase readily available to share with us?

Indeed, I'm not likely to install test releases. (Due to the way I work
with my Windows VM, it's a bit clumsy to create a snapshot.) It's easier
for me to provide you a test case, with the unit tests from Gnulib.

I ran the command
  ./gnulib-tool --create-testdir --dir=../testdir-posix-spawn --single-configure \
     posix_spawn \
     posix_spawnattr_destroy \
     posix_spawnattr_getflags \
     posix_spawnattr_getpgroup \
     posix_spawnattr_getschedparam \
     posix_spawnattr_getschedpolicy \
     posix_spawnattr_getsigdefault \
     posix_spawnattr_getsigmask \
     posix_spawnattr_init \
     posix_spawnattr_setflags \
     posix_spawnattr_setpgroup \
     posix_spawnattr_setschedparam \
     posix_spawnattr_setschedpolicy \
     posix_spawnattr_setsigdefault \
     posix_spawnattr_setsigmask \
     posix_spawn_file_actions_addclose \
     posix_spawn_file_actions_adddup2 \
     posix_spawn_file_actions_addopen \
     posix_spawn_file_actions_addchdir \
     posix_spawn_file_actions_addfchdir \
     posix_spawn_file_actions_destroy \
     posix_spawn_file_actions_init \
     posix_spawnp

You can download the resulting tarball from
https://haible.de/bruno/gnu/testdir-posix-spawn.tar.gz .

When configuring it, set the environment variable
gl_cv_func_posix_spawnp_secure_exec=yes . This will prevent the
autoconfiguration from attempting to override the entire posix_spawn facility:
  $ env gl_cv_func_posix_spawnp_secure_exec=yes ./configure
Verify through
  $ grep REPLACE_POSIX_SPAWN config.status
that the values of REPLACE_POSIX_SPAWN and REPLACE_POSIX_SPAWNP are 0;
if they are 1, the output of 'configure' should reveal why.

Then build it:
  $ make
Verify through
  $ ls -l gllib/*.o
that no posix_spawn_*.o object file was built.

Then run
  $ make check
and it will run the unit tests against the Cygwin libc. It's likely
that you will see 1 test failure (test-posix_spawnp-script); but
other than that, there ought to be no test failures.

Bruno


================ Test program for EBADF check ================
#include <spawn.h>

int
main (void)
{
  posix_spawn_file_actions_t actions;

  if (posix_spawn_file_actions_init (&actions) != 0)
    return 1;

  if (posix_spawn_file_actions_addfchdir_np (&actions, -3) != 0)
    return 2;
  else
    return 3;
}