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plugin: qemu block device: add hints option and EFI disk hint

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For '-drive', qemu-server sets special cache options for EFI disk
using RBD. In preparation to seamlessly switch to the new '-blockdev'
interface, do the same here. Note that the issue from bug #3329, which
is solved by these cache options, still affects current versions.

With -blockdev, 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.

The default is already 'writeback' and no cache mode can be set for an
EFI drive configuration in Proxmox VE currently, so there will not be
a clash.

┌─────────────┬─────────────────┬──────────────┬────────────────┐
│             │ 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             │
└─────────────┴─────────────────┴──────────────┴────────────────┘

Table from 'man kvm'.

Alternatively, the option could only be set once when allocating the
RBD volume. However, then we would need to detect all cases were a
volume could potentially be used as an EFI disk later. Having a custom
disk type would help a lot there. The approach here was chosen as it
is catch-all and should not be too costly either.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
This commit is contained in:
Fiona Ebner
2025-07-02 18:27:44 +02:00
committed by Fabian Grünbichler
parent f9c390bdfd
commit 590fb76238
6 changed files with 45 additions and 8 deletions
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4
src/PVE/Storage.pm
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@ -721,7 +721,7 @@ sub abs_filesystem_path {
# see the documentation for the plugin method
sub qemu_blockdev_options {
my ($cfg, $volid) = @_;
my ($cfg, $volid, $options) = @_;
my ($storeid, $volname) = parse_volume_id($volid);
@ -733,7 +733,7 @@ sub qemu_blockdev_options {
die "cannot use volume of type '$vtype' as a QEMU blockdevice\n"
if $vtype ne 'images' && $vtype ne 'iso' && $vtype ne 'import';
return $plugin->qemu_blockdev_options($scfg, $storeid, $volname);
return $plugin->qemu_blockdev_options($scfg, $storeid, $volname, $options);
}
# used as last resort to adapt volnames when migrating