uploads_info.php

<?php
  
  /**
	 * Returns uploads info for given subsite or primary site.
	 *
	 * @param int $blog_id Optional, defaults to primary.
	 *
	 * @return array
	 *
	 * NOTE: Must be run from primary site.
	 */
	public function uploads_info( $blog_id = 0 ) {
		static $primary_uploads = array();

		if ( ! empty( $blog_id ) && is_multisite() ) {
			switch_to_blog( $blog_id );
		}

		$uploads    = wp_upload_dir();
		$upload_dir = $uploads['basedir'];

		if ( ! empty( $blog_id ) && is_multisite() ) {
			restore_current_blog();

			if ( empty( $primary_uploads ) ) {
				$primary_uploads = $this->uploads_info();
			}

			$main_uploads             = $primary_uploads['basedir'];
			$uploads['short_basedir'] = str_replace( trailingslashit( $main_uploads ), '', trailingslashit( $upload_dir ) );

			if ( defined( 'UPLOADBLOGSDIR' ) && get_site_option( 'ms_files_rewriting' ) ) {

				// Get local upload path info from DB
				switch_to_blog( $blog_id );
				$upload_path = get_option( 'upload_path' );
				if ( ! empty( $upload_path ) ) {
					$uploads['short_basedir'] = str_replace( trailingslashit( UPLOADBLOGSDIR ), '', trailingslashit( $upload_path ) );
				}
				restore_current_blog();
			}
		}

		return $uploads;
	}