tst: Provide test for select

This change adds new test to assess select()'s timeout related
functionality (the rdfs set provides valid fd - stderr - but during
normal program operation there is no data to be read, so one just
waits for timeout).

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

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

misc/Makefile

@@ -88,7 +88,7 @@ tests := tst-dirname tst-tsearch tst-fdset tst-mntent tst-hsearch \
 	 tst-preadvwritev tst-preadvwritev64 tst-makedev tst-empty \
 	 tst-preadvwritev2 tst-preadvwritev64v2 tst-warn-wide \
 	 tst-ldbl-warn tst-ldbl-error tst-dbl-efgcvt tst-ldbl-efgcvt \
-	 tst-mntent-autofs tst-syscalls tst-mntent-escape
+	 tst-mntent-autofs tst-syscalls tst-mntent-escape tst-select
 
 # Tests which need libdl.
 ifeq (yes,$(build-shared))

misc/tst-select.c

@@ -0,0 +1,71 @@
+/* Test for select 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 <errno.h>
+#include <stdbool.h>
+#include <sys/select.h>
+#include <support/check.h>
+#include <support/xtime.h>
+#include <support/timespec.h>
+
+#define TST_SELECT_TIMEOUT 1
+#define TST_SELECT_FD_ERR 2
+
+static int
+test_select_timeout (bool zero_tmo)
+{
+  const int fds = TST_SELECT_FD_ERR;
+  int timeout = TST_SELECT_TIMEOUT;
+  struct timeval to = { 0, 0 };
+  struct timespec ts;
+  fd_set rfds;
+
+  FD_ZERO (&rfds);
+  FD_SET (fds, &rfds);
+
+  if (zero_tmo)
+    timeout = 0;
+
+  to.tv_sec = timeout;
+  ts = xclock_now (CLOCK_REALTIME);
+  ts = timespec_add (ts, (struct timespec) { timeout, 0 });
+
+  /* Wait for timeout.  */
+  int ret = select (fds + 1, &rfds, NULL, NULL, &to);
+  if (ret == -1)
+    FAIL_EXIT1 ("select failed: %m\n");
+
+  TEST_TIMESPEC_NOW_OR_AFTER (CLOCK_REALTIME, ts);
+
+  return 0;
+}
+
+static int
+do_test (void)
+{
+  /* Check if select exits immediately.  */
+  test_select_timeout (true);
+
+  /* Check if select exits after specified timeout.  */
+  test_select_timeout (false);
+
+  return 0;
+}
+
+#include <support/test-driver.c>