@$fnames->{filename}

##</code><code>##

my $res_files = list_dirs($dir,$datanames);

sub list_dirs {
   my ( $locations, $fnames ) = @_;
   ...
   foreach my $href ( @{ $fnames } ) {
       my $filename = $href{'filename'};
       # do something with filename ...
   }
}

##</code><code>##

my $res_files = list_dirs($dir,$datanames);

sub list_dirs {
   my ( $locations, $fnames ) = @_;

   my @filenames = map { $_->{'filename'} } @{ $fnames };
   ...
}

##</code><code>##

use Path::Iterator::Rule;
...
my $res_files = list_dirs($dir,$datanames);

sub list_dirs {
   my ( $locations, $fnames ) = @_;
   # assumes each is a simple arrayref

   my $finder = Path::Iterator::Rule->new;
   $finder->name( @{ $fnames } );
   my $get_next_match = $finder->iter( @{ $locations } );

   my @found_filenames;
   while ( defined ( my $match = $get_next_match->() ) ) {
       push @found_filenames, $match;
   }

   return \@found_filenames;
}