Re: [PATCH qemu-server v2 4/11] virtiofs: add live migration support

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

On Mon Feb 23, 2026 at 4:40 PM CET, Markus Frank wrote:
> 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>
> ---
> v2:
> * fixed broken file-handles migration method by adding
>   '--modcaps=+dac_read_search' to the virtiofsd command as stated in the
>   virtiofsd documentation
>
>  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..9b577704 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} };
> +            if (my $dirid = $entry->{dirid}) {

Seems like the if (...) is unnecessary here as dirfd is a default key
and not optional?

> +                $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 db4b9c78..1a3db50b 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;
> +
> +            if (my $method = $dir_properties->{'live-migration-method'}) {
> +                # migration-on-error=abort would result in a stopped VM on the target node
> +                push @$cmd, '--migration-on-error=guest-error';
> +                if ($method eq 'find-paths') {
> +                    push @$cmd, '--migration-mode=find-paths';
> +                    push @$cmd, '--migration-verify-handles';
> +                    push @$cmd, '--migration-confirm-paths';
> +                }
> +                if ($method eq 'file-handles') {

nit: Since $method can only be one value, an elsif would be more
     readable here

> +                    push @$cmd, '--migration-mode=file-handles';
> +                    push @$cmd, '--modcaps=+dac_read_search';
> +                }
> +            }
> +
>              push @$cmd, '--syslog';
>              exec(@$cmd);
>          } elsif (!defined($pid2)) {