1.. _Deprecated features: 2 3Deprecated features 4=================== 5 6In general features are intended to be supported indefinitely once 7introduced into QEMU. In the event that a feature needs to be removed, 8it will be listed in this section. The feature will remain functional for the 9release in which it was deprecated and one further release. After these two 10releases, the feature is liable to be removed. Deprecated features may also 11generate warnings on the console when QEMU starts up, or if activated via a 12monitor command, however, this is not a mandatory requirement. 13 14As a special exception to this general timeframe, rather than have an 15indefinite lifetime, versioned machine types are only intended to be 16supported for a period of 6 years, equivalent to 18 QEMU releases. All 17versioned machine types will be automatically marked deprecated after an 18initial 3 years (9 QEMU releases) has passed, and will then be deleted after 19a further 3 year period has passed. It is recommended that a deprecated 20machine type is only used for incoming migrations and restore of saved state, 21for pre-existing VM deployments. They should be scheduled for updating to a 22newer machine type during an appropriate service window. Newly deployed VMs 23should exclusively use a non-deprecated machine type, with use of the most 24recent version highly recommended. Non-versioned machine types follow the 25general feature deprecation policy. 26 27Prior to the 2.10.0 release there was no official policy on how 28long features would be deprecated prior to their removal, nor 29any documented list of which features were deprecated. Thus 30any features deprecated prior to 2.10.0 will be treated as if 31they were first deprecated in the 2.10.0 release. 32 33What follows is a list of all features currently marked as 34deprecated. 35 36System emulator command line arguments 37-------------------------------------- 38 39Short-form boolean options (since 6.0) 40'''''''''''''''''''''''''''''''''''''' 41 42Boolean options such as ``share=on``/``share=off`` could be written 43in short form as ``share`` and ``noshare``. This is now deprecated 44and will cause a warning. 45 46``delay`` option for socket character devices (since 6.0) 47''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 48 49The replacement for the ``nodelay`` short-form boolean option is ``nodelay=on`` 50rather than ``delay=off``. 51 52Plugin argument passing through ``arg=<string>`` (since 6.1) 53'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 54 55Passing TCG plugins arguments through ``arg=`` is redundant is makes the 56command-line less readable, especially when the argument itself consist of a 57name and a value, e.g. ``-plugin plugin_name,arg="arg_name=arg_value"``. 58Therefore, the usage of ``arg`` is redundant. Single-word arguments are treated 59as short-form boolean values, and passed to plugins as ``arg_name=on``. 60However, short-form booleans are deprecated and full explicit ``arg_name=on`` 61form is preferred. 62 63``-smp`` (Unsupported "parameter=1" SMP configurations) (since 9.0) 64''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 65 66Specified CPU topology parameters must be supported by the machine. 67 68In the SMP configuration, users should provide the CPU topology parameters that 69are supported by the target machine. 70 71However, historically it was allowed for users to specify the unsupported 72topology parameter as "1", which is meaningless. So support for this kind of 73configurations (e.g. -smp drawers=1,books=1,clusters=1 for x86 PC machine) is 74marked deprecated since 9.0, users have to ensure that all the topology members 75described with -smp are supported by the target machine. 76 77``-runas`` (since 9.1) 78---------------------- 79 80Use ``-run-with user=..`` instead. 81 82 83User-mode emulator command line arguments 84----------------------------------------- 85 86``-p`` (since 9.0) 87'''''''''''''''''' 88 89The ``-p`` option pretends to control the host page size. However, 90it is not possible to change the host page size, and using the 91option only causes failures. 92 93QEMU Machine Protocol (QMP) commands 94------------------------------------ 95 96``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8) 97''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 98 99Use argument ``id`` instead. 100 101``eject`` argument ``device`` (since 2.8) 102''''''''''''''''''''''''''''''''''''''''' 103 104Use argument ``id`` instead. 105 106``blockdev-change-medium`` argument ``device`` (since 2.8) 107'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 108 109Use argument ``id`` instead. 110 111``block_set_io_throttle`` argument ``device`` (since 2.8) 112''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 113 114Use argument ``id`` instead. 115 116``blockdev-add`` empty string argument ``backing`` (since 2.10) 117''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 118 119Use argument value ``null`` instead. 120 121``block-commit`` arguments ``base`` and ``top`` (since 3.1) 122''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 123 124Use arguments ``base-node`` and ``top-node`` instead. 125 126``nbd-server-add`` and ``nbd-server-remove`` (since 5.2) 127'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 128 129Use the more generic commands ``block-export-add`` and ``block-export-del`` 130instead. As part of this deprecation, where ``nbd-server-add`` used a 131single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``. 132 133``query-qmp-schema`` return value member ``values`` (since 6.2) 134''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 135 136Member ``values`` in return value elements with meta-type ``enum`` is 137deprecated. Use ``members`` instead. 138 139``drive-backup`` (since 6.2) 140'''''''''''''''''''''''''''' 141 142Use ``blockdev-backup`` in combination with ``blockdev-add`` instead. 143This change primarily separates the creation/opening process of the backup 144target with explicit, separate steps. ``blockdev-backup`` uses mostly the 145same arguments as ``drive-backup``, except the ``format`` and ``mode`` 146options are removed in favor of using explicit ``blockdev-create`` and 147``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for 148details. 149 150Incorrectly typed ``device_add`` arguments (since 6.2) 151'''''''''''''''''''''''''''''''''''''''''''''''''''''' 152 153Due to shortcomings in the internal implementation of ``device_add``, QEMU 154incorrectly accepts certain invalid arguments: Any object or list arguments are 155silently ignored. Other argument types are not checked, but an implicit 156conversion happens, so that e.g. string values can be assigned to integer 157device properties or vice versa. 158 159This is a bug in QEMU that will be fixed in the future so that previously 160accepted incorrect commands will return an error. Users should make sure that 161all arguments passed to ``device_add`` are consistent with the documented 162property types. 163 164Host Architectures 165------------------ 166 167BE MIPS (since 7.2) 168''''''''''''''''''' 169 170As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of 171MIPS moved out of support making it hard to maintain our 172cross-compilation CI tests of the architecture. As we no longer have 173CI coverage support may bitrot away before the deprecation process 174completes. The little endian variants of MIPS (both 32 and 64 bit) are 175still a supported host architecture. 176 177System emulation on 32-bit x86 hosts (since 8.0) 178'''''''''''''''''''''''''''''''''''''''''''''''' 179 180Support for 32-bit x86 host deployments is increasingly uncommon in mainstream 181OS distributions given the widespread availability of 64-bit x86 hardware. 182The QEMU project no longer considers 32-bit x86 support for system emulation to 183be an effective use of its limited resources, and thus intends to discontinue 184it. Since all recent x86 hardware from the past >10 years is capable of the 18564-bit x86 extensions, a corresponding 64-bit OS should be used instead. 186 187 188System emulator CPUs 189-------------------- 190 191``power5+`` and ``power7+`` CPU names (since 9.0) 192''''''''''''''''''''''''''''''''''''''''''''''''' 193 194The character "+" in device (and thus also CPU) names is not allowed 195in the QEMU object model anymore. ``power5+``, ``power5+_v2.1``, 196``power7+`` and ``power7+_v2.1`` are currently still supported via 197an alias, but for consistency these will get removed in a future 198release, too. Use ``power5p_v2.1`` and ``power7p_v2.1`` instead. 199 200``Sun-UltraSparc-IIIi+`` and ``Sun-UltraSparc-IV+`` CPU names (since 9.1) 201''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 202 203The character "+" in device (and thus also CPU) names is not allowed 204in the QEMU object model anymore. ``Sun-UltraSparc-IIIi+`` and 205``Sun-UltraSparc-IV+`` are currently still supported via a workaround, 206but for consistency these will get removed in a future release, too. 207Use ``Sun-UltraSparc-IIIi-plus`` and ``Sun-UltraSparc-IV-plus`` instead. 208 209CRIS CPU architecture (since 9.0) 210''''''''''''''''''''''''''''''''' 211 212The CRIS architecture was pulled from Linux in 4.17 and the compiler 213is no longer packaged in any distro making it harder to run the 214``check-tcg`` tests. Unless we can improve the testing situation there 215is a chance the code will bitrot without anyone noticing. 216 217System emulator machines 218------------------------ 219 220Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1) 221'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 222 223The ``dtb-kaslr-seed`` property on the ``virt`` board has been 224deprecated; use the new name ``dtb-randomness`` instead. The new name 225better reflects the way this property affects all random data within 226the device tree blob, not just the ``kaslr-seed`` node. 227 228``pc-i440fx-2.4`` up to ``pc-i440fx-2.12`` (since 9.1) 229'''''''''''''''''''''''''''''''''''''''''''''''''''''' 230 231These old machine types are quite neglected nowadays and thus might have 232various pitfalls with regards to live migration. Use a newer machine type 233instead. 234 235``shix`` (since 9.0) 236'''''''''''''''''''' 237 238The machine is no longer in existence and has been long unmaintained 239in QEMU. This also holds for the TC51828 16MiB flash that it uses. 240 241``pseries-2.1`` up to ``pseries-2.12`` (since 9.0) 242'''''''''''''''''''''''''''''''''''''''''''''''''' 243 244Older pseries machines before version 3.0 have undergone many changes 245to correct issues, mostly regarding migration compatibility. These are 246no longer maintained and removing them will make the code easier to 247read and maintain. Use versions 3.0 and above as a replacement. 248 249Arm machines ``akita``, ``borzoi``, ``cheetah``, ``connex``, ``mainstone``, ``n800``, ``n810``, ``spitz``, ``terrier``, ``tosa``, ``verdex``, ``z2`` (since 9.0) 250'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 251 252QEMU includes models of some machine types where the QEMU code that 253emulates their SoCs is very old and unmaintained. This code is now 254blocking our ability to move forward with various changes across 255the codebase, and over many years nobody has been interested in 256trying to modernise it. We don't expect any of these machines to have 257a large number of users, because they're all modelling hardware that 258has now passed away into history. We are therefore dropping support 259for all machine types using the PXA2xx and OMAP2 SoCs. We are also 260dropping the ``cheetah`` OMAP1 board, because we don't have any 261test images for it and don't know of anybody who does; the ``sx1`` 262and ``sx1-v1`` OMAP1 machines remain supported for now. 263 264PPC 405 ``ref405ep`` machine (since 9.1) 265'''''''''''''''''''''''''''''''''''''''' 266 267The ``ref405ep`` machine and PPC 405 CPU have no known users, firmware 268images are not available, OpenWRT dropped support in 2019, U-Boot in 2692017, Linux also is dropping support in 2024. It is time to let go of 270this ancient hardware and focus on newer CPUs and platforms. 271 272Arm ``tacoma-bmc`` machine (since 9.1) 273'''''''''''''''''''''''''''''''''''''''' 274 275The ``tacoma-bmc`` machine was a board including an AST2600 SoC based 276BMC and a witherspoon like OpenPOWER system. It was used for bring up 277of the AST2600 SoC in labs. It can be easily replaced by the 278``rainier-bmc`` machine which is a real product. 279 280Backend options 281--------------- 282 283Using non-persistent backing file with pmem=on (since 6.1) 284'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 285 286This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 287device. However enabling ``memory-backend-file.pmem`` option, when backing file 288is (a) not DAX capable or (b) not on a filesystem that support direct mapping 289of persistent memory, is not safe and may lead to data loss or corruption in case 290of host crash. 291Options are: 292 293 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 294 (without persistence guaranties) with backing file on non DAX storage 295 - move backing file to NVDIMM storage and keep ``pmem=on`` 296 (to have NVDIMM with persistence guaranties). 297 298Device options 299-------------- 300 301Emulated device options 302''''''''''''''''''''''' 303 304``-device nvme-ns,eui64-default=on|off`` (since 7.1) 305^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 306 307In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 308identifier that is not globally unique. If an EUI-64 identifier is required, the 309user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 310 311``-device nvme,use-intel-id=on|off`` (since 7.1) 312^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 313 314The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 315from Intel that was not properly allocated. Since version 5.2, the controller 316has used a properly allocated identifier. Deprecate the ``use-intel-id`` 317machine compatibility parameter. 318 319``-device cxl-type3,memdev=xxxx`` (since 8.0) 320^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 321 322The ``cxl-type3`` device initially only used a single memory backend. With 323the addition of volatile memory support, it is now necessary to distinguish 324between persistent and volatile memory backends. As such, memdev is deprecated 325in favor of persistent-memdev. 326 327``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1) 328^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 329 330The 9p ``proxy`` filesystem backend driver has been deprecated and will be 331removed (along with its proxy helper daemon) in a future version of QEMU. Please 332use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem 333backend, or alternatively consider deploying virtiofsd instead. 334 335The 9p ``proxy`` backend was originally developed as an alternative to the 9p 336``local`` backend. The idea was to enhance security by dispatching actual low 337level filesystem operations from 9p server (QEMU process) over to a separate 338process (the virtfs-proxy-helper binary). However this alternative never gained 339momentum. The proxy backend is much slower than the local backend, hasn't seen 340any development in years, and showed to be less secure, especially due to the 341fact that its helper daemon must be run as root, whereas with the local backend 342QEMU is typically run as unprivileged user and allows to tighten behaviour by 343mapping permissions et al by using its 'mapped' security model option. 344 345Nowadays it would make sense to reimplement the ``proxy`` backend by using 346QEMU's ``vhost`` feature, which would eliminate the high latency costs under 347which the 9p ``proxy`` backend currently suffers. However as of to date nobody 348has indicated plans for such kind of reimplementation unfortunately. 349 350RISC-V 'any' CPU type ``-cpu any`` (since 8.2) 351^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 352 353The 'any' CPU type was introduced back in 2018 and has been around since the 354initial RISC-V QEMU port. Its usage has always been unclear: users don't know 355what to expect from a CPU called 'any', and in fact the CPU does not do anything 356special that isn't already done by the default CPUs rv32/rv64. 357 358After the introduction of the 'max' CPU type, RISC-V now has a good coverage 359of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete 360CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any' 361CPU type starting in 8.2. 362 363RISC-V CPU properties which start with capital 'Z' (since 8.2) 364^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 365 366All RISC-V CPU properties which start with capital 'Z' are being deprecated 367starting in 8.2. The reason is that they were wrongly added with capital 'Z' 368in the past. CPU properties were later added with lower-case names, which 369is the format we want to use from now on. 370 371Users which try to use these deprecated properties will receive a warning 372recommending to switch to their stable counterparts: 373 374- "Zifencei" should be replaced with "zifencei" 375- "Zicsr" should be replaced with "zicsr" 376- "Zihintntl" should be replaced with "zihintntl" 377- "Zihintpause" should be replaced with "zihintpause" 378- "Zawrs" should be replaced with "zawrs" 379- "Zfa" should be replaced with "zfa" 380- "Zfh" should be replaced with "zfh" 381- "Zfhmin" should be replaced with "zfhmin" 382- "Zve32f" should be replaced with "zve32f" 383- "Zve64f" should be replaced with "zve64f" 384- "Zve64d" should be replaced with "zve64d" 385 386``-device sd-card,spec_version=1`` (since 9.1) 387^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 388 389SD physical layer specification v2.00 supersedes the v1.10 one. 390v2.00 is the default since QEMU 3.0.0. 391 392Block device options 393'''''''''''''''''''' 394 395``"backing": ""`` (since 2.12) 396^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 397 398In order to prevent QEMU from automatically opening an image's backing 399chain, use ``"backing": null`` instead. 400 401``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1) 402^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 403 404Options for ``rbd`` should be specified according to its runtime options, 405like other block drivers. Legacy parsing of keyvalue pair encoded 406filenames is useful to open images with the old format for backing files; 407These image files should be updated to use the current format. 408 409Example of legacy encoding:: 410 411 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"} 412 413The above, converted to the current supported format:: 414 415 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"} 416 417``iscsi,password=xxx`` (since 8.0) 418^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 419 420Specifying the iSCSI password in plain text on the command line using the 421``password`` option is insecure. The ``password-secret`` option should be 422used instead, to refer to a ``--object secret...`` instance that provides 423a password via a file, or encrypted. 424 425Character device options 426'''''''''''''''''''''''' 427 428Backend ``memory`` (since 9.0) 429^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 430 431``memory`` is a deprecated synonym for ``ringbuf``. 432 433CPU device properties 434''''''''''''''''''''' 435 436``pcommit`` on x86 (since 9.1) 437^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 438 439The PCOMMIT instruction was never included in any physical processor. 440It was implemented as a no-op instruction in TCG up to QEMU 9.0, but 441only with ``-cpu max`` (which does not guarantee migration compatibility 442across versions). 443 444``pmu-num=n`` on RISC-V CPUs (since 8.2) 445^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 446 447In order to support more flexible counter configurations this has been replaced 448by a ``pmu-mask`` property. If set of counters is continuous then the mask can 449be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits 450must be left clear. 451 452 453Backwards compatibility 454----------------------- 455 456Runnability guarantee of CPU models (since 4.1) 457''''''''''''''''''''''''''''''''''''''''''''''' 458 459Previous versions of QEMU never changed existing CPU models in 460ways that introduced additional host software or hardware 461requirements to the VM. This allowed management software to 462safely change the machine type of an existing VM without 463introducing new requirements ("runnability guarantee"). This 464prevented CPU models from being updated to include CPU 465vulnerability mitigations, leaving guests vulnerable in the 466default configuration. 467 468The CPU model runnability guarantee won't apply anymore to 469existing CPU models. Management software that needs runnability 470guarantees must resolve the CPU model aliases using the 471``alias-of`` field returned by the ``query-cpu-definitions`` QMP 472command. 473 474While those guarantees are kept, the return value of 475``query-cpu-definitions`` will have existing CPU model aliases 476point to a version that doesn't break runnability guarantees 477(specifically, version 1 of those CPU models). In future QEMU 478versions, aliases will point to newer CPU model versions 479depending on the machine type, so management software must 480resolve CPU model aliases before starting a virtual machine. 481 482RISC-V "virt" board "riscv,delegate" DT property (since 9.1) 483'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 484 485The "riscv,delegate" DT property was added in QEMU 7.0 as part of 486the AIA APLIC support. The property changed name during the review 487process in Linux and the correct name ended up being 488"riscv,delegation". Changing the DT property name will break all 489available firmwares that are using the current (wrong) name. The 490property is kept as is in 9.1, together with "riscv,delegation", to 491give more time for firmware developers to change their code. 492 493Migration 494--------- 495 496``fd:`` URI when used for file migration (since 9.1) 497'''''''''''''''''''''''''''''''''''''''''''''''''''' 498 499The ``fd:`` URI can currently provide a file descriptor that 500references either a socket or a plain file. These are two different 501types of migration. In order to reduce ambiguity, the ``fd:`` URI 502usage of providing a file descriptor to a plain file has been 503deprecated in favor of explicitly using the ``file:`` URI with the 504file descriptor being passed as an ``fdset``. Refer to the ``add-fd`` 505command documentation for details on the ``fdset`` usage. 506