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 the release in which it was deprecated and one further release. After these two releases, the feature is liable to be removed. 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

-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.

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The acl option to the -vnc argument has been replaced by the tls-authz and sasl-authz options.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

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.

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.

Short-form boolean options (since 6.0)

Boolean options such as share=on/share=off could be written in short form as share and noshare. This is now deprecated and will cause a warning.

--enable-fips (since 6.0)

This option restricts usage of certain cryptographic algorithms when the host is operating in FIPS mode.

If FIPS compliance is required, QEMU should be built with the libgcrypt library enabled as a cryptography provider.

Neither the nettle library, or the built-in cryptography provider are supported on FIPS enabled hosts.

QEMU Machine Protocol (QMP) commands

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.

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

nbd-server-add and nbd-server-remove (since 5.2)

Use the more generic commands block-export-add and block-export-del instead. As part of this deprecation, where nbd-server-add used a single bitmap, the new block-export-add uses a list of bitmaps.

Human Monitor Protocol (HMP) commands

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

moxie CPU (since 5.2.0)

The moxie guest CPU support is deprecated and will be removed in a future version of QEMU. It’s unclear whether anybody is still using CPU emulation in QEMU, and there are no test images available to make sure that the code is still working.

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.

Icelake-Client CPU Model (since 5.2.0)

Icelake-Client CPU Models are deprecated. Use Icelake-Server CPU Models instead.

MIPS I7200 CPU Model (since 5.2)

The I7200 guest CPU relies on the nanoMIPS ISA, which is deprecated (the ISA has never been upstreamed to a compiler toolchain). Therefore this CPU is also deprecated.

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

Raspberry Pi raspi2 and raspi3 machines (since 5.2)

The Raspberry Pi machines come in various models (A, A+, B, B+). To be able to distinguish which model QEMU is implementing, the raspi2 and raspi3 machines have been renamed raspi2b and raspi3b.

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"}

sheepdog driver (since 5.2.0)

The sheepdog block device driver is deprecated. The corresponding upstream server project is no longer actively maintained. Users are recommended to switch to an alternative distributed block device driver such as RBD. The qemu-img convert command can be used to liberate existing data by moving it out of sheepdog volumes into an alternative storage backend.

linux-user mode CPUs

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.

MIPS I7200 CPU (since 5.2)

The I7200 guest CPU relies on the nanoMIPS ISA, which is deprecated (the ISA has never been upstreamed to a compiler toolchain). Therefore this CPU is also deprecated.

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 the 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.

Guest Emulator ISAs

nanoMIPS ISA

The nanoMIPS ISA has never been upstreamed to any compiler toolchain. As it is hard to generate binaries for it, declare it deprecated.