On June 12, 2025 4:02 pm, Fiona Ebner wrote:
> With the 'blockdev' command line option, the cache options are split
> up. While cache.direct and cache.no-flush can be set in the -blockdev
> options, cache.writeback is a front-end property and was intentionally
> removed from the 'blockdev' options by QEMU commit aaa436f998 ("block:
> Remove cache.writeback from blockdev-add"). It needs to be configured
> as the 'write-cache' property for the ide-hd/scsi-hd/virtio-blk
> device.
>
> Table from 'man kvm':
>
> ┌─────────────┬─────────────────┬──────────────┬────────────────┐
> │ │ cache.writeback │ cache.direct │ cache.no-flush │
> ├─────────────┼─────────────────┼──────────────┼────────────────┤
> │writeback │ on │ off │ off │
> ├─────────────┼─────────────────┼──────────────┼────────────────┤
> │none │ on │ on │ off │
> ├─────────────┼─────────────────┼──────────────┼────────────────┤
> │writethrough │ off │ off │ off │
> ├─────────────┼─────────────────┼──────────────┼────────────────┤
> │directsync │ off │ on │ off │
> ├─────────────┼─────────────────┼──────────────┼────────────────┤
> │unsafe │ on │ off │ on │
> └─────────────┴─────────────────┴──────────────┴────────────────┘
>
> Suggested-by: Alexandre Derumier <alexandre.derum...@groupe-cyllene.com>
> Signed-off-by: Fiona Ebner <f.eb...@proxmox.com>
> ---
> PVE/QemuServer.pm | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
> index 82304096..f9e1b3f9 100644
> --- a/PVE/QemuServer.pm
> +++ b/PVE/QemuServer.pm
> @@ -1317,6 +1317,8 @@ sub print_drivedevice_full {
> my $device = '';
> my $maxdev = 0;
>
> + my $machine_version = extract_version($machine_type, kvm_user_version());
> +
> my $drive_id = PVE::QemuServer::Drive::get_drive_id($drive);
> if ($drive->{interface} eq 'virtio') {
> my $pciaddr = print_pci_addr("$drive_id", $bridges, $arch,
> $machine_type);
> @@ -1327,7 +1329,6 @@ sub print_drivedevice_full {
> my ($maxdev, $controller, $controller_prefix) = scsihw_infos($conf,
> $drive);
> my $unit = $drive->{index} % $maxdev;
>
> - my $machine_version = extract_version($machine_type,
> kvm_user_version());
> my $device_type = PVE::QemuServer::Drive::get_scsi_device_type(
> $drive, $storecfg, $machine_version);
>
> @@ -1403,6 +1404,15 @@ sub print_drivedevice_full {
> $device .= ",serial=$serial";
> }
>
> + if (min_version($machine_version, 10, 0)) {
should we add a comment here (and for similar conditionals in following
patches) that this is for the switch to blockdev? obvious now, might be
lass obvious down the line ;)
> + if (!drive_is_cdrom($drive)) {
> + my $write_cache = 'on';
> + if (my $cache = $drive->{cache}) {
> + $write_cache = 'off' if $cache eq 'writethrough' || $cache eq
> 'directsync';
> + }
> + $device .= ",write-cache=$write_cache";
> + }
> + }
>
> return $device;
> }
> --
> 2.39.5
>
>
>
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>
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