socket: Add the __sockaddr_un_set function

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

socket/sockaddr_un_set.c

@@ -0,0 +1,41 @@
+/* Set the sun_path member of struct sockaddr_un.
+   Copyright (C) 2022 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 <errno.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+
+int
+__sockaddr_un_set (struct sockaddr_un *addr, const char *pathname)
+{
+  size_t name_length = strlen (pathname);
+
+  /* The kernel supports names of exactly sizeof (addr->sun_path)
+     bytes, without a null terminator, but userspace does not; see the
+     SUN_LEN macro.  */
+  if (name_length >= sizeof (addr->sun_path))
+    {
+      __set_errno (EINVAL);     /* Error code used by the kernel.  */
+      return -1;
+    }
+
+  addr->sun_family = AF_UNIX;
+  memcpy (addr->sun_path, pathname, name_length + 1);
+  return 0;
+}