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.

 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``.

 ``-smp`` ("parameter=0" SMP configurations) (since 6.2)
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''

 Specified CPU topology parameters must be greater than zero.

 In the SMP configuration, users should either provide a CPU topology
 parameter with a reasonable value (greater than zero) or just omit it
 and QEMU will compute the missing value.

 However, historically it was implicitly allowed for users to provide
 a parameter with zero value, which is meaningless and could also possibly
 cause unexpected results in the -smp parsing. So support for this kind of
 configurations (e.g. -smp 8,sockets=0) is deprecated since 6.2 and will
 be removed in the near future, users have to ensure that all the topology
 members described with -smp are greater than zero.

 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.

 ``-no-hpet`` (since 8.0)
 ''''''''''''''''''''''''

 The HPET setting has been turned into a machine property.
 Use ``-machine hpet=off`` instead.

 ``-no-acpi`` (since 8.0)
 ''''''''''''''''''''''''

 The ``-no-acpi`` setting has been turned into a machine property.
 Use ``-machine acpi=off`` instead.

 ``-async-teardown`` (since 8.1)
 '''''''''''''''''''''''''''''''

 Use ``-run-with async-teardown=on`` instead.

 ``-chroot`` (since 8.1)
 '''''''''''''''''''''''

 Use ``-run-with chroot=dir`` instead.

 ``-singlestep`` (since 8.1)
 '''''''''''''''''''''''''''

 The ``-singlestep`` option has been turned into an accelerator property,
 and given a name that better reflects what it actually does.
 Use ``-accel tcg,one-insn-per-tb=on`` instead.

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

 ``-singlestep`` (since 8.1)
 '''''''''''''''''''''''''''

 The ``-singlestep`` option has been given a name that better reflects
 what it actually does. For both linux-user and bsd-user, use the
 new ``-one-insn-per-tb`` option instead.

 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.

 ``StatusInfo`` member ``singlestep`` (since 8.1)
 ''''''''''''''''''''''''''''''''''''''''''''''''

 The ``singlestep`` member of the ``StatusInfo`` returned from the
 ``query-status`` command is deprecated. This member has a confusing
 name and it never did what the documentation claimed or what its name
 suggests. We do not believe that anybody is actually using the
 information provided in this member.

 The information it reports is whether the TCG JIT is in "one
 instruction per translated block" mode (which can be set on the
 command line or via the HMP, but not via QMP). The information remains
 available via the HMP 'info jit' command.

 QEMU Machine Protocol (QMP) events
 ----------------------------------

 ``MEM_UNPLUG_ERROR`` (since 6.2)
 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead.

 ``vcpu`` trace events (since 8.1)
 '''''''''''''''''''''''''''''''''

 The ability to instrument QEMU helper functions with vCPU-aware trace
 points was removed in 7.0. However QMP still exposed the vcpu
 parameter. This argument has now been deprecated and the remaining
 remaining trace points that used it are selected just by name.

 Human Monitor Protocol (HMP) commands
 -------------------------------------

 ``singlestep`` (since 8.1)
 ''''''''''''''''''''''''''

 The ``singlestep`` command has been replaced by the ``one-insn-per-tb``
 command, which has the same behaviour but a less misleading name.

 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.


 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.

 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 virtio-blk,scsi=on|off`` (since 5.0)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 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.

 ``-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.

 ``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 The 9p ``proxy`` filesystem backend driver has been deprecated and will be
 removed (along with its proxy helper daemon) in a future version of QEMU. Please
 use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem
 backend, or alternatively consider deploying virtiofsd instead.

 The 9p ``proxy`` backend was originally developed as an alternative to the 9p
 ``local`` backend. The idea was to enhance security by dispatching actual low
 level filesystem operations from 9p server (QEMU process) over to a separate
 process (the virtfs-proxy-helper binary). However this alternative never gained
 momentum. The proxy backend is much slower than the local backend, hasn't seen
 any development in years, and showed to be less secure, especially due to the
 fact that its helper daemon must be run as root, whereas with the local backend
 QEMU is typically run as unprivileged user and allows to tighten behaviour by
 mapping permissions et al by using its 'mapped' security model option.

 Nowadays it would make sense to reimplement the ``proxy`` backend by using
 QEMU's ``vhost`` feature, which would eliminate the high latency costs under
 which the 9p ``proxy`` backend currently suffers. However as of to date nobody
 has indicated plans for such kind of reimplementation unfortunately.


 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.

 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.

 QEMU guest agent
 ----------------

 ``--blacklist`` command line option (since 7.2)
 '''''''''''''''''''''''''''''''''''''''''''''''

 ``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better
 wording for what this option does). The short form ``-b`` still stays
 the same and thus is the preferred way for scripts that should run with
 both, older and future versions of QEMU.

 ``blacklist`` config file option (since 7.2)
 ''''''''''''''''''''''''''''''''''''''''''''

 The ``blacklist`` config file option has been renamed to ``block-rpcs``
 (to be in sync with the renaming of the corresponding command line
 option).

 Migration
 ---------

 ``skipped`` MigrationStats field (since 8.1)
 ''''''''''''''''''''''''''''''''''''''''''''

 ``skipped`` field in Migration stats has been deprecated.  It hasn't
 been used for more than 10 years.
	.. _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.

	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``.

	``-smp`` ("parameter=0" SMP configurations) (since 6.2)
	'''''''''''''''''''''''''''''''''''''''''''''''''''''''

	Specified CPU topology parameters must be greater than zero.

	In the SMP configuration, users should either provide a CPU topology
	parameter with a reasonable value (greater than zero) or just omit it
	and QEMU will compute the missing value.

	However, historically it was implicitly allowed for users to provide
	a parameter with zero value, which is meaningless and could also possibly
	cause unexpected results in the -smp parsing. So support for this kind of
	configurations (e.g. -smp 8,sockets=0) is deprecated since 6.2 and will
	be removed in the near future, users have to ensure that all the topology
	members described with -smp are greater than zero.

	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.

	``-no-hpet`` (since 8.0)
	''''''''''''''''''''''''

	The HPET setting has been turned into a machine property.
	Use ``-machine hpet=off`` instead.

	``-no-acpi`` (since 8.0)
	''''''''''''''''''''''''

	The ``-no-acpi`` setting has been turned into a machine property.
	Use ``-machine acpi=off`` instead.

	``-async-teardown`` (since 8.1)
	'''''''''''''''''''''''''''''''

	Use ``-run-with async-teardown=on`` instead.

	``-chroot`` (since 8.1)
	'''''''''''''''''''''''

	Use ``-run-with chroot=dir`` instead.

	``-singlestep`` (since 8.1)
	'''''''''''''''''''''''''''

	The ``-singlestep`` option has been turned into an accelerator property,
	and given a name that better reflects what it actually does.
	Use ``-accel tcg,one-insn-per-tb=on`` instead.

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

	``-singlestep`` (since 8.1)
	'''''''''''''''''''''''''''

	The ``-singlestep`` option has been given a name that better reflects
	what it actually does. For both linux-user and bsd-user, use the
	new ``-one-insn-per-tb`` option instead.

	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.

	``StatusInfo`` member ``singlestep`` (since 8.1)
	''''''''''''''''''''''''''''''''''''''''''''''''

	The ``singlestep`` member of the ``StatusInfo`` returned from the
	``query-status`` command is deprecated. This member has a confusing
	name and it never did what the documentation claimed or what its name
	suggests. We do not believe that anybody is actually using the
	information provided in this member.

	The information it reports is whether the TCG JIT is in "one
	instruction per translated block" mode (which can be set on the
	command line or via the HMP, but not via QMP). The information remains
	available via the HMP 'info jit' command.

	QEMU Machine Protocol (QMP) events
	----------------------------------

	``MEM_UNPLUG_ERROR`` (since 6.2)
	''''''''''''''''''''''''''''''''''''''''''''''''''''''''

	Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead.

	``vcpu`` trace events (since 8.1)
	'''''''''''''''''''''''''''''''''

	The ability to instrument QEMU helper functions with vCPU-aware trace
	points was removed in 7.0. However QMP still exposed the vcpu
	parameter. This argument has now been deprecated and the remaining
	remaining trace points that used it are selected just by name.

	Human Monitor Protocol (HMP) commands
	-------------------------------------

	``singlestep`` (since 8.1)
	''''''''''''''''''''''''''

	The ``singlestep`` command has been replaced by the ``one-insn-per-tb``
	command, which has the same behaviour but a less misleading name.

	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.


	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.

	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 virtio-blk,scsi=on\|off`` (since 5.0)
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	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.

	``-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.

	``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1)
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	The 9p ``proxy`` filesystem backend driver has been deprecated and will be
	removed (along with its proxy helper daemon) in a future version of QEMU. Please
	use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem
	backend, or alternatively consider deploying virtiofsd instead.

	The 9p ``proxy`` backend was originally developed as an alternative to the 9p
	``local`` backend. The idea was to enhance security by dispatching actual low
	level filesystem operations from 9p server (QEMU process) over to a separate
	process (the virtfs-proxy-helper binary). However this alternative never gained
	momentum. The proxy backend is much slower than the local backend, hasn't seen
	any development in years, and showed to be less secure, especially due to the
	fact that its helper daemon must be run as root, whereas with the local backend
	QEMU is typically run as unprivileged user and allows to tighten behaviour by
	mapping permissions et al by using its 'mapped' security model option.

	Nowadays it would make sense to reimplement the ``proxy`` backend by using
	QEMU's ``vhost`` feature, which would eliminate the high latency costs under
	which the 9p ``proxy`` backend currently suffers. However as of to date nobody
	has indicated plans for such kind of reimplementation unfortunately.


	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.

	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.

	QEMU guest agent
	----------------

	``--blacklist`` command line option (since 7.2)
	'''''''''''''''''''''''''''''''''''''''''''''''

	``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better
	wording for what this option does). The short form ``-b`` still stays
	the same and thus is the preferred way for scripts that should run with
	both, older and future versions of QEMU.

	``blacklist`` config file option (since 7.2)
	''''''''''''''''''''''''''''''''''''''''''''

	The ``blacklist`` config file option has been renamed to ``block-rpcs``
	(to be in sync with the renaming of the corresponding command line
	option).

	Migration
	---------

	``skipped`` MigrationStats field (since 8.1)
	''''''''''''''''''''''''''''''''''''''''''''

	``skipped`` field in Migration stats has been deprecated. It hasn't
	been used for more than 10 years.