[PATCH manager v8 16/22] fix #4369: api: optionally only suggest unique IDs

["Michael Köppl" <m.koeppl@proxmox.com>]

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 with unique=1 in the next-id
datacenter option and the previously used IDs are tracked as a list in
the file `/etc/pve/virtual-guest/used-guest-ids`.

Originally-by: Daniel Krambrock <krambrock@hrz.uni-marburg.de>
Originally-by: Severen Redwood <severen.redwood@sitehost.co.nz>
Signed-off-by: Michael Köppl <m.koeppl@proxmox.com>
Reviewed-by: Fiona Ebner <f.ebner@proxmox.com>
Tested-by: Fiona Ebner <f.ebner@proxmox.com>
---
 PVE/API2/Cluster.pm | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/PVE/API2/Cluster.pm b/PVE/API2/Cluster.pm
index 4e5efbfd9..e5017f6c4 100644
--- a/PVE/API2/Cluster.pm
+++ b/PVE/API2/Cluster.pm
@@ -11,6 +11,7 @@ use PVE::DataCenterConfig;
 use PVE::Exception qw(raise_param_exc);
 use PVE::Firewall;
 use PVE::GuestHelpers;
+use PVE::GuestID;
 use PVE::HA::Config;
 use PVE::HA::Env::PVE2;
 use PVE::INotify;
@@ -1045,8 +1046,13 @@ __PACKAGE__->register_method({
         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->{$i});
+        if ($next_id->{unique}) {
+            my $id = PVE::GuestID::get_next_unused_id($lower);
+            return $id if $id < $upper;
+        } 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";
-- 
2.47.3