[1/3] support: Add support_process_state_wait

  It allows parent process to wait for children state using a polling
strategy over procfs on Linux.  The polling is used over ptrace to
avoid the need to handle signals on the target pid and to handle some
system specific limitations (such as YAMA).

The polling has some limitations, such as resource consumption due
the procfs read in a loop and the lack of synchronization after the
state is obtained.

The interface idea is to simplify some sleep synchronization in waitid
tests.
---
 support/Makefile                    |   2 +
 support/process_state.h             |  41 +++++++++++
 support/support_process_state.c     |  89 ++++++++++++++++++++++++
 support/tst-support-process_state.c | 101 ++++++++++++++++++++++++++++
 4 files changed, 233 insertions(+)
 create mode 100644 support/process_state.h
 create mode 100644 support/support_process_state.c
 create mode 100644 support/tst-support-process_state.c
  

Ping.

On 20/11/2019 11:15, Adhemerval Zanella wrote:
> It allows parent process to wait for children state using a polling
> strategy over procfs on Linux.  The polling is used over ptrace to
> avoid the need to handle signals on the target pid and to handle some
> system specific limitations (such as YAMA).
> 
> The polling has some limitations, such as resource consumption due
> the procfs read in a loop and the lack of synchronization after the
> state is obtained.
> 
> The interface idea is to simplify some sleep synchronization in waitid
> tests.
> ---
>  support/Makefile                    |   2 +
>  support/process_state.h             |  41 +++++++++++
>  support/support_process_state.c     |  89 ++++++++++++++++++++++++
>  support/tst-support-process_state.c | 101 ++++++++++++++++++++++++++++
>  4 files changed, 233 insertions(+)
>  create mode 100644 support/process_state.h
>  create mode 100644 support/support_process_state.c
>  create mode 100644 support/tst-support-process_state.c
> 
> diff --git a/support/Makefile b/support/Makefile
> index 23c6d74627..b0d28200af 100644
> --- a/support/Makefile
> +++ b/support/Makefile
> @@ -56,6 +56,7 @@ libsupport-routines = \
>    support_format_hostent \
>    support_format_netent \
>    support_isolate_in_subprocess \
> +  support_process_state \
>    support_ptrace \
>    support_openpty \
>    support_paths \
> @@ -223,6 +224,7 @@ tests = \
>    tst-support_capture_subprocess \
>    tst-support_descriptors \
>    tst-support_format_dns_packet \
> +  tst-support-process_state \
>    tst-support_quote_blob \
>    tst-support_quote_string \
>    tst-support_record_failure \
> diff --git a/support/process_state.h b/support/process_state.h
> new file mode 100644
> index 0000000000..d616f0e3e6
> --- /dev/null
> +++ b/support/process_state.h
> @@ -0,0 +1,41 @@
> +/* Wait for process state.
> +   Copyright (C) 2019 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/>.  */
> +
> +#ifndef SUPPORT_PROCESS_STATE_H
> +#define SUPPORT_PROCESS_STATE_H
> +
> +#include <sys/types.h>
> +
> +enum process_state_t
> +{
> +  process_state_running      = 0x01,  /* R (running)  */
> +  process_state_sleeping     = 0x02,  /* S (sleeping)  */
> +  process_state_disk_sleep   = 0x04,  /* D (disk sleep)  */
> +  process_state_stopped      = 0x08,  /* T (stopped)  */
> +  process_state_tracing_stop = 0x10,  /* t (tracing stop)  */
> +  process_state_dead         = 0x20,  /* X (dead)  */
> +  process_state_zombie       = 0x40,  /* Z (zombie)  */
> +  process_state_parked       = 0x80,  /* P (parked)  */
> +};
> +
> +/* Wait for process PID to reach state STATE.  It can be a combination of
> +   multiple possible states ('process_state_running | process_state_sleeping')
> +   where the function return when any of these state are observed.  */
> +void support_process_state_wait (pid_t pid, enum process_state_t state);
> +
> +#endif
> diff --git a/support/support_process_state.c b/support/support_process_state.c
> new file mode 100644
> index 0000000000..77c684c49c
> --- /dev/null
> +++ b/support/support_process_state.c
> @@ -0,0 +1,89 @@
> +/* Wait for process state.
> +   Copyright (C) 2019 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 <stdio.h>
> +#include <fcntl.h>
> +#include <time.h>
> +
> +#include <array_length.h>
> +
> +#include <support/process_state.h>
> +#include <support/xunistd.h>
> +#include <support/check.h>
> +
> +void
> +support_process_state_wait (pid_t pid, enum process_state_t state)
> +{
> +#ifdef __linux__
> +  /* For Linux it does a polling check on /proc/<pid>/status checking on
> +     third field.  */
> +
> +  /* It mimics the kernel states from fs/proc/array.c  */
> +  static struct process_states_t
> +  {
> +    enum process_state_t s;
> +    char v;
> +  } process_states[] = {
> +    { process_state_running,      'R' },
> +    { process_state_sleeping,     'S' },
> +    { process_state_disk_sleep,   'D' },
> +    { process_state_stopped,      'T' },
> +    { process_state_tracing_stop, 't' },
> +    { process_state_dead,         'X' },
> +    { process_state_zombie,       'Z' },
> +    { process_state_parked,       'P' },
> +  };
> +
> +  char proc_path[sizeof ("/proc/" + 3) * sizeof (pid_t) + sizeof ("/stat")
> +		 + 1];
> +  snprintf (proc_path, sizeof (proc_path), "/proc/%i/stat", pid);
> +
> +  int fd = xopen (proc_path, O_RDONLY, 0600);
> +
> +  char statbuf[3 * sizeof (pid_t)  /* pid.  */
> +               + 2                 /* ' (' */
> +               + 64                /* task name.  */
> +               + 2                 /* ' )'  */
> +               + 1                 /* <state>, 1 char.  */
> +               + 1];               /* Final \0.  */
> +  for (;;)
> +    {
> +      ssize_t ret = read (fd, statbuf, sizeof (statbuf) - 1);
> +      TEST_VERIFY (ret >= 0);
> +      statbuf[ret] = '\0';
> +
> +      char cur_state;
> +      int sret = sscanf (statbuf, "%*i %*s %c", &cur_state);
> +      TEST_VERIFY (sret == 1);
> +
> +      for (size_t i = 0; i < array_length (process_states); ++i)
> +	if (state & process_states[i].s && cur_state == process_states[i].v)
> +	  {
> +	    close (fd);
> +	    return;
> +	  }
> +
> +      xlseek (fd, 0, SEEK_SET);
> +      nanosleep (&(struct timespec) { 0, 10000000 }, NULL);
> +    }
> +
> +  close (fd);
> +#else
> +  sleep (2);
> +#endif
> +}
> diff --git a/support/tst-support-process_state.c b/support/tst-support-process_state.c
> new file mode 100644
> index 0000000000..3482f12fa5
> --- /dev/null
> +++ b/support/tst-support-process_state.c
> @@ -0,0 +1,101 @@
> +/* Wait for process state tests.
> +   Copyright (C) 2019 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 <stdio.h>
> +#include <sys/wait.h>
> +#include <unistd.h>
> +#include <errno.h>
> +
> +#include <support/test-driver.h>
> +#include <support/process_state.h>
> +#include <support/check.h>
> +#include <support/xsignal.h>
> +#include <support/xunistd.h>
> +
> +static void
> +sigusr1_handler (int signo)
> +{
> +}
> +
> +static void
> +test_child (void)
> +{
> +  xsignal (SIGUSR1, sigusr1_handler);
> +
> +  raise (SIGSTOP);
> +
> +  TEST_COMPARE (pause (), -1);
> +  TEST_COMPARE (errno, EINTR);
> +
> +  while (1)
> +    asm ("");
> +}
> +
> +static int
> +do_test (void)
> +{
> +  pid_t pid = xfork ();
> +  if (pid == 0)
> +    {
> +      test_child ();
> +      _exit (127);
> +    }
> +
> +  /* Adding process_state_tracing_stop ('t') allows the test to work under
> +     trace programs such as ptrace.  */
> +  enum process_state_t stop_state = process_state_stopped
> +				    | process_state_tracing_stop;
> +
> +  if (test_verbose)
> +    printf ("info: waiting pid %d, state_stopped/state_tracing_stop\n",
> +	    (int) pid);
> +  support_process_state_wait (pid, stop_state);
> +
> +  if (kill (pid, SIGCONT) != 0)
> +    FAIL_RET ("kill (%d, SIGCONT): %m\n", pid);
> +
> +  if (test_verbose)
> +    printf ("info: waiting pid %d, state_sleeping\n", (int) pid);
> +  support_process_state_wait (pid, process_state_sleeping);
> +
> +  if (kill (pid, SIGUSR1) != 0)
> +    FAIL_RET ("kill (%d, SIGUSR1): %m\n", pid);
> +
> +  if (test_verbose)
> +    printf ("info: waiting pid %d, state_running\n", (int) pid);
> +  support_process_state_wait (pid, process_state_running);
> +
> +  if (kill (pid, SIGKILL) != 0)
> +    FAIL_RET ("kill (%d, SIGKILL): %m\n", pid);
> +
> +  if (test_verbose)
> +    printf ("info: waiting pid %d, state_zombie\n", (int) pid);
> +  support_process_state_wait (pid, process_state_zombie);
> +
> +  siginfo_t info;
> +  int r = waitid (P_PID, pid, &info, WEXITED);
> +  TEST_COMPARE (r, 0);
> +  TEST_COMPARE (info.si_signo, SIGCHLD);
> +  TEST_COMPARE (info.si_code, CLD_KILLED);
> +  TEST_COMPARE (info.si_status, SIGKILL);
> +  TEST_COMPARE (info.si_pid, pid);
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>
>
  

* Adhemerval Zanella:

> It allows parent process to wait for children state using a polling
> strategy over procfs on Linux.  The polling is used over ptrace to
> avoid the need to handle signals on the target pid and to handle some
> system specific limitations (such as YAMA).
>
> The polling has some limitations, such as resource consumption due
> the procfs read in a loop and the lack of synchronization after the
> state is obtained.
>
> The interface idea is to simplify some sleep synchronization in waitid
> tests.

The goal is to reduce timeouts, I assume, replacing arbitrary two-second
waits.

> diff --git a/support/process_state.h b/support/process_state.h
> new file mode 100644
> index 0000000000..d616f0e3e6
> --- /dev/null
> +++ b/support/process_state.h
> @@ -0,0 +1,41 @@

> +enum process_state_t
> +{
> +  process_state_running      = 0x01,  /* R (running)  */
> +  process_state_sleeping     = 0x02,  /* S (sleeping)  */
> +  process_state_disk_sleep   = 0x04,  /* D (disk sleep)  */
> +  process_state_stopped      = 0x08,  /* T (stopped)  */
> +  process_state_tracing_stop = 0x10,  /* t (tracing stop)  */
> +  process_state_dead         = 0x20,  /* X (dead)  */
> +  process_state_zombie       = 0x40,  /* Z (zombie)  */
> +  process_state_parked       = 0x80,  /* P (parked)  */
> +};

Maybe drop the reversed _t suffix and add a support_ prefix?

> +
> +/* Wait for process PID to reach state STATE.  It can be a combination of
> +   multiple possible states ('process_state_running | process_state_sleeping')
> +   where the function return when any of these state are observed.  */
> +void support_process_state_wait (pid_t pid, enum process_state_t state);

This interface does not allow to poll for a process not to have a
specific state.  I guess we can adjust it once the need arises, so you
can leave it for now.

> --- /dev/null
> +++ b/support/support_process_state.c
> @@ -0,0 +1,89 @@

> +void
> +support_process_state_wait (pid_t pid, enum process_state_t state)
> +{
> +#ifdef __linux__
> +  /* For Linux it does a polling check on /proc/<pid>/status checking on
> +     third field.  */
> +
> +  /* It mimics the kernel states from fs/proc/array.c  */
> +  static struct process_states_t
> +  {
> +    enum process_state_t s;
> +    char v;
> +  } process_states[] = {
> +    { process_state_running,      'R' },
> +    { process_state_sleeping,     'S' },
> +    { process_state_disk_sleep,   'D' },
> +    { process_state_stopped,      'T' },
> +    { process_state_tracing_stop, 't' },
> +    { process_state_dead,         'X' },
> +    { process_state_zombie,       'Z' },
> +    { process_state_parked,       'P' },
> +  };

Should be const.

> +  char proc_path[sizeof ("/proc/" + 3) * sizeof (pid_t) + sizeof ("/stat")
> +		 + 1];
> +  snprintf (proc_path, sizeof (proc_path), "/proc/%i/stat", pid);
> +
> +  int fd = xopen (proc_path, O_RDONLY, 0600);
> +
> +  char statbuf[3 * sizeof (pid_t)  /* pid.  */
> +               + 2                 /* ' (' */
> +               + 64                /* task name.  */
> +               + 2                 /* ' )'  */
> +               + 1                 /* <state>, 1 char.  */
> +               + 1];               /* Final \0.  */
> +  for (;;)
> +    {
> +      ssize_t ret = read (fd, statbuf, sizeof (statbuf) - 1);
> +      TEST_VERIFY (ret >= 0);
> +      statbuf[ret] = '\0';
> +
> +      char cur_state;
> +      int sret = sscanf (statbuf, "%*i %*s %c", &cur_state);
> +      TEST_VERIFY (sret == 1);

Hmm.  Does this work if COMM includes a space?  I think it's safer to
parse /proc/PID/status.

> +      for (size_t i = 0; i < array_length (process_states); ++i)
> +	if (state & process_states[i].s && cur_state == process_states[i].v)
> +	  {
> +	    close (fd);
> +	    return;
> +	  }
> +
> +      xlseek (fd, 0, SEEK_SET);
> +      nanosleep (&(struct timespec) { 0, 10000000 }, NULL);
> +    }
> +
> +  close (fd);

Should this have a fallback timeout?

The sleep should probably be usleep or nanosleep, to avoid interfering
with laram.

The test looks reasonable.

Thanks,
Florian