<?php
function ds_flush_blogs_rewrite($blog) {
	global $wp_rewrite;
		
	switch_to_blog($blog);
	$wp_rewrite->flush_rules();
	restore_current_blog();
}

function update_siteurl() {
	global $wpdb;
	
	$sites = $wpdb->get_results($wpdb->prepare("SELECT * FROM $wpdb->blogs"));
	
	foreach ( $sites as $site ) { 
		$id = $site->blog_id;
		ds_flush_blogs_rewrite($id);
		$url = get_site_url($site->blog_id);
		update_blog_option($id,'siteurl',$url);
		update_blog_option($id,'home',$url);
	}	
}
add_filter('login_redirect','update_siteurl', 100, 3);
?>