hurd: fixes for ptsname_r

ptsname_r on failure returns the value that is also set as errno; furthermore,
add more checks to it.
* set errno and return it on __term_get_peername failure
* set errno to ERANGE other than returning it
Also, change the type of `peername' to string_t, and check its length with
__strnlen.

In ptsname do not set errno manually, since ptsname_r has set it already.

2012-04-28  Pino Toscano  <toscano.pino@tiscali.it>

	* sysdeps/mach/hurd/ptsname.c (ptsname): Do not manually set errno.
	(__ptsname_r): Set errno and return it on __term_get_peername failure.
	Set errno if the buffer is too short.  Make PEERNAME a string_t,
	and check its length with __strnlen.
--- a/sysdeps/mach/hurd/ptsname.c
+++ b/sysdeps/mach/hurd/ptsname.c
@@ -35,8 +35,6 @@
   error_t err;
 
   err = __ptsname_r (fd, peername, sizeof (peername));
-  if (err)
-    __set_errno (err);
 
   return err ? NULL : peername;
 }
@@ -47,17 +45,19 @@
 int
 __ptsname_internal (int fd, char *buf, size_t buflen, struct stat64 *stp)
 {
-  char peername[1024];  /* XXX */
+  string_t peername;
   size_t len;
   error_t err;
 
-  peername[0] = '\0';
   if (err = HURD_DPORT_USE (fd, __term_get_peername (port, peername)))
-    return _hurd_fd_error (fd, err);
+    return __hurd_dfail (fd, err), errno;
 
-  len = strlen (peername) + 1;
+  len = __strnlen (peername, sizeof peername - 1) + 1;
   if (len > buflen)
-    return ERANGE;
+    {
+      errno = ERANGE;
+      return ERANGE;
+    }
 
   memcpy (buf, peername, len);
   return 0;