Bug#705254: Provide "is-enabled" command for update-rc.d

[Borut Mrak]

I'm working on update-rc.d to add this feature (got bitten by this using 
saltstack service states on Jessie w/ systemd).

I simplified Michael's idea a little bit (I think).
Instead of checking if links correspond to Default-Start + Default-Stop, 
i'm just checking if there are all the Default-Start links available.

For is-disabled I'm only checking that there are no S links present in 
Default-Start runlevels.

IMO, no links == disabled (I know they get recreated on upgrades, but 
that is out of scope for this feature).

Here is a function I added to update-rc.d. I welcome any comments. It 
seems to work for me, but is more of a proof of concepts, needs cleaning 
up (there's also a few lines in insserv_updatercd to call it when action 
is is-enabled or is-disabled).



sub is_enabled_disabled {
    my ($act, $name) = (shift, shift);
    my ($defstart_lvls, $defstop_lvls, @start_links, $lvl);
    my $lsb_header = lsb_header_for_script($name);
    my @runlevels = split('','S2345');

    ($defstart_lvls, $defstop_lvls) = parse_def_start_stop($lsb_header);

    #print "start levels: @$defstart_lvls\n";
    #print "stop levels: @$defstop_lvls\n";

    foreach $lvl (@runlevels) {
        push(@start_links,$_) for glob("/etc/rc$lvl.d/S[0-9][0-9]$name");
    }

    if("is-enabled" eq $act) {
        foreach $lvl (@$defstart_lvls) {
            if ( !grep( m{^/etc/rc$lvl.d/}, @start_links) ) {
                #not enabled in all runlevels, return error
                print "$name not started in runlevel $lvl\n";
                exit 1;
            }
        }
        exit 0;
    }

    if("is-disabled" eq $act) {
      foreach $lvl (@$defstart_lvls) {
        if ( grep( m{^/etc/rc$lvl.d/}, @start_links) ) {
          print "$name starts in runlevel $lvl, not disabled.\n";
          exit 1;
        }
      }
      exit 0;
    }
}