Get post from all blogs on wordpress multisite.

gistfile1.php

function get_posts_from_all($showposts, $denyBlogs = array()) {

	global $wpdb;

        // current blog id
	$mysiteid = $GLOBALS['blog_id'];

	// get child blog ids
	$blogList = $wpdb->get_results(" SELECT blog_id FROM $wpdb->blogs ORDER BY blog_id" );

	// post count
	$pcount = 0;

	$should_get_amount = $showposts * count($blogList);

	foreach ($blogList as $blog) {

		$blog_id = $blog->blog_id;

		if (in_array($blog_id, $denyBlogs))
		  continue; // skip denied
		    
		// change to target blog
		switch_to_blog($blog->blog_id);

		// get blog site and url
		$siteurl = get_site_url();
		$blog_name = get_option('blogname');

		// amount of post should get
		$should_get_amount = $should_get_amount - $pcount;
		$my_posts = get_posts("showposts=$should_get_amount&post_status=publish");
		if (have_posts()) {

		      // insert values. Use timestams as the key.
			foreach ($my_posts as $post) {
		        if($pcount < $showposts):

			    	$pcount++;

			        setup_postdata($post);
			 
			        $get_post_time = $post->post_date;
			        // create key -> post_time + blogid + post id = unique key!
			        $unix_time = strtotime($get_post_time) . ':' . $blog_id . '-' . $post->ID;
			        $entryAry[$unix_time]['quid'] = $post->guid;
			        $entryAry[$unix_time]['ID'] = $post->ID;
			        $entryAry[$unix_time]['title'] = $post->post_title;
			        $entryAry[$unix_time]['date'] = date('Y/m/d', strtotime($post->post_date));
			        $entryAry[$unix_time]['siteurl'] = $siteurl;
			        $entryAry[$unix_time]['blogname'] = $blog_name;
			        $entryAry[$unix_time]['blog_id'] = $blog_id;
			 
			        // category info
			        $entryAry[$unix_time]['categories'] = get_the_category($post->ID);
			 
			        // Category link can get only whithin the proper blog.
			        $categories_link = '';
			        $categories = get_categories();
			        foreach ($categories as $category) {
			          $categories_link .= '
			          <li>
			            <a class="TextCtg" href="' . get_category_link($category->cat_ID) . '">' . $category->cat_name . '</a>
			          </li>
			          ';
			        }
			        $entryAry[$unix_time]['categories']['link'] = $categories_link;
		    	endif;
			}
		}
	}

	// reset blog
	restore_current_blog();

	// chenge to current blog
	switch_to_blog($mysiteid);

	if (count($entryAry) > 0) {
		krsort($entryAry); // to sort as modified.
		return $entryAry;
	} else {
		return false;
	}
}