docs/about/deprecated.rst - qemu - Git at Google

 .. _Deprecated features:

 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.

 As a special exception to this general timeframe, rather than have an
 indefinite lifetime, versioned machine types are only intended to be
 supported for a period of 6 years, equivalent to 18 QEMU releases. All
 versioned machine types will be automatically marked deprecated after an
 initial 3 years (9 QEMU releases) has passed, and will then be deleted after
 a further 3 year period has passed. It is recommended that a deprecated
 machine type is only used for incoming migrations and restore of saved state,
 for pre-existing VM deployments. They should be scheduled for updating to a
 newer machine type during an appropriate service window. Newly deployed VMs
 should exclusively use a non-deprecated machine type, with use of the most
 recent version highly recommended. Non-versioned machine types follow the
 general feature deprecation policy.

 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
 --------------------------------------

 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``.

 Plugin argument passing through ``arg=<string>`` (since 6.1)
 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 Passing TCG plugins arguments through ``arg=`` is redundant is makes the
 command-line less readable, especially when the argument itself consist of a
 name and a value, e.g. ``-plugin plugin_name,arg="arg_name=arg_value"``.
 Therefore, the usage of ``arg`` is redundant. Single-word arguments are treated
 as short-form boolean values, and passed to plugins as ``arg_name=on``.
 However, short-form booleans are deprecated and full explicit ``arg_name=on``
 form is preferred.

 ``-smp`` (Unsupported "parameter=1" SMP configurations) (since 9.0)
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 Specified CPU topology parameters must be supported by the machine.

 In the SMP configuration, users should provide the CPU topology parameters that
 are supported by the target machine.

 However, historically it was allowed for users to specify the unsupported
 topology parameter as "1", which is meaningless. So support for this kind of
 configurations (e.g. -smp drawers=1,books=1,clusters=1 for x86 PC machine) is
 marked deprecated since 9.0, users have to ensure that all the topology members
 described with -smp are supported by the target machine.

 ``-runas`` (since 9.1)
 ----------------------

 Use ``-run-with user=..`` instead.


 User-mode emulator command line arguments
 -----------------------------------------

 ``-p`` (since 9.0)
 ''''''''''''''''''

 The ``-p`` option pretends to control the host page size.  However,
 it is not possible to change the host page size, and using the
 option only causes failures.

 QEMU Machine Protocol (QMP) commands
 ------------------------------------

 ``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8)
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 Use argument ``id`` instead.

 ``eject`` argument ``device`` (since 2.8)
 '''''''''''''''''''''''''''''''''''''''''

 Use argument ``id`` instead.

 ``blockdev-change-medium`` argument ``device`` (since 2.8)
 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 Use argument ``id`` instead.

 ``block_set_io_throttle`` argument ``device`` (since 2.8)
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 Use argument ``id`` instead.

 ``blockdev-add`` empty string argument ``backing`` (since 2.10)
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 Use argument value ``null`` instead.

 ``block-commit`` arguments ``base`` and ``top`` (since 3.1)
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 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``.

 ``query-qmp-schema`` return value member ``values`` (since 6.2)
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 Member ``values`` in return value elements with meta-type ``enum`` is
 deprecated.  Use ``members`` instead.

 ``drive-backup`` (since 6.2)
 ''''''''''''''''''''''''''''

 Use ``blockdev-backup`` in combination with ``blockdev-add`` instead.
 This change primarily separates the creation/opening process of the backup
 target with explicit, separate steps. ``blockdev-backup`` uses mostly the
 same arguments as ``drive-backup``, except the ``format`` and ``mode``
 options are removed in favor of using explicit ``blockdev-create`` and
 ``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for
 details.

 Incorrectly typed ``device_add`` arguments (since 6.2)
 ''''''''''''''''''''''''''''''''''''''''''''''''''''''

 Due to shortcomings in the internal implementation of ``device_add``, QEMU
 incorrectly accepts certain invalid arguments: Any object or list arguments are
 silently ignored. Other argument types are not checked, but an implicit
 conversion happens, so that e.g. string values can be assigned to integer
 device properties or vice versa.

 This is a bug in QEMU that will be fixed in the future so that previously
 accepted incorrect commands will return an error. Users should make sure that
 all arguments passed to ``device_add`` are consistent with the documented
 property types.

 Host Architectures
 ------------------

 BE MIPS (since 7.2)
 '''''''''''''''''''

 As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of
 MIPS moved out of support making it hard to maintain our
 cross-compilation CI tests of the architecture. As we no longer have
 CI coverage support may bitrot away before the deprecation process
 completes. The little endian variants of MIPS (both 32 and 64 bit) are
 still a supported host architecture.

 System emulation on 32-bit x86 hosts (since 8.0)
 ''''''''''''''''''''''''''''''''''''''''''''''''

 Support for 32-bit x86 host deployments is increasingly uncommon in mainstream
 OS distributions given the widespread availability of 64-bit x86 hardware.
 The QEMU project no longer considers 32-bit x86 support for system emulation to
 be an effective use of its limited resources, and thus intends to discontinue
 it. Since all recent x86 hardware from the past >10 years is capable of the
 64-bit x86 extensions, a corresponding 64-bit OS should be used instead.

 TCG Plugin support not enabled by default on 32-bit hosts (since 9.2)
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 While it is still possible to enable TCG plugin support for 32-bit
 hosts there are a number of potential pitfalls when instrumenting
 64-bit guests. The plugin APIs typically pass most addresses as
 uint64_t but practices like encoding that address in a host pointer
 for passing as user-data will lose data. As most software analysis
 benefits from having plenty of host memory it seems reasonable to
 encourage users to use 64 bit builds of QEMU for analysis work
 whatever targets they are instrumenting.

 TCG Plugin support not enabled by default with TCI (since 9.2)
 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 While the TCG interpreter can interpret the TCG ops used by plugins it
 is going to be so much slower it wouldn't make sense for any serious
 instrumentation. Due to implementation differences there will also be
 anomalies in things like memory instrumentation.

 System emulator CPUs
 --------------------

 ``power5+`` and ``power7+`` CPU names (since 9.0)
 '''''''''''''''''''''''''''''''''''''''''''''''''

 The character "+" in device (and thus also CPU) names is not allowed
 in the QEMU object model anymore. ``power5+``, ``power5+_v2.1``,
 ``power7+`` and ``power7+_v2.1`` are currently still supported via
 an alias, but for consistency these will get removed in a future
 release, too. Use ``power5p_v2.1`` and ``power7p_v2.1`` instead.

 ``Sun-UltraSparc-IIIi+`` and ``Sun-UltraSparc-IV+`` CPU names (since 9.1)
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 The character "+" in device (and thus also CPU) names is not allowed
 in the QEMU object model anymore. ``Sun-UltraSparc-IIIi+`` and
 ``Sun-UltraSparc-IV+`` are currently still supported via a workaround,
 but for consistency these will get removed in a future release, too.
 Use ``Sun-UltraSparc-IIIi-plus`` and ``Sun-UltraSparc-IV-plus`` instead.

 System emulator machines
 ------------------------

 Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1)
 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 The ``dtb-kaslr-seed`` property on the ``virt`` board has been
 deprecated; use the new name ``dtb-randomness`` instead. The new name
 better reflects the way this property affects all random data within
 the device tree blob, not just the ``kaslr-seed`` node.

 ``pc-i440fx-2.4`` up to ``pc-i440fx-2.12`` (since 9.1)
 ''''''''''''''''''''''''''''''''''''''''''''''''''''''

 These old machine types are quite neglected nowadays and thus might have
 various pitfalls with regards to live migration. Use a newer machine type
 instead.

 ``pseries-2.1`` up to ``pseries-2.12`` (since 9.0)
 ''''''''''''''''''''''''''''''''''''''''''''''''''

 Older pseries machines before version 3.0 have undergone many changes
 to correct issues, mostly regarding migration compatibility. These are
 no longer maintained and removing them will make the code easier to
 read and maintain. Use versions 3.0 and above as a replacement.

 Arm machines ``akita``, ``borzoi``, ``cheetah``, ``connex``, ``mainstone``, ``n800``, ``n810``, ``spitz``, ``terrier``, ``tosa``, ``verdex``, ``z2`` (since 9.0)
 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 QEMU includes models of some machine types where the QEMU code that
 emulates their SoCs is very old and unmaintained. This code is now
 blocking our ability to move forward with various changes across
 the codebase, and over many years nobody has been interested in
 trying to modernise it. We don't expect any of these machines to have
 a large number of users, because they're all modelling hardware that
 has now passed away into history. We are therefore dropping support
 for all machine types using the PXA2xx and OMAP2 SoCs. We are also
 dropping the ``cheetah`` OMAP1 board, because we don't have any
 test images for it and don't know of anybody who does; the ``sx1``
 and ``sx1-v1`` OMAP1 machines remain supported for now.

 PPC 405 ``ref405ep`` machine (since 9.1)
 ''''''''''''''''''''''''''''''''''''''''

 The ``ref405ep`` machine and PPC 405 CPU have no known users, firmware
 images are not available, OpenWRT dropped support in 2019, U-Boot in
 2017, Linux also is dropping support in 2024. It is time to let go of
 this ancient hardware and focus on newer CPUs and platforms.

 Arm ``tacoma-bmc`` machine (since 9.1)
 ''''''''''''''''''''''''''''''''''''''''

 The ``tacoma-bmc`` machine was a board including an AST2600 SoC based
 BMC and a witherspoon like OpenPOWER system. It was used for bring up
 of the AST2600 SoC in labs.  It can be easily replaced by the
 ``rainier-bmc`` machine which is a real product.

 Backend options
 ---------------

 Using non-persistent backing file with pmem=on (since 6.1)
 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM
 device. However enabling ``memory-backend-file.pmem`` option, when backing file
 is (a) not DAX capable or (b) not on a filesystem that support direct mapping
 of persistent memory, is not safe and may lead to data loss or corruption in case
 of host crash.
 Options are:

     - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM
       (without persistence guaranties) with backing file on non DAX storage
     - move backing file to NVDIMM storage and keep ``pmem=on``
       (to have NVDIMM with persistence guaranties).

 Device options
 --------------

 Emulated device options
 '''''''''''''''''''''''

 ``-device nvme-ns,eui64-default=on|off`` (since 7.1)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64
 identifier that is not globally unique. If an EUI-64 identifier is required, the
 user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``.

 ``-device nvme,use-intel-id=on|off`` (since 7.1)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 The ``nvme`` device originally used a PCI Vendor/Device Identifier combination
 from Intel that was not properly allocated. Since version 5.2, the controller
 has used a properly allocated identifier. Deprecate the ``use-intel-id``
 machine compatibility parameter.

 ``-device cxl-type3,memdev=xxxx`` (since 8.0)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 The ``cxl-type3`` device initially only used a single memory backend.  With
 the addition of volatile memory support, it is now necessary to distinguish
 between persistent and volatile memory backends.  As such, memdev is deprecated
 in favor of persistent-memdev.


 RISC-V CPU properties which start with capital 'Z' (since 8.2)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 All RISC-V CPU properties which start with capital 'Z' are being deprecated
 starting in 8.2. The reason is that they were wrongly added with capital 'Z'
 in the past. CPU properties were later added with lower-case names, which
 is the format we want to use from now on.

 Users which try to use these deprecated properties will receive a warning
 recommending to switch to their stable counterparts:

 - "Zifencei" should be replaced with "zifencei"
 - "Zicsr" should be replaced with "zicsr"
 - "Zihintntl" should be replaced with "zihintntl"
 - "Zihintpause" should be replaced with "zihintpause"
 - "Zawrs" should be replaced with "zawrs"
 - "Zfa" should be replaced with "zfa"
 - "Zfh" should be replaced with "zfh"
 - "Zfhmin" should be replaced with "zfhmin"
 - "Zve32f" should be replaced with "zve32f"
 - "Zve64f" should be replaced with "zve64f"
 - "Zve64d" should be replaced with "zve64d"

 ``-device sd-card,spec_version=1`` (since 9.1)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 SD physical layer specification v2.00 supersedes the v1.10 one.
 v2.00 is the default since QEMU 3.0.0.

 Block device options
 ''''''''''''''''''''

 ``"backing": ""`` (since 2.12)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 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)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 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"}

 ``iscsi,password=xxx`` (since 8.0)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 Specifying the iSCSI password in plain text on the command line using the
 ``password`` option is insecure. The ``password-secret`` option should be
 used instead, to refer to a ``--object secret...`` instance that provides
 a password via a file, or encrypted.

 Character device options
 ''''''''''''''''''''''''

 Backend ``memory`` (since 9.0)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 ``memory`` is a deprecated synonym for ``ringbuf``.

 CPU device properties
 '''''''''''''''''''''

 ``pcommit`` on x86 (since 9.1)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 The PCOMMIT instruction was never included in any physical processor.
 It was implemented as a no-op instruction in TCG up to QEMU 9.0, but
 only with ``-cpu max`` (which does not guarantee migration compatibility
 across versions).

 ``pmu-num=n`` on RISC-V CPUs (since 8.2)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 In order to support more flexible counter configurations this has been replaced
 by a ``pmu-mask`` property. If set of counters is continuous then the mask can
 be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits
 must be left clear.


 Backwards compatibility
 -----------------------

 Runnability guarantee of CPU models (since 4.1)
 '''''''''''''''''''''''''''''''''''''''''''''''

 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.

 RISC-V "virt" board "riscv,delegate" DT property (since 9.1)
 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 The "riscv,delegate" DT property was added in QEMU 7.0 as part of
 the AIA APLIC support.  The property changed name during the review
 process in Linux and the correct name ended up being
 "riscv,delegation".  Changing the DT property name will break all
 available firmwares that are using the current (wrong) name.  The
 property is kept as is in 9.1, together with "riscv,delegation", to
 give more time for firmware developers to change their code.

 Migration
 ---------

 ``fd:`` URI when used for file migration (since 9.1)
 ''''''''''''''''''''''''''''''''''''''''''''''''''''

 The ``fd:`` URI can currently provide a file descriptor that
 references either a socket or a plain file. These are two different
 types of migration. In order to reduce ambiguity, the ``fd:`` URI
 usage of providing a file descriptor to a plain file has been
 deprecated in favor of explicitly using the ``file:`` URI with the
 file descriptor being passed as an ``fdset``. Refer to the ``add-fd``
 command documentation for details on the ``fdset`` usage.
	.. _Deprecated features:

	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.

	As a special exception to this general timeframe, rather than have an
	indefinite lifetime, versioned machine types are only intended to be
	supported for a period of 6 years, equivalent to 18 QEMU releases. All
	versioned machine types will be automatically marked deprecated after an
	initial 3 years (9 QEMU releases) has passed, and will then be deleted after
	a further 3 year period has passed. It is recommended that a deprecated
	machine type is only used for incoming migrations and restore of saved state,
	for pre-existing VM deployments. They should be scheduled for updating to a
	newer machine type during an appropriate service window. Newly deployed VMs
	should exclusively use a non-deprecated machine type, with use of the most
	recent version highly recommended. Non-versioned machine types follow the
	general feature deprecation policy.

	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
	--------------------------------------

	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``.

	Plugin argument passing through ``arg=<string>`` (since 6.1)
	''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	Passing TCG plugins arguments through ``arg=`` is redundant is makes the
	command-line less readable, especially when the argument itself consist of a
	name and a value, e.g. ``-plugin plugin_name,arg="arg_name=arg_value"``.
	Therefore, the usage of ``arg`` is redundant. Single-word arguments are treated
	as short-form boolean values, and passed to plugins as ``arg_name=on``.
	However, short-form booleans are deprecated and full explicit ``arg_name=on``
	form is preferred.

	``-smp`` (Unsupported "parameter=1" SMP configurations) (since 9.0)
	'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	Specified CPU topology parameters must be supported by the machine.

	In the SMP configuration, users should provide the CPU topology parameters that
	are supported by the target machine.

	However, historically it was allowed for users to specify the unsupported
	topology parameter as "1", which is meaningless. So support for this kind of
	configurations (e.g. -smp drawers=1,books=1,clusters=1 for x86 PC machine) is
	marked deprecated since 9.0, users have to ensure that all the topology members
	described with -smp are supported by the target machine.

	``-runas`` (since 9.1)
	----------------------

	Use ``-run-with user=..`` instead.


	User-mode emulator command line arguments
	-----------------------------------------

	``-p`` (since 9.0)
	''''''''''''''''''

	The ``-p`` option pretends to control the host page size. However,
	it is not possible to change the host page size, and using the
	option only causes failures.

	QEMU Machine Protocol (QMP) commands
	------------------------------------

	``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8)
	'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	Use argument ``id`` instead.

	``eject`` argument ``device`` (since 2.8)
	'''''''''''''''''''''''''''''''''''''''''

	Use argument ``id`` instead.

	``blockdev-change-medium`` argument ``device`` (since 2.8)
	''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	Use argument ``id`` instead.

	``block_set_io_throttle`` argument ``device`` (since 2.8)
	'''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	Use argument ``id`` instead.

	``blockdev-add`` empty string argument ``backing`` (since 2.10)
	'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	Use argument value ``null`` instead.

	``block-commit`` arguments ``base`` and ``top`` (since 3.1)
	'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	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``.

	``query-qmp-schema`` return value member ``values`` (since 6.2)
	'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	Member ``values`` in return value elements with meta-type ``enum`` is
	deprecated. Use ``members`` instead.

	``drive-backup`` (since 6.2)
	''''''''''''''''''''''''''''

	Use ``blockdev-backup`` in combination with ``blockdev-add`` instead.
	This change primarily separates the creation/opening process of the backup
	target with explicit, separate steps. ``blockdev-backup`` uses mostly the
	same arguments as ``drive-backup``, except the ``format`` and ``mode``
	options are removed in favor of using explicit ``blockdev-create`` and
	``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for
	details.

	Incorrectly typed ``device_add`` arguments (since 6.2)
	''''''''''''''''''''''''''''''''''''''''''''''''''''''

	Due to shortcomings in the internal implementation of ``device_add``, QEMU
	incorrectly accepts certain invalid arguments: Any object or list arguments are
	silently ignored. Other argument types are not checked, but an implicit
	conversion happens, so that e.g. string values can be assigned to integer
	device properties or vice versa.

	This is a bug in QEMU that will be fixed in the future so that previously
	accepted incorrect commands will return an error. Users should make sure that
	all arguments passed to ``device_add`` are consistent with the documented
	property types.

	Host Architectures
	------------------

	BE MIPS (since 7.2)
	'''''''''''''''''''

	As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of
	MIPS moved out of support making it hard to maintain our
	cross-compilation CI tests of the architecture. As we no longer have
	CI coverage support may bitrot away before the deprecation process
	completes. The little endian variants of MIPS (both 32 and 64 bit) are
	still a supported host architecture.

	System emulation on 32-bit x86 hosts (since 8.0)
	''''''''''''''''''''''''''''''''''''''''''''''''

	Support for 32-bit x86 host deployments is increasingly uncommon in mainstream
	OS distributions given the widespread availability of 64-bit x86 hardware.
	The QEMU project no longer considers 32-bit x86 support for system emulation to
	be an effective use of its limited resources, and thus intends to discontinue
	it. Since all recent x86 hardware from the past >10 years is capable of the
	64-bit x86 extensions, a corresponding 64-bit OS should be used instead.

	TCG Plugin support not enabled by default on 32-bit hosts (since 9.2)
	'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	While it is still possible to enable TCG plugin support for 32-bit
	hosts there are a number of potential pitfalls when instrumenting
	64-bit guests. The plugin APIs typically pass most addresses as
	uint64_t but practices like encoding that address in a host pointer
	for passing as user-data will lose data. As most software analysis
	benefits from having plenty of host memory it seems reasonable to
	encourage users to use 64 bit builds of QEMU for analysis work
	whatever targets they are instrumenting.

	TCG Plugin support not enabled by default with TCI (since 9.2)
	''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	While the TCG interpreter can interpret the TCG ops used by plugins it
	is going to be so much slower it wouldn't make sense for any serious
	instrumentation. Due to implementation differences there will also be
	anomalies in things like memory instrumentation.

	System emulator CPUs
	--------------------

	``power5+`` and ``power7+`` CPU names (since 9.0)
	'''''''''''''''''''''''''''''''''''''''''''''''''

	The character "+" in device (and thus also CPU) names is not allowed
	in the QEMU object model anymore. ``power5+``, ``power5+_v2.1``,
	``power7+`` and ``power7+_v2.1`` are currently still supported via
	an alias, but for consistency these will get removed in a future
	release, too. Use ``power5p_v2.1`` and ``power7p_v2.1`` instead.

	``Sun-UltraSparc-IIIi+`` and ``Sun-UltraSparc-IV+`` CPU names (since 9.1)
	'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	The character "+" in device (and thus also CPU) names is not allowed
	in the QEMU object model anymore. ``Sun-UltraSparc-IIIi+`` and
	``Sun-UltraSparc-IV+`` are currently still supported via a workaround,
	but for consistency these will get removed in a future release, too.
	Use ``Sun-UltraSparc-IIIi-plus`` and ``Sun-UltraSparc-IV-plus`` instead.

	System emulator machines
	------------------------

	Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1)
	''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	The ``dtb-kaslr-seed`` property on the ``virt`` board has been
	deprecated; use the new name ``dtb-randomness`` instead. The new name
	better reflects the way this property affects all random data within
	the device tree blob, not just the ``kaslr-seed`` node.

	``pc-i440fx-2.4`` up to ``pc-i440fx-2.12`` (since 9.1)
	''''''''''''''''''''''''''''''''''''''''''''''''''''''

	These old machine types are quite neglected nowadays and thus might have
	various pitfalls with regards to live migration. Use a newer machine type
	instead.

	``pseries-2.1`` up to ``pseries-2.12`` (since 9.0)
	''''''''''''''''''''''''''''''''''''''''''''''''''

	Older pseries machines before version 3.0 have undergone many changes
	to correct issues, mostly regarding migration compatibility. These are
	no longer maintained and removing them will make the code easier to
	read and maintain. Use versions 3.0 and above as a replacement.

	Arm machines ``akita``, ``borzoi``, ``cheetah``, ``connex``, ``mainstone``, ``n800``, ``n810``, ``spitz``, ``terrier``, ``tosa``, ``verdex``, ``z2`` (since 9.0)
	''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	QEMU includes models of some machine types where the QEMU code that
	emulates their SoCs is very old and unmaintained. This code is now
	blocking our ability to move forward with various changes across
	the codebase, and over many years nobody has been interested in
	trying to modernise it. We don't expect any of these machines to have
	a large number of users, because they're all modelling hardware that
	has now passed away into history. We are therefore dropping support
	for all machine types using the PXA2xx and OMAP2 SoCs. We are also
	dropping the ``cheetah`` OMAP1 board, because we don't have any
	test images for it and don't know of anybody who does; the ``sx1``
	and ``sx1-v1`` OMAP1 machines remain supported for now.

	PPC 405 ``ref405ep`` machine (since 9.1)
	''''''''''''''''''''''''''''''''''''''''

	The ``ref405ep`` machine and PPC 405 CPU have no known users, firmware
	images are not available, OpenWRT dropped support in 2019, U-Boot in
	2017, Linux also is dropping support in 2024. It is time to let go of
	this ancient hardware and focus on newer CPUs and platforms.

	Arm ``tacoma-bmc`` machine (since 9.1)
	''''''''''''''''''''''''''''''''''''''''

	The ``tacoma-bmc`` machine was a board including an AST2600 SoC based
	BMC and a witherspoon like OpenPOWER system. It was used for bring up
	of the AST2600 SoC in labs. It can be easily replaced by the
	``rainier-bmc`` machine which is a real product.

	Backend options
	---------------

	Using non-persistent backing file with pmem=on (since 6.1)
	''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM
	device. However enabling ``memory-backend-file.pmem`` option, when backing file
	is (a) not DAX capable or (b) not on a filesystem that support direct mapping
	of persistent memory, is not safe and may lead to data loss or corruption in case
	of host crash.
	Options are:

	- modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM
	(without persistence guaranties) with backing file on non DAX storage
	- move backing file to NVDIMM storage and keep ``pmem=on``
	(to have NVDIMM with persistence guaranties).

	Device options
	--------------

	Emulated device options
	'''''''''''''''''''''''

	``-device nvme-ns,eui64-default=on\|off`` (since 7.1)
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64
	identifier that is not globally unique. If an EUI-64 identifier is required, the
	user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``.

	``-device nvme,use-intel-id=on\|off`` (since 7.1)
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	The ``nvme`` device originally used a PCI Vendor/Device Identifier combination
	from Intel that was not properly allocated. Since version 5.2, the controller
	has used a properly allocated identifier. Deprecate the ``use-intel-id``
	machine compatibility parameter.

	``-device cxl-type3,memdev=xxxx`` (since 8.0)
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	The ``cxl-type3`` device initially only used a single memory backend. With
	the addition of volatile memory support, it is now necessary to distinguish
	between persistent and volatile memory backends. As such, memdev is deprecated
	in favor of persistent-memdev.


	RISC-V CPU properties which start with capital 'Z' (since 8.2)
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	All RISC-V CPU properties which start with capital 'Z' are being deprecated
	starting in 8.2. The reason is that they were wrongly added with capital 'Z'
	in the past. CPU properties were later added with lower-case names, which
	is the format we want to use from now on.

	Users which try to use these deprecated properties will receive a warning
	recommending to switch to their stable counterparts:

	- "Zifencei" should be replaced with "zifencei"
	- "Zicsr" should be replaced with "zicsr"
	- "Zihintntl" should be replaced with "zihintntl"
	- "Zihintpause" should be replaced with "zihintpause"
	- "Zawrs" should be replaced with "zawrs"
	- "Zfa" should be replaced with "zfa"
	- "Zfh" should be replaced with "zfh"
	- "Zfhmin" should be replaced with "zfhmin"
	- "Zve32f" should be replaced with "zve32f"
	- "Zve64f" should be replaced with "zve64f"
	- "Zve64d" should be replaced with "zve64d"

	``-device sd-card,spec_version=1`` (since 9.1)
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	SD physical layer specification v2.00 supersedes the v1.10 one.
	v2.00 is the default since QEMU 3.0.0.

	Block device options
	''''''''''''''''''''

	``"backing": ""`` (since 2.12)
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	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)
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	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"}

	``iscsi,password=xxx`` (since 8.0)
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	Specifying the iSCSI password in plain text on the command line using the
	``password`` option is insecure. The ``password-secret`` option should be
	used instead, to refer to a ``--object secret...`` instance that provides
	a password via a file, or encrypted.

	Character device options
	''''''''''''''''''''''''

	Backend ``memory`` (since 9.0)
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	``memory`` is a deprecated synonym for ``ringbuf``.

	CPU device properties
	'''''''''''''''''''''

	``pcommit`` on x86 (since 9.1)
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	The PCOMMIT instruction was never included in any physical processor.
	It was implemented as a no-op instruction in TCG up to QEMU 9.0, but
	only with ``-cpu max`` (which does not guarantee migration compatibility
	across versions).

	``pmu-num=n`` on RISC-V CPUs (since 8.2)
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	In order to support more flexible counter configurations this has been replaced
	by a ``pmu-mask`` property. If set of counters is continuous then the mask can
	be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits
	must be left clear.


	Backwards compatibility
	-----------------------

	Runnability guarantee of CPU models (since 4.1)
	'''''''''''''''''''''''''''''''''''''''''''''''

	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.

	RISC-V "virt" board "riscv,delegate" DT property (since 9.1)
	''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	The "riscv,delegate" DT property was added in QEMU 7.0 as part of
	the AIA APLIC support. The property changed name during the review
	process in Linux and the correct name ended up being
	"riscv,delegation". Changing the DT property name will break all
	available firmwares that are using the current (wrong) name. The
	property is kept as is in 9.1, together with "riscv,delegation", to
	give more time for firmware developers to change their code.

	Migration
	---------

	``fd:`` URI when used for file migration (since 9.1)
	''''''''''''''''''''''''''''''''''''''''''''''''''''

	The ``fd:`` URI can currently provide a file descriptor that
	references either a socket or a plain file. These are two different
	types of migration. In order to reduce ambiguity, the ``fd:`` URI
	usage of providing a file descriptor to a plain file has been
	deprecated in favor of explicitly using the ``file:`` URI with the
	file descriptor being passed as an ``fdset``. Refer to the ``add-fd``
	command documentation for details on the ``fdset`` usage.