Re: [pve-devel] [PATCH qemu-server] template backup: work around regression with IDE/SATA and blockdev

["Fabian Grünbichler" <f.gruenbichler@proxmox.com>]

On August 12, 2025 3:03 pm, Fiona Ebner wrote:
> IDE/SATA do not support being configured as read-only, so the inserted
> block node needs to be marked as writable too, but -blockdev will
> complain if it's marked as writable but the actual backing device is
> read-only (e.g. read-only LV).
> 
> To cleanly solve this, 'ide-hd', which is used by both IDE and SATA,
> should not be used as the front-end, but disks be attached differently
> for template backup.
> 
> For now, use a stop-gap fix, setting the machine version to pre-10.0
> in the temporary config used to start the template VM in pre-launch
> mode for backup. With -drive, it seems that the check for the actual
> device being the same r/rw mode is not done.
> 
> Reported in the community forum:
> https://forum.proxmox.com/threads/169638/
> 
> Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
> ---
>  src/PVE/QemuServer.pm                             |  7 +++++++
>  src/test/cfg2cmd/efi-raw-template.conf.cmd        |  7 +++----
>  .../cfg2cmd/q35-linux-hostpci-template.conf.cmd   | 12 +++++-------
>  src/test/cfg2cmd/simple1-template.conf.cmd        | 15 +++++++--------
>  4 files changed, 22 insertions(+), 19 deletions(-)
> 
> diff --git a/src/PVE/QemuServer.pm b/src/PVE/QemuServer.pm
> index cfc54568..6781311e 100644
> --- a/src/PVE/QemuServer.pm
> +++ b/src/PVE/QemuServer.pm
> @@ -3212,6 +3212,13 @@ sub config_to_command {
>              template => 1, # in case below code checks that
>              kvm => 0, # to prevent an error on hosts without virtualization extensions
>              vga => 'none', # to not start a vnc server
> +            # FIXME machine version is set to pre-10.0, because IDE/SATA do not support being
> +            # configured as read-only, so the inserted block node needs to be marked as writable
> +            # too, but -blockdev will complain if it's marked as writable but the actual backing
> +            # device is read-only (e.g. read-only LV).
> +            # To cleanly solve this, ide-hd should not be used as the front-end, but disks be
> +            # attached differently for template backup.
> +            machine => 'pc-i440fx-9.2+pve1',

this should be conditionalized on not using snapshot-as-volume-chain
qcow2 images and/or IDE devices being present to avoid regressing not
yet broken setups..

>              scsihw => $conf->{scsihw}, # so that the scsi disks are correctly added
>              bios => $conf->{bios}, # so efidisk gets included if it exists
>              name => $conf->{name}, # so it's correct in the process list
> diff --git a/src/test/cfg2cmd/efi-raw-template.conf.cmd b/src/test/cfg2cmd/efi-raw-template.conf.cmd
> index d027d776..3a6c1b04 100644
> --- a/src/test/cfg2cmd/efi-raw-template.conf.cmd
> +++ b/src/test/cfg2cmd/efi-raw-template.conf.cmd
> @@ -8,9 +8,8 @@
>    -mon 'chardev=qmp-event,mode=control' \
>    -pidfile /var/run/qemu-server/8006.pid \
>    -daemonize \
> -  -object '{"id":"throttle-drive-efidisk0","limits":{},"qom-type":"throttle-group"}' \
> -  -blockdev '{"driver":"raw","file":{"driver":"file","filename":"/usr/share/pve-edk2-firmware//OVMF_CODE.fd"},"node-name":"pflash0","read-only":true}' \
> -  -blockdev '{"detect-zeroes":"on","discard":"ignore","driver":"throttle","file":{"cache":{"direct":false,"no-flush":false},"detect-zeroes":"on","discard":"ignore","driver":"raw","file":{"aio":"io_uring","cache":{"direct":false,"no-flush":false},"detect-zeroes":"on","discard":"ignore","driver":"file","filename":"/var/lib/vz/images/100/base-100-disk-0.raw","node-name":"e2ab65c8ec567acbeb645244f6c4982","read-only":true},"node-name":"f2ab65c8ec567acbeb645244f6c4982","read-only":true,"size":131072},"node-name":"drive-efidisk0","read-only":true,"throttle-group":"throttle-drive-efidisk0"}' \
> +  -drive 'if=pflash,unit=0,format=raw,readonly=on,file=/usr/share/pve-edk2-firmware//OVMF_CODE.fd' \
> +  -drive 'if=pflash,unit=1,id=drive-efidisk0,format=raw,file=/var/lib/vz/images/100/base-100-disk-0.raw,size=131072,readonly=on' \
>    -smp '1,sockets=1,cores=1,maxcpus=1' \
>    -nodefaults \
>    -boot 'menu=on,strict=on,reboot-timeout=1000,splash=/usr/share/qemu-server/bootsplash.jpg' \
> @@ -26,5 +25,5 @@
>    -device 'usb-tablet,id=tablet,bus=uhci.0,port=1' \
>    -device 'virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3,free-page-reporting=on' \
>    -iscsi 'initiator-name=iqn.1993-08.org.debian:01:aabbccddeeff' \
> -  -machine 'pflash0=pflash0,pflash1=drive-efidisk0,accel=tcg,type=pc+pve0' \
> +  -machine 'accel=tcg,type=pc-i440fx-9.2+pve1' \
>    -snapshot
> diff --git a/src/test/cfg2cmd/q35-linux-hostpci-template.conf.cmd b/src/test/cfg2cmd/q35-linux-hostpci-template.conf.cmd
> index 20e3c81d..7172fb4c 100644
> --- a/src/test/cfg2cmd/q35-linux-hostpci-template.conf.cmd
> +++ b/src/test/cfg2cmd/q35-linux-hostpci-template.conf.cmd
> @@ -8,9 +8,8 @@
>    -mon 'chardev=qmp-event,mode=control' \
>    -pidfile /var/run/qemu-server/8006.pid \
>    -daemonize \
> -  -object '{"id":"throttle-drive-efidisk0","limits":{},"qom-type":"throttle-group"}' \
> -  -blockdev '{"driver":"raw","file":{"driver":"file","filename":"/usr/share/pve-edk2-firmware//OVMF_CODE.fd"},"node-name":"pflash0","read-only":true}' \
> -  -blockdev '{"detect-zeroes":"on","discard":"ignore","driver":"throttle","file":{"cache":{"direct":false,"no-flush":false},"detect-zeroes":"on","discard":"ignore","driver":"qcow2","file":{"aio":"io_uring","cache":{"direct":false,"no-flush":false},"detect-zeroes":"on","discard":"ignore","driver":"file","filename":"/var/lib/vz/images/100/base-100-disk-1.qcow2","node-name":"eb6bec0e3c391fabb7fb7dd73ced9bf","read-only":true},"node-name":"fb6bec0e3c391fabb7fb7dd73ced9bf","read-only":true},"node-name":"drive-efidisk0","read-only":true,"throttle-group":"throttle-drive-efidisk0"}' \
> +  -drive 'if=pflash,unit=0,format=raw,readonly=on,file=/usr/share/pve-edk2-firmware//OVMF_CODE.fd' \
> +  -drive 'if=pflash,unit=1,id=drive-efidisk0,format=qcow2,file=/var/lib/vz/images/100/base-100-disk-1.qcow2,readonly=on' \
>    -smp '1,sockets=1,cores=1,maxcpus=1' \
>    -nodefaults \
>    -boot 'menu=on,strict=on,reboot-timeout=1000,splash=/usr/share/qemu-server/bootsplash.jpg' \
> @@ -18,7 +17,6 @@
>    -nographic \
>    -cpu qemu64 \
>    -m 512 \
> -  -object '{"id":"throttle-drive-scsi0","limits":{},"qom-type":"throttle-group"}' \
>    -global 'PIIX4_PM.disable_s3=1' \
>    -global 'PIIX4_PM.disable_s4=1' \
>    -device 'pci-bridge,id=pci.1,chassis_nr=1,bus=pci.0,addr=0x1e' \
> @@ -28,7 +26,7 @@
>    -device 'virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3,free-page-reporting=on' \
>    -iscsi 'initiator-name=iqn.1993-08.org.debian:01:aabbccddeeff' \
>    -device 'virtio-scsi-pci,id=scsihw0,bus=pci.0,addr=0x5' \
> -  -blockdev '{"detect-zeroes":"on","discard":"ignore","driver":"throttle","file":{"cache":{"direct":true,"no-flush":false},"detect-zeroes":"on","discard":"ignore","driver":"raw","file":{"aio":"io_uring","cache":{"direct":true,"no-flush":false},"detect-zeroes":"on","discard":"ignore","driver":"file","filename":"/var/lib/vz/images/100/base-100-disk-2.raw","node-name":"e24dfe239201bb9924fc4cfb899ca70","read-only":true},"node-name":"f24dfe239201bb9924fc4cfb899ca70","read-only":true},"node-name":"drive-scsi0","read-only":true,"throttle-group":"throttle-drive-scsi0"}' \
> -  -device 'scsi-hd,bus=scsihw0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0,device_id=drive-scsi0,write-cache=on' \
> -  -machine 'pflash0=pflash0,pflash1=drive-efidisk0,accel=tcg,type=pc+pve0' \
> +  -drive 'file=/var/lib/vz/images/100/base-100-disk-2.raw,if=none,id=drive-scsi0,format=raw,cache=none,aio=io_uring,detect-zeroes=on,readonly=on' \
> +  -device 'scsi-hd,bus=scsihw0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0' \
> +  -machine 'accel=tcg,type=pc-i440fx-9.2+pve1' \
>    -snapshot
> diff --git a/src/test/cfg2cmd/simple1-template.conf.cmd b/src/test/cfg2cmd/simple1-template.conf.cmd
> index df51a4a5..5bde9fd6 100644
> --- a/src/test/cfg2cmd/simple1-template.conf.cmd
> +++ b/src/test/cfg2cmd/simple1-template.conf.cmd
> @@ -15,8 +15,6 @@
>    -nographic \
>    -cpu qemu64 \
>    -m 512 \
> -  -object '{"id":"throttle-drive-scsi0","limits":{},"qom-type":"throttle-group"}' \
> -  -object '{"id":"throttle-drive-sata0","limits":{},"qom-type":"throttle-group"}' \
>    -global 'PIIX4_PM.disable_s3=1' \
>    -global 'PIIX4_PM.disable_s4=1' \
>    -device 'pci-bridge,id=pci.1,chassis_nr=1,bus=pci.0,addr=0x1e' \
> @@ -25,12 +23,13 @@
>    -device 'usb-tablet,id=tablet,bus=uhci.0,port=1' \
>    -device 'virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3,free-page-reporting=on' \
>    -iscsi 'initiator-name=iqn.1993-08.org.debian:01:aabbccddeeff' \
> -  -device 'ide-cd,bus=ide.1,unit=0,id=ide2,bootindex=200' \
> +  -drive 'if=none,id=drive-ide2,media=cdrom,aio=io_uring' \
> +  -device 'ide-cd,bus=ide.1,unit=0,drive=drive-ide2,id=ide2,bootindex=200' \
>    -device 'virtio-scsi-pci,id=scsihw0,bus=pci.0,addr=0x5' \
> -  -blockdev '{"detect-zeroes":"unmap","discard":"unmap","driver":"throttle","file":{"cache":{"direct":true,"no-flush":false},"detect-zeroes":"unmap","discard":"unmap","driver":"qcow2","file":{"aio":"io_uring","cache":{"direct":true,"no-flush":false},"detect-zeroes":"unmap","discard":"unmap","driver":"file","filename":"/var/lib/vz/images/8006/base-8006-disk-1.qcow2","node-name":"e1085774206ae4a6b6bf8426ff08f16","read-only":true},"node-name":"f1085774206ae4a6b6bf8426ff08f16","read-only":true},"node-name":"drive-scsi0","read-only":true,"throttle-group":"throttle-drive-scsi0"}' \
> -  -device 'scsi-hd,bus=scsihw0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0,device_id=drive-scsi0,write-cache=on' \
> +  -drive 'file=/var/lib/vz/images/8006/base-8006-disk-1.qcow2,if=none,id=drive-scsi0,discard=on,format=qcow2,cache=none,aio=io_uring,detect-zeroes=unmap,readonly=on' \
> +  -device 'scsi-hd,bus=scsihw0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0' \
>    -device 'ahci,id=ahci0,multifunction=on,bus=pci.0,addr=0x7' \
> -  -blockdev '{"detect-zeroes":"unmap","discard":"unmap","driver":"throttle","file":{"cache":{"direct":true,"no-flush":false},"detect-zeroes":"unmap","discard":"unmap","driver":"qcow2","file":{"aio":"io_uring","cache":{"direct":true,"no-flush":false},"detect-zeroes":"unmap","discard":"unmap","driver":"file","filename":"/var/lib/vz/images/8006/base-8006-disk-0.qcow2","node-name":"eab334c2e07734480f33dd80d89871b","read-only":false},"node-name":"fab334c2e07734480f33dd80d89871b","read-only":false},"node-name":"drive-sata0","read-only":false,"throttle-group":"throttle-drive-sata0"}' \
> -  -device 'ide-hd,bus=ahci0.0,drive=drive-sata0,id=sata0,write-cache=on' \
> -  -machine 'accel=tcg,smm=off,type=pc+pve0' \
> +  -drive 'file=/var/lib/vz/images/8006/base-8006-disk-0.qcow2,if=none,id=drive-sata0,discard=on,format=qcow2,cache=none,aio=io_uring,detect-zeroes=unmap' \
> +  -device 'ide-hd,bus=ahci0.0,drive=drive-sata0,id=sata0' \
> +  -machine 'accel=tcg,smm=off,type=pc-i440fx-9.2+pve1' \
>    -snapshot
> -- 
> 2.47.2
> 
> 
> 
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