[gnome-control-center] user-accounts: use POSIX for max login name length

[Ryan Lortie <desrt src gnome org>]

commit 07d24bbdab3d6dc37f685ae22c741ead8b8221c1
Author: Ryan Lortie <desrt desrt ca>
Date:   Wed Feb 12 12:07:34 2014 -0500

    user-accounts: use POSIX for max login name length
    
    Use the POSIX-specified way of determining the maximum length of a valid
    username on this system.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=724193

 panels/user-accounts/um-utils.c |   21 +++++++++++++++++++--
 1 files changed, 19 insertions(+), 2 deletions(-)
---
diff --git a/panels/user-accounts/um-utils.c b/panels/user-accounts/um-utils.c
index f721c26..b1b67ba 100644
--- a/panels/user-accounts/um-utils.c
+++ b/panels/user-accounts/um-utils.c
@@ -23,8 +23,9 @@
 #include <math.h>
 #include <stdlib.h>
 #include <sys/types.h>
+#include <limits.h>
+#include <unistd.h>
 #include <pwd.h>
-#include <utmp.h>
 
 #include <gio/gio.h>
 #include <gio/gunixoutputstream.h>
@@ -463,8 +464,24 @@ down_arrow (GtkStyleContext *context,
         cairo_restore (cr);
 }
 
+static guint
+get_login_name_max (void)
+{
+#ifdef LOGIN_NAME_MAX
+        return LOGIN_NAME_MAX
+#else
+        static gint length;
+
+        if (!length) {
+                length = sysconf (_SC_LOGIN_NAME_MAX);
+                g_assert_cmpint (length, >=, 0);
+        }
+
+        return length;
+#endif
+}
 
-#define MAXNAMELEN  (UT_NAMESIZE - 1)
+#define MAXNAMELEN  get_login_name_max ()
 
 static gboolean
 is_username_used (const gchar *username)