hurd: add getrandom and getentropy implementations

* sysdeps/mach/hurd/getentropy.c: New file.
* sysdeps/mach/hurd/getrandom.c: Likewise.

sysdeps/mach/hurd/getentropy.c

@@ -0,0 +1,64 @@
+/* Implementation of getentropy based on getrandom.
+   Copyright (C) 2016-2019 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 <sys/random.h>
+#include <assert.h>
+#include <errno.h>
+#include <unistd.h>
+
+/* Write LENGTH bytes of randomness starting at BUFFER.  Return 0 on
+   success and -1 on failure.  */
+int
+getentropy (void *buffer, size_t length)
+{
+  /* The interface is documented to return EIO for buffer lengths
+     longer than 256 bytes.  */
+  if (length > 256)
+    {
+      __set_errno (EIO);
+      return -1;
+    }
+
+  /* Try to fill the buffer completely.  Even with the 256 byte limit
+     above, we might still receive an EINTR error (when blocking
+     during boot).  */
+  void *end = buffer + length;
+  while (buffer < end)
+    {
+      /* NB: No cancellation point.  */
+      ssize_t bytes = getrandom (buffer, end - buffer, 0);
+      if (bytes < 0)
+        {
+          if (errno == EINTR)
+            /* Try again if interrupted by a signal.  */
+            continue;
+          else
+            return -1;
+        }
+      if (bytes == 0)
+        {
+          /* No more bytes available.  This should not happen under
+             normal circumstances.  */
+          __set_errno (EIO);
+          return -1;
+        }
+      /* Try again in case of a short read.  */
+      buffer += bytes;
+    }
+  return 0;
+}

sysdeps/mach/hurd/getrandom.c

@@ -0,0 +1,43 @@
+/* Hurdish implementation of getrandom
+   Copyright (C) 2016-2019 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 <sys/random.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <not-cancel.h>
+
+/* Write up to LENGTH bytes of randomness starting at BUFFER.
+   Return the number of bytes written, or -1 on error.  */
+ssize_t
+getrandom (void *buffer, size_t length, unsigned int flags)
+{
+  const char *random_source = "/dev/urandom";
+  size_t amount_read;
+  int fd;
+
+  if (flags & GRND_RANDOM)
+    random_source = "/dev/random";
+
+  fd = __open_nocancel(random_source, O_RDONLY | O_CLOEXEC);
+  if (fd == -1)
+    return -1;
+
+  amount_read = __read_nocancel(fd, buffer, length);
+  __close_nocancel_nostatus(fd);
+  return amount_read;
+}