posix: Fix tst-spawn6 terminal handling (BZ #28853)

  The test changes the current foreground process group, which might
break testing depending of how the make check is issued.  For instance:

  nohup make -j1 test t=posix/tst-spawn6 | less

Will set 'make' and 'less' to be in the foreground process group in
the current session.  When tst-spawn6 new child takes over it becomes
the foreground process and 'less' is stopped and backgrounded which
interrupts the 'make check' command.

To fix it a pseudo-terminal is allocated, the test starts in new
session (so there is no controlling terminal associated), and the
pseudo-terminal is set as the controlling one (similar to what
login_tty does).

Checked on x86_64-linux-gnu.
---
 posix/tst-spawn6.c | 62 ++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 51 insertions(+), 11 deletions(-)
  

On 2/2/22 16:59, Adhemerval Zanella wrote:
> The test changes the current foreground process group, which might
> break testing depending of how the make check is issued.  For instance:
> 
>   nohup make -j1 test t=posix/tst-spawn6 | less
> 
> Will set 'make' and 'less' to be in the foreground process group in
> the current session.  When tst-spawn6 new child takes over it becomes
> the foreground process and 'less' is stopped and backgrounded which
> interrupts the 'make check' command.
> 
> To fix it a pseudo-terminal is allocated, the test starts in new
> session (so there is no controlling terminal associated), and the
> pseudo-terminal is set as the controlling one (similar to what
> login_tty does).
> 
> Checked on x86_64-linux-gnu.

OK for glibc 2.35, and this fixes the test issues reported in bug 28853.

Tested on x86_64.

Tested-by: Carlos O'Donell <carlos@redhat.com>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

> ---
>  posix/tst-spawn6.c | 62 ++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 51 insertions(+), 11 deletions(-)
> 
> diff --git a/posix/tst-spawn6.c b/posix/tst-spawn6.c
> index 911e90a461..044abd8535 100644
> --- a/posix/tst-spawn6.c
> +++ b/posix/tst-spawn6.c
> @@ -29,7 +29,14 @@
>  #include <support/check.h>
>  #include <support/xunistd.h>
>  #include <sys/wait.h>
> +#include <sys/ioctl.h>
>  #include <stdlib.h>
> +#include <termios.h>
> +
> +#ifndef PATH_MAX
> +# define PATH_MAX 1024
> +#endif
> +static char ptmxpath[PATH_MAX];

OK.

>  
>  static int
>  handle_restart (const char *argv1, const char *argv2)
> @@ -115,7 +122,7 @@ run_subprogram (int argc, char *argv[], const posix_spawnattr_t *attr,
>  }
>  
>  static int
> -do_test (int argc, char *argv[])
> +run_test (int argc, char *argv[])
>  {
>    /* We must have either:
>       - four parameters left if called initially:
> @@ -127,16 +134,7 @@ do_test (int argc, char *argv[])
>         + --setgrpr             optional
>     */
>  
> -  if (restart)
> -    return handle_restart (argv[1], argv[2]);
> -
> -  int tcfd = open64 (_PATH_TTY, O_RDONLY, 0600);
> -  if (tcfd == -1)
> -    {
> -      if (errno == ENXIO)
> -	FAIL_UNSUPPORTED ("terminal not available, skipping test");
> -      FAIL_EXIT1 ("open64 (\"%s\", 0x%x, 0600): %m", _PATH_TTY, O_RDONLY);
> -    }
> +  int tcfd = xopen (ptmxpath, O_RDONLY, 0600);
>  
>    /* Check setting the controlling terminal without changing the group.  */
>    {
> @@ -198,5 +196,47 @@ do_test (int argc, char *argv[])
>    return 0;
>  }
>  
> +static int
> +do_test (int argc, char *argv[])
> +{
> +  if (restart)
> +    return handle_restart (argv[1], argv[2]);
> +

OK. In hindsight I think this can all be simplified using forkpty().

> +  pid_t pid = xfork ();
> +  if (pid == 0)
> +    {
> +      /* Create a pseudo-terminal to avoid interfering with the one using by
> +	 test itself, creates a new session (so there is no controlling
> +	 terminal), and set the pseudo-terminal as the controlling one.  */
> +      int ptmx = posix_openpt (0);
> +      if (ptmx == -1)
> +	{
> +	  if (errno == ENXIO)
> +	    FAIL_UNSUPPORTED ("terminal not available, skipping test");
> +	  FAIL_EXIT1 ("posix_openpt (0): %m");
> +	}
> +      TEST_VERIFY_EXIT (grantpt (ptmx) == 0);
> +      TEST_VERIFY_EXIT (unlockpt (ptmx) == 0);
> +
> +      TEST_VERIFY_EXIT (setsid () != -1);
> +      TEST_VERIFY_EXIT (ioctl (ptmx, TIOCSCTTY, NULL) == 0);
> +      while (dup2 (ptmx, STDIN_FILENO) == -1 && errno == EBUSY)
> +	;
> +      while (dup2 (ptmx, STDOUT_FILENO) == -1 && errno == EBUSY)
> +	;
> +      while (dup2 (ptmx, STDERR_FILENO) == -1 && errno == EBUSY)
> +	;

OK. This connects to the ptm side of the terminal.


> +      TEST_VERIFY_EXIT (ptsname_r (ptmx, ptmxpath, sizeof ptmxpath) == 0);

OK. This is OK as-is, but it fills ptmxpath with the pts side of the ptm/pts pair. So we end
up operating on the pts side, but I think that's fine because it's the terminal that matters.

> +      xclose (ptmx);
> +
> +      run_test (argc, argv);
> +      _exit (0);
> +    }
> +  int status;
> +  xwaitpid (pid, &status, 0);
> +  TEST_VERIFY (WIFEXITED (status));
> +  exit (0);
> +}
> +
>  #define TEST_FUNCTION_ARGV do_test
>  #include <support/test-driver.c>