tst: Provide test for ppoll

This change adds new test to assess ppoll()'s timeout related
functionality (the struct pollfd does not provide valid fd to wait
for - just wait for timeout).

To be more specific - two use cases are checked:
- if ppoll() times out immediately when passed struct timespec has zero
values of tv_nsec and tv_sec.
- if ppoll() times out after timeout specified in passed argument

sysdeps/unix/sysv/linux/Makefile

@@ -107,7 +107,7 @@ tests += tst-clone tst-clone2 tst-clone3 tst-fanotify tst-personality \
 	 test-errno-linux tst-memfd_create tst-mlock2 tst-pkey \
 	 tst-rlimit-infinity tst-ofdlocks tst-gettid tst-gettid-kill \
 	 tst-tgkill tst-sysvsem-linux tst-sysvmsg-linux tst-sysvshm-linux \
-	 tst-timerfd
+	 tst-timerfd tst-ppoll
 tests-internal += tst-ofdlocks-compat tst-sigcontext-get_pc
 
 CFLAGS-tst-sigcontext-get_pc.c = -fasynchronous-unwind-tables

sysdeps/unix/sysv/linux/tst-ppoll.c

@@ -0,0 +1,56 @@
+/* Test for ppoll timeout
+   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 <time.h>
+#include <poll.h>
+#include <errno.h>
+#include <support/check.h>
+#include <support/xtime.h>
+#include <support/timespec.h>
+#include <stdbool.h>
+
+static int test_ppoll_timeout (bool zero_tmo)
+{
+  /* We wait for half a second.  */
+  struct timespec ts;
+  xclock_gettime (CLOCK_REALTIME, &ts);
+  struct timespec timeout = make_timespec (0, zero_tmo ? 0 : TIMESPEC_HZ/2);
+  ts = timespec_add (ts, timeout);
+
+  /* Ignore fds - just wait for timeout.  */
+  struct pollfd fds = { -1, 0, 0 };
+  TEST_COMPARE (ppoll (&fds, 1, &timeout, 0), 0);
+
+  TEST_TIMESPEC_NOW_OR_AFTER (CLOCK_REALTIME, ts);
+
+  return 0;
+}
+
+static int
+do_test (void)
+{
+  /* Check if ppoll exits immediately.  */
+  test_ppoll_timeout (true);
+
+  /* Check if ppoll exits after specified timeout.  */
+  test_ppoll_timeout (false);
+
+  return 0;
+}
+
+#include <support/test-driver.c>