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 appendix. 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.

-net ...,name=NAME (since 3.1)
------------------------------

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

-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.

-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,mem=SIZE (since 4.1)
-------------------------------

The parameter mem of -numa node is used to assign a part of guest RAM to a NUMA node. But when using it, it's impossible to manage specified RAM chunk on the host side (like bind it to a host node, setting bind policy, ...), so guest end-ups 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 actualy manage node RAM on the host side. Use parameter memdev with MEMORY-BACKEND-RAM backend as an 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. In future new machine versions will not accept the option but it will still work with old machine types. User can check QAPI schema to see if the legacy option is supported by looking at MachineInfo::numa-mem-supported property.

-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 4.1)
------------------------

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 has no changes to the default behaviour to avoid breakages. This default will change in a future QEMU release, so please prepare now. All users of the virt or sifive_u machine must change their command line usage.

QEMU 4.1 has three options, please migrate to one of these three: 1. ``-bios none`` - This is the current default behavior if no -bios option is included. QEMU will not automatically load any firmware. It is up to the user to load all the images they need. 2. ``-bios default`` - In a future QEMU release this will become the default behaviour if no -bios option is specified. 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 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.

QEMU Machine Protocol (QMP) commands
====================================

change (since 2.5.0)
--------------------

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

migrate_set_downtime and migrate_set_speed (since 2.8.0)
--------------------------------------------------------

Use ``migrate-set-parameters'' instead.

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

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

query-block result field dirty-bitmaps[i].status (since 4.0)
------------------------------------------------------------

The ``status'' field of the ``BlockDirtyInfo'' structure, returned by the query-block command 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
=====================================

The hub_id parameter of 'hostfwd_add' / 'hostfwd_remove' (since 3.1)
--------------------------------------------------------------------

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

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.

Guest Emulator ISAs
===================

RISC-V ISA privledge specification version 1.09.1 (since 4.1)
-------------------------------------------------------------

The RISC-V ISA privledge specification version 1.09.1 has been deprecated. 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
====================

RISC-V ISA CPUs (since 4.1)
---------------------------

The RISC-V cpus with the ISA version in the CPU name have been depcreated. 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 ISA CPUs (since 4.1)
---------------------------

The RISC-V no MMU cpus have been depcreated. The two CPUs: ``rv32imacu-nommu`` and ``rv64imacu-nommu`` should 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 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 4.2)
-----------------------------

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

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.

prep (PowerPC) (since 3.1)
--------------------------

This machine type uses an unmaintained firmware, broken in lots of ways, and unable to start post-2004 operating systems. 40p machine type should be used instead.

spike_v1.9.1 and spike_v1.10 (since 4.1)
----------------------------------------

The version specific Spike machines have been deprecated 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=v1.9.1`` command line argument.

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"}

Related binaries
================

qemu-nbd --partition (since 4.0.0)
----------------------------------

The ``qemu-nbd --partition $digit'' code (also spelled -P) can only handle MBR partitions, and has never correctly handled logical partitions beyond partition 5.  If you know the offset and length of the partition (perhaps by using sfdisk within the guest), you can achieve the effect of exporting just that subset of the disk by use of 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.backing.driver=file,file.backing.filename=file.qcow2

Alternatively, the nbdkit project provides a more powerful partition filter on top of its nbd plugin, which can be used to select an arbitrary MBR or GPT partition on top of any other full-image NBD export.  Using this to rewrite the above example results in:

qemu-nbd -t -k /tmp/sock -f qcow2 file.qcow2 & nbdkit -f --filter=partition nbd socket=/tmp/sock partition=1

Note that if you are exposing the export via /dev/nbd0, it is easier to just export the entire image and then mount only /dev/nbd0p1 than it is to reinvoke qemu-nbd -c /dev/nbd0 limited to just a subset of the image.

qemu-img convert -n -o (since 4.2.0)
------------------------------------

All options specified in -o are image creation options, so they have no effect when used with -n to skip image creation. Silently ignored options can be confusing, so this combination of options will be made an error in future versions.

Build system
============

Python 2 support (since 4.1.0)
------------------------------

In the future, QEMU will require Python 3 to be available at build time.  Support for Python 2 in scripts shipped with QEMU is 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 te ``alias-of'' field returned by the ``query-cpu-definitions'' QMP command.

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.

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.