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``pseries-2.1`` up to ``pseries-2.12`` (since 9.0) 236'''''''''''''''''''''''''''''''''''''''''''''''''' 237 238Older pseries machines before version 3.0 have undergone many changes 239to correct issues, mostly regarding migration compatibility. These are 240no longer maintained and removing them will make the code easier to 241read and maintain. Use versions 3.0 and above as a replacement. 242 243Arm machines ``akita``, ``borzoi``, ``cheetah``, ``connex``, ``mainstone``, ``n800``, ``n810``, ``spitz``, ``terrier``, ``tosa``, ``verdex``, ``z2`` (since 9.0) 244'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 245 246QEMU includes models of some machine types where the QEMU code that 247emulates their SoCs is very old and unmaintained. This code is now 248blocking our ability to move forward with various changes across 249the codebase, and over many years nobody has been interested in 250trying to modernise it. We don't expect any of these machines to have 251a large number of users, because they're all modelling hardware that 252has now passed away into history. We are therefore dropping support 253for all machine types using the PXA2xx and OMAP2 SoCs. We are also 254dropping the ``cheetah`` OMAP1 board, because we don't have any 255test images for it and don't know of anybody who does; the ``sx1`` 256and ``sx1-v1`` OMAP1 machines remain supported for now. 257 258PPC 405 ``ref405ep`` machine (since 9.1) 259'''''''''''''''''''''''''''''''''''''''' 260 261The ``ref405ep`` machine and PPC 405 CPU have no known users, firmware 262images are not available, OpenWRT dropped support in 2019, U-Boot in 2632017, Linux also is dropping support in 2024. It is time to let go of 264this ancient hardware and focus on newer CPUs and platforms. 265 266Arm ``tacoma-bmc`` machine (since 9.1) 267'''''''''''''''''''''''''''''''''''''''' 268 269The ``tacoma-bmc`` machine was a board including an AST2600 SoC based 270BMC and a witherspoon like OpenPOWER system. It was used for bring up 271of the AST2600 SoC in labs. It can be easily replaced by the 272``rainier-bmc`` machine which is a real product. 273 274Backend options 275--------------- 276 277Using non-persistent backing file with pmem=on (since 6.1) 278'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 279 280This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 281device. However enabling ``memory-backend-file.pmem`` option, when backing file 282is (a) not DAX capable or (b) not on a filesystem that support direct mapping 283of persistent memory, is not safe and may lead to data loss or corruption in case 284of host crash. 285Options are: 286 287 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 288 (without persistence guaranties) with backing file on non DAX storage 289 - move backing file to NVDIMM storage and keep ``pmem=on`` 290 (to have NVDIMM with persistence guaranties). 291 292Device options 293-------------- 294 295Emulated device options 296''''''''''''''''''''''' 297 298``-device nvme-ns,eui64-default=on|off`` (since 7.1) 299^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 300 301In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 302identifier that is not globally unique. If an EUI-64 identifier is required, the 303user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 304 305``-device nvme,use-intel-id=on|off`` (since 7.1) 306^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 307 308The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 309from Intel that was not properly allocated. Since version 5.2, the controller 310has used a properly allocated identifier. Deprecate the ``use-intel-id`` 311machine compatibility parameter. 312 313``-device cxl-type3,memdev=xxxx`` (since 8.0) 314^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 315 316The ``cxl-type3`` device initially only used a single memory backend. With 317the addition of volatile memory support, it is now necessary to distinguish 318between persistent and volatile memory backends. As such, memdev is deprecated 319in favor of persistent-memdev. 320 321``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1) 322^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 323 324The 9p ``proxy`` filesystem backend driver has been deprecated and will be 325removed (along with its proxy helper daemon) in a future version of QEMU. Please 326use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem 327backend, or alternatively consider deploying virtiofsd instead. 328 329The 9p ``proxy`` backend was originally developed as an alternative to the 9p 330``local`` backend. The idea was to enhance security by dispatching actual low 331level filesystem operations from 9p server (QEMU process) over to a separate 332process (the virtfs-proxy-helper binary). However this alternative never gained 333momentum. The proxy backend is much slower than the local backend, hasn't seen 334any development in years, and showed to be less secure, especially due to the 335fact that its helper daemon must be run as root, whereas with the local backend 336QEMU is typically run as unprivileged user and allows to tighten behaviour by 337mapping permissions et al by using its 'mapped' security model option. 338 339Nowadays it would make sense to reimplement the ``proxy`` backend by using 340QEMU's ``vhost`` feature, which would eliminate the high latency costs under 341which the 9p ``proxy`` backend currently suffers. However as of to date nobody 342has indicated plans for such kind of reimplementation unfortunately. 343 344RISC-V 'any' CPU type ``-cpu any`` (since 8.2) 345^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 346 347The 'any' CPU type was introduced back in 2018 and has been around since the 348initial RISC-V QEMU port. Its usage has always been unclear: users don't know 349what to expect from a CPU called 'any', and in fact the CPU does not do anything 350special that isn't already done by the default CPUs rv32/rv64. 351 352After the introduction of the 'max' CPU type, RISC-V now has a good coverage 353of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete 354CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any' 355CPU type starting in 8.2. 356 357RISC-V CPU properties which start with capital 'Z' (since 8.2) 358^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 359 360All RISC-V CPU properties which start with capital 'Z' are being deprecated 361starting in 8.2. The reason is that they were wrongly added with capital 'Z' 362in the past. CPU properties were later added with lower-case names, which 363is the format we want to use from now on. 364 365Users which try to use these deprecated properties will receive a warning 366recommending to switch to their stable counterparts: 367 368- "Zifencei" should be replaced with "zifencei" 369- "Zicsr" should be replaced with "zicsr" 370- "Zihintntl" should be replaced with "zihintntl" 371- "Zihintpause" should be replaced with "zihintpause" 372- "Zawrs" should be replaced with "zawrs" 373- "Zfa" should be replaced with "zfa" 374- "Zfh" should be replaced with "zfh" 375- "Zfhmin" should be replaced with "zfhmin" 376- "Zve32f" should be replaced with "zve32f" 377- "Zve64f" should be replaced with "zve64f" 378- "Zve64d" should be replaced with "zve64d" 379 380``-device sd-card,spec_version=1`` (since 9.1) 381^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 382 383SD physical layer specification v2.00 supersedes the v1.10 one. 384v2.00 is the default since QEMU 3.0.0. 385 386Block device options 387'''''''''''''''''''' 388 389``"backing": ""`` (since 2.12) 390^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 391 392In order to prevent QEMU from automatically opening an image's backing 393chain, use ``"backing": null`` instead. 394 395``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1) 396^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 397 398Options for ``rbd`` should be specified according to its runtime options, 399like other block drivers. Legacy parsing of keyvalue pair encoded 400filenames is useful to open images with the old format for backing files; 401These image files should be updated to use the current format. 402 403Example of legacy encoding:: 404 405 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"} 406 407The above, converted to the current supported format:: 408 409 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"} 410 411``iscsi,password=xxx`` (since 8.0) 412^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 413 414Specifying the iSCSI password in plain text on the command line using the 415``password`` option is insecure. The ``password-secret`` option should be 416used instead, to refer to a ``--object secret...`` instance that provides 417a password via a file, or encrypted. 418 419Character device options 420'''''''''''''''''''''''' 421 422Backend ``memory`` (since 9.0) 423^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 424 425``memory`` is a deprecated synonym for ``ringbuf``. 426 427CPU device properties 428''''''''''''''''''''' 429 430``pcommit`` on x86 (since 9.1) 431^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 432 433The PCOMMIT instruction was never included in any physical processor. 434It was implemented as a no-op instruction in TCG up to QEMU 9.0, but 435only with ``-cpu max`` (which does not guarantee migration compatibility 436across versions). 437 438``pmu-num=n`` on RISC-V CPUs (since 8.2) 439^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 440 441In order to support more flexible counter configurations this has been replaced 442by a ``pmu-mask`` property. If set of counters is continuous then the mask can 443be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits 444must be left clear. 445 446 447Backwards compatibility 448----------------------- 449 450Runnability guarantee of CPU models (since 4.1) 451''''''''''''''''''''''''''''''''''''''''''''''' 452 453Previous versions of QEMU never changed existing CPU models in 454ways that introduced additional host software or hardware 455requirements to the VM. This allowed management software to 456safely change the machine type of an existing VM without 457introducing new requirements ("runnability guarantee"). This 458prevented CPU models from being updated to include CPU 459vulnerability mitigations, leaving guests vulnerable in the 460default configuration. 461 462The CPU model runnability guarantee won't apply anymore to 463existing CPU models. Management software that needs runnability 464guarantees must resolve the CPU model aliases using the 465``alias-of`` field returned by the ``query-cpu-definitions`` QMP 466command. 467 468While those guarantees are kept, the return value of 469``query-cpu-definitions`` will have existing CPU model aliases 470point to a version that doesn't break runnability guarantees 471(specifically, version 1 of those CPU models). In future QEMU 472versions, aliases will point to newer CPU model versions 473depending on the machine type, so management software must 474resolve CPU model aliases before starting a virtual machine. 475 476RISC-V "virt" board "riscv,delegate" DT property (since 9.1) 477'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 478 479The "riscv,delegate" DT property was added in QEMU 7.0 as part of 480the AIA APLIC support. The property changed name during the review 481process in Linux and the correct name ended up being 482"riscv,delegation". Changing the DT property name will break all 483available firmwares that are using the current (wrong) name. The 484property is kept as is in 9.1, together with "riscv,delegation", to 485give more time for firmware developers to change their code. 486 487Migration 488--------- 489 490``fd:`` URI when used for file migration (since 9.1) 491'''''''''''''''''''''''''''''''''''''''''''''''''''' 492 493The ``fd:`` URI can currently provide a file descriptor that 494references either a socket or a plain file. These are two different 495types of migration. In order to reduce ambiguity, the ``fd:`` URI 496usage of providing a file descriptor to a plain file has been 497deprecated in favor of explicitly using the ``file:`` URI with the 498file descriptor being passed as an ``fdset``. Refer to the ``add-fd`` 499command documentation for details on the ``fdset`` usage. 500