Deprecated features — QEMU documentation

# 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

### `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>`.

### `-chardev` backend aliases `tty` and `parport` (since 6.0)

`tty` and `parport` are aliases that will be removed. Instead, the actual backend names `serial` and `parallel` should be used.

### 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.

### 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.

### `delay` option for socket character devices (since 6.0)

The replacement for the `nodelay` short-form boolean option is `nodelay=on` rather than `delay=off`.

### `--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.

### `-writeconfig` (since 6.0)

The `-writeconfig` option is not able to serialize the entire contents of the QEMU command line. It is thus considered a failed experiment and deprecated, with no current replacement.

### Userspace local APIC with KVM (x86, since 6.0)

Using `-M kernel-irqchip=off` with x86 machine types that include a local APIC is deprecated. The `split` setting is supported, as is using `-M kernel-irqchip=off` with the ISA PC machine type.

### hexadecimal sizes with scaling multipliers (since 6.0)

Input parameters that take a size value should only use a size suffix (such as ‘k’ or ‘M’) when the base is written in decimal, and not when the value is hexadecimal. That is, ‘0x20M’ is deprecated, and should be written either as ‘32M’ or as ‘0x2000000’.

### `-spice password=string` (since 6.0)

This option is insecure because the SPICE password remains visible in the process listing. This is replaced by the new `password-secret` option which lets the password be securely provided on the command line using a `secret` object instance.

### `opened` property of `rng-*` objects (since 6.0.0)

The only effect of specifying `opened=on` in the command line or QMP `object-add` is that the device is opened immediately, possibly before all other options have been processed. This will either have no effect (if `opened` was the last option) or cause errors. The property is therefore useless and should not be specified.

### `loaded` property of `secret` and `secret_keyring` objects (since 6.0.0)

The only effect of specifying `loaded=on` in the command line or QMP `object-add` is that the secret is loaded immediately, possibly before all other options have been processed. This will either have no effect (if `loaded` was the last option) or cause options to be effectively ignored as if they were not given. The property is therefore useless and should not be specified.

## 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.

### `blockdev-add` empty string argument `backing` (since 2.10.0)

Use argument value `null` instead.

### `block-commit` arguments `base` and `top` (since 3.1.0)

Use arguments `base-node` and `top-node` instead.

### `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`.

## System accelerators

### MIPS `Trap-and-Emul` KVM support (since 6.0)

The MIPS `Trap-and-Emul` KVM host and guest support has been removed from Linux upstream kernel, declare it deprecated.

## 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 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

### `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.

## Related binaries

### qemu-img amend to adjust backing file (since 5.1)

The use of `qemu-img amend` to modify the name or format of a qcow2 backing image is deprecated; this functionality was never fully documented or tested, and interferes with other amend operations that need access to the original backing image (such as deciding whether a v3 zero cluster may be left unallocated when converting to a v2 image). Rather, any changes to the backing chain should be performed with `qemu-img rebase -u` either before or after the remaining changes being performed by amend, as appropriate.

### qemu-img backing file without format (since 5.1)

The use of `qemu-img create`, `qemu-img rebase`, or `qemu-img convert` to create or modify an image that depends on a backing file now recommends that an explicit backing format be provided. This is for safety: if QEMU probes a different format than what you thought, the data presented to the guest will be corrupt; similarly, presenting a raw image to a guest allows a potential security exploit if a future probe sees a non-raw image based on guest writes.

To avoid the warning message, or even future refusal to create an unsafe image, you must pass `-o backing_fmt=` (or the shorthand `-F` during create) to specify the intended backing format. You may use `qemu-img rebase -u` to retroactively add a backing format to an existing image. However, be aware that there are already potential security risks to blindly using `qemu-img info` to probe the format of an untrusted backing image, when deciding what format to add into an existing image.

## 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.