[PATCH manager v2 1/2] close #4369: api: optionally only suggest unique IDs

[Severen Redwood]

At the moment, the `/cluster/nextid` API endpoint will return the lowest
available VM/CT ID, which means that it will suggest re-using VM IDs.
This can be undesirable, so add an optional check to ensure that it
chooses an ID which is not and has never been in use.

This optional behaviour is enabled when `unique-next-id: 1` in
the data centre config, and the previously used IDs are tracked as a
list in the file `/etc/pve/used_vmids.list`.

Co-authored-by: Daniel Krambrock <krambrock at hrz.uni-marburg.de>
Signed-off-by: Severen Redwood <severen.redwood at sitehost.co.nz>
---
 PVE/API2/Cluster.pm | 13 +++++++--
 PVE/Makefile        |  1 +
 PVE/UsedVmidList.pm | 70 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 82 insertions(+), 2 deletions(-)
 create mode 100644 PVE/UsedVmidList.pm

diff --git a/PVE/API2/Cluster.pm b/PVE/API2/Cluster.pm
index 04387ab4..d0b02d78 100644
--- a/PVE/API2/Cluster.pm
+++ b/PVE/API2/Cluster.pm
@@ -20,6 +20,7 @@ use PVE::RPCEnvironment;
 use PVE::SafeSyslog;
 use PVE::Storage;
 use PVE::Tools qw(extract_param);
+use PVE::UsedVmidList;
 
 use PVE::API2::ACMEAccount;
 use PVE::API2::ACMEPlugin;
@@ -813,12 +814,20 @@ __PACKAGE__->register_method({
 
 	my $dc_conf = PVE::Cluster::cfs_read_file('datacenter.cfg');
 	my $next_id = $dc_conf->{'next-id'} // {};
+	my $want_unique = $dc_conf->{'unique-next-id'} // 0;
 
 	my $lower = $next_id->{lower} // 100;
 	my $upper = $next_id->{upper} // (1000 * 1000); # note, lower than the schema-maximum
 
-	for (my $i = $lower; $i < $upper; $i++) {
-	    return $i if !defined($idlist->{$i});
+	if ($want_unique) {
+	    my $used_ids = PVE::Cluster::cfs_read_file('used_vmids.list');
+	    for (my $i = $lower; $i < $upper; $i++) {
+	        return $i if !defined($idlist->{$i}) and !defined($used_ids->{$i});
+	    }
+	} else {
+	    for (my $i = $lower; $i < $upper; $i++) {
+	        return $i if !defined($idlist->{$i});
+	    }
 	}
 
 	die "unable to get any free VMID in range [$lower, $upper]\n";
diff --git a/PVE/Makefile b/PVE/Makefile
index efcb250d..29775e78 100644
--- a/PVE/Makefile
+++ b/PVE/Makefile
@@ -15,6 +15,7 @@ PERLSOURCE = 			\
 	NodeConfig.pm		\
 	PullMetric.pm		\
 	Report.pm		\
+	UsedVmidList.pm		\
 	VZDump.pm
 
 all: pvecfg.pm $(SUBDIRS)
diff --git a/PVE/UsedVmidList.pm b/PVE/UsedVmidList.pm
new file mode 100644
index 00000000..b88a8681
--- /dev/null
+++ b/PVE/UsedVmidList.pm
@@ -0,0 +1,70 @@
+package PVE::UsedVmidList;
+
+use strict;
+use warnings;
+
+use PVE::Cluster;
+
+my $read_id_list = sub {
+    my ($filename, $raw) = @_;
+
+    return {} if !defined($raw);
+
+    my %used_ids;
+    my @lines = split(/\n/, $raw);
+    foreach my $line (@lines) {
+	if ($line =~ m/^(\d+)$/) {
+	    $used_ids{$1} = 1;
+	} elsif ($line =~ m/^(\d+)-(\d+)$/) {
+	    foreach my $id ($1..$2) {
+		$used_ids{$id} = 1;
+	    }
+	} else {
+	    warn "Skipping invalid entry in used_vmids.list: $line\n";
+	}
+    }
+
+    return \%used_ids;
+};
+
+my $write_id_list = sub {
+    my ($filename, $used_ids) = @_;
+    my @used_ids = sort {$a <=> $b} keys(%$used_ids);
+
+    my @lines;
+    my $len = scalar(@used_ids);
+    for (my $i = 0; $i < $len; $i++) {
+	my $line = "$used_ids[$i]";
+
+	my $j = $i;
+	while ($j + 1 < $len and $used_ids[$j] + 1 == $used_ids[$j + 1]) {
+	    $j++;
+	}
+
+	# If we find a range of consecutive IDs, write $ids[$i]-$ids[$j] to
+	# denote the range so that we avoid storing each individual integer.
+	if ($i != $j) {
+	    $line .= "-$used_ids[$j]";
+	}
+
+	$i = $j;
+	push(@lines, $line);
+    }
+
+    return join("\n", @lines) . "\n";
+};
+
+PVE::Cluster::cfs_register_file('used_vmids.list', $read_id_list, $write_id_list);
+
+sub add_vmid {
+    my ($vmid) = @_;
+
+    PVE::Cluster::cfs_lock_file('used_vmids.list', 10, sub {
+	my $used_ids = PVE::Cluster::cfs_read_file('used_vmids.list');
+
+	$used_ids->{$vmid} = 1;
+	PVE::Cluster::cfs_write_file('used_vmids.list', $used_ids);
+    });
+}
+
+1;
-- 
2.46.2