support: Add support_process_state_wait

It allows parent process to wait for child 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 limitation (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 waitid
tests and is to reduce timeouts by replacing arbitrary waits.

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 \
@@ -95,6 +96,7 @@ libsupport-routines = \
   xfopen \
   xfork \
   xftruncate \
+  xgetline \
   xgetsockname \
   xlisten \
   xlseek \
@@ -224,6 +226,7 @@ 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 \

support/process_state.h

@@ -0,0 +1,43 @@
+/* Wait for process state.
+   Copyright (C) 2020 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 support_process_state
+{
+  support_process_state_running      = 0x01,  /* R (running).  */
+  support_process_state_sleeping     = 0x02,  /* S (sleeping).  */
+  support_process_state_disk_sleep   = 0x04,  /* D (disk sleep).  */
+  support_process_state_stopped      = 0x08,  /* T (stopped).  */
+  support_process_state_tracing_stop = 0x10,  /* t (tracing stop).  */
+  support_process_state_dead         = 0x20,  /* X (dead).  */
+  support_process_state_zombie       = 0x40,  /* Z (zombie).  */
+  support_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.
+   For an invalid state not represented by SUPPORT_PROCESS_STATE, it fallbacks
+   to a 2 second sleep.  */
+void support_process_state_wait (pid_t pid, enum support_process_state state);
+
+#endif

support/support_process_state.c

@@ -0,0 +1,92 @@
+/* Wait for process state.
+   Copyright (C) 2020 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 <stdlib.h>
+#include <time.h>
+#include <string.h>
+
+#include <array_length.h>
+
+#include <support/process_state.h>
+#include <support/xstdio.h>
+#include <support/check.h>
+
+void
+support_process_state_wait (pid_t pid, enum support_process_state 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 const struct process_states
+  {
+    enum support_process_state s;
+    char v;
+  } process_states[] = {
+    { support_process_state_running,      'R' },
+    { support_process_state_sleeping,     'S' },
+    { support_process_state_disk_sleep,   'D' },
+    { support_process_state_stopped,      'T' },
+    { support_process_state_tracing_stop, 't' },
+    { support_process_state_dead,         'X' },
+    { support_process_state_zombie,       'Z' },
+    { support_process_state_parked,       'P' },
+  };
+
+  char spath[sizeof ("/proc/" + 3) * sizeof (pid_t) + sizeof ("/status") + 1];
+  snprintf (spath, sizeof (spath), "/proc/%i/status", pid);
+
+  FILE *fstatus = xfopen (spath, "r");
+  char *line = NULL;
+  size_t linesiz = 0;
+
+  for (;;)
+    {
+      char cur_state = -1;
+      while (xgetline (&line, &linesiz, fstatus) != -1)
+	if (strncmp (line, "State:", strlen ("State:")) == 0)
+	  {
+	    TEST_COMPARE (sscanf (line, "%*s %c", &cur_state), 1);
+	    break;
+	  }
+      /* Fallback to nanosleep for invalid state.  */
+      if (cur_state == -1)
+	break;
+
+      for (size_t i = 0; i < array_length (process_states); ++i)
+	if (state & process_states[i].s && cur_state == process_states[i].v)
+	  {
+	    free (line);
+	    xfclose (fstatus);
+	    return;
+	  }
+
+      rewind (fstatus);
+      fflush (fstatus);
+
+      if (nanosleep (&(struct timespec) { 0, 10000000 }, NULL) != 0)
+	FAIL_EXIT1 ("nanosleep: %m");
+    }
+
+  free (line);
+  xfclose (fstatus);
+  /* Fallback to nanosleep if an invalid state is found.  */
+#endif
+  nanosleep (&(struct timespec) { 2, 0 }, NULL);
+}

support/tst-support-process_state.c

@@ -0,0 +1,105 @@
+/* Wait for process state tests.
+   Copyright (C) 2020 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>
+
+#ifndef WEXITED
+# define WEXITED	0
+#endif
+
+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 support_process_state stop_state = support_process_state_stopped
+				    | support_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, support_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, support_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, support_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>

support/xgetline.c

@@ -0,0 +1,33 @@
+/* fopen with error checking.
+   Copyright (C) 2020 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 <support/xstdio.h>
+#include <support/check.h>
+#include <errno.h>
+
+ssize_t
+xgetline (char **lineptr, size_t *n, FILE *stream)
+{
+  int old_errno = errno;
+  errno = 0;
+  size_t ret = getline (lineptr, n, stream);
+  if (!feof (stream) && ferror (stream))
+    FAIL_EXIT1 ("getline failed: %m");
+  errno = old_errno;
+  return ret;
+}

support/xstdio.h

@@ -27,6 +27,8 @@ __BEGIN_DECLS
 FILE *xfopen (const char *path, const char *mode);
 void xfclose (FILE *);
 
+ssize_t xgetline (char **lineptr, size_t *n, FILE *stream);
+
 __END_DECLS
 
 #endif /* SUPPORT_XSTDIO_H */