apt-cudf 4.0.2-4 / usr / sbin / update-cudf-solvers

#!/usr/bin/perl -w
#
# update-cudf-solvers: register available CUDF solvers and bind them to APT
#
# Copyright: © Stefano Zacchiroli 2011 <zack@debian.org>
# License: GNU Lesser General Public License, version 3 or above

use strict;

use File::Basename;
use File::Path qw(make_path);
use Getopt::Long;
use Pod::Usage;

# configuration
my $cudf_dir = "/usr/share/cudf/solvers";
my $edsp_dir = "/usr/lib/apt/solvers";
my $apt_cudf = "/usr/bin/apt-cudf";

# globals
my $debug = 0;
my $help_action = 0;
my $list_action = 0;
my $remove_action = 0;

sub warning($) {
    my ($msg) = @_;
    print STDERR "update-cudf-solvers: W: $msg\n";
}

sub debug($) {
    my ($msg) = @_;
    print STDERR "update-cudf-solvers: I: $msg\n" if $debug;
}

sub die_usage() {
    my %podflags = ( "verbose" => 1,
		     "exitval" => 2 );
    pod2usage(%podflags);
}

sub shallow_find($) {
    my ($dir, $pred) = @_;
    my @found = ();
    foreach my $f (`find $dir -maxdepth 1 -mindepth 1 -type f -o -type l`) {
	chomp $f;
	push @found, basename $f;
    }
    return @found;
}

# check whether a given EDSP solver path originates from a CUDF solver
sub is_cudf_solver($) {
    my ($path) = @_;
    return (-l $path && readlink($path) eq $apt_cudf);
}

# install: act on new CUDF solvers; make them available as EDSP solvers
sub install_new($$) {
    my ($cudf_solvers, $edsp_solvers) = @_;
    foreach my $cudf_name (@$cudf_solvers) {
	my $edsp_solver = "$edsp_dir/$cudf_name";
	next if is_cudf_solver($edsp_solver);
	if (-e $edsp_solver || -l $edsp_solver) {
	    # either existing non CUDF solver or dangling symlink
	    warning "refuse to overwrite $edsp_solver with a symlink to $apt_cudf, skipping";
	} else {	# file exists, but doesn't point to apt-cudf
	    debug "symlink $edsp_solver to $apt_cudf";
	    symlink $apt_cudf, $edsp_solver
		or warning "cannot symlink $edsp_solver to $apt_cudf, skipping";
	}
    }
}

# garbage collection: act on old EDSP solvers; get rid of them
sub remove_old($$) {
    my ($cudf_solvers, $edsp_solvers) = @_;
    foreach my $edsp_name (@$edsp_solvers) {
	my $edsp_solver = "$edsp_dir/$edsp_name";
	next unless is_cudf_solver($edsp_solver);
	if (! grep {"$_" eq "$edsp_name"} @$cudf_solvers) {	
	    # EDSP && CUDF solver, no longer existing
	    debug "unlink (gone) $edsp_solver";
	    unlink $edsp_solver
		or warning "cannot unlink $edsp_solver, skipping";
	}
    }
}

# remove all EDSP solvers originating from CUDF solvers
sub remove_all($$) {
    my ($cudf_solvers, $edsp_solvers) = @_;
    foreach my $edsp_name (@$edsp_solvers) {
	my $edsp_solver = "$edsp_dir/$edsp_name";
	if (is_cudf_solver($edsp_solver)) {
	    unlink $edsp_solver
		or warning "cannot unlink $edsp_solver, skipping";
	}
    }
}

sub main() {
    my $getopt = GetOptions(
	"d|debug" => \$debug,
	"h|help" => \$help_action,
	"l|list" => \$list_action,
	"r|remove" => \$remove_action,
	);
    die_usage if (! $getopt || $help_action);

    -d $edsp_dir or make_path($edsp_dir, { mode => 0755 });

    my @cudf_solvers = shallow_find($cudf_dir);
    my @edsp_solvers = shallow_find($edsp_dir);
    if ($debug) {
	foreach my $s (@cudf_solvers) { debug "found cudf solver: $s"; }
	foreach my $s (@edsp_solvers) { debug "found edsp solver: $s"; }
    }

    if ($list_action) {
	foreach my $s (@cudf_solvers) { print "cudf: $s\n"; }
	foreach my $s (@edsp_solvers) { print "edsp: $s\n"; }
    } elsif ($remove_action) {
	remove_all(\@cudf_solvers, \@edsp_solvers);
    } else {
	install_new(\@cudf_solvers, \@edsp_solvers);
	remove_old(\@cudf_solvers, \@edsp_solvers);
    }
    exit 0;
}

main();

__END__

=head1 NAME

update-cudf-solvers - register available CUDF solvers as APT external solvers

=head1 SYNOPSIS

=over

=item B<update-cudf-solvers> [I<OPTION>]...

=item B<update-cudf-solvers> [I<OPTION>]... --remove

=item B<update-cudf-solvers> [I<OPTION>]... --list

=back

=head1 DESCRIPTION

update-cudf-solvers maintain the list of installed CUDF solvers and register
them as external solvers for APT.

The first form (without mandatory options) should be invoked each time a new
CUDF solver specification file is added to or removed from the CUDF solver
specification directory (by default F</usr/share/cudf/solvers>).
update-cudf-solvers will synchronize the differences with APT external solvers,
by installing suitable symlinks to the F</usr/bin/apt-cudf> wrapper under
F</usr/lib/apt/solvers>.

The second form (with the mandatory C<--remove> option) will remove all
installed external APT solvers that originated from CUDF solvers. It's a
cleanup operation meant to be used only upon removal of the apt-cudf package.

The third form just lists available solvers and exit.

Note that other, non-CUDF based, APT external solvers might be present under
F</usr/lib/apt/solvers>. update-cudf-solvers leaves the untouched and act only
on (present or past) APT solvers corresponding to CUDF solvers.

=head1 TRIGGER-BASED OPERATION

The directory F</usr/share/cudf/solvers> is monitored by a dpkg trigger that
invokes update-cudf-solvers as needed. In all but exceptional circumstances,
you should not be required to opearte update-cudf-solvers manually.

=head1 OPTIONS

=over 4

=item -d

=item --debug

Print debugging information during operation.

=item -h

=item --help

Show usage information and exit.

=item -l

=item --list

List available solvers and exit. Both CUDF and APT's external solvers (AKA
"EDSP solvers") will be listed.

=item -r

=item --remove

Unregister all CUDF solvers.

=back

=head1 SEE ALSO

apt-get(8), apt-cudf(8),
L<README.cudf-solvers|file:///usr/share/doc/apt-cudf/README.cudf-solvers>,
L<README.Debian|file:///usr/share/doc/apt-cudf/README.Debian>

=head1 AUTHOR

Copyright: (C) 2011 Stefano Zacchiroli <zack@debian.org>

License: GNU Lesser General Public License (GPL), version 3 or above

=cut