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From: Fiona Ebner <f.ebner@proxmox.com>
To: pve-devel@lists.proxmox.com
Subject: [pve-devel] [PATCH qemu-server v2 26/32] print drive device: explicitly set write-cache starting with machine version 10.0
Date: Wed, 18 Jun 2025 15:02:03 +0200	[thread overview]
Message-ID: <20250618130209.90649-27-f.ebner@proxmox.com> (raw)
In-Reply-To: <20250618130209.90649-1-f.ebner@proxmox.com>

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.derumier@groupe-cyllene.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---

Changes in v2:
* Comment that the version guard is for the switch to -blockdev.

 src/PVE/QemuServer.pm | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/PVE/QemuServer.pm b/src/PVE/QemuServer.pm
index f8adb890..0b983ab9 100644
--- a/src/PVE/QemuServer.pm
+++ b/src/PVE/QemuServer.pm
@@ -1403,6 +1403,8 @@ 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, $arch);
@@ -1413,7 +1415,6 @@ sub print_drivedevice_full {
         my ($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);
 
@@ -1489,6 +1490,16 @@ sub print_drivedevice_full {
         $device .= ",serial=$serial";
     }
 
+    if (min_version($machine_version, 10, 0)) { # for the switch to -blockdev
+        if (!drive_is_cdrom($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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  parent reply	other threads:[~2025-06-18 13:03 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-06-18 13:01 [pve-devel] [PATCH-SERIES common/qemu-server v2 00/32] preparation for switch to blockdev Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH common v2 01/32] schema: parse property string: support skipping keys Fiona Ebner
2025-06-20 11:00   ` Fabian Grünbichler
2025-06-18 13:01 ` [pve-devel] [PATCH common v2 02/32] json schema: add helper to convert to JSON boolean Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 03/32] buildsys: order Perl source files in QemuServer/Makefile Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 04/32] drive: code cleanup: drop unused $vmid parameter from get_path_and_format() Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 05/32] cfg2cmd: require at least QEMU binary version 6.0 Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 06/32] drive: parse: use hash argument for optional parameters Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 07/32] drive: parse: properly handle dropped properties for restore Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 08/32] drive: remove geometry options gone since QEMU 3.1 Fiona Ebner
2025-06-20 11:03   ` Fabian Grünbichler
2025-06-20 11:20     ` Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 09/32] clone disk: io uring check: fix call to determine cache direct Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 10/32] drive: move storage_allows_io_uring_default() and drive_uses_cache_direct() helpers to drive module Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 11/32] drive: introduce aio_cmdline_option() helper Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 12/32] drive: introduce detect_zeroes_cmdline_option() helper Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 13/32] vm start: assert that migration type is set for 'tcp' migration Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 14/32] introduce StateFile module for state file related helpers Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 15/32] vm start: move state file handling to dedicated module Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 16/32] vm start: move config_to_command() call further down Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 17/32] vm start/commandline: also clean up pci reservation when config_to_command() fails Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 18/32] vm start/commandline: activate volumes before config_to_command() Fiona Ebner
2025-06-20 11:33   ` Fabian Grünbichler
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 19/32] pci: add missing includes Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 20/32] test: add tests for PCI reservations Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 21/32] cfg2cmd: print vga: fix call to print_pcie_addr() Fiona Ebner
2025-06-18 13:01 ` [pve-devel] [PATCH qemu-server v2 22/32] pci: code cleanup: remove superfluous machine type paramater from print_pci_addr Fiona Ebner
2025-06-18 15:19   ` Fiona Ebner
2025-06-18 13:02 ` [pve-devel] [PATCH qemu-server v2 23/32] cfg2cmd: collect optional parameters as a hash Fiona Ebner
2025-06-18 13:02 ` [pve-devel] [PATCH qemu-server v2 24/32] qm: showcmd: never reserve PCI devices Fiona Ebner
2025-06-18 13:02 ` [pve-devel] [PATCH qemu-server v2 25/32] vm devices list: prepare querying block device names for -blockdev Fiona Ebner
2025-06-18 13:02 ` Fiona Ebner [this message]
2025-06-18 13:02 ` [pve-devel] [PATCH qemu-server v2 27/32] print drive device: set {r, w}error front-end properties starting with machine version 10.0 Fiona Ebner
2025-06-18 13:02 ` [pve-devel] [PATCH qemu-server v2 28/32] print drive device: don't reference any drive for 'none' " Fiona Ebner
2025-06-18 13:02 ` [pve-devel] [PATCH qemu-server v2 29/32] drive: create a throttle group for each drive " Fiona Ebner
2025-06-18 13:02 ` [pve-devel] [PATCH qemu-server v2 30/32] blockdev: add helpers to generate blockdev commandline Fiona Ebner
2025-06-18 13:02 ` [pve-devel] [RFC qemu-server v2 31/32] blockdev: add support for NBD paths Fiona Ebner
2025-06-18 13:02 ` [pve-devel] [RFC qemu-server v2 32/32] command line: switch to blockdev starting with machine version 10.0 Fiona Ebner
2025-06-23  9:12   ` DERUMIER, Alexandre via pve-devel
2025-06-23  9:31     ` Fiona Ebner
2025-06-23 13:06       ` DERUMIER, Alexandre via pve-devel
2025-06-20 13:03 ` [pve-devel] partially-applied: [PATCH-SERIES common/qemu-server v2 00/32] preparation for switch to blockdev Fabian Grünbichler

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