Deprecated features

In general features are intended to be supported indefinitely once introduced into QEMU. In the event that a feature needs to be removed, it will be listed in this section. The feature will remain functional for 2 releases prior to actual removal. Deprecated features may also generate warnings on the console when QEMU starts up, or if activated via a monitor command, however, this is not a mandatory requirement.

Prior to the 2.10.0 release there was no official policy on how long features would be deprecated prior to their removal, nor any documented list of which features were deprecated. Thus any features deprecated prior to 2.10.0 will be treated as if they were first deprecated in the 2.10.0 release.

What follows is a list of all features currently marked as deprecated.

System emulator command line arguments

-machine enforce-config-section=on|off (since 3.1)

The enforce-config-section parameter is replaced by the -global migration.send-configuration={on|off} option.

-no-kvm (since 1.3.0)

The -no-kvm argument is now a synonym for setting -accel tcg.

-usbdevice (since 2.10.0)

The -usbdevice DEV argument is now a synonym for setting the -device usb-DEV argument instead. The deprecated syntax would automatically enable USB support on the machine type. If using the new syntax, USB support must be explicitly enabled via the -machine usb=on argument.

-drive file=json:{...{'driver':'file'}} (since 3.0)

The ‘file’ driver for drives is no longer appropriate for character or host devices and will only accept regular files (S_IFREG). The correct driver for these file types is ‘host_cdrom’ or ‘host_device’ as appropriate.

-smp (invalid topologies) (since 3.1)

CPU topology properties should describe whole machine topology including possible CPUs.

However, historically it was possible to start QEMU with an incorrect topology where n <= sockets * cores * threads < maxcpus, which could lead to an incorrect topology enumeration by the guest. Support for invalid topologies will be removed, the user must ensure topologies described with -smp include all possible cpus, i.e. sockets * cores * threads = maxcpus.

-vnc acl (since 4.0.0)

The acl option to the -vnc argument has been replaced by the tls-authz and sasl-authz options.

QEMU_AUDIO_ environment variables and -audio-help (since 4.0)

The -audiodev argument is now the preferred way to specify audio backend settings instead of environment variables. To ease migration to the new format, the -audiodev-help option can be used to convert the current values of the environment variables to -audiodev options.

Creating sound card devices and vnc without audiodev= property (since 4.2)

When not using the deprecated legacy audio config, each sound card should specify an audiodev= property. Additionally, when using vnc, you should specify an audiodev= propery if you plan to transmit audio through the VNC protocol.

Creating sound card devices using -soundhw (since 5.1)

Sound card devices should be created using -device instead. The names are the same for most devices. The exceptions are hda which needs two devices (-device intel-hda -device hda-duplex) and pcspk which can be activated using -machine pcspk-audiodev=<name>.

-mon ...,control=readline,pretty=on|off (since 4.1)

The pretty=on|off switch has no effect for HMP monitors, but is silently ignored. Using the switch with HMP monitors will become an error in the future.

-realtime (since 4.1)

The -realtime mlock=on|off argument has been replaced by the -overcommit mem-lock=on|off argument.

-numa node (without memory specified) (since 4.1)

Splitting RAM by default between NUMA nodes has the same issues as mem parameter described above with the difference that the role of the user plays QEMU using implicit generic or board specific splitting rule. Use memdev with memory-backend-ram backend or mem (if it’s supported by used machine type) to define mapping explictly instead.

-mem-path fallback to RAM (since 4.1)

Currently if guest RAM allocation from file pointed by mem-path fails, QEMU falls back to allocating from RAM, which might result in unpredictable behavior since the backing file specified by the user is ignored. In the future, users will be responsible for making sure the backing storage specified with -mem-path can actually provide the guest RAM configured with -m and QEMU will fail to start up if RAM allocation is unsuccessful.

RISC-V -bios (since 5.1)

QEMU 4.1 introduced support for the -bios option in QEMU for RISC-V for the RISC-V virt machine and sifive_u machine. QEMU 4.1 had no changes to the default behaviour to avoid breakages.

QEMU 5.1 changes the default behaviour from -bios none to -bios default.

QEMU 5.1 has three options:
  1. -bios default - This is the current default behavior if no -bios option
    is included. This option will load the default OpenSBI firmware automatically. The firmware is included with the QEMU release and no user interaction is required. All a user needs to do is specify the kernel they want to boot with the -kernel option
  2. -bios none - QEMU will not automatically load any firmware. It is up
    to the user to load all the images they need.
  3. -bios <file> - Tells QEMU to load the specified file as the firmwrae.

-tb-size option (since 5.0)

QEMU 5.0 introduced an alternative syntax to specify the size of the translation block cache, -accel tcg,tb-size=. The new syntax deprecates the previously available -tb-size option.

-show-cursor option (since 5.0)

Use -display sdl,show-cursor=on or
-display gtk,show-cursor=on instead.

Configuring floppies with ``-global

Use -device floppy,... instead:

-global isa-fdc.driveA=...
-global sysbus-fdc.driveA=...
-global SUNW,fdtwo.drive=...

become

-device floppy,unit=0,drive=...

and

-global isa-fdc.driveB=...
-global sysbus-fdc.driveB=...

become

-device floppy,unit=1,drive=...

-drive with bogus interface type

Drives with interface types other than if=none are for onboard devices. It is possible to use drives the board doesn’t pick up with -device. This usage is now deprecated. Use if=none instead.

QEMU Machine Protocol (QMP) commands

change (since 2.5.0)

Use blockdev-change-medium or change-vnc-password instead.

blockdev-open-tray, blockdev-close-tray argument device (since 2.8.0)

Use argument id instead.

eject argument device (since 2.8.0)

Use argument id instead.

blockdev-change-medium argument device (since 2.8.0)

Use argument id instead.

block_set_io_throttle argument device (since 2.8.0)

Use argument id instead.

migrate_set_downtime and migrate_set_speed (since 2.8.0)

Use migrate-set-parameters instead.

query-named-block-nodes result encryption_key_missing (since 2.10.0)

Always false.

query-block result inserted.encryption_key_missing (since 2.10.0)

Always false.

blockdev-add empty string argument backing (since 2.10.0)

Use argument value null instead.

migrate-set-cache-size and query-migrate-cache-size (since 2.11.0)

Use migrate-set-parameters and query-migrate-parameters instead.

block-commit arguments base and top (since 3.1.0)

Use arguments base-node and top-node instead.

object-add option props (since 5.0)

Specify the properties for the object as top-level arguments instead.

query-named-block-nodes and query-block result dirty-bitmaps[i].status (since 4.0)

The status field of the BlockDirtyInfo structure, returned by these commands is deprecated. Two new boolean fields, recording and busy effectively replace it.

query-block result field dirty-bitmaps (Since 4.2)

The dirty-bitmaps field of the BlockInfo structure, returned by the query-block command is itself now deprecated. The dirty-bitmaps field of the BlockDeviceInfo struct should be used instead, which is the type of the inserted field in query-block replies, as well as the type of array items in query-named-block-nodes.

Since the dirty-bitmaps field is optionally present in both the old and new locations, clients must use introspection to learn where to anticipate the field if/when it does appear in command output.

query-cpus (since 2.12.0)

The query-cpus command is replaced by the query-cpus-fast command.

query-cpus-fast arch output member (since 3.0.0)

The arch output member of the query-cpus-fast command is replaced by the target output member.

cpu-add (since 4.0)

Use device_add for hotplugging vCPUs instead of cpu-add. See documentation of query-hotpluggable-cpus for additional details.

query-events (since 4.0)

The query-events command has been superseded by the more powerful and accurate query-qmp-schema command.

chardev client socket with wait option (since 4.0)

Character devices creating sockets in client mode should not specify the ‘wait’ field, which is only applicable to sockets in server mode

Human Monitor Protocol (HMP) commands

cpu-add (since 4.0)

Use device_add for hotplugging vCPUs instead of cpu-add. See documentation of query-hotpluggable-cpus for additional details.

acl_show, acl_reset, acl_policy, acl_add, acl_remove (since 4.0.0)

The acl_show, acl_reset, acl_policy, acl_add, and acl_remove commands are deprecated with no replacement. Authorization for VNC should be performed using the pluggable QAuthZ objects.

System emulator CPUS

compat property of server class POWER CPUs (since 5.0)

The compat property used to set backwards compatibility modes for the processor has been deprecated. The max-cpu-compat property of the pseries machine type should be used instead.

System emulator devices

ide-drive (since 4.2)

The ‘ide-drive’ device is deprecated. Users should use ‘ide-hd’ or ‘ide-cd’ as appropriate to get an IDE hard disk or CD-ROM as needed.

scsi-disk (since 4.2)

The ‘scsi-disk’ device is deprecated. Users should use ‘scsi-hd’ or ‘scsi-cd’ as appropriate to get a SCSI hard disk or CD-ROM as needed.

System emulator machines

mips r4k platform (since 5.0)

This machine type is very old and unmaintained. Users should use the malta machine type instead.

mips fulong2e machine (since 5.1)

This machine has been renamed fuloong2e.

pc-1.0, pc-1.1, pc-1.2 and pc-1.3 (since 5.0)

These machine types are very old and likely can not be used for live migration from old QEMU versions anymore. A newer machine type should be used instead.

Device options

Emulated device options

-device virtio-blk,scsi=on|off (since 5.0.0)

The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0 and later do not support it because the virtio-scsi device was introduced for full SCSI support. Use virtio-scsi instead when SCSI passthrough is required.

Note this also applies to -device virtio-blk-pci,scsi=on|off, which is an alias.

Block device options

"backing": "" (since 2.12.0)

In order to prevent QEMU from automatically opening an image’s backing chain, use "backing": null instead.

rbd keyvalue pair encoded filenames: "" (since 3.1.0)

Options for rbd should be specified according to its runtime options, like other block drivers. Legacy parsing of keyvalue pair encoded filenames is useful to open images with the old format for backing files; These image files should be updated to use the current format.

Example of legacy encoding:

json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"}

The above, converted to the current supported format:

json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"}

linux-user mode CPUs

lm32 CPUs (since 5.2.0)

The lm32 guest CPU support is deprecated and will be removed in a future version of QEMU. The only public user of this architecture was the milkymist project, which has been dead for years; there was never an upstream Linux port.

unicore32 CPUs (since 5.2.0)

The unicore32 guest CPU support is deprecated and will be removed in a future version of QEMU. Support for this CPU was removed from the upstream Linux kernel, and there is no available upstream toolchain to build binaries for it.

tilegx CPUs (since 5.1.0)

The tilegx guest CPU support (which was only implemented in linux-user mode) is deprecated and will be removed in a future version of QEMU. Support for this CPU was removed from the upstream Linux kernel in 2018, and has also been dropped from glibc.

ppc64abi32 CPUs (since 5.2.0)

The ppc64abi32 architecture has a number of issues which regularly trip up our CI testing and is suspected to be quite broken. For that reason the maintainers strongly suspect no one actually uses it.

Backwards compatibility

Runnability guarantee of CPU models (since 4.1.0)

Previous versions of QEMU never changed existing CPU models in ways that introduced additional host software or hardware requirements to the VM. This allowed management software to safely change the machine type of an existing VM without introducing new requirements (“runnability guarantee”). This prevented CPU models from being updated to include CPU vulnerability mitigations, leaving guests vulnerable in the default configuration.

The CPU model runnability guarantee won’t apply anymore to existing CPU models. Management software that needs runnability guarantees must resolve the CPU model aliases using te alias-of field returned by the query-cpu-definitions QMP command.

While those guarantees are kept, the return value of query-cpu-definitions will have existing CPU model aliases point to a version that doesn’t break runnability guarantees (specifically, version 1 of those CPU models). In future QEMU versions, aliases will point to newer CPU model versions depending on the machine type, so management software must resolve CPU model aliases before starting a virtual machine.

Recently removed features

What follows is a record of recently removed, formerly deprecated features that serves as a record for users who have encountered trouble after a recent upgrade.

System emulator command line arguments

-net ...,name=name (removed in 5.1)

The name parameter of the -net option was a synonym for the id parameter, which should now be used instead.

QEMU Machine Protocol (QMP) commands

block-dirty-bitmap-add “autoload” parameter (since 4.2.0)

The “autoload” parameter has been ignored since 2.12.0. All bitmaps are automatically loaded from qcow2 images.

Human Monitor Protocol (HMP) commands

The hub_id parameter of hostfwd_add / hostfwd_remove (removed in 5.0)

The [hub_id name] parameter tuple of the ‘hostfwd_add’ and ‘hostfwd_remove’ HMP commands has been replaced by netdev_id.

Guest Emulator ISAs

RISC-V ISA privledge specification version 1.09.1 (removed in 5.1)

The RISC-V ISA privledge specification version 1.09.1 has been removed. QEMU supports both the newer version 1.10.0 and the ratified version 1.11.0, these should be used instead of the 1.09.1 version.

System emulator CPUS

KVM guest support on 32-bit Arm hosts (removed in 5.2)

The Linux kernel has dropped support for allowing 32-bit Arm systems to host KVM guests as of the 5.7 kernel. Accordingly, QEMU is deprecating its support for this configuration and will remove it in a future version. Running 32-bit guests on a 64-bit Arm host remains supported.

RISC-V ISA Specific CPUs (removed in 5.1)

The RISC-V cpus with the ISA version in the CPU name have been removed. The four CPUs are: rv32gcsu-v1.9.1, rv32gcsu-v1.10.0, rv64gcsu-v1.9.1 and rv64gcsu-v1.10.0. Instead the version can be specified via the CPU priv_spec option when using the rv32 or rv64 CPUs.

RISC-V no MMU CPUs (removed in 5.1)

The RISC-V no MMU cpus have been removed. The two CPUs: rv32imacu-nommu and rv64imacu-nommu can no longer be used. Instead the MMU status can be specified via the CPU mmu option when using the rv32 or rv64 CPUs.

System emulator machines

spike_v1.9.1 and spike_v1.10 (removed in 5.1)

The version specific Spike machines have been removed in favour of the generic spike machine. If you need to specify an older version of the RISC-V spec you can use the -cpu rv64gcsu,priv_spec=v1.10.0 command line argument.

Related binaries

qemu-nbd --partition (removed in 5.0)

The qemu-nbd --partition $digit code (also spelled -P) could only handle MBR partitions, and never correctly handled logical partitions beyond partition 5. Exporting a partition can still be done by utilizing the --image-opts option with a raw blockdev using the offset and size parameters layered on top of any other existing blockdev. For example, if partition 1 is 100MiB long starting at 1MiB, the old command:

qemu-nbd -t -P 1 -f qcow2 file.qcow2

can be rewritten as:

qemu-nbd -t --image-opts driver=raw,offset=1M,size=100M,file.driver=qcow2,file.file.driver=file,file.file.filename=file.qcow2

qemu-img convert -n -o (removed in 5.1)

All options specified in -o are image creation options, so they are now rejected when used with -n to skip image creation.

qemu-img create -b bad file $size (removed in 5.1)

When creating an image with a backing file that could not be opened, qemu-img create used to issue a warning about the failure but proceed with the image creation if an explicit size was provided. However, as the -u option exists for this purpose, it is safer to enforce that any failure to open the backing image (including if the backing file is missing or an incorrect format was specified) is an error when -u is not used.

Command line options

-numa node,mem=size (removed in 5.1)

The parameter mem of -numa node was used to assign a part of guest RAM to a NUMA node. But when using it, it’s impossible to manage a specified RAM chunk on the host side (like bind it to a host node, setting bind policy, …), so the guest ends up with the fake NUMA configuration with suboptiomal performance. However since 2014 there is an alternative way to assign RAM to a NUMA node using parameter memdev, which does the same as mem and adds means to actually manage node RAM on the host side. Use parameter memdev with memory-backend-ram backend as replacement for parameter mem to achieve the same fake NUMA effect or a properly configured memory-backend-file backend to actually benefit from NUMA configuration. New machine versions (since 5.1) will not accept the option but it will still work with old machine types. User can check the QAPI schema to see if the legacy option is supported by looking at MachineInfo::numa-mem-supported property.

Block devices

VXHS backend (removed in 5.1)

The VXHS code does not compile since v2.12.0. It was removed in 5.1.