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 14Prior to the 2.10.0 release there was no official policy on how 15long features would be deprecated prior to their removal, nor 16any documented list of which features were deprecated. Thus 17any features deprecated prior to 2.10.0 will be treated as if 18they were first deprecated in the 2.10.0 release. 19 20What follows is a list of all features currently marked as 21deprecated. 22 23System emulator command line arguments 24-------------------------------------- 25 26Short-form boolean options (since 6.0) 27'''''''''''''''''''''''''''''''''''''' 28 29Boolean options such as ``share=on``/``share=off`` could be written 30in short form as ``share`` and ``noshare``. This is now deprecated 31and will cause a warning. 32 33``delay`` option for socket character devices (since 6.0) 34''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 35 36The replacement for the ``nodelay`` short-form boolean option is ``nodelay=on`` 37rather than ``delay=off``. 38 39Plugin argument passing through ``arg=<string>`` (since 6.1) 40'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 41 42Passing TCG plugins arguments through ``arg=`` is redundant is makes the 43command-line less readable, especially when the argument itself consist of a 44name and a value, e.g. ``-plugin plugin_name,arg="arg_name=arg_value"``. 45Therefore, the usage of ``arg`` is redundant. Single-word arguments are treated 46as short-form boolean values, and passed to plugins as ``arg_name=on``. 47However, short-form booleans are deprecated and full explicit ``arg_name=on`` 48form is preferred. 49 50``-smp`` (Unsupported "parameter=1" SMP configurations) (since 9.0) 51''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 52 53Specified CPU topology parameters must be supported by the machine. 54 55In the SMP configuration, users should provide the CPU topology parameters that 56are supported by the target machine. 57 58However, historically it was allowed for users to specify the unsupported 59topology parameter as "1", which is meaningless. So support for this kind of 60configurations (e.g. -smp drawers=1,books=1,clusters=1 for x86 PC machine) is 61marked deprecated since 9.0, users have to ensure that all the topology members 62described with -smp are supported by the target machine. 63 64``-runas`` (since 9.1) 65---------------------- 66 67Use ``-run-with user=..`` instead. 68 69 70User-mode emulator command line arguments 71----------------------------------------- 72 73``-p`` (since 9.0) 74'''''''''''''''''' 75 76The ``-p`` option pretends to control the host page size. However, 77it is not possible to change the host page size, and using the 78option only causes failures. 79 80QEMU Machine Protocol (QMP) commands 81------------------------------------ 82 83``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8) 84''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 85 86Use argument ``id`` instead. 87 88``eject`` argument ``device`` (since 2.8) 89''''''''''''''''''''''''''''''''''''''''' 90 91Use argument ``id`` instead. 92 93``blockdev-change-medium`` argument ``device`` (since 2.8) 94'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 95 96Use argument ``id`` instead. 97 98``block_set_io_throttle`` argument ``device`` (since 2.8) 99''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 100 101Use argument ``id`` instead. 102 103``blockdev-add`` empty string argument ``backing`` (since 2.10) 104''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 105 106Use argument value ``null`` instead. 107 108``block-commit`` arguments ``base`` and ``top`` (since 3.1) 109''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 110 111Use arguments ``base-node`` and ``top-node`` instead. 112 113``nbd-server-add`` and ``nbd-server-remove`` (since 5.2) 114'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 115 116Use the more generic commands ``block-export-add`` and ``block-export-del`` 117instead. As part of this deprecation, where ``nbd-server-add`` used a 118single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``. 119 120``query-qmp-schema`` return value member ``values`` (since 6.2) 121''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 122 123Member ``values`` in return value elements with meta-type ``enum`` is 124deprecated. Use ``members`` instead. 125 126``drive-backup`` (since 6.2) 127'''''''''''''''''''''''''''' 128 129Use ``blockdev-backup`` in combination with ``blockdev-add`` instead. 130This change primarily separates the creation/opening process of the backup 131target with explicit, separate steps. ``blockdev-backup`` uses mostly the 132same arguments as ``drive-backup``, except the ``format`` and ``mode`` 133options are removed in favor of using explicit ``blockdev-create`` and 134``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for 135details. 136 137Incorrectly typed ``device_add`` arguments (since 6.2) 138'''''''''''''''''''''''''''''''''''''''''''''''''''''' 139 140Due to shortcomings in the internal implementation of ``device_add``, QEMU 141incorrectly accepts certain invalid arguments: Any object or list arguments are 142silently ignored. Other argument types are not checked, but an implicit 143conversion happens, so that e.g. string values can be assigned to integer 144device properties or vice versa. 145 146This is a bug in QEMU that will be fixed in the future so that previously 147accepted incorrect commands will return an error. Users should make sure that 148all arguments passed to ``device_add`` are consistent with the documented 149property types. 150 151QEMU Machine Protocol (QMP) events 152---------------------------------- 153 154``MEM_UNPLUG_ERROR`` (since 6.2) 155'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 156 157Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead. 158 159``vcpu`` trace events (since 8.1) 160''''''''''''''''''''''''''''''''' 161 162The ability to instrument QEMU helper functions with vCPU-aware trace 163points was removed in 7.0. However QMP still exposed the vcpu 164parameter. This argument has now been deprecated and the remaining 165remaining trace points that used it are selected just by name. 166 167Host Architectures 168------------------ 169 170BE MIPS (since 7.2) 171''''''''''''''''''' 172 173As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of 174MIPS moved out of support making it hard to maintain our 175cross-compilation CI tests of the architecture. As we no longer have 176CI coverage support may bitrot away before the deprecation process 177completes. The little endian variants of MIPS (both 32 and 64 bit) are 178still a supported host architecture. 179 180System emulation on 32-bit x86 hosts (since 8.0) 181'''''''''''''''''''''''''''''''''''''''''''''''' 182 183Support for 32-bit x86 host deployments is increasingly uncommon in mainstream 184OS distributions given the widespread availability of 64-bit x86 hardware. 185The QEMU project no longer considers 32-bit x86 support for system emulation to 186be an effective use of its limited resources, and thus intends to discontinue 187it. Since all recent x86 hardware from the past >10 years is capable of the 18864-bit x86 extensions, a corresponding 64-bit OS should be used instead. 189 190 191System emulator CPUs 192-------------------- 193 194``power5+`` and ``power7+`` CPU names (since 9.0) 195''''''''''''''''''''''''''''''''''''''''''''''''' 196 197The character "+" in device (and thus also CPU) names is not allowed 198in the QEMU object model anymore. ``power5+``, ``power5+_v2.1``, 199``power7+`` and ``power7+_v2.1`` are currently still supported via 200an alias, but for consistency these will get removed in a future 201release, too. Use ``power5p_v2.1`` and ``power7p_v2.1`` instead. 202 203``Sun-UltraSparc-IIIi+`` and ``Sun-UltraSparc-IV+`` CPU names (since 9.1) 204''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 205 206The character "+" in device (and thus also CPU) names is not allowed 207in the QEMU object model anymore. ``Sun-UltraSparc-IIIi+`` and 208``Sun-UltraSparc-IV+`` are currently still supported via a workaround, 209but for consistency these will get removed in a future release, too. 210Use ``Sun-UltraSparc-IIIi-plus`` and ``Sun-UltraSparc-IV-plus`` instead. 211 212CRIS CPU architecture (since 9.0) 213''''''''''''''''''''''''''''''''' 214 215The CRIS architecture was pulled from Linux in 4.17 and the compiler 216is no longer packaged in any distro making it harder to run the 217``check-tcg`` tests. Unless we can improve the testing situation there 218is a chance the code will bitrot without anyone noticing. 219 220System emulator machines 221------------------------ 222 223Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1) 224'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 225 226The ``dtb-kaslr-seed`` property on the ``virt`` board has been 227deprecated; use the new name ``dtb-randomness`` instead. The new name 228better reflects the way this property affects all random data within 229the device tree blob, not just the ``kaslr-seed`` node. 230 231``pc-i440fx-2.0`` up to ``pc-i440fx-2.3`` (since 8.2) 232''''''''''''''''''''''''''''''''''''''''''''''''''''' 233 234These old machine types are quite neglected nowadays and thus might have 235various pitfalls with regards to live migration. Use a newer machine type 236instead. 237 238``shix`` (since 9.0) 239'''''''''''''''''''' 240 241The machine is no longer in existence and has been long unmaintained 242in QEMU. This also holds for the TC51828 16MiB flash that it uses. 243 244``pseries-2.1`` up to ``pseries-2.12`` (since 9.0) 245'''''''''''''''''''''''''''''''''''''''''''''''''' 246 247Older pseries machines before version 3.0 have undergone many changes 248to correct issues, mostly regarding migration compatibility. These are 249no longer maintained and removing them will make the code easier to 250read and maintain. Use versions 3.0 and above as a replacement. 251 252Arm machines ``akita``, ``borzoi``, ``cheetah``, ``connex``, ``mainstone``, ``n800``, ``n810``, ``spitz``, ``terrier``, ``tosa``, ``verdex``, ``z2`` (since 9.0) 253'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 254 255QEMU includes models of some machine types where the QEMU code that 256emulates their SoCs is very old and unmaintained. This code is now 257blocking our ability to move forward with various changes across 258the codebase, and over many years nobody has been interested in 259trying to modernise it. We don't expect any of these machines to have 260a large number of users, because they're all modelling hardware that 261has now passed away into history. We are therefore dropping support 262for all machine types using the PXA2xx and OMAP2 SoCs. We are also 263dropping the ``cheetah`` OMAP1 board, because we don't have any 264test images for it and don't know of anybody who does; the ``sx1`` 265and ``sx1-v1`` OMAP1 machines remain supported for now. 266 267PPC 405 ``ref405ep`` machine (since 9.1) 268'''''''''''''''''''''''''''''''''''''''' 269 270The ``ref405ep`` machine and PPC 405 CPU have no known users, firmware 271images are not available, OpenWRT dropped support in 2019, U-Boot in 2722017, Linux also is dropping support in 2024. It is time to let go of 273this ancient hardware and focus on newer CPUs and platforms. 274 275Backend options 276--------------- 277 278Using non-persistent backing file with pmem=on (since 6.1) 279'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 280 281This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 282device. However enabling ``memory-backend-file.pmem`` option, when backing file 283is (a) not DAX capable or (b) not on a filesystem that support direct mapping 284of persistent memory, is not safe and may lead to data loss or corruption in case 285of host crash. 286Options are: 287 288 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 289 (without persistence guaranties) with backing file on non DAX storage 290 - move backing file to NVDIMM storage and keep ``pmem=on`` 291 (to have NVDIMM with persistence guaranties). 292 293Device options 294-------------- 295 296Emulated device options 297''''''''''''''''''''''' 298 299``-device nvme-ns,eui64-default=on|off`` (since 7.1) 300^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 301 302In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 303identifier that is not globally unique. If an EUI-64 identifier is required, the 304user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 305 306``-device nvme,use-intel-id=on|off`` (since 7.1) 307^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 308 309The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 310from Intel that was not properly allocated. Since version 5.2, the controller 311has used a properly allocated identifier. Deprecate the ``use-intel-id`` 312machine compatibility parameter. 313 314``-device cxl-type3,memdev=xxxx`` (since 8.0) 315^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 316 317The ``cxl-type3`` device initially only used a single memory backend. With 318the addition of volatile memory support, it is now necessary to distinguish 319between persistent and volatile memory backends. As such, memdev is deprecated 320in favor of persistent-memdev. 321 322``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1) 323^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 324 325The 9p ``proxy`` filesystem backend driver has been deprecated and will be 326removed (along with its proxy helper daemon) in a future version of QEMU. Please 327use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem 328backend, or alternatively consider deploying virtiofsd instead. 329 330The 9p ``proxy`` backend was originally developed as an alternative to the 9p 331``local`` backend. The idea was to enhance security by dispatching actual low 332level filesystem operations from 9p server (QEMU process) over to a separate 333process (the virtfs-proxy-helper binary). However this alternative never gained 334momentum. The proxy backend is much slower than the local backend, hasn't seen 335any development in years, and showed to be less secure, especially due to the 336fact that its helper daemon must be run as root, whereas with the local backend 337QEMU is typically run as unprivileged user and allows to tighten behaviour by 338mapping permissions et al by using its 'mapped' security model option. 339 340Nowadays it would make sense to reimplement the ``proxy`` backend by using 341QEMU's ``vhost`` feature, which would eliminate the high latency costs under 342which the 9p ``proxy`` backend currently suffers. However as of to date nobody 343has indicated plans for such kind of reimplementation unfortunately. 344 345RISC-V 'any' CPU type ``-cpu any`` (since 8.2) 346^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 347 348The 'any' CPU type was introduced back in 2018 and has been around since the 349initial RISC-V QEMU port. Its usage has always been unclear: users don't know 350what to expect from a CPU called 'any', and in fact the CPU does not do anything 351special that isn't already done by the default CPUs rv32/rv64. 352 353After the introduction of the 'max' CPU type, RISC-V now has a good coverage 354of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete 355CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any' 356CPU type starting in 8.2. 357 358RISC-V CPU properties which start with capital 'Z' (since 8.2) 359^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 360 361All RISC-V CPU properties which start with capital 'Z' are being deprecated 362starting in 8.2. The reason is that they were wrongly added with capital 'Z' 363in the past. CPU properties were later added with lower-case names, which 364is the format we want to use from now on. 365 366Users which try to use these deprecated properties will receive a warning 367recommending to switch to their stable counterparts: 368 369- "Zifencei" should be replaced with "zifencei" 370- "Zicsr" should be replaced with "zicsr" 371- "Zihintntl" should be replaced with "zihintntl" 372- "Zihintpause" should be replaced with "zihintpause" 373- "Zawrs" should be replaced with "zawrs" 374- "Zfa" should be replaced with "zfa" 375- "Zfh" should be replaced with "zfh" 376- "Zfhmin" should be replaced with "zfhmin" 377- "Zve32f" should be replaced with "zve32f" 378- "Zve64f" should be replaced with "zve64f" 379- "Zve64d" should be replaced with "zve64d" 380 381Block device options 382'''''''''''''''''''' 383 384``"backing": ""`` (since 2.12) 385^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 386 387In order to prevent QEMU from automatically opening an image's backing 388chain, use ``"backing": null`` instead. 389 390``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1) 391^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 392 393Options for ``rbd`` should be specified according to its runtime options, 394like other block drivers. Legacy parsing of keyvalue pair encoded 395filenames is useful to open images with the old format for backing files; 396These image files should be updated to use the current format. 397 398Example of legacy encoding:: 399 400 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"} 401 402The above, converted to the current supported format:: 403 404 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"} 405 406``iscsi,password=xxx`` (since 8.0) 407^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 408 409Specifying the iSCSI password in plain text on the command line using the 410``password`` option is insecure. The ``password-secret`` option should be 411used instead, to refer to a ``--object secret...`` instance that provides 412a password via a file, or encrypted. 413 414Character device options 415'''''''''''''''''''''''' 416 417Backend ``memory`` (since 9.0) 418^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 419 420``memory`` is a deprecated synonym for ``ringbuf``. 421 422CPU device properties 423''''''''''''''''''''' 424 425``pcommit`` on x86 (since 9.1) 426^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 427 428The PCOMMIT instruction was never included in any physical processor. 429It was implemented as a no-op instruction in TCG up to QEMU 9.0, but 430only with ``-cpu max`` (which does not guarantee migration compatibility 431across versions). 432 433``pmu-num=n`` on RISC-V CPUs (since 8.2) 434^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 435 436In order to support more flexible counter configurations this has been replaced 437by a ``pmu-mask`` property. If set of counters is continuous then the mask can 438be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits 439must be left clear. 440 441 442Backwards compatibility 443----------------------- 444 445Runnability guarantee of CPU models (since 4.1) 446''''''''''''''''''''''''''''''''''''''''''''''' 447 448Previous versions of QEMU never changed existing CPU models in 449ways that introduced additional host software or hardware 450requirements to the VM. This allowed management software to 451safely change the machine type of an existing VM without 452introducing new requirements ("runnability guarantee"). This 453prevented CPU models from being updated to include CPU 454vulnerability mitigations, leaving guests vulnerable in the 455default configuration. 456 457The CPU model runnability guarantee won't apply anymore to 458existing CPU models. Management software that needs runnability 459guarantees must resolve the CPU model aliases using the 460``alias-of`` field returned by the ``query-cpu-definitions`` QMP 461command. 462 463While those guarantees are kept, the return value of 464``query-cpu-definitions`` will have existing CPU model aliases 465point to a version that doesn't break runnability guarantees 466(specifically, version 1 of those CPU models). In future QEMU 467versions, aliases will point to newer CPU model versions 468depending on the machine type, so management software must 469resolve CPU model aliases before starting a virtual machine. 470 471QEMU guest agent 472---------------- 473 474``--blacklist`` command line option (since 7.2) 475''''''''''''''''''''''''''''''''''''''''''''''' 476 477``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better 478wording for what this option does). The short form ``-b`` still stays 479the same and thus is the preferred way for scripts that should run with 480both, older and future versions of QEMU. 481 482``blacklist`` config file option (since 7.2) 483'''''''''''''''''''''''''''''''''''''''''''' 484 485The ``blacklist`` config file option has been renamed to ``block-rpcs`` 486(to be in sync with the renaming of the corresponding command line 487option). 488 489Migration 490--------- 491 492``fd:`` URI when used for file migration (since 9.1) 493'''''''''''''''''''''''''''''''''''''''''''''''''''' 494 495The ``fd:`` URI can currently provide a file descriptor that 496references either a socket or a plain file. These are two different 497types of migration. In order to reduce ambiguity, the ``fd:`` URI 498usage of providing a file descriptor to a plain file has been 499deprecated in favor of explicitly using the ``file:`` URI with the 500file descriptor being passed as an ``fdset``. Refer to the ``add-fd`` 501command documentation for details on the ``fdset`` usage. 502