[RFC qemu-server 1/1] fix #7053: api: migrate: save and restore migration params for HA managed VMs

[Daniel Kral <d.kral@proxmox.com>]

If a HA-managed VM's migrate API endpoint is called from a web API or
CLI environment, it is first relayed to the HA Manager by queueing a
'migrate' CRM command with `ha-manager migrate vm:$vmid $target_node`.
This command doesn't take any additional migration parameters though.

As soon as the HA Manager reads the CRM command in the next HA Manager
round, it passes the migration request - if valid - to the HA resource
state. This migration request is then picked up by the LRM, where the HA
resource is assigned to and calls the migrate_vm API endpoint, which
will then initial the VM migration.

As the migrate_vm API request is proxied to the node, where the HA
resource is assigned to, this allows the migrate parameters to stored
locally while the migration request is passed through the HA stack.

Signed-off-by: Daniel Kral <d.kral@proxmox.com>
---
 src/PVE/API2/Qemu.pm | 54 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/src/PVE/API2/Qemu.pm b/src/PVE/API2/Qemu.pm
index 1f0864f5..027896a3 100644
--- a/src/PVE/API2/Qemu.pm
+++ b/src/PVE/API2/Qemu.pm
@@ -3,6 +3,7 @@ package PVE::API2::Qemu;
 use strict;
 use warnings;
 use Cwd 'abs_path';
+use File::stat qw();
 use Net::SSLeay;
 use IO::Socket::IP;
 use IO::Socket::UNIX;
@@ -5367,6 +5368,52 @@ __PACKAGE__->register_method({
     },
 });
 
+my sub migrate_params_filename {
+    my ($vmid) = @_;
+    return "/run/qemu-server/$vmid.migrate_params";
+}
+
+my sub save_migrate_params {
+    my ($vmid, $params) = @_;
+
+    my $migrate_params_file = migrate_params_filename($vmid);
+
+    warn "existing migration parameters file for '$vmid' will be overwritten\n"
+        if -f $migrate_params_file;
+
+    PVE::Tools::file_set_contents($migrate_params_file, encode_json($params), 0640);
+}
+
+my sub try_to_restore_migrate_params {
+    my ($vmid, $params) = @_;
+
+    my $migrate_params_file = migrate_params_filename($vmid);
+    my @migrate_params_denylist = qw(node vmid target online force with-local-disks targetstorage);
+
+    if (-f $migrate_params_file) {
+        my $stat = File::stat::lstat($migrate_params_file);
+        # prevent that non-root users could write the migrate parameters file
+        my $has_correct_perms = $stat->uid == 0 && ($stat->mode & 037) == 0;
+
+        if (PVE::HA::Config::vm_is_ha_managed($vmid) && $has_correct_perms) {
+            my $migration_params = {};
+            eval {
+                my $data = PVE::Tools::file_get_contents($migrate_params_file);
+                $migration_params = decode_json($data) // {};
+            };
+            for my $key (keys %$migration_params) {
+                next if grep { $key eq $_ } @migrate_params_denylist;
+
+                $params->{$key} = $migration_params->{$key};
+            }
+        } else {
+            warn "remove orphan migration parameters file\n";
+        }
+
+        unlink $migrate_params_file;
+    }
+}
+
 __PACKAGE__->register_method({
     name => 'migrate_vm',
     path => '{vmid}/migrate',
@@ -5464,6 +5511,13 @@ __PACKAGE__->register_method({
 
         my $vmid = extract_param($param, 'vmid');
 
+        if (PVE::HA::Config::vm_is_ha_managed($vmid) && $rpcenv->{type} ne 'ha') {
+            save_migrate_params($vmid, $param);
+        } else {
+            # always try to restore to remove oprhaned migration parameters files
+            try_to_restore_migrate_params($vmid, $param);
+        }
+
         raise_param_exc({ force => "Only root may use this option." })
             if $param->{force} && $authuser ne 'root@pam';
 
-- 
2.47.3