substr($fn, 0, length($pfx)) eq $pfx or return;
$ctx->{snap_pfx} = $fn;
my $v = $ctx->{snap_ver} = substr($fn, length($pfx), length($fn));
substr($fn, 0, length($pfx)) eq $pfx or return;
$ctx->{snap_pfx} = $fn;
my $v = $ctx->{snap_ver} = substr($fn, length($pfx), length($fn));