[PATCH qemu-server v3 4/11] virtiofs: add live migration support

[Markus Frank <m.frank@proxmox.com>]

There are two migration methods with virtiofsd.

Virtiofsd in the 'find-paths' migration mode, tries to find the path
inside of the shared directory for every filesystem object that must be
transferred to the destination.
Add two extra parameters that verify file handles and confirm paths.

In the 'file-handles' migration mode every filesystem object is
converted to a file handle. This migration mode requires the
DAC_READ_SEARCH capability.

Add a parameter so that migration does not abort if an error occurs.
Aborting on error would result in a stopped VM on the destination node.

Signed-off-by: Markus Frank <m.frank@proxmox.com>
---
v3 changes:
* removed the unnecessary 'if' around the $dirid initialisation
* changed if to elsif
* always start virtiofsd with '--migration-on-error=guest-error' as a
  safety measure

 src/PVE/QemuMigrate/Helpers.pm | 14 +++++++++++---
 src/PVE/QemuServer/Virtiofs.pm | 18 ++++++++++++++++++
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/src/PVE/QemuMigrate/Helpers.pm b/src/PVE/QemuMigrate/Helpers.pm
index 466517da..6c6294dd 100644
--- a/src/PVE/QemuMigrate/Helpers.pm
+++ b/src/PVE/QemuMigrate/Helpers.pm
@@ -21,7 +21,6 @@ sub check_non_migratable_resources {
     if ($state) {
         push @blockers, "amd-sev" if $conf->{"amd-sev"};
         push @blockers, "intel-tdx" if $conf->{"intel-tdx"};
-        push @blockers, "virtiofs" if PVE::QemuServer::Virtiofs::virtiofs_enabled($conf);
     }
 
     if (scalar(@blockers) && !$noerr) {
@@ -100,8 +99,17 @@ sub check_local_resources {
         }
         if ($k =~ m/^virtiofs/) {
             my $entry = parse_property_string('pve-qm-virtiofs', $conf->{$k});
-            $add_missing_mapping->('dir', $k, $entry->{dirid});
-            $mapped_res->{$k} = { name => $entry->{dirid} };
+
+            my $dirid = $entry->{dirid};
+            $add_missing_mapping->('dir', $k, $dirid);
+            my $mapped_device = { name => $dirid };
+            $mapped_res->{$k} = $mapped_device;
+
+            if ($dir_map->{ids}->{$dirid}->{'live-migration-method'}) {
+                $mapped_device->{'live-migration'} = 1;
+                # don't add mapped device with live migration as blocker
+                next;
+            }
         }
         # sockets are safe: they will recreated be on the target side post-migrate
         next if $k =~ m/^serial/ && ($conf->{$k} eq 'socket');
diff --git a/src/PVE/QemuServer/Virtiofs.pm b/src/PVE/QemuServer/Virtiofs.pm
index 8567d2af..f9d7136a 100644
--- a/src/PVE/QemuServer/Virtiofs.pm
+++ b/src/PVE/QemuServer/Virtiofs.pm
@@ -177,6 +177,9 @@ sub start_virtiofsd {
 
     my $dir_cfg = PVE::Mapping::Dir::find_on_current_node($virtiofs->{dirid});
 
+    my $dirid = $virtiofs->{dirid};
+    my $dir_properties = PVE::Mapping::Dir::config()->{ids}->{$dirid};
+
     my $virtiofsd_bin = '/usr/libexec/virtiofsd';
     if (!-f $virtiofsd_bin) {
         die "virtiofsd is not installed. To use virtio-fs, install virtiofsd via apt.\n";
@@ -201,6 +204,21 @@ sub start_virtiofsd {
             push @$cmd, '--readonly' if $virtiofs->{readonly};
             push @$cmd, '--cache=' . $virtiofs->{cache} if $virtiofs->{cache};
             push @$cmd, '--inode-file-handles=prefer' if $prefer_inode_fh;
+
+            # migration-on-error=abort would result in a stopped VM on the target node
+            push @$cmd, '--migration-on-error=guest-error';
+
+            if (my $method = $dir_properties->{'live-migration-method'}) {
+                if ($method eq 'find-paths') {
+                    push @$cmd, '--migration-mode=find-paths';
+                    push @$cmd, '--migration-verify-handles';
+                    push @$cmd, '--migration-confirm-paths';
+                } elsif ($method eq 'file-handles') {
+                    push @$cmd, '--migration-mode=file-handles';
+                    push @$cmd, '--modcaps=+dac_read_search';
+                }
+            }
+
             push @$cmd, '--syslog';
             exec(@$cmd);
         } elsif (!defined($pid2)) {
-- 
2.47.3