Gluster v3.4.1 symlink bug

symlink_test.php

<?php
/**
 * Usage:
 *
 * Execute this script simultaneously on two separate gluster clients and you
 * will see errors.  Set the $gluster_path and $local_path variables below as
 * needed for your environment.  You may set $gluster_path to a different local
 * path and then execute two copies of this on the same machine to prove that
 * the problem does not occur with local filesystems.
 */

// Set these values for your environment.
$gluster_path = '/mnt/gfs';
$local_path = '/tmp';

// Set up the target directory if it doesn't exist.
if (!is_dir("$gluster_path/test-target")) { mkdir("$gluster_path/test-target"); }

// Sync the system time, since we want to execute our actions as closely aligned
// as possible.
$sync_results = exec('ntpdate -u time-c.nist.gov');
echo "Synced system time: $sync_results\n";

// Run the symlink creation tests with and without clearing the stat cache
// before using is_link to ensure that this isn't a bug in PHP's stat cache.
test_symlinks(100, FALSE, $gluster_path, $local_path);
test_symlinks(100, TRUE, $gluster_path, $local_path);

/**
 * Once each second, on the second, create a symlink on gluster to a directory
 * on gluster.  Then create a symlink on the local filesystem to the symlink we
 * just created on gluster.  We do this on the second in an attempt to collide
 * with the other client.
 *
 * @param int $n
 *   The number of iterations to perform.
 * @param bool $clearstatcache
 *   Whether we should clear the stat cache.
 * @param string $gluster_path
 *   Path to a gluster mount or directory on a gluster mount.
 * @param string $local_path
 *   Path to a local directory, such as tmp.
 */
function test_symlinks($n = 100, $clearstatcache = TRUE, $gluster_path = '/mnt/gfs', $local_path = '/tmp') {
  $old_testlink = NULL;
  $i = 0;
  $partial_failures = 0;
  $total_failures = 0;
  $gluster_failures = 0;

  while($i < $n) {
    // Set up our file paths.
    $testsrc = $gluster_path . '/test-target';
    $testlink = $gluster_path . '/test' . time();
    $testlink2 = $local_path . '/test' . time();

    // Only run if the time has changed and we're at the start of a new second.
    if ($testlink != $old_testlink) {
      $old_testlink = $testlink;
      $i++;

      // If the symlink on gluster doesn't exist, attempt to create it.
      if ($clearstatcache) { clearstatcache(); }
      if (!is_link($testlink)) {
        @symlink($testsrc, $testlink);

        // If the symlink on gluster still doesn't exist, record a gluster
        // failure.
        if ($clearstatcache) { clearstatcache(); }
        if (!is_link($testlink)) {
          echo "Failed to create gluster link: $testlink.\n";
          $gluster_failures++;
          continue;
        }
      }

      // Create a local symlink to the gluster symlink.
      @symlink($testlink, $testlink2);

      // If the local symlink doesn't exist, we need to record a failure.
      if ($clearstatcache) { clearstatcache(); }
      if (!is_link($testlink2)) {
        echo "Failed to create local link: $testlink2.\n";

        // Determine whether the failure is because the gluster symlink doesn't
        // exist or if we just failed to create the local symlink to it.
        if ($clearstatcache) { clearstatcache(); }
        if (!is_link($testlink)) {
          echo "Failed because target $testlink isn't actually a link.";
          $partial_failures++;
        }
        else {
          echo "But, target $testlink is actually a link.\n";
          $total_failures++;
        }
      }
    }

  }

  // Output the results.
  echo "\n\nClear Stat Cache: " . ($clearstatcache ? "TRUE" : "FALSE") . "\nAttempts: $i\nGluster Failures: $gluster_failures\nPartial Failures: $partial_failures\nTotal Failures: $total_failures\n\n";
}