tests: replace read by xread

With fortification enabled, read calls return result needs to be checked,
has it gets the __wur macro enabled.

Note on read call removal from  sysdeps/pthread/tst-cancel20.c and
sysdeps/pthread/tst-cancel21.c:
It is assumed that this second read call was there to overcome the race
condition between pipe closure and thread cancellation that could happen
in the original code. Since this race condition got fixed by
d0e3ffb7a58854248f1d5e737610d50cd0a60f46 the second call seems
superfluous. Hence, instead of checking for the return value of read, it
looks reasonable to simply remove it.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

1 files changed, 36 insertions, 0 deletions

diff --git a/support/xread.c b/support/xread.c
new file mode 100644
index 0000000000..19f76fcfeb
--- /dev/null
+++ b/support/xread.c
@@ -0,0 +1,36 @@
+/* read with error checking and retries.
+   Copyright (C) 2023 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/xunistd.h>
+
+#include <support/check.h>
+
+void
+xread (int fd, void *buffer, size_t length)
+{
+  char *p = buffer;
+  char *end = p + length;
+  while (p < end)
+    {
+      ssize_t ret = read (fd, p, end - p);
+      if (ret < 0)
+        FAIL_EXIT1 ("read of %zu bytes failed after %td: %m",
+                    length, p - (char *) buffer);
+      p += ret;
+    }
+}