package MyApache::SF_Upload;
...
use vars qw($UPLOAD_DIR $dir_size);

sub handler {
...
    # Check that the directory is not getting full.
    $dir_size = 0;
    my $dirsz = dir_size( $UPLOAD_DIR ."/$dad" );
    if ( $dirsz > MAX_DIR_SIZE ) {
      $apr->log_error("Upload directory is nearly full, $dirsz" );
      return 507; # HTTP_INSUFFICIENT_STORAGE
      }
    $apr->warn("Upload directory is nearly full, $dirsz" );
...
   }

sub dir_size {
    my $dir = shift;
    
    # Loop through files and sum the sizes; this will descend down subdirs
    opendir DIR, $dir or die "Unable to open $dir: $!";
    while ( $_ = readdir DIR ) {
        stat("$dir/$_"); 
        if (-d _ ) {
          $dir_size += dir_size("$dir/$_")
                unless ($_ eq "." || $_ eq "..");
          }     
        else {
          $dir_size += -s _ ;
          }
        warn("DIR filename: $dir/$_ at $dir_size");
    }
    return $dir_size;
}