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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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20
src/PVE/Storage/RBDPlugin.pm
View File

@ -374,6 +374,16 @@ my sub rbd_volume_exists {
return 0;
}
# Needs to be public, so qemu-server can mock it for cfg2cmd.
sub rbd_volume_config_set {
my ($scfg, $storeid, $volname, $key, $value) = @_;
my $cmd = $rbd_cmd->($scfg, $storeid, 'config', 'image', 'set', $volname, $key, $value);
run_rbd_command($cmd, errmsg => "rbd config image set $volname $key $value error");
return;
}
# Configuration
sub type {
@ -514,7 +524,7 @@ sub path {
}
sub qemu_blockdev_options {
my ($class, $scfg, $storeid, $volname) = @_;
my ($class, $scfg, $storeid, $volname, $options) = @_;
my $cmd_option = PVE::CephConfig::ceph_connect_option($scfg, $storeid);
my ($name) = ($class->parse_volname($volname))[1];
@ -547,6 +557,14 @@ sub qemu_blockdev_options {
$blockdev->{user} = "$cmd_option->{userid}" if $cmd_option->{keyring};
# SPI flash does lots of read-modify-write OPs, without writeback this gets really slow #3329
if ($options->{hints}->{'efi-disk'}) {
# Querying the value would just cost more and the 'rbd image config get' command will just
# fail if the config has not been set yet, so it's not even straight-forward to do so.
# Simply set the value (possibly again).
rbd_volume_config_set($scfg, $storeid, $name, 'rbd_cache_policy', 'writeback');
}
return $blockdev;
}