use PerlIO;

my $fd;
open($fd, '+>>:raw', 'somefile.data') || die $!;

my $layers = ':' . join(':', PerlIO::get_layers($fd));

print "$layers\n";

#
# this doesn't complain, but the layers aren't being properly applied
#
my $fd3;
open($fd3, "+>>&", fileno($fd)) || die $!;
binmode $fd3, $layers;

print join(',', PerlIO::get_layers($fd3)), "\n";